From 2fadfaefd026a25415b2f0848e343600ea15bdee Mon Sep 17 00:00:00 2001
From: Mark Paluch <mpaluch@pivotal.io>
Date: Tue, 25 Apr 2017 17:34:25 +0200
Subject: [PATCH] Java 8 code cleanup.

Replace nullable elements with Optional. Replace explicit type arguments with diamond syntax. Replace anonymous inner classes with lambdas.
---
 .../VaultPropertySourceRegistrar.java         |   2 +-
 .../authentication/AppIdAuthentication.java   |   2 +-
 .../authentication/AppRoleAuthentication.java |   2 +-
 .../authentication/AwsEc2Authentication.java  |  31 +++--
 .../CubbyholeAuthentication.java              |  21 ++-
 .../LifecycleAwareSessionManager.java         |  43 +++---
 .../authentication/MacAddressUserId.java      | 122 +++++++-----------
 .../vault/authentication/Sha256.java          |   8 +-
 .../authentication/SimpleSessionManager.java  |  13 +-
 .../vault/client/VaultClients.java            |  16 +--
 .../vault/client/VaultErrorMessage.java       |  63 ---------
 .../vault/client/VaultResponses.java          |   1 +
 .../vault/core/VaultPkiTemplate.java          |  43 +++---
 .../vault/core/VaultSysTemplate.java          |  73 +++++------
 .../vault/core/VaultTemplate.java             |  49 +++----
 .../vault/core/VaultTokenTemplate.java        |  21 ++-
 .../vault/core/VaultTransitTemplate.java      |  12 +-
 .../env/LeaseAwareVaultPropertySource.java    |   2 +-
 .../vault/core/env/VaultPropertySource.java   |   2 +-
 .../core/lease/SecretLeaseContainer.java      |  64 +++------
 .../core/lease/SecretLeaseEventPublisher.java |   4 +-
 .../lease/event/SecretLeaseCreatedEvent.java  |   2 +-
 .../vault/core/util/PropertyTransformers.java |   4 +-
 .../vault/support/JsonMapFlattener.java       |   8 +-
 .../vault/support/KeystoreUtil.java           |  29 ++---
 .../support/VaultCertificateRequest.java      |  11 +-
 .../vault/support/VaultTokenRequest.java      |  10 +-
 .../AppIdAuthenticationIntegrationTests.java  |  31 ++---
 ...AppRoleAuthenticationIntegrationTests.java |  33 ++---
 ...ificateAuthenticationIntegrationTests.java |  33 +++--
 ...bbyholeAuthenticationIntegrationTests.java |  18 +--
 ...leAwareSessionManagerIntegrationTests.java |  29 ++---
 .../VaultTemplateTransitIntegrationTests.java |   4 +-
 .../VaultTokenTemplateIntegrationTests.java   |  20 +--
 34 files changed, 320 insertions(+), 506 deletions(-)
 delete mode 100644 spring-vault-core/src/main/java/org/springframework/vault/client/VaultErrorMessage.java

diff --git a/spring-vault-core/src/main/java/org/springframework/vault/annotation/VaultPropertySourceRegistrar.java b/spring-vault-core/src/main/java/org/springframework/vault/annotation/VaultPropertySourceRegistrar.java
index 824cb908..d05df632 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/annotation/VaultPropertySourceRegistrar.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/annotation/VaultPropertySourceRegistrar.java
@@ -181,7 +181,7 @@ class VaultPropertySourceRegistrar implements ImportBeanDefinitionRegistrar,
 	static Set<AnnotationAttributes> attributesForRepeatable(AnnotationMetadata metadata,
 			String containerClassName, String annotationClassName) {
 
-		Set<AnnotationAttributes> result = new LinkedHashSet<AnnotationAttributes>();
+		Set<AnnotationAttributes> result = new LinkedHashSet<>();
 		addAttributesIfNotNull(result,
 				metadata.getAnnotationAttributes(annotationClassName, false));
 
diff --git a/spring-vault-core/src/main/java/org/springframework/vault/authentication/AppIdAuthentication.java b/spring-vault-core/src/main/java/org/springframework/vault/authentication/AppIdAuthentication.java
index c87db9b0..c6a6b29b 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/authentication/AppIdAuthentication.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/authentication/AppIdAuthentication.java
@@ -91,7 +91,7 @@ public class AppIdAuthentication implements ClientAuthentication {
 
 	private Map<String, String> getAppIdLogin(String appId, String userId) {
 
-		Map<String, String> login = new HashMap<String, String>();
+		Map<String, String> login = new HashMap<>();
 		login.put("app_id", appId);
 		login.put("user_id", userId);
 		return login;
diff --git a/spring-vault-core/src/main/java/org/springframework/vault/authentication/AppRoleAuthentication.java b/spring-vault-core/src/main/java/org/springframework/vault/authentication/AppRoleAuthentication.java
index cc591b5c..fc9285aa 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/authentication/AppRoleAuthentication.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/authentication/AppRoleAuthentication.java
@@ -93,7 +93,7 @@ public class AppRoleAuthentication implements ClientAuthentication {
 
 	private Map<String, String> getAppRoleLogin(String roleId, String secretId) {
 
-		Map<String, String> login = new HashMap<String, String>();
+		Map<String, String> login = new HashMap<>();
 		login.put("role_id", roleId);
 		if (secretId != null) {
 			login.put("secret_id", secretId);
diff --git a/spring-vault-core/src/main/java/org/springframework/vault/authentication/AwsEc2Authentication.java b/spring-vault-core/src/main/java/org/springframework/vault/authentication/AwsEc2Authentication.java
index d79ab504..1a3275c7 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/authentication/AwsEc2Authentication.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/authentication/AwsEc2Authentication.java
@@ -49,13 +49,15 @@ public class AwsEc2Authentication implements ClientAuthentication {
 
 	private static final Log logger = LogFactory.getLog(AwsEc2Authentication.class);
 
+	private final static char[] EMPTY = new char[0];
+
 	private final AwsEc2AuthenticationOptions options;
 
 	private final RestOperations vaultRestOperations;
 
 	private final RestOperations awsMetadataRestOperations;
 
-	private final AtomicReference<char[]> nonce = new AtomicReference<char[]>();
+	private final AtomicReference<char[]> nonce = new AtomicReference<>(EMPTY);
 
 	/**
 	 * Create a new {@link AwsEc2Authentication}.
@@ -77,7 +79,8 @@ public class AwsEc2Authentication implements ClientAuthentication {
 	 * @param awsMetadataRestOperations must not be {@literal null}.
 	 */
 	public AwsEc2Authentication(AwsEc2AuthenticationOptions options,
-			RestOperations vaultRestOperations, RestOperations awsMetadataRestOperations) {
+			RestOperations vaultRestOperations,
+			RestOperations awsMetadataRestOperations) {
 
 		Assert.notNull(options, "AwsEc2AuthenticationOptions must not be null");
 		Assert.notNull(vaultRestOperations, "Vault RestOperations must not be null");
@@ -109,10 +112,9 @@ public class AwsEc2Authentication implements ClientAuthentication {
 				if (response.getAuth().get("metadata") instanceof Map) {
 					Map<Object, Object> metadata = (Map<Object, Object>) response
 							.getAuth().get("metadata");
-					logger.debug(String
-							.format("Login successful using AWS-EC2 authentication for instance %s, AMI %s",
-									metadata.get("instance_id"),
-									metadata.get("instance_id")));
+					logger.debug(String.format(
+							"Login successful using AWS-EC2 authentication for instance %s, AMI %s",
+							metadata.get("instance_id"), metadata.get("instance_id")));
 				}
 				else {
 					logger.debug("Login successful using AWS-EC2 authentication");
@@ -129,21 +131,21 @@ public class AwsEc2Authentication implements ClientAuthentication {
 
 	protected Map<String, String> getEc2Login() {
 
-		Map<String, String> login = new HashMap<String, String>();
+		Map<String, String> login = new HashMap<>();
 
 		if (StringUtils.hasText(options.getRole())) {
 			login.put("role", options.getRole());
 		}
 
-		if (this.nonce.get() == null) {
-			this.nonce.compareAndSet(null, createNonce());
+		if (this.nonce.get() == EMPTY) {
+			this.nonce.compareAndSet(EMPTY, createNonce());
 		}
 
 		login.put("nonce", new String(this.nonce.get()));
 
 		try {
-			String pkcs7 = awsMetadataRestOperations.getForObject(
-					options.getIdentityDocumentUri(), String.class);
+			String pkcs7 = awsMetadataRestOperations
+					.getForObject(options.getIdentityDocumentUri(), String.class);
 			if (StringUtils.hasText(pkcs7)) {
 				login.put("pkcs7", pkcs7.replaceAll("\\r", "").replace("\\n", ""));
 			}
@@ -151,9 +153,10 @@ public class AwsEc2Authentication implements ClientAuthentication {
 			return login;
 		}
 		catch (RestClientException e) {
-			throw new VaultException(String.format(
-					"Cannot obtain Identity Document from %s",
-					options.getIdentityDocumentUri()), e);
+			throw new VaultException(
+					String.format("Cannot obtain Identity Document from %s",
+							options.getIdentityDocumentUri()),
+					e);
 		}
 	}
 
diff --git a/spring-vault-core/src/main/java/org/springframework/vault/authentication/CubbyholeAuthentication.java b/spring-vault-core/src/main/java/org/springframework/vault/authentication/CubbyholeAuthentication.java
index e6e3275a..9d32043e 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/authentication/CubbyholeAuthentication.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/authentication/CubbyholeAuthentication.java
@@ -180,10 +180,9 @@ public class CubbyholeAuthentication implements ClientAuthentication {
 		try {
 
 			ResponseEntity<VaultResponse> entity = restOperations.exchange(
-					options.getPath(),
-					HttpMethod.GET,
-					new HttpEntity<Object>(VaultHttpHeaders.from(options
-							.getInitialToken())), VaultResponse.class);
+					options.getPath(), HttpMethod.GET,
+					new HttpEntity<>(VaultHttpHeaders.from(options.getInitialToken())),
+					VaultResponse.class);
 
 			return entity.getBody().getData();
 		}
@@ -222,10 +221,9 @@ public class CubbyholeAuthentication implements ClientAuthentication {
 		}
 
 		if (data == null || data.isEmpty()) {
-			throw new VaultException(
-					String.format(
-							"Cannot retrieve Token from Cubbyhole: Response at %s does not contain a token",
-							options.getPath()));
+			throw new VaultException(String.format(
+					"Cannot retrieve Token from Cubbyhole: Response at %s does not contain a token",
+					options.getPath()));
 		}
 
 		if (data.size() == 1) {
@@ -233,9 +231,8 @@ public class CubbyholeAuthentication implements ClientAuthentication {
 			return VaultToken.of(token);
 		}
 
-		throw new VaultException(
-				String.format(
-						"Cannot retrieve Token from Cubbyhole: Response at %s does not contain an unique token",
-						options.getPath()));
+		throw new VaultException(String.format(
+				"Cannot retrieve Token from Cubbyhole: Response at %s does not contain an unique token",
+				options.getPath()));
 	}
 }
diff --git a/spring-vault-core/src/main/java/org/springframework/vault/authentication/LifecycleAwareSessionManager.java b/spring-vault-core/src/main/java/org/springframework/vault/authentication/LifecycleAwareSessionManager.java
index 212cb903..7afc170b 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/authentication/LifecycleAwareSessionManager.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/authentication/LifecycleAwareSessionManager.java
@@ -17,6 +17,7 @@ package org.springframework.vault.authentication;
 
 import java.util.Date;
 import java.util.Map;
+import java.util.Optional;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 
@@ -82,7 +83,7 @@ public class LifecycleAwareSessionManager implements SessionManager, DisposableB
 
 	private final Object lock = new Object();
 
-	private volatile VaultToken token;
+	private volatile Optional<VaultToken> token = Optional.empty();
 
 	/**
 	 * Create a {@link LifecycleAwareSessionManager} given {@link ClientAuthentication},
@@ -126,19 +127,17 @@ public class LifecycleAwareSessionManager implements SessionManager, DisposableB
 	@Override
 	public void destroy() {
 
-		VaultToken token = this.token;
-		this.token = null;
+		Optional<VaultToken> token = this.token;
+		this.token = Optional.empty();
 
-		if (token instanceof LoginToken) {
-			revoke(token);
-		}
+		token.filter(LoginToken.class::isInstance).ifPresent(this::revoke);
 	}
 
 	private void revoke(VaultToken token) {
 
 		try {
-			restOperations.postForObject("/auth/token/revoke-self",
-					new HttpEntity<Object>(VaultHttpHeaders.from(token)), Map.class);
+			restOperations.postForObject("/auth/token/revoke-self", new HttpEntity<>(
+					VaultHttpHeaders.from(token)), Map.class);
 		}
 		catch (HttpStatusCodeException e) {
 			logger.warn(String.format("Cannot revoke VaultToken: %s",
@@ -159,14 +158,14 @@ public class LifecycleAwareSessionManager implements SessionManager, DisposableB
 
 		logger.info("Renewing token");
 
-		if (token == null) {
+		if (!token.isPresent()) {
 			getSessionToken();
 			return false;
 		}
 
 		try {
-			restOperations.postForObject("/auth/token/renew-self",
-					new HttpEntity<Object>(VaultHttpHeaders.from(token)), Map.class);
+			restOperations.postForObject("/auth/token/renew-self", new HttpEntity<>(
+					VaultHttpHeaders.from(token.get())), Map.class);
 			return true;
 		}
 		catch (HttpStatusCodeException e) {
@@ -189,12 +188,12 @@ public class LifecycleAwareSessionManager implements SessionManager, DisposableB
 	@Override
 	public VaultToken getSessionToken() {
 
-		if (token == null) {
+		if (!token.isPresent()) {
 
 			synchronized (lock) {
 
-				if (token == null) {
-					token = login();
+				if (!token.isPresent()) {
+					token = Optional.ofNullable(clientAuthentication.login());
 
 					if (isTokenRenewable()) {
 						scheduleRenewal();
@@ -203,7 +202,8 @@ public class LifecycleAwareSessionManager implements SessionManager, DisposableB
 			}
 		}
 
-		return token;
+		return token.orElseThrow(() -> new IllegalStateException(
+				"Cannot obtain VaultToken"));
 	}
 
 	protected VaultToken login() {
@@ -212,13 +212,12 @@ public class LifecycleAwareSessionManager implements SessionManager, DisposableB
 
 	protected boolean isTokenRenewable() {
 
-		if (token instanceof LoginToken) {
+		return token.filter(LoginToken.class::isInstance) //
+				.filter(it -> {
 
-			LoginToken loginToken = (LoginToken) token;
-			return loginToken.getLeaseDuration() > 0 && loginToken.isRenewable();
-		}
-
-		return false;
+					LoginToken loginToken = (LoginToken) it;
+					return loginToken.getLeaseDuration() > 0 && loginToken.isRenewable();
+				}).isPresent();
 	}
 
 	private void scheduleRenewal() {
@@ -246,7 +245,7 @@ public class LifecycleAwareSessionManager implements SessionManager, DisposableB
 	}
 
 	private OneShotTrigger createTrigger() {
-		return new OneShotTrigger(refreshTrigger.nextExecutionTime((LoginToken) token));
+		return new OneShotTrigger(refreshTrigger.nextExecutionTime((LoginToken) token.get()));
 	}
 
 	/**
diff --git a/spring-vault-core/src/main/java/org/springframework/vault/authentication/MacAddressUserId.java b/spring-vault-core/src/main/java/org/springframework/vault/authentication/MacAddressUserId.java
index 4dbd657f..410b2e8d 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/authentication/MacAddressUserId.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/authentication/MacAddressUserId.java
@@ -16,19 +16,18 @@
 package org.springframework.vault.authentication;
 
 import java.io.IOException;
-import java.lang.reflect.Method;
 import java.net.InetAddress;
 import java.net.NetworkInterface;
-import java.util.ArrayList;
+import java.net.SocketException;
 import java.util.Collections;
 import java.util.Comparator;
 import java.util.List;
+import java.util.Optional;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 
 import org.springframework.util.Assert;
-import org.springframework.util.ReflectionUtils;
 import org.springframework.util.StringUtils;
 
 /**
@@ -42,10 +41,6 @@ import org.springframework.util.StringUtils;
  */
 public class MacAddressUserId implements AppIdUserIdMechanism {
 
-	// Compatibility with Java 1.7 and greater
-	private static final Method GET_INDEX = ReflectionUtils
-			.findMethod(NetworkInterface.class, "getIndex");
-
 	private final Log log = LogFactory.getLog(MacAddressUserId.class);
 
 	private final String networkInterfaceHint;
@@ -92,7 +87,7 @@ public class MacAddressUserId implements AppIdUserIdMechanism {
 
 		try {
 
-			NetworkInterface networkInterface = null;
+			Optional<NetworkInterface> networkInterface = Optional.empty();
 			List<NetworkInterface> interfaces = Collections
 					.list(NetworkInterface.getNetworkInterfaces());
 
@@ -108,7 +103,7 @@ public class MacAddressUserId implements AppIdUserIdMechanism {
 				}
 			}
 
-			if (networkInterface == null) {
+			if (!networkInterface.isPresent()) {
 
 				if (StringUtils.hasText(networkInterfaceHint)) {
 					log.warn(String.format(
@@ -117,96 +112,79 @@ public class MacAddressUserId implements AppIdUserIdMechanism {
 				}
 
 				InetAddress localHost = InetAddress.getLocalHost();
-				networkInterface = NetworkInterface.getByInetAddress(localHost);
-
-				if (networkInterface == null
-						|| networkInterface.getHardwareAddress() == null) {
+				networkInterface = Optional
+						.ofNullable(NetworkInterface.getByInetAddress(localHost));
 
+				if (!networkInterface.filter(MacAddressUserId::hasNetworkAddress)
+						.isPresent()) {
 					networkInterface = getNetworkInterfaceWithHardwareAddress(interfaces);
 				}
-
-				if (networkInterface == null) {
-					throw new IllegalStateException(String.format(
-							"Cannot determine NetworkInterface for %s", localHost));
-				}
 			}
 
-			byte[] mac = networkInterface.getHardwareAddress();
-			if (mac == null) {
-				throw new IllegalStateException(
-						String.format("Network interface %s has no hardware address",
-								networkInterface.getName()));
-			}
-
-			return Sha256.toSha256(Sha256.toHexString(mac));
+			return networkInterface.map(MacAddressUserId::getRequiredNetworkAddress) //
+					.map(Sha256::toHexString) //
+					.map(Sha256::toSha256) //
+					.orElseThrow(() -> new IllegalStateException(
+							"Cannot determine NetworkInterface"));
 		}
 		catch (IOException e) {
 			throw new IllegalStateException(e);
 		}
+
 	}
 
-	private static NetworkInterface getNetworkInterface(Number hint,
+	private static Optional<NetworkInterface> getNetworkInterface(Number hint,
 			List<NetworkInterface> interfaces) {
 
 		if (interfaces.size() > hint.intValue() && hint.intValue() >= 0) {
-			return interfaces.get(hint.intValue());
+			return Optional.of(interfaces.get(hint.intValue()));
 		}
 
-		return null;
+		return Optional.empty();
 	}
 
-	private static NetworkInterface getNetworkInterface(String hint,
+	private static Optional<NetworkInterface> getNetworkInterface(String hint,
 			List<NetworkInterface> interfaces) {
 
-		for (NetworkInterface anInterface : interfaces) {
-			if (hint.equals(anInterface.getDisplayName())
-					|| hint.equals(anInterface.getName())) {
-				return anInterface;
-			}
-		}
-
-		return null;
+		return interfaces.stream() //
+				.filter(anInterface -> matchesHint(hint, anInterface)) //
+				.findFirst();
 	}
 
-	private static NetworkInterface getNetworkInterfaceWithHardwareAddress(
-			List<NetworkInterface> interfaces) throws IOException {
+	private static boolean matchesHint(String hint, NetworkInterface networkInterface) {
 
-		List<NetworkInterface> networkInterfacesToUse = interfaces;
-
-		if (GET_INDEX != null) {
-			networkInterfacesToUse = new ArrayList<NetworkInterface>(interfaces);
-			Collections.sort(networkInterfacesToUse,
-					NetworkInterfaceIndexComparator.INSTANCE);
-		}
-
-		for (NetworkInterface anInterface : networkInterfacesToUse) {
-			byte[] hardwareAddress = anInterface.getHardwareAddress();
-			if (hardwareAddress != null) {
-				return anInterface;
-			}
-		}
-
-		return null;
+		return hint.equals(networkInterface.getDisplayName())
+				|| hint.equals(networkInterface.getName());
 	}
 
-	/**
-	 * @since 1.0.1
-	 */
-	enum NetworkInterfaceIndexComparator implements Comparator<NetworkInterface> {
-		INSTANCE;
+	private static Optional<NetworkInterface> getNetworkInterfaceWithHardwareAddress(
+			List<NetworkInterface> interfaces) {
 
-		@Override
-		public int compare(NetworkInterface o1, NetworkInterface o2) {
+		return interfaces.stream() //
+				.filter(MacAddressUserId::hasNetworkAddress) //
+				.sorted(Comparator.comparingInt(NetworkInterface::getIndex)) //
+				.findFirst();
+	}
 
-			try {
-				int left = (Integer) GET_INDEX.invoke(o1);
-				int right = (Integer) GET_INDEX.invoke(o2);
-				return (left < right) ? -1 : ((left == right) ? 0 : 1);
-			}
-			catch (Exception e) {
-				throw new IllegalStateException(
-						"Cannot retrieve index from NetworkInterface", e);
-			}
+	private static Optional<byte[]> getNetworkAddress(NetworkInterface it) {
+
+		try {
+			return Optional.ofNullable(it.getHardwareAddress());
 		}
+		catch (SocketException e) {
+			throw new IllegalStateException(String
+					.format("Cannot determine hardware address for %s", it.getName()));
+		}
+	}
+
+	private static byte[] getRequiredNetworkAddress(NetworkInterface it) {
+
+		return getNetworkAddress(it) //
+				.orElseThrow(() -> new IllegalStateException(String.format(
+						"Network interface %s has no hardware address", it.getName())));
+	}
+
+	private static boolean hasNetworkAddress(NetworkInterface it) {
+		return getNetworkAddress(it).isPresent();
 	}
 }
diff --git a/spring-vault-core/src/main/java/org/springframework/vault/authentication/Sha256.java b/spring-vault-core/src/main/java/org/springframework/vault/authentication/Sha256.java
index 162bac3e..d1d4587f 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/authentication/Sha256.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/authentication/Sha256.java
@@ -17,6 +17,7 @@
 package org.springframework.vault.authentication;
 
 import java.nio.charset.Charset;
+import java.nio.charset.StandardCharsets;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
 
@@ -29,7 +30,7 @@ import org.springframework.util.Assert;
  */
 class Sha256 {
 
-	private static final Charset US_ASCII = Charset.forName("US-ASCII");
+	private static final Charset US_ASCII = StandardCharsets.US_ASCII;
 
 	/**
 	 * Generates a hex-encoded SHA256 checksum from the supplied {@code content}.
@@ -64,10 +65,11 @@ class Sha256 {
 	}
 
 	static String toHexString(byte[] bytes) {
+
 		StringBuilder sb = new StringBuilder(bytes.length * 2);
 
-		for (int i = 0; i < bytes.length; i++) {
-			sb.append(String.format("%X", bytes[i]));
+		for (byte b : bytes) {
+			sb.append(String.format("%X", b));
 		}
 
 		return sb.toString();
diff --git a/spring-vault-core/src/main/java/org/springframework/vault/authentication/SimpleSessionManager.java b/spring-vault-core/src/main/java/org/springframework/vault/authentication/SimpleSessionManager.java
index 4f357e10..452d26cf 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/authentication/SimpleSessionManager.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/authentication/SimpleSessionManager.java
@@ -15,6 +15,8 @@
  */
 package org.springframework.vault.authentication;
 
+import java.util.Optional;
+
 import org.springframework.util.Assert;
 import org.springframework.vault.support.VaultToken;
 
@@ -34,7 +36,7 @@ public class SimpleSessionManager implements SessionManager {
 
 	private final Object lock = new Object();
 
-	private volatile VaultToken token;
+	private volatile Optional<VaultToken> token = Optional.empty();
 
 	/**
 	 * Create a new {@link SimpleSessionManager} using a {@link ClientAuthentication}.
@@ -51,14 +53,15 @@ public class SimpleSessionManager implements SessionManager {
 	@Override
 	public VaultToken getSessionToken() {
 
-		if (token == null) {
+		if (!token.isPresent()) {
 			synchronized (lock) {
-				if (token == null) {
-					token = clientAuthentication.login();
+				if (!token.isPresent()) {
+					token = Optional.of(clientAuthentication.login());
 				}
 			}
 		}
 
-		return token;
+		return token
+				.orElseThrow(() -> new IllegalStateException("Cannot obtain VaultToken"));
 	}
 }
diff --git a/spring-vault-core/src/main/java/org/springframework/vault/client/VaultClients.java b/spring-vault-core/src/main/java/org/springframework/vault/client/VaultClients.java
index 7ac5f8f5..1fbac987 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/client/VaultClients.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/client/VaultClients.java
@@ -15,17 +15,13 @@
  */
 package org.springframework.vault.client;
 
-import java.io.IOException;
 import java.net.URI;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
 
-import org.springframework.http.HttpRequest;
-import org.springframework.http.client.ClientHttpRequestExecution;
 import org.springframework.http.client.ClientHttpRequestFactory;
 import org.springframework.http.client.ClientHttpRequestInterceptor;
-import org.springframework.http.client.ClientHttpResponse;
 import org.springframework.http.converter.ByteArrayHttpMessageConverter;
 import org.springframework.http.converter.HttpMessageConverter;
 import org.springframework.http.converter.StringHttpMessageConverter;
@@ -88,7 +84,7 @@ public class VaultClients {
 	 */
 	public static RestTemplate createRestTemplate() {
 
-		List<HttpMessageConverter<?>> messageConverters = new ArrayList<HttpMessageConverter<?>>(
+		List<HttpMessageConverter<?>> messageConverters = new ArrayList<>(
 				3);
 		messageConverters.add(new ByteArrayHttpMessageConverter());
 		messageConverters.add(new StringHttpMessageConverter());
@@ -96,14 +92,8 @@ public class VaultClients {
 
 		RestTemplate restTemplate = new RestTemplate(messageConverters);
 
-		restTemplate.getInterceptors().add(new ClientHttpRequestInterceptor() {
-
-			@Override
-			public ClientHttpResponse intercept(HttpRequest request, byte[] body,
-					ClientHttpRequestExecution execution) throws IOException {
-				return execution.execute(request, body);
-			}
-		});
+		restTemplate.getInterceptors()
+				.add((request, body, execution) -> execution.execute(request, body));
 
 		return restTemplate;
 	}
diff --git a/spring-vault-core/src/main/java/org/springframework/vault/client/VaultErrorMessage.java b/spring-vault-core/src/main/java/org/springframework/vault/client/VaultErrorMessage.java
deleted file mode 100644
index 69d53ed1..00000000
--- a/spring-vault-core/src/main/java/org/springframework/vault/client/VaultErrorMessage.java
+++ /dev/null
@@ -1,63 +0,0 @@
-/*
- * Copyright 2016 the original author or authors.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package org.springframework.vault.client;
-
-import java.io.IOException;
-import java.util.Collection;
-import java.util.Map;
-
-import com.fasterxml.jackson.databind.ObjectMapper;
-
-/**
- * Utility to obtain a Vault error message.
- * 
- * @author Mark Paluch
- */
-class VaultErrorMessage {
-
-	private static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();
-
-	/**
-	 * Obtain the error message from a JSON response.
-	 * 
-	 * @param json
-	 * @return
-	 */
-	static String getError(String json) {
-
-		if (json.contains("\"errors\":")) {
-
-			try {
-				Map<String, Object> map = OBJECT_MAPPER.readValue(json.getBytes(),
-						Map.class);
-				if (map.containsKey("errors")) {
-
-					Collection<String> errors = (Collection<String>) map.get("errors");
-					if (errors.size() == 1) {
-						return errors.iterator().next();
-					}
-					return errors.toString();
-				}
-
-			}
-			catch (IOException o_O) {
-				// ignore
-			}
-		}
-		return json;
-	}
-}
diff --git a/spring-vault-core/src/main/java/org/springframework/vault/client/VaultResponses.java b/spring-vault-core/src/main/java/org/springframework/vault/client/VaultResponses.java
index 2d7ea4f0..13ddf8cc 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/client/VaultResponses.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/client/VaultResponses.java
@@ -129,6 +129,7 @@ public abstract class VaultResponses {
 	 * @param json must not be {@literal null}.
 	 * @return
 	 */
+	@SuppressWarnings("unchecked")
 	public static String getError(String json) {
 
 		Assert.notNull(json, "Error JSON must not be null!");
diff --git a/spring-vault-core/src/main/java/org/springframework/vault/core/VaultPkiTemplate.java b/spring-vault-core/src/main/java/org/springframework/vault/core/VaultPkiTemplate.java
index d5f4a3ae..3b9e6a09 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/core/VaultPkiTemplate.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/core/VaultPkiTemplate.java
@@ -25,11 +25,10 @@ import org.springframework.vault.client.VaultResponses;
 import org.springframework.vault.support.VaultCertificateRequest;
 import org.springframework.vault.support.VaultCertificateResponse;
 import org.springframework.web.client.HttpStatusCodeException;
-import org.springframework.web.client.RestOperations;
 
 /**
  * Default implementation of {@link VaultPkiOperations}.
- * 
+ *
  * @author Mark Paluch
  */
 public class VaultPkiTemplate implements VaultPkiOperations {
@@ -41,7 +40,7 @@ public class VaultPkiTemplate implements VaultPkiOperations {
 	/**
 	 * Create a new {@link VaultPkiTemplate} given {@link VaultPkiOperations} and the
 	 * mount {@code path}.
-	 * 
+	 *
 	 * @param vaultOperations must not be {@literal null}.
 	 * @param path must not be empty or {@literal null}.
 	 */
@@ -61,21 +60,17 @@ public class VaultPkiTemplate implements VaultPkiOperations {
 		Assert.hasText(roleName, "Role name must not be empty");
 		Assert.notNull(certificateRequest, "Certificate request must not be null");
 
-		final Map<String, Object> request = new HashMap<String, Object>();
+		final Map<String, Object> request = new HashMap<>();
 		request.put("common_name", certificateRequest.getCommonName());
 
 		if (!certificateRequest.getAltNames().isEmpty()) {
-			request.put(
-					"alt_names",
-					StringUtils.collectionToDelimitedString(
-							certificateRequest.getAltNames(), ","));
+			request.put("alt_names", StringUtils
+					.collectionToDelimitedString(certificateRequest.getAltNames(), ","));
 		}
 
 		if (!certificateRequest.getIpSubjectAltNames().isEmpty()) {
-			request.put(
-					"ip_sans",
-					StringUtils.collectionToDelimitedString(
-							certificateRequest.getIpSubjectAltNames(), ","));
+			request.put("ip_sans", StringUtils.collectionToDelimitedString(
+					certificateRequest.getIpSubjectAltNames(), ","));
 		}
 
 		if (certificateRequest.getTtl() != null) {
@@ -88,22 +83,16 @@ public class VaultPkiTemplate implements VaultPkiOperations {
 			request.put("exclude_cn_from_sans", true);
 		}
 
-		return vaultOperations
-				.doWithSession(new RestOperationsCallback<VaultCertificateResponse>() {
-					@Override
-					public VaultCertificateResponse doWithRestOperations(
-							RestOperations restOperations) {
+		return vaultOperations.doWithSession(restOperations -> {
 
-						try {
-							return restOperations.postForObject(
-									"{path}/issue/{roleName}", request,
-									VaultCertificateResponse.class, path, roleName);
-						}
-						catch (HttpStatusCodeException e) {
-							throw VaultResponses.buildException(e);
-						}
-					}
-				});
+			try {
+				return restOperations.postForObject("{path}/issue/{roleName}", request,
+						VaultCertificateResponse.class, path, roleName);
+			}
+			catch (HttpStatusCodeException e) {
+				throw VaultResponses.buildException(e);
+			}
+		});
 	}
 
 }
diff --git a/spring-vault-core/src/main/java/org/springframework/vault/core/VaultSysTemplate.java b/spring-vault-core/src/main/java/org/springframework/vault/core/VaultSysTemplate.java
index 85f5ec4d..b5506639 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/core/VaultSysTemplate.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/core/VaultSysTemplate.java
@@ -79,20 +79,16 @@ public class VaultSysTemplate implements VaultSysOperations {
 	@Override
 	public boolean isInitialized() {
 
-		return vaultOperations.doWithVault(new RestOperationsCallback<Boolean>() {
+		return vaultOperations.doWithVault(restOperations -> {
 
-			@Override
-			public Boolean doWithRestOperations(RestOperations restOperations) {
+			try {
+				Map<String, Boolean> body = restOperations.getForObject("/sys/init",
+						Map.class);
 
-				try {
-					Map<String, Boolean> body = restOperations.getForObject("/sys/init",
-							Map.class);
-
-					return body.get("initialized");
-				}
-				catch (HttpStatusCodeException e) {
-					throw VaultResponses.buildException(e);
-				}
+				return body.get("initialized");
+			}
+			catch (HttpStatusCodeException e) {
+				throw VaultResponses.buildException(e);
 			}
 		});
 	}
@@ -104,24 +100,20 @@ public class VaultSysTemplate implements VaultSysOperations {
 		Assert.notNull(vaultInitializationRequest, "VaultInitialization must not be null");
 
 		return vaultOperations
-				.doWithVault(new RestOperationsCallback<VaultInitializationResponse>() {
+				.doWithVault(
+						(RestOperationsCallback<VaultInitializationResponse>) restOperations -> {
 
-					@Override
-					public VaultInitializationResponse doWithRestOperations(
-							RestOperations restOperations) {
+							try {
+								ResponseEntity<VaultInitializationResponseImpl> exchange = restOperations
+										.exchange("/sys/init", HttpMethod.PUT,
+												new HttpEntity<Object>(
+														vaultInitializationRequest),
+												VaultInitializationResponseImpl.class);
 
-						try {
-							ResponseEntity<VaultInitializationResponseImpl> exchange = restOperations
-									.exchange("/sys/init", HttpMethod.PUT,
-											new HttpEntity<Object>(
-													vaultInitializationRequest),
-											VaultInitializationResponseImpl.class);
-
-							return exchange.getBody();
-						}
-						catch (HttpStatusCodeException e) {
-							throw VaultResponses.buildException(e);
-						}
+								return exchange.getBody();
+							}
+							catch (HttpStatusCodeException e) {
+								throw VaultResponses.buildException(e);
 					}
 				});
 	}
@@ -135,21 +127,16 @@ public class VaultSysTemplate implements VaultSysOperations {
 	public VaultUnsealStatus unseal(final String keyShare) {
 
 		return vaultOperations
-				.doWithVault(new RestOperationsCallback<VaultUnsealStatus>() {
-					@Override
-					public VaultUnsealStatus doWithRestOperations(
-							RestOperations restOperations) {
+				.doWithVault(
+						(RestOperationsCallback<VaultUnsealStatus>) restOperations -> {
 
-						ResponseEntity<VaultUnsealStatusImpl> response = restOperations
-								.exchange(
-										"/sys/unseal",
-										HttpMethod.PUT,
-										new HttpEntity<Object>(Collections.singletonMap(
-												"key", keyShare)),
-										VaultUnsealStatusImpl.class);
+							ResponseEntity<VaultUnsealStatusImpl> response = restOperations
+									.exchange("/sys/unseal", HttpMethod.PUT,
+											new HttpEntity<Object>(Collections
+													.singletonMap("key", keyShare)),
+											VaultUnsealStatusImpl.class);
 
-						return response.getBody();
-					}
+							return response.getBody();
 				});
 	}
 
@@ -259,7 +246,7 @@ public class VaultSysTemplate implements VaultSysOperations {
 		private static class VaultMountsResponse extends
 				VaultResponseSupport<Map<String, VaultMount>> {
 
-			private Map<String, VaultMount> topLevelMounts = new HashMap<String, VaultMount>();
+			private Map<String, VaultMount> topLevelMounts = new HashMap<>();
 
 			@JsonIgnore
 			public Map<String, VaultMount> getTopLevelMounts() {
@@ -316,7 +303,7 @@ public class VaultSysTemplate implements VaultSysOperations {
 	@Data
 	static class VaultInitializationResponseImpl implements VaultInitializationResponse {
 
-		private List<String> keys = new ArrayList<String>();
+		private List<String> keys = new ArrayList<>();
 
 		@JsonProperty("root_token")
 		private String rootToken;
diff --git a/spring-vault-core/src/main/java/org/springframework/vault/core/VaultTemplate.java b/spring-vault-core/src/main/java/org/springframework/vault/core/VaultTemplate.java
index 2fffddd1..b2474c4b 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/core/VaultTemplate.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/core/VaultTemplate.java
@@ -15,7 +15,6 @@
  */
 package org.springframework.vault.core;
 
-import java.io.IOException;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
@@ -24,13 +23,9 @@ import org.springframework.beans.factory.DisposableBean;
 import org.springframework.beans.factory.InitializingBean;
 import org.springframework.core.ParameterizedTypeReference;
 import org.springframework.http.HttpMethod;
-import org.springframework.http.HttpRequest;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.ResponseEntity;
-import org.springframework.http.client.ClientHttpRequestExecution;
 import org.springframework.http.client.ClientHttpRequestFactory;
-import org.springframework.http.client.ClientHttpRequestInterceptor;
-import org.springframework.http.client.ClientHttpResponse;
 import org.springframework.http.client.SimpleClientHttpRequestFactory;
 import org.springframework.util.Assert;
 import org.springframework.vault.authentication.ClientAuthentication;
@@ -126,17 +121,12 @@ public class VaultTemplate implements InitializingBean, VaultOperations, Disposa
 		RestTemplate restTemplate = VaultClients.createRestTemplate(endpoint,
 				requestFactory);
 
-		restTemplate.getInterceptors().add(new ClientHttpRequestInterceptor() {
+		restTemplate.getInterceptors().add((request, body, execution) -> {
 
-			@Override
-			public ClientHttpResponse intercept(HttpRequest request, byte[] body,
-					ClientHttpRequestExecution execution) throws IOException {
+			request.getHeaders().add(VaultHttpHeaders.VAULT_TOKEN,
+					sessionManager.getSessionToken().getToken());
 
-				request.getHeaders().add(VaultHttpHeaders.VAULT_TOKEN,
-						sessionManager.getSessionToken().getToken());
-
-				return execution.execute(request, body);
-			}
+			return execution.execute(request, body);
 		});
 
 		return restTemplate;
@@ -208,14 +198,15 @@ public class VaultTemplate implements InitializingBean, VaultOperations, Disposa
 
 	@SuppressWarnings("unchecked")
 	@Override
-	public <T> VaultResponseSupport<T> read(final String path, final Class<T> responseType) {
+	public <T> VaultResponseSupport<T> read(final String path,
+			final Class<T> responseType) {
 
 		final ParameterizedTypeReference<VaultResponseSupport<T>> ref = VaultResponses
 				.getTypeReference(responseType);
 
 		try {
-			ResponseEntity<VaultResponseSupport<T>> exchange = sessionTemplate.exchange(
-					path, HttpMethod.GET, null, ref);
+			ResponseEntity<VaultResponseSupport<T>> exchange = sessionTemplate
+					.exchange(path, HttpMethod.GET, null, ref);
 
 			return exchange.getBody();
 		}
@@ -303,27 +294,23 @@ public class VaultTemplate implements InitializingBean, VaultOperations, Disposa
 
 	private <T> T doRead(final String path, final Class<T> responseType) {
 
-		return doWithSession(new RestOperationsCallback<T>() {
+		return doWithSession(restOperations -> {
 
-			@Override
-			public T doWithRestOperations(RestOperations restOperations) {
+			try {
+				return restOperations.getForObject(path, responseType);
+			}
+			catch (HttpStatusCodeException e) {
 
-				try {
-					return restOperations.getForObject(path, responseType);
+				if (e.getStatusCode() == HttpStatus.NOT_FOUND) {
+					return null;
 				}
-				catch (HttpStatusCodeException e) {
 
-					if (e.getStatusCode() == HttpStatus.NOT_FOUND) {
-						return null;
-					}
-
-					throw VaultResponses.buildException(e, path);
-				}
+				throw VaultResponses.buildException(e, path);
 			}
 		});
 	}
 
-	private static class VaultListResponse extends
-			VaultResponseSupport<Map<String, Object>> {
+	private static class VaultListResponse
+			extends VaultResponseSupport<Map<String, Object>> {
 	}
 }
diff --git a/spring-vault-core/src/main/java/org/springframework/vault/core/VaultTokenTemplate.java b/spring-vault-core/src/main/java/org/springframework/vault/core/VaultTokenTemplate.java
index b27b3923..0b1f2e46 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/core/VaultTokenTemplate.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/core/VaultTokenTemplate.java
@@ -25,7 +25,6 @@ import org.springframework.vault.support.VaultToken;
 import org.springframework.vault.support.VaultTokenRequest;
 import org.springframework.vault.support.VaultTokenResponse;
 import org.springframework.web.client.HttpStatusCodeException;
-import org.springframework.web.client.RestOperations;
 
 /**
  * Default implementation of {@link VaultTokenOperations}.
@@ -106,19 +105,15 @@ public class VaultTokenTemplate implements VaultTokenOperations {
 
 		Assert.hasText(path, "Path must not be empty");
 
-		return vaultOperations.doWithSession(new RestOperationsCallback<T>() {
+		return vaultOperations.doWithSession(restOperations -> {
+			try {
+				ResponseEntity<T> exchange = restOperations.exchange(path,
+						HttpMethod.POST, new HttpEntity<>(body), responseType);
 
-			@Override
-			public T doWithRestOperations(RestOperations restOperations) {
-				try {
-					ResponseEntity<T> exchange = restOperations.exchange(path,
-							HttpMethod.POST, new HttpEntity<Object>(body), responseType);
-
-					return exchange.getBody();
-				}
-				catch (HttpStatusCodeException e) {
-					throw VaultResponses.buildException(e, path);
-				}
+				return exchange.getBody();
+			}
+			catch (HttpStatusCodeException e) {
+				throw VaultResponses.buildException(e, path);
 			}
 		});
 	}
diff --git a/spring-vault-core/src/main/java/org/springframework/vault/core/VaultTransitTemplate.java b/spring-vault-core/src/main/java/org/springframework/vault/core/VaultTransitTemplate.java
index 96383ae9..94a87096 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/core/VaultTransitTemplate.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/core/VaultTransitTemplate.java
@@ -144,7 +144,7 @@ public class VaultTransitTemplate implements VaultTransitOperations {
 		Assert.hasText(keyName, "KeyName must not be empty");
 		Assert.notNull(plaintext, "Plain text must not be null");
 
-		Map<String, String> request = new LinkedHashMap<String, String>();
+		Map<String, String> request = new LinkedHashMap<>();
 
 		request.put("plaintext", Base64Utils.encodeToString(plaintext.getBytes()));
 
@@ -160,7 +160,7 @@ public class VaultTransitTemplate implements VaultTransitOperations {
 		Assert.hasText(keyName, "KeyName must not be empty");
 		Assert.notNull(plaintext, "Plain text must not be null");
 
-		Map<String, String> request = new LinkedHashMap<String, String>();
+		Map<String, String> request = new LinkedHashMap<>();
 
 		request.put("plaintext", Base64Utils.encodeToString(plaintext));
 
@@ -179,7 +179,7 @@ public class VaultTransitTemplate implements VaultTransitOperations {
 		Assert.hasText(keyName, "KeyName must not be empty");
 		Assert.hasText(keyName, "Cipher text must not be empty");
 
-		Map<String, String> request = new LinkedHashMap<String, String>();
+		Map<String, String> request = new LinkedHashMap<>();
 
 		request.put("ciphertext", ciphertext);
 
@@ -197,7 +197,7 @@ public class VaultTransitTemplate implements VaultTransitOperations {
 		Assert.hasText(keyName, "KeyName must not be empty");
 		Assert.hasText(keyName, "Cipher text must not be empty");
 
-		Map<String, String> request = new LinkedHashMap<String, String>();
+		Map<String, String> request = new LinkedHashMap<>();
 
 		request.put("ciphertext", ciphertext);
 
@@ -218,7 +218,7 @@ public class VaultTransitTemplate implements VaultTransitOperations {
 		Assert.hasText(keyName, "KeyName must not be empty");
 		Assert.hasText(ciphertext, "Cipher text must not be empty");
 
-		Map<String, String> request = new LinkedHashMap<String, String>();
+		Map<String, String> request = new LinkedHashMap<>();
 		request.put("ciphertext", ciphertext);
 
 		return (String) vaultOperations
@@ -233,7 +233,7 @@ public class VaultTransitTemplate implements VaultTransitOperations {
 		Assert.hasText(keyName, "KeyName must not be empty");
 		Assert.hasText(ciphertext, "Cipher text must not be empty");
 
-		Map<String, String> request = new LinkedHashMap<String, String>();
+		Map<String, String> request = new LinkedHashMap<>();
 
 		request.put("ciphertext", ciphertext);
 
diff --git a/spring-vault-core/src/main/java/org/springframework/vault/core/env/LeaseAwareVaultPropertySource.java b/spring-vault-core/src/main/java/org/springframework/vault/core/env/LeaseAwareVaultPropertySource.java
index a6b0e946..d23f13d8 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/core/env/LeaseAwareVaultPropertySource.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/core/env/LeaseAwareVaultPropertySource.java
@@ -60,7 +60,7 @@ public class LeaseAwareVaultPropertySource
 
 	private final RequestedSecret requestedSecret;
 
-	private final Map<String, String> properties = new ConcurrentHashMap<String, String>();
+	private final Map<String, String> properties = new ConcurrentHashMap<>();
 
 	private final PropertyTransformer propertyTransformer;
 
diff --git a/spring-vault-core/src/main/java/org/springframework/vault/core/env/VaultPropertySource.java b/spring-vault-core/src/main/java/org/springframework/vault/core/env/VaultPropertySource.java
index 9e7ce8ef..c3784feb 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/core/env/VaultPropertySource.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/core/env/VaultPropertySource.java
@@ -49,7 +49,7 @@ public class VaultPropertySource extends EnumerablePropertySource<VaultOperation
 
 	private final String path;
 
-	private final Map<String, String> properties = new LinkedHashMap<String, String>();
+	private final Map<String, String> properties = new LinkedHashMap<>();
 
 	private final PropertyTransformer propertyTransformer;
 
diff --git a/spring-vault-core/src/main/java/org/springframework/vault/core/lease/SecretLeaseContainer.java b/spring-vault-core/src/main/java/org/springframework/vault/core/lease/SecretLeaseContainer.java
index e2f68143..8ec567a5 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/core/lease/SecretLeaseContainer.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/core/lease/SecretLeaseContainer.java
@@ -54,7 +54,6 @@ import org.springframework.vault.core.lease.event.LeaseErrorListener;
 import org.springframework.vault.core.lease.event.LeaseListener;
 import org.springframework.vault.support.VaultResponseSupport;
 import org.springframework.web.client.HttpStatusCodeException;
-import org.springframework.web.client.RestOperations;
 
 /**
  * Event-based container to request secrets from Vault and renew the associated
@@ -128,9 +127,9 @@ public class SecretLeaseContainer extends SecretLeaseEventPublisher implements
 	private static final int STATUS_STARTED = 1;
 	private static final int STATUS_DESTROYED = 2;
 
-	private final List<RequestedSecret> requestedSecrets = new CopyOnWriteArrayList<RequestedSecret>();
+	private final List<RequestedSecret> requestedSecrets = new CopyOnWriteArrayList<>();
 
-	private final Map<RequestedSecret, LeaseRenewalScheduler> renewals = new ConcurrentHashMap<RequestedSecret, LeaseRenewalScheduler>();
+	private final Map<RequestedSecret, LeaseRenewalScheduler> renewals = new ConcurrentHashMap<>();
 
 	private final VaultOperations operations;
 
@@ -279,7 +278,7 @@ public class SecretLeaseContainer extends SecretLeaseEventPublisher implements
 		Assert.state(this.status != STATUS_DESTROYED,
 				"Container is destroyed and cannot be started");
 
-		Map<RequestedSecret, LeaseRenewalScheduler> renewals = new HashMap<RequestedSecret, LeaseRenewalScheduler>(
+		Map<RequestedSecret, LeaseRenewalScheduler> renewals = new HashMap<>(
 				this.renewals);
 
 		if (UPDATER.compareAndSet(this, STATUS_INITIAL, STATUS_STARTED)) {
@@ -429,24 +428,20 @@ public class SecretLeaseContainer extends SecretLeaseEventPublisher implements
 
 		}
 
-		leaseRenewal.scheduleRenewal(requestedSecret, new RenewLease() {
+		leaseRenewal.scheduleRenewal(requestedSecret, lease1 -> {
 
-			@Override
-			public Lease renewLease(Lease lease) {
+			Lease newLease = doRenewLease(requestedSecret, lease1);
 
-				Lease newLease = doRenewLease(requestedSecret, lease);
+			if (!Lease.none().equals(newLease)) {
 
-				if (!Lease.none().equals(newLease)) {
+				potentiallyScheduleLeaseRenewal(requestedSecret, newLease, leaseRenewal);
 
-					potentiallyScheduleLeaseRenewal(requestedSecret, newLease,
-							leaseRenewal);
-
-					onAfterLeaseRenewed(requestedSecret, newLease);
-				}
-
-				return newLease;
+				onAfterLeaseRenewed(requestedSecret, newLease);
 			}
+
+			return newLease;
 		}, lease, getMinRenewalSeconds(), getExpiryThresholdSeconds());
+
 	}
 
 	// -------------------------------------------------------------------------
@@ -483,7 +478,6 @@ public class SecretLeaseContainer extends SecretLeaseEventPublisher implements
 	protected Lease doRenewLease(final RequestedSecret requestedSecret, final Lease lease) {
 
 		try {
-
 			Lease renewed = lease.hasLeaseId() ? renew(lease) : lease;
 
 			if (!renewed.hasLeaseId() || renewed.getLeaseDuration() == 0
@@ -514,19 +508,10 @@ public class SecretLeaseContainer extends SecretLeaseEventPublisher implements
 	}
 
 	private Lease renew(final Lease lease) {
-
 		ResponseEntity<Map<String, Object>> entity = operations
-				.doWithSession(new RestOperationsCallback<ResponseEntity<Map<String, Object>>>() {
-
-					@Override
-					@SuppressWarnings("unchecked")
-					public ResponseEntity<Map<String, Object>> doWithRestOperations(
-							RestOperations restOperations) {
-						return (ResponseEntity) restOperations.exchange(
-								"/sys/renew/{leaseId}", HttpMethod.PUT, null, Map.class,
-								lease.getLeaseId());
-					}
-				});
+				.doWithSession(restOperations -> (ResponseEntity) restOperations
+						.exchange("/sys/renew/{leaseId}", HttpMethod.PUT, null,
+								Map.class, lease.getLeaseId()));
 
 		Map<String, Object> body = entity.getBody();
 		String leaseId = (String) body.get("lease_id");
@@ -567,17 +552,10 @@ public class SecretLeaseContainer extends SecretLeaseEventPublisher implements
 			onBeforeLeaseRevocation(requestedSecret, lease);
 
 			operations
-					.doWithSession(new RestOperationsCallback<ResponseEntity<Map<String, Object>>>() {
+					.doWithSession((RestOperationsCallback<ResponseEntity<Map<String, Object>>>) restOperations -> (ResponseEntity) restOperations
+							.exchange("/sys/revoke/{leaseId}", HttpMethod.PUT, null,
+									Map.class, lease.getLeaseId()));
 
-						@Override
-						@SuppressWarnings("unchecked")
-						public ResponseEntity<Map<String, Object>> doWithRestOperations(
-								RestOperations restOperations) {
-							return (ResponseEntity) restOperations.exchange(
-									"/sys/revoke/{leaseId}", HttpMethod.PUT, null,
-									Map.class, lease.getLeaseId());
-						}
-					});
 			onAfterLeaseRevocation(requestedSecret, lease);
 		}
 		catch (HttpStatusCodeException e) {
@@ -603,9 +581,9 @@ public class SecretLeaseContainer extends SecretLeaseEventPublisher implements
 
 		private final TaskScheduler taskScheduler;
 
-		final AtomicReference<Lease> currentLeaseRef = new AtomicReference<Lease>();
+		final AtomicReference<Lease> currentLeaseRef = new AtomicReference<>();
 
-		final Map<Lease, ScheduledFuture<?>> schedules = new ConcurrentHashMap<Lease, ScheduledFuture<?>>();
+		final Map<Lease, ScheduledFuture<?>> schedules = new ConcurrentHashMap<>();
 
 		/**
 		 *
@@ -664,7 +642,7 @@ public class SecretLeaseContainer extends SecretLeaseEventPublisher implements
 
 					if (log.isDebugEnabled()) {
 						if (lease.hasLeaseId()) {
-							log.debug(String.format("Renewing lease %s for secret %s",
+							log.debug(String.format("Renewing lease %sfor secret %s",
 									lease.getLeaseId(), requestedSecret.getPath()));
 						}
 						else {
@@ -713,7 +691,7 @@ public class SecretLeaseContainer extends SecretLeaseEventPublisher implements
 		void disableScheduleRenewal() {
 
 			currentLeaseRef.set(null);
-			Set<Lease> leases = new HashSet<Lease>(schedules.keySet());
+			Set<Lease> leases = new HashSet<>(schedules.keySet());
 
 			for (Lease lease : leases) {
 				cancelSchedule(lease);
diff --git a/spring-vault-core/src/main/java/org/springframework/vault/core/lease/SecretLeaseEventPublisher.java b/spring-vault-core/src/main/java/org/springframework/vault/core/lease/SecretLeaseEventPublisher.java
index d68e4c0a..bdfcc5bd 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/core/lease/SecretLeaseEventPublisher.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/core/lease/SecretLeaseEventPublisher.java
@@ -49,9 +49,9 @@ import org.springframework.vault.core.lease.event.SecretLeaseExpiredEvent;
  */
 public class SecretLeaseEventPublisher implements InitializingBean {
 
-	private final Set<LeaseListener> leaseListeners = new CopyOnWriteArraySet<LeaseListener>();
+	private final Set<LeaseListener> leaseListeners = new CopyOnWriteArraySet<>();
 
-	private final Set<LeaseErrorListener> leaseErrorListeners = new CopyOnWriteArraySet<LeaseErrorListener>();
+	private final Set<LeaseErrorListener> leaseErrorListeners = new CopyOnWriteArraySet<>();
 
 	/**
 	 * Add a {@link LeaseListener} to the container. The listener starts receiving events
diff --git a/spring-vault-core/src/main/java/org/springframework/vault/core/lease/event/SecretLeaseCreatedEvent.java b/spring-vault-core/src/main/java/org/springframework/vault/core/lease/event/SecretLeaseCreatedEvent.java
index bdfd8570..589f0b12 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/core/lease/event/SecretLeaseCreatedEvent.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/core/lease/event/SecretLeaseCreatedEvent.java
@@ -44,7 +44,7 @@ public class SecretLeaseCreatedEvent extends SecretLeaseEvent {
 			Map<String, Object> secrets) {
 
 		super(requestedSecret, lease);
-		this.secrets = Collections.unmodifiableMap(new HashMap<String, Object>(secrets));
+		this.secrets = Collections.unmodifiableMap(new HashMap<>(secrets));
 	}
 
 	public Map<String, Object> getSecrets() {
diff --git a/spring-vault-core/src/main/java/org/springframework/vault/core/util/PropertyTransformers.java b/spring-vault-core/src/main/java/org/springframework/vault/core/util/PropertyTransformers.java
index 3c3236d7..ef0e6fef 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/core/util/PropertyTransformers.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/core/util/PropertyTransformers.java
@@ -120,7 +120,7 @@ public abstract class PropertyTransformers {
 		@Override
 		public Map<String, String> transformProperties(Map<String, String> input) {
 
-			Map<String, String> target = new LinkedHashMap<String, String>(input.size(),
+			Map<String, String> target = new LinkedHashMap<>(input.size(),
 					1);
 
 			for (Entry<String, String> entry : input.entrySet()) {
@@ -165,7 +165,7 @@ public abstract class PropertyTransformers {
 		@Override
 		public Map<String, String> transformProperties(Map<String, String> input) {
 
-			Map<String, String> target = new LinkedHashMap<String, String>(input.size(),
+			Map<String, String> target = new LinkedHashMap<>(input.size(),
 					1);
 
 			for (Entry<String, String> entry : input.entrySet()) {
diff --git a/spring-vault-core/src/main/java/org/springframework/vault/support/JsonMapFlattener.java b/spring-vault-core/src/main/java/org/springframework/vault/support/JsonMapFlattener.java
index d516b483..77754d2c 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/support/JsonMapFlattener.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/support/JsonMapFlattener.java
@@ -35,16 +35,16 @@ import org.springframework.util.StringUtils;
  * considered as sub-documents.
  * <p>
  * Input:
- * 
+ *
  * <pre>
  * <code>
  *     {"key": {"nested: "value"}, "another.key": ["one", "two"] }
  * </code>
  * </pre>
- * 
+ *
  * <br>
  * Result
- * 
+ *
  * <pre>
  * <code> key.nested=value
  *  another.key[0]=one
@@ -70,7 +70,7 @@ public abstract class JsonMapFlattener {
 
 		Assert.notNull(inputMap, "Input Map must not be null");
 
-		Map<String, String> resultMap = new LinkedHashMap<String, String>();
+		Map<String, String> resultMap = new LinkedHashMap<>();
 
 		doFlatten("", inputMap.entrySet().iterator(), resultMap);
 
diff --git a/spring-vault-core/src/main/java/org/springframework/vault/support/KeystoreUtil.java b/spring-vault-core/src/main/java/org/springframework/vault/support/KeystoreUtil.java
index 16650459..7586be84 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/support/KeystoreUtil.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/support/KeystoreUtil.java
@@ -41,8 +41,8 @@ import java.util.List;
 class KeystoreUtil {
 
 	/**
-	 * Create a {@link KeyStore} containing the {@link KeySpec} and
-	 * {@link X509Certificate certificates} using the given {@code keyAlias}.
+	 * Create a {@link KeyStore} containing the {@link KeySpec} and {@link X509Certificate
+	 * certificates} using the given {@code keyAlias}.
 	 *
 	 * @param keyAlias
 	 * @param certificates
@@ -51,14 +51,15 @@ class KeystoreUtil {
 	 * @throws IOException
 	 */
 	static KeyStore createKeyStore(String keyAlias, KeySpec privateKeySpec,
-			X509Certificate... certificates) throws GeneralSecurityException, IOException {
+			X509Certificate... certificates)
+			throws GeneralSecurityException, IOException {
 
 		KeyFactory kf = KeyFactory.getInstance("RSA");
 		PrivateKey privateKey = kf.generatePrivate(privateKeySpec);
 
 		KeyStore keyStore = createKeyStore();
 
-		List<X509Certificate> certChain = new ArrayList<X509Certificate>();
+		List<X509Certificate> certChain = new ArrayList<>();
 		Collections.addAll(certChain, certificates);
 
 		keyStore.setKeyEntry(keyAlias, privateKey, new char[0],
@@ -67,18 +68,15 @@ class KeystoreUtil {
 		return keyStore;
 	}
 
-	static X509Certificate getCertificate(byte[] source) throws CertificateException,
-			IOException {
+	static X509Certificate getCertificate(byte[] source)
+			throws CertificateException, IOException {
 
 		CertificateFactory certificateFactory = CertificateFactory.getInstance("X.509");
 
 		List<X509Certificate> certificates = getCertificates(certificateFactory, source);
 
-		if (certificates.isEmpty()) {
-			return null;
-		}
-
-		return certificates.get(0);
+		return certificates.stream().findFirst().orElseThrow(
+				() -> new IllegalArgumentException("No X509Certificate found"));
 	}
 
 	/**
@@ -88,7 +86,8 @@ class KeystoreUtil {
 	 * @throws GeneralSecurityException
 	 * @throws IOException
 	 */
-	private static KeyStore createKeyStore() throws GeneralSecurityException, IOException {
+	private static KeyStore createKeyStore()
+			throws GeneralSecurityException, IOException {
 
 		KeyStore keyStore = KeyStore.getInstance(KeyStore.getDefaultType());
 		keyStore.load(null, new char[0]);
@@ -99,7 +98,7 @@ class KeystoreUtil {
 	private static List<X509Certificate> getCertificates(CertificateFactory cf,
 			byte[] source) throws CertificateException, IOException {
 
-		List<X509Certificate> x509Certificates = new ArrayList<X509Certificate>();
+		List<X509Certificate> x509Certificates = new ArrayList<>();
 
 		ByteArrayInputStream bis = new ByteArrayInputStream(source);
 		while (bis.available() > 0) {
@@ -299,8 +298,8 @@ class KeystoreUtil {
 
 			// We can't handle length longer than 4 bytes
 			if (i >= 0xFF || num > 4) {
-				throw new IllegalStateException("Invalid DER: length field too big (" + i
-						+ ")");
+				throw new IllegalStateException(
+						"Invalid DER: length field too big (" + i + ")");
 			}
 
 			byte[] bytes = new byte[num];
diff --git a/spring-vault-core/src/main/java/org/springframework/vault/support/VaultCertificateRequest.java b/spring-vault-core/src/main/java/org/springframework/vault/support/VaultCertificateRequest.java
index bfc6ad1f..9e51eef0 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/support/VaultCertificateRequest.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/support/VaultCertificateRequest.java
@@ -107,8 +107,8 @@ public class VaultCertificateRequest {
 	public static class VaultCertificateRequestBuilder {
 
 		private String commonName;
-		private List<String> altNames = new ArrayList<String>();
-		private List<String> ipSubjectAltNames = new ArrayList<String>();
+		private List<String> altNames = new ArrayList<>();
+		private List<String> ipSubjectAltNames = new ArrayList<>();
 		private Integer ttl;
 		private Boolean excludeCommonNameFromSubjectAltNames;
 
@@ -249,7 +249,8 @@ public class VaultCertificateRequest {
 				altNames = java.util.Collections.singletonList(this.altNames.get(0));
 				break;
 			default:
-				altNames = java.util.Collections.unmodifiableList(new ArrayList<String>(
+				altNames = java.util.Collections
+						.unmodifiableList(new ArrayList<>(
 						this.altNames));
 			}
 
@@ -264,7 +265,7 @@ public class VaultCertificateRequest {
 				break;
 			default:
 				ipSubjectAltNames = java.util.Collections
-						.unmodifiableList(new ArrayList<String>(this.ipSubjectAltNames));
+						.unmodifiableList(new ArrayList<>(this.ipSubjectAltNames));
 			}
 
 			return new VaultCertificateRequest(commonName, altNames, ipSubjectAltNames,
@@ -273,7 +274,7 @@ public class VaultCertificateRequest {
 
 		private static <E> List<E> toList(Iterable<E> iter) {
 
-			List<E> list = new ArrayList<E>();
+			List<E> list = new ArrayList<>();
 			for (E item : iter) {
 				list.add(item);
 			}
diff --git a/spring-vault-core/src/main/java/org/springframework/vault/support/VaultTokenRequest.java b/spring-vault-core/src/main/java/org/springframework/vault/support/VaultTokenRequest.java
index 468cf388..4413be1d 100644
--- a/spring-vault-core/src/main/java/org/springframework/vault/support/VaultTokenRequest.java
+++ b/spring-vault-core/src/main/java/org/springframework/vault/support/VaultTokenRequest.java
@@ -168,9 +168,9 @@ public class VaultTokenRequest {
 
 		private String id;
 
-		private List<String> policies = new ArrayList<String>();
+		private List<String> policies = new ArrayList<>();
 
-		private Map<String, String> meta = new LinkedHashMap<String, String>();
+		private Map<String, String> meta = new LinkedHashMap<>();
 
 		private Boolean noParent;
 
@@ -414,7 +414,7 @@ public class VaultTokenRequest {
 				policies = Collections.singletonList(this.policies.get(0));
 				break;
 			default:
-				policies = Collections.unmodifiableList(new ArrayList<String>(
+				policies = Collections.unmodifiableList(new ArrayList<>(
 						this.policies));
 
 			}
@@ -425,7 +425,7 @@ public class VaultTokenRequest {
 				break;
 			default:
 				meta = Collections
-						.unmodifiableMap(new LinkedHashMap<String, String>(this.meta));
+						.unmodifiableMap(new LinkedHashMap<>(this.meta));
 			}
 
 			return new VaultTokenRequest(id, policies, meta, noParent, noDefaultPolicy,
@@ -434,7 +434,7 @@ public class VaultTokenRequest {
 
 		private static <E> List<E> toList(Iterable<E> iter) {
 
-			List<E> list = new ArrayList<E>();
+			List<E> list = new ArrayList<>();
 			for (E item : iter) {
 				list.add(item);
 			}
diff --git a/spring-vault-core/src/test/java/org/springframework/vault/authentication/AppIdAuthenticationIntegrationTests.java b/spring-vault-core/src/test/java/org/springframework/vault/authentication/AppIdAuthenticationIntegrationTests.java
index 80b4c16c..612d027f 100644
--- a/spring-vault-core/src/test/java/org/springframework/vault/authentication/AppIdAuthenticationIntegrationTests.java
+++ b/spring-vault-core/src/test/java/org/springframework/vault/authentication/AppIdAuthenticationIntegrationTests.java
@@ -22,12 +22,10 @@ import org.junit.Before;
 import org.junit.Test;
 
 import org.springframework.vault.VaultException;
-import org.springframework.vault.core.RestOperationsCallback;
 import org.springframework.vault.support.VaultToken;
 import org.springframework.vault.util.IntegrationTestSupport;
 import org.springframework.vault.util.Settings;
 import org.springframework.vault.util.TestRestTemplateFactory;
-import org.springframework.web.client.RestOperations;
 import org.springframework.web.client.RestTemplate;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -47,27 +45,24 @@ public class AppIdAuthenticationIntegrationTests extends IntegrationTestSupport
 		}
 
 		prepare().getVaultOperations().doWithSession(
-				new RestOperationsCallback<Object>() {
-					@Override
-					public Object doWithRestOperations(RestOperations restOperations) {
+				restOperations -> {
 
-						Map<String, String> appIdData = new HashMap<String, String>();
-						appIdData.put("value", "dummy"); // policy
-						appIdData.put("display_name", "this is my test application");
+					Map<String, String> appIdData = new HashMap<String, String>();
+					appIdData.put("value", "dummy"); // policy
+					appIdData.put("display_name", "this is my test application");
 
-						restOperations.postForEntity("auth/app-id/map/app-id/myapp",
-								appIdData, Map.class);
+					restOperations.postForEntity("auth/app-id/map/app-id/myapp",
+							appIdData, Map.class);
 
-						Map<String, String> userIdData = new HashMap<String, String>();
-						userIdData.put("value", "myapp"); // name of the app-id
-						userIdData.put("cidr_block", "0.0.0.0/0");
+					Map<String, String> userIdData = new HashMap<String, String>();
+					userIdData.put("value", "myapp"); // name of the app-id
+					userIdData.put("cidr_block", "0.0.0.0/0");
 
-						restOperations.postForEntity(
-								"auth/app-id/map/user-id/static-userid-value",
-								userIdData, Map.class);
+					restOperations.postForEntity(
+							"auth/app-id/map/user-id/static-userid-value", userIdData,
+							Map.class);
 
-						return null;
-					}
+					return null;
 				});
 	}
 
diff --git a/spring-vault-core/src/test/java/org/springframework/vault/authentication/AppRoleAuthenticationIntegrationTests.java b/spring-vault-core/src/test/java/org/springframework/vault/authentication/AppRoleAuthenticationIntegrationTests.java
index 784d7bd5..745a7e8e 100644
--- a/spring-vault-core/src/test/java/org/springframework/vault/authentication/AppRoleAuthenticationIntegrationTests.java
+++ b/spring-vault-core/src/test/java/org/springframework/vault/authentication/AppRoleAuthenticationIntegrationTests.java
@@ -23,11 +23,9 @@ import org.junit.Before;
 import org.junit.Test;
 
 import org.springframework.vault.VaultException;
-import org.springframework.vault.core.RestOperationsCallback;
 import org.springframework.vault.core.VaultOperations;
 import org.springframework.vault.support.VaultResponse;
 import org.springframework.vault.util.IntegrationTestSupport;
-import org.springframework.web.client.RestOperations;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.hamcrest.CoreMatchers.anyOf;
@@ -56,28 +54,25 @@ public class AppRoleAuthenticationIntegrationTests extends IntegrationTestSuppor
 			prepare().mountAuth("approle");
 		}
 
-		getVaultOperations().doWithSession(new RestOperationsCallback<Object>() {
-			@Override
-			public Object doWithRestOperations(RestOperations restOperations) {
+		getVaultOperations().doWithSession(restOperations -> {
 
-				Map<String, String> withSecretId = new HashMap<String, String>();
-				withSecretId.put("policies", "dummy"); // policy
-				withSecretId.put("bound_cidr_list", "0.0.0.0/0");
-				withSecretId.put("bind_secret_id", "true");
+			Map<String, String> withSecretId = new HashMap<String, String>();
+			withSecretId.put("policies", "dummy"); // policy
+			withSecretId.put("bound_cidr_list", "0.0.0.0/0");
+			withSecretId.put("bind_secret_id", "true");
 
-				restOperations.postForEntity("auth/approle/role/with-secret-id",
-						withSecretId, Map.class);
+			restOperations.postForEntity("auth/approle/role/with-secret-id", withSecretId,
+					Map.class);
 
-				Map<String, String> noSecretIdRole = new HashMap<String, String>();
-				noSecretIdRole.put("policies", "dummy"); // policy
-				noSecretIdRole.put("bound_cidr_list", "0.0.0.0/0");
-				noSecretIdRole.put("bind_secret_id", "false");
+			Map<String, String> noSecretIdRole = new HashMap<String, String>();
+			noSecretIdRole.put("policies", "dummy"); // policy
+			noSecretIdRole.put("bound_cidr_list", "0.0.0.0/0");
+			noSecretIdRole.put("bind_secret_id", "false");
 
-				restOperations.postForEntity("auth/approle/role/no-secret-id",
-						noSecretIdRole, Map.class);
+			restOperations.postForEntity("auth/approle/role/no-secret-id", noSecretIdRole,
+					Map.class);
 
-				return null;
-			}
+			return null;
 		});
 	}
 
diff --git a/spring-vault-core/src/test/java/org/springframework/vault/authentication/ClientCertificateAuthenticationIntegrationTests.java b/spring-vault-core/src/test/java/org/springframework/vault/authentication/ClientCertificateAuthenticationIntegrationTests.java
index 22306cc9..f3cad3ec 100644
--- a/spring-vault-core/src/test/java/org/springframework/vault/authentication/ClientCertificateAuthenticationIntegrationTests.java
+++ b/spring-vault-core/src/test/java/org/springframework/vault/authentication/ClientCertificateAuthenticationIntegrationTests.java
@@ -16,7 +16,7 @@
 package org.springframework.vault.authentication;
 
 import java.io.File;
-import java.nio.charset.Charset;
+import java.nio.charset.StandardCharsets;
 import java.util.Collections;
 import java.util.Map;
 
@@ -36,7 +36,6 @@ import org.springframework.vault.support.VaultToken;
 import org.springframework.vault.util.IntegrationTestSupport;
 import org.springframework.vault.util.Settings;
 import org.springframework.vault.util.TestRestTemplateFactory;
-import org.springframework.web.client.RestOperations;
 import org.springframework.web.client.RestTemplate;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -48,8 +47,8 @@ import static org.springframework.vault.util.Settings.findWorkDir;
  *
  * @author Mark Paluch
  */
-public class ClientCertificateAuthenticationIntegrationTests extends
-		IntegrationTestSupport {
+public class ClientCertificateAuthenticationIntegrationTests
+		extends IntegrationTestSupport {
 
 	@Before
 	public void before() throws Exception {
@@ -58,19 +57,17 @@ public class ClientCertificateAuthenticationIntegrationTests extends
 			prepare().mountAuth("cert");
 		}
 
-		prepare().getVaultOperations().doWithSession(
-				new RestOperationsCallback<Object>() {
-					@Override
-					public Object doWithRestOperations(RestOperations restOperations) {
-						File workDir = findWorkDir();
+		prepare().getVaultOperations()
+				.doWithSession((RestOperationsCallback<Object>) restOperations -> {
+					File workDir = findWorkDir();
 
-						String certificate = Files.contentOf(new File(workDir,
-								"ca/certs/client.cert.pem"), Charset.forName("US-ASCII"));
+					String certificate = Files.contentOf(
+							new File(workDir, "ca/certs/client.cert.pem"),
+							StandardCharsets.US_ASCII);
 
-						return restOperations.postForEntity("auth/cert/certs/my-role",
-								Collections.singletonMap("certificate", certificate),
-								Map.class);
-					}
+					return restOperations.postForEntity("auth/cert/certs/my-role",
+							Collections.singletonMap("certificate", certificate),
+							Map.class);
 				});
 	}
 
@@ -106,9 +103,9 @@ public class ClientCertificateAuthenticationIntegrationTests extends
 
 		SslConfiguration original = createSslConfiguration();
 
-		SslConfiguration sslConfiguration = new SslConfiguration(new FileSystemResource(
-				new File(findWorkDir(), "client-cert.jks")), "changeit",
-				original.getTrustStore(), original.getTrustStorePassword());
+		SslConfiguration sslConfiguration = new SslConfiguration(
+				new FileSystemResource(new File(findWorkDir(), "client-cert.jks")),
+				"changeit", original.getTrustStore(), original.getTrustStorePassword());
 
 		return sslConfiguration;
 	}
diff --git a/spring-vault-core/src/test/java/org/springframework/vault/authentication/CubbyholeAuthenticationIntegrationTests.java b/spring-vault-core/src/test/java/org/springframework/vault/authentication/CubbyholeAuthenticationIntegrationTests.java
index c6201aa9..bd99d719 100644
--- a/spring-vault-core/src/test/java/org/springframework/vault/authentication/CubbyholeAuthenticationIntegrationTests.java
+++ b/spring-vault-core/src/test/java/org/springframework/vault/authentication/CubbyholeAuthenticationIntegrationTests.java
@@ -24,13 +24,11 @@ import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpMethod;
 import org.springframework.http.ResponseEntity;
 import org.springframework.vault.VaultException;
-import org.springframework.vault.core.RestOperationsCallback;
 import org.springframework.vault.support.VaultResponse;
 import org.springframework.vault.support.VaultToken;
 import org.springframework.vault.util.IntegrationTestSupport;
 import org.springframework.vault.util.Settings;
 import org.springframework.vault.util.TestRestTemplateFactory;
-import org.springframework.web.client.RestOperations;
 import org.springframework.web.client.RestTemplate;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -49,18 +47,14 @@ public class CubbyholeAuthenticationIntegrationTests extends IntegrationTestSupp
 
 		ResponseEntity<VaultResponse> response = prepare().getVaultOperations()
 				.doWithSession(
-						new RestOperationsCallback<ResponseEntity<VaultResponse>>() {
-							@Override
-							public ResponseEntity<VaultResponse> doWithRestOperations(
-									RestOperations restOperations) {
+						restOperations -> {
 
-								HttpHeaders headers = new HttpHeaders();
-								headers.add("X-Vault-Wrap-TTL", "10m");
+							HttpHeaders headers = new HttpHeaders();
+							headers.add("X-Vault-Wrap-TTL", "10m");
 
-								return restOperations.exchange("auth/token/create",
-										HttpMethod.POST, new HttpEntity<Object>(headers),
-										VaultResponse.class);
-							}
+							return restOperations.exchange("auth/token/create",
+									HttpMethod.POST, new HttpEntity<Object>(headers),
+									VaultResponse.class);
 						});
 
 		Map<String, String> wrapInfo = response.getBody().getWrapInfo();
diff --git a/spring-vault-core/src/test/java/org/springframework/vault/authentication/LifecycleAwareSessionManagerIntegrationTests.java b/spring-vault-core/src/test/java/org/springframework/vault/authentication/LifecycleAwareSessionManagerIntegrationTests.java
index 106e1486..048809f6 100644
--- a/spring-vault-core/src/test/java/org/springframework/vault/authentication/LifecycleAwareSessionManagerIntegrationTests.java
+++ b/spring-vault-core/src/test/java/org/springframework/vault/authentication/LifecycleAwareSessionManagerIntegrationTests.java
@@ -25,13 +25,11 @@ import org.junit.Test;
 
 import org.springframework.http.HttpStatus;
 import org.springframework.scheduling.concurrent.ThreadPoolTaskScheduler;
-import org.springframework.vault.core.RestOperationsCallback;
 import org.springframework.vault.core.VaultTokenOperations;
 import org.springframework.vault.support.VaultToken;
 import org.springframework.vault.support.VaultTokenRequest;
 import org.springframework.vault.util.IntegrationTestSupport;
 import org.springframework.web.client.HttpStatusCodeException;
-import org.springframework.web.client.RestOperations;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.fail;
@@ -114,23 +112,20 @@ public class LifecycleAwareSessionManagerIntegrationTests extends IntegrationTes
 		sessionManager.destroy();
 
 		prepare().getVaultOperations().doWithSession(
-				new RestOperationsCallback<Object>() {
-					@Override
-					public Object doWithRestOperations(RestOperations restOperations) {
+				restOperations -> {
 
-						try {
-							restOperations.getForEntity("auth/token/lookup/{token}",
-									Map.class, loginToken.toCharArray());
-							fail("Missing HttpStatusCodeException");
-						}
-						catch (HttpStatusCodeException e) {
-							// Compatibility across Vault versions.
-							assertThat(e.getStatusCode()).isIn(HttpStatus.BAD_REQUEST,
-									HttpStatus.NOT_FOUND, HttpStatus.FORBIDDEN);
-						}
-
-						return null;
+					try {
+						restOperations.getForEntity("auth/token/lookup/{token}",
+								Map.class, loginToken.toCharArray());
+						fail("Missing HttpStatusCodeException");
 					}
+					catch (HttpStatusCodeException e) {
+						// Compatibility across Vault versions.
+						assertThat(e.getStatusCode()).isIn(HttpStatus.BAD_REQUEST,
+								HttpStatus.NOT_FOUND, HttpStatus.FORBIDDEN);
+					}
+
+					return null;
 				});
 	}
 
diff --git a/spring-vault-core/src/test/java/org/springframework/vault/core/VaultTemplateTransitIntegrationTests.java b/spring-vault-core/src/test/java/org/springframework/vault/core/VaultTemplateTransitIntegrationTests.java
index 18d79646..36c52a6b 100644
--- a/spring-vault-core/src/test/java/org/springframework/vault/core/VaultTemplateTransitIntegrationTests.java
+++ b/spring-vault-core/src/test/java/org/springframework/vault/core/VaultTemplateTransitIntegrationTests.java
@@ -102,9 +102,7 @@ public class VaultTemplateTransitIntegrationTests extends IntegrationTestSupport
 
 		if (vaultVersion.isGreaterThanOrEqualTo(Version.parse("0.6.4"))) {
 			List<String> keys = vaultOperations.opsForTransit().getKeys();
-			for (String keyName : keys) {
-				deleteKey(keyName);
-			}
+			keys.forEach(this::deleteKey);
 		}
 		else {
 			deleteKey("mykey");
diff --git a/spring-vault-core/src/test/java/org/springframework/vault/core/VaultTokenTemplateIntegrationTests.java b/spring-vault-core/src/test/java/org/springframework/vault/core/VaultTokenTemplateIntegrationTests.java
index 55debe34..f1684f4d 100644
--- a/spring-vault-core/src/test/java/org/springframework/vault/core/VaultTokenTemplateIntegrationTests.java
+++ b/spring-vault-core/src/test/java/org/springframework/vault/core/VaultTokenTemplateIntegrationTests.java
@@ -35,7 +35,6 @@ import org.springframework.vault.client.VaultHttpHeaders;
 import org.springframework.vault.support.VaultTokenRequest;
 import org.springframework.vault.support.VaultTokenResponse;
 import org.springframework.vault.util.IntegrationTestSupport;
-import org.springframework.web.client.RestOperations;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -162,19 +161,14 @@ public class VaultTokenTemplateIntegrationTests extends IntegrationTestSupport {
 	private ResponseEntity<String> lookupSelf(final VaultTokenResponse tokenResponse) {
 
 		return vaultOperations
-				.doWithVault(new RestOperationsCallback<ResponseEntity<String>>() {
-					@Override
-					public ResponseEntity<String> doWithRestOperations(
-							RestOperations restOperations) {
-						HttpHeaders headers = new HttpHeaders();
-						headers.add(VaultHttpHeaders.VAULT_TOKEN, tokenResponse
-								.getToken()
-								.getToken());
+				.doWithVault(restOperations -> {
+					HttpHeaders headers = new HttpHeaders();
+					headers.add(VaultHttpHeaders.VAULT_TOKEN,
+							tokenResponse.getToken().getToken());
 
-						return restOperations.exchange("auth/token/lookup-self",
-								HttpMethod.GET, new HttpEntity<Object>(headers),
-								String.class);
-					}
+					return restOperations.exchange("auth/token/lookup-self",
+							HttpMethod.GET, new HttpEntity<Object>(headers),
+							String.class);
 				});
 
 	}