Added an option to use SC-Zookeeper in a non-web app

without this change when you don't use web environment then your context fails to start
    with this change we allow users to use sc-zookeeper as a clients without the need to register in SC-Zookeeper

    fixes #91

README.adoc

@@ -95,11 +95,11 @@ a modified file in the correct place. Just commit it and push the change.
 If you don't have an IDE preference we would recommend that you use
 http://www.springsource.com/developer/sts[Spring Tools Suite] or
 http://eclipse.org[Eclipse] when working with the code. We use the
-http://eclipse.org/m2e/[m2eclipe] eclipse plugin for maven support. Other IDEs and tools
+http://eclipse.org/m2e/[m2eclipse] eclipse plugin for maven support. Other IDEs and tools
 should also work without issue as long as they use Maven 3.3.3 or better.
 
 ==== Importing into eclipse with m2eclipse
-We recommend the http://eclipse.org/m2e/[m2eclipe] eclipse plugin when working with
+We recommend the http://eclipse.org/m2e/[m2eclipse] eclipse plugin when working with
 eclipse. If you don't already have m2eclipse installed it is available from the "eclipse
 marketplace".
 

spring-cloud-zookeeper-discovery/src/main/java/org/springframework/cloud/zookeeper/discovery/ZookeeperDiscoveryClient.java

@@ -84,6 +84,9 @@ public class ZookeeperDiscoveryClient implements DiscoveryClient {
 	public List<org.springframework.cloud.client.ServiceInstance> getInstances(
 			final String serviceId) {
 		try {
+			if (this.serviceDiscovery.getServiceDiscovery() == null) {
+				return Collections.EMPTY_LIST;
+			}
 			String serviceIdToQuery = getServiceIdToQuery(serviceId);
 			Collection<ServiceInstance<ZookeeperInstance>> zkInstances = this.serviceDiscovery
 				.getServiceDiscovery().queryForInstances(serviceIdToQuery);

spring-cloud-zookeeper-discovery/src/main/java/org/springframework/cloud/zookeeper/discovery/ZookeeperLifecycle.java

@@ -43,6 +43,7 @@ public class ZookeeperLifecycle extends AbstractDiscoveryLifecycle {
 			this.serviceDiscovery.setPort(this.properties.getInstancePort());
 			this.serviceDiscovery.build();
 		}
+		this.serviceDiscovery.buildServiceDiscovery();
 	}
 
 	@Override
@@ -91,6 +92,7 @@ public class ZookeeperLifecycle extends AbstractDiscoveryLifecycle {
 	protected void setConfiguredPort(int port) {
 		this.serviceDiscovery.setPort(port);
 		this.serviceDiscovery.build();
+		this.serviceDiscovery.buildServiceDiscovery();
 	}
 
 	@Override

spring-cloud-zookeeper-discovery/src/main/java/org/springframework/cloud/zookeeper/discovery/ZookeeperServerList.java

@@ -21,14 +21,14 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
 
-import com.netflix.client.config.IClientConfig;
-import com.netflix.loadbalancer.AbstractServerList;
-
 import org.apache.curator.x.discovery.ServiceDiscovery;
 import org.apache.curator.x.discovery.ServiceInstance;
 import org.springframework.cloud.zookeeper.discovery.dependency.ZookeeperDependencies;
 import org.springframework.util.StringUtils;
 
+import com.netflix.client.config.IClientConfig;
+import com.netflix.loadbalancer.AbstractServerList;
+
 import static org.springframework.util.ReflectionUtils.rethrowRuntimeException;
 
 /**
@@ -76,6 +76,9 @@ public class ZookeeperServerList extends AbstractServerList<ZookeeperServer> {
 	@SuppressWarnings("unchecked")
 	private List<ZookeeperServer> getServers() {
 		try {
+			if (this.serviceDiscovery == null) {
+				return Collections.EMPTY_LIST;
+			}
 			Collection<ServiceInstance<ZookeeperInstance>> instances = this.serviceDiscovery
 					.queryForInstances(this.serviceId);
 			if (instances == null || instances.isEmpty()) {

spring-cloud-zookeeper-discovery/src/main/java/org/springframework/cloud/zookeeper/discovery/ZookeeperServiceDiscovery.java

@@ -90,9 +90,13 @@ public class ZookeeperServiceDiscovery implements ApplicationContextAware {
 		this.context = context;
 	}
 
+	/**
+	 * Builds Service Instance - needs to be used when you want to register your application
+	 * in Zookeeper
+	 */
 	public void build() {
 		if (this.built.compareAndSet(false, true)) {
-			if (this.port.get() <= 0) {
+			if (this.port.get() <= 0 && this.properties.isRegister()) {
 				throw new IllegalStateException("Cannot create instance whose port is not greater than 0");
 			}
 			String host = this.properties.getInstanceHost();
@@ -100,13 +104,22 @@ public class ZookeeperServiceDiscovery implements ApplicationContextAware {
 				throw new IllegalStateException("instanceHost must not be empty");
 			}
 			UriSpec uriSpec = new UriSpec(this.properties.getUriSpec());
-			configureServiceInstance(this.serviceInstance, this.appName,
-					this.context, this.port, host, uriSpec);
-			configureServiceDiscovery(this.serviceDiscovery, this.curator, this.properties,
-					this.instanceSerializer, this.serviceInstance);
+			if (this.properties.isRegister()) {
+				configureServiceInstance(this.serviceInstance, this.appName,
+						this.context, this.port, host, uriSpec);
+			}
 		}
 	}
 
+	/**
+	 * Builds Service Discovery - needs to be used if you want to use Zookeeper as a client application.
+	 * You don't have to register in Zookeeper to use Service Discovery.
+	 */
+	public void buildServiceDiscovery() {
+		configureServiceDiscovery(this.serviceDiscovery, this.curator, this.properties,
+				this.instanceSerializer, this.serviceInstance);
+	}
+
 	/**
 	 * One can override this method to provide custom way of registering a service
 	 * instance (e.g. when no payload is required).

spring-cloud-zookeeper-discovery/src/test/java/org/springframework/cloud/zookeeper/discovery/issues/issue91/Issue91Tests.java

@@ -0,0 +1,101 @@
+package org.springframework.cloud.zookeeper.discovery.issues.issue91;
+
+import org.apache.curator.test.TestingServer;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.actuate.autoconfigure.EndpointMBeanExportAutoConfiguration;
+import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
+import org.springframework.boot.autoconfigure.jmx.JmxAutoConfiguration;
+import org.springframework.cloud.client.discovery.DiscoveryClient;
+import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
+import org.springframework.cloud.client.loadbalancer.LoadBalanced;
+import org.springframework.context.ConfigurableApplicationContext;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.util.SocketUtils;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
+import org.springframework.web.client.RestTemplate;
+
+import com.jayway.awaitility.Awaitility;
+
+import static org.assertj.core.api.BDDAssertions.then;
+
+/**
+ * @author Marcin Grzejszczak
+ */
+public class Issue91Tests {
+
+	TestingServer server;
+	String connectionString;
+
+	@Before
+	public void setup() throws Exception {
+		this.server = new TestingServer(SocketUtils.findAvailableTcpPort());
+		this.connectionString = "--spring.cloud.zookeeper.connectString=" + this.server.getConnectString();
+	}
+
+	@After
+	public void cleanup() throws Exception {
+		this.server.close();
+	}
+
+	@Test
+	public void should_work_when_using_web_client_without_the_web_environment()
+			throws Exception {
+		SpringApplication producerApp = new SpringApplication(HelloProducer.class);
+		producerApp.setWebEnvironment(true);
+		SpringApplication clientApplication = new SpringApplication(HelloClient.class);
+		clientApplication.setWebEnvironment(false);
+
+		try (ConfigurableApplicationContext producerContext = producerApp.run(this.connectionString, "--server.port=0",
+				"--spring.application.name=hello-world")) {
+			try (final ConfigurableApplicationContext context = clientApplication.run(this.connectionString,
+					"--spring.cloud.zookeeper.discovery.register=false")) {
+				Awaitility.await().until(new Runnable() {
+					@Override public void run() {
+						try {
+							HelloClient bean = context.getBean(HelloClient.class);
+							then(bean.discoveryClient.getServices()).isNotEmpty();
+							then(bean.discoveryClient.getInstances("hello-world")).isNotEmpty();
+							String string = bean.restTemplate.getForObject("http://hello-world/", String.class);
+							then(string).isEqualTo("foo");
+						} catch (IllegalStateException e) {
+							throw new AssertionError(e);
+						}
+					}
+				});
+			}
+		}
+	}
+}
+
+@EnableAutoConfiguration(exclude = {EndpointMBeanExportAutoConfiguration.class,
+		JmxAutoConfiguration.class})
+@EnableDiscoveryClient
+@Configuration
+class HelloClient {
+	@LoadBalanced @Bean RestTemplate restTemplate() {
+		return new RestTemplate();
+	}
+
+	@Autowired DiscoveryClient discoveryClient;
+
+	@Autowired RestTemplate restTemplate;
+}
+
+@EnableAutoConfiguration(exclude = {EndpointMBeanExportAutoConfiguration.class,
+		JmxAutoConfiguration.class})
+@EnableDiscoveryClient
+@RestController
+class HelloProducer {
+
+	@RequestMapping("/")
+	public String foo() {
+		return "foo";
+	}
+
+}