Refactor ServerWebExchange#getAttribute options

Issue: SPR-15718

spring-web/src/main/java/org/springframework/web/server/ServerWebExchange.java

@@ -19,7 +19,6 @@ package org.springframework.web.server;
 import java.security.Principal;
 import java.time.Instant;
 import java.util.Map;
-import java.util.Optional;
 import java.util.function.Consumer;
 
 import reactor.core.publisher.Mono;
@@ -29,6 +28,7 @@ import org.springframework.http.codec.multipart.Part;
 import org.springframework.http.server.reactive.ServerHttpRequest;
 import org.springframework.http.server.reactive.ServerHttpResponse;
 import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
 import org.springframework.util.MultiValueMap;
 import org.springframework.web.server.i18n.LocaleContextResolver;
 
@@ -63,7 +63,37 @@ public interface ServerWebExchange {
 	 * @param <T> the attribute type
 	 * @return the attribute value
 	 */
-	<T> Optional<T> getAttribute(String name);
+	@SuppressWarnings("unchecked")
+	@Nullable
+	default <T> T getAttribute(String name) {
+		return (T) getAttributes().get(name);
+	}
+
+	/**
+	 * Return the request attribute value or if not present raise an
+	 * {@link IllegalArgumentException}.
+	 * @param name the attribute name
+	 * @param <T> the attribute type
+	 * @return the attribute value
+	 */
+	@SuppressWarnings("unchecked")
+	default <T> T getRequiredAttribute(String name) {
+		T value = getAttribute(name);
+		Assert.notNull(value, "Required attribute '" + name + "' is missing.");
+		return value;
+	}
+
+	/**
+	 * Return the request attribute value, or a default, fallback value.
+	 * @param name the attribute name
+	 * @param defaultValue a default value to return instead
+	 * @param <T> the attribute type
+	 * @return the attribute value
+	 */
+	@SuppressWarnings("unchecked")
+	default <T> T getAttributeOrDefault(String name, T defaultValue) {
+		return (T) getAttributes().getOrDefault(name, defaultValue);
+	}
 
 	/**
 	 * Return the web session for the current request. Always guaranteed  to

spring-web/src/main/java/org/springframework/web/server/ServerWebExchangeDecorator.java

@@ -18,7 +18,6 @@ package org.springframework.web.server;
 import java.security.Principal;
 import java.time.Instant;
 import java.util.Map;
-import java.util.Optional;
 
 import reactor.core.publisher.Mono;
 
@@ -76,11 +75,6 @@ public class ServerWebExchangeDecorator implements ServerWebExchange {
 		return getDelegate().getAttributes();
 	}
 
-	@Override
-	public <T> Optional<T> getAttribute(String name) {
-		return getDelegate().getAttribute(name);
-	}
-
 	@Override
 	public Mono<WebSession> getSession() {
 		return getDelegate().getSession();

spring-web/src/main/java/org/springframework/web/server/adapter/DefaultServerWebExchange.java

@@ -23,7 +23,6 @@ import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
-import java.util.Optional;
 import java.util.concurrent.ConcurrentHashMap;
 
 import reactor.core.publisher.Mono;
@@ -46,9 +45,9 @@ import org.springframework.util.CollectionUtils;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
 import org.springframework.util.StringUtils;
-import org.springframework.web.server.i18n.LocaleContextResolver;
 import org.springframework.web.server.ServerWebExchange;
 import org.springframework.web.server.WebSession;
+import org.springframework.web.server.i18n.LocaleContextResolver;
 import org.springframework.web.server.session.WebSessionManager;
 
 /**
@@ -178,11 +177,6 @@ public class DefaultServerWebExchange implements ServerWebExchange {
 		return this.attributes;
 	}
 
-	@Override @SuppressWarnings("unchecked")
-	public <T> Optional<T> getAttribute(String name) {
-		return Optional.ofNullable((T) this.attributes.get(name));
-	}
-
 	@Override
 	public Mono<WebSession> getSession() {
 		return this.sessionMono;