Change ServerRequest.attribute(String) to return Object

This commit changes `ServerRequest.attribute(String)`` to return
`Optional<Object>` instead of `Optional<T>`, where `T` was infered
from a type parameter.

spring-test/src/main/java/org/springframework/mock/web/reactive/function/server/MockServerRequest.java

@@ -156,12 +156,6 @@ public class MockServerRequest implements ServerRequest {
 		return (Flux<S>) this.body;
 	}
 
-	@SuppressWarnings("unchecked")
-	@Override
-	public <S> Optional<S> attribute(String name) {
-		return Optional.ofNullable((S) this.attributes.get(name));
-	}
-
 	@Override
 	public Map<String, Object> attributes() {
 		return this.attributes;

spring-webflux/src/main/java/org/springframework/web/reactive/function/server/DefaultServerRequest.java

@@ -145,11 +145,6 @@ class DefaultServerRequest implements ServerRequest {
 		return flux.onErrorMap(UnsupportedMediaTypeException.class, ERROR_MAPPER);
 	}
 
-	@Override
-	public <T> Optional<T> attribute(String name) {
-		return Optional.ofNullable(this.exchange.getAttribute(name));
-	}
-
 	@Override
 	public Map<String, Object> attributes() {
 		return this.exchange.getAttributes();

spring-webflux/src/main/java/org/springframework/web/reactive/function/server/RequestPredicates.java

@@ -521,7 +521,7 @@ public abstract class RequestPredicates {
 		}
 
 		@Override
-		public <T> Optional<T> attribute(String name) {
+		public Optional<Object> attribute(String name) {
 			return this.request.attribute(name);
 		}
 

spring-webflux/src/main/java/org/springframework/web/reactive/function/server/ServerRequest.java

@@ -129,10 +129,17 @@ public interface ServerRequest {
 	/**
 	 * Return the request attribute value if present.
 	 * @param name the attribute name
-	 * @param <T> the attribute type
 	 * @return the attribute value
 	 */
-	<T> Optional<T> attribute(String name);
+	default Optional<Object> attribute(String name) {
+		Map<String, Object> attributes = attributes();
+		if (attributes.containsKey(name)) {
+			return Optional.of(attributes.get(name));
+		}
+		else {
+			return Optional.empty();
+		}
+	}
 
 	/**
 	 * Return a mutable map of request attributes.

spring-webflux/src/main/java/org/springframework/web/reactive/function/server/support/ServerRequestWrapper.java

@@ -124,7 +124,7 @@ public class ServerRequestWrapper implements ServerRequest {
 	}
 
 	@Override
-	public <T> Optional<T> attribute(String name) {
+	public Optional<Object> attribute(String name) {
 		return this.delegate.attribute(name);
 	}
 

spring-webflux/src/test/java/org/springframework/web/reactive/function/server/MockServerRequest.java

@@ -155,12 +155,6 @@ public class MockServerRequest implements ServerRequest {
 		return (Flux<S>) this.body;
 	}
 
-	@SuppressWarnings("unchecked")
-	@Override
-	public <S> Optional<S> attribute(String name) {
-		return Optional.ofNullable((S) this.attributes.get(name));
-	}
-
 	@Override
 	public Map<String, Object> attributes() {
 		return this.attributes;