Add @SessionAttribute with Servlet-based support

Issue: SPR-13894

spring-web/src/main/java/org/springframework/web/bind/annotation/RequestMapping.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2016 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.
@@ -126,6 +126,10 @@ import org.springframework.core.annotation.AliasFor;
  * {@link org.springframework.validation.Errors} argument.
  * Instead a {@link org.springframework.web.bind.MethodArgumentNotValidException}
  * exception is raised.
+ * <li>{@link SessionAttribute @SessionAttribute} annotated parameters for access
+ * to existing, permanent session attributes (e.g. user authentication object)
+ * as opposed to model attributes temporarily stored in the session as part of
+ * a controller workflow via {@link SessionAttributes}.
  * <li>{@link org.springframework.http.HttpEntity HttpEntity&lt;?&gt;} parameters
  * (Servlet-only) for access to the Servlet request HTTP headers and contents.
  * The request stream will be converted to the entity body using

spring-web/src/main/java/org/springframework/web/bind/annotation/SessionAttribute.java

@@ -0,0 +1,73 @@
+/*
+ * Copyright 2002-2015 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.web.bind.annotation;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+import org.springframework.core.annotation.AliasFor;
+
+/**
+ * Annotation to bind a method parameter to a session attribute.
+ *
+ * <p>The main motivation is to provide convenient access to existing, permanent
+ * session attributes (e.g. user authentication object) with an optional/required
+ * check and a cast to the target method parameter type.
+ *
+ * <p>For use cases that require adding or removing session attributes consider
+ * injecting {@code org.springframework.web.context.request.WebRequest} or
+ * {@code javax.servlet.http.HttpSession} into the controller method.
+ *
+ * <p>For temporary storage of model attributes in the session as part of the
+ * workflow for a controller, consider using {@link SessionAttributes} instead.
+ *
+ * @author Rossen Stoyanchev
+ * @since 4.3
+ * @see RequestMapping
+ * @see SessionAttributes
+ */
+@Target(ElementType.PARAMETER)
+@Retention(RetentionPolicy.RUNTIME)
+@Documented
+public @interface SessionAttribute {
+
+	/**
+	 * Alias for {@link #name}.
+	 */
+	@AliasFor("name")
+	String value() default "";
+
+	/**
+	 * The name of the session attribute to bind to.
+	 * <p>The default name is inferred from the method parameter name.
+	 */
+	@AliasFor("value")
+	String name() default "";
+
+	/**
+	 * Whether the session attribute is required.
+	 * <p>Defaults to {@code true}, leading to an exception being thrown
+	 * if the attribute is missing in the session or there is no session.
+	 * Switch this to {@code false} if you prefer a {@code null} or Java 1.8+
+	 * {@code java.util.Optional} if the attribute doesn't exist.
+	 */
+	boolean required() default true;
+
+}