Add Servlet 3.1 methods to mock request

Issue: SPR-11492

spring-web/src/test/java/org/springframework/mock/web/test/MockHttpServletRequest.java

@@ -351,6 +351,10 @@ public class MockHttpServletRequest implements HttpServletRequest {
 		return (this.content != null ? this.content.length : -1);
 	}
 
+	public long getContentLengthLong() {
+		return getContentLength();
+	}
+
 	public void setContentType(String contentType) {
 		this.contentType = contentType;
 		if (contentType != null) {
@@ -1001,6 +1005,20 @@ public class MockHttpServletRequest implements HttpServletRequest {
 		return getSession(true);
 	}
 
+	/**
+	 * The implementation of this (Servlet 3.1+) method calls
+	 * {@link MockHttpSession#changeSessionId()} if the session is a mock session.
+	 * Otherwise it simply returns the current session id.
+	 * @since 4.0.3
+	 */
+	public String changeSessionId() {
+		Assert.isTrue(this.session != null, "The request does not have a session");
+		if (this.session instanceof MockHttpSession) {
+			return ((MockHttpSession) session).changeSessionId();
+		}
+		return this.session.getId();
+	}
+
 	public void setRequestedSessionIdValid(boolean requestedSessionIdValid) {
 		this.requestedSessionIdValid = requestedSessionIdValid;
 	}

spring-web/src/test/java/org/springframework/mock/web/test/MockHttpSession.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2013 the original author or authors.
+ * Copyright 2002-2014 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.
@@ -54,7 +54,7 @@ public class MockHttpSession implements HttpSession {
 
 	private static int nextId = 1;
 
-	private final String id;
+	private String id;
 
 	private final long creationTime = System.currentTimeMillis();
 
@@ -111,6 +111,16 @@ public class MockHttpSession implements HttpSession {
 		return this.id;
 	}
 
+	/**
+	 * As of Servlet 3.1 the id of a session can be changed.
+	 * @return the new session id.
+	 * @since 4.0.3
+	 */
+	public String changeSessionId() {
+		this.id = Integer.toString(nextId++);
+		return this.id;
+	}
+
 	public void access() {
 		this.lastAccessedTime = System.currentTimeMillis();
 		this.isNew = false;