Publish binding event for replaced attributes in MockHttpSession

Issue: SPR-17109

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

@@ -42,6 +42,7 @@ import org.springframework.util.StringUtils;
  * @author Rod Johnson
  * @author Mark Fisher
  * @author Sam Brannen
+ * @author Vedran Pavic
  * @since 1.0.2
  */
 @SuppressWarnings("deprecation")
@@ -180,9 +181,14 @@ public class MockHttpSession implements HttpSession {
 		assertIsValid();
 		Assert.notNull(name, "Attribute name must not be null");
 		if (value != null) {
-			this.attributes.put(name, value);
-			if (value instanceof HttpSessionBindingListener) {
-				((HttpSessionBindingListener) value).valueBound(new HttpSessionBindingEvent(this, name, value));
+			Object oldValue = this.attributes.put(name, value);
+			if (value != oldValue) {
+				if (oldValue instanceof HttpSessionBindingListener) {
+					((HttpSessionBindingListener) oldValue).valueUnbound(new HttpSessionBindingEvent(this, name, oldValue));
+				}
+				if (value instanceof HttpSessionBindingListener) {
+					((HttpSessionBindingListener) value).valueBound(new HttpSessionBindingEvent(this, name, value));
+				}
 			}
 		}
 		else {

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2013 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -16,6 +16,10 @@
 
 package org.springframework.mock.web;
 
+import java.util.concurrent.atomic.AtomicInteger;
+import javax.servlet.http.HttpSessionBindingEvent;
+import javax.servlet.http.HttpSessionBindingListener;
+
 import org.junit.Test;
 
 import static org.junit.Assert.*;
@@ -24,11 +28,12 @@ import static org.junit.Assert.*;
  * Unit tests for {@link MockHttpSession}.
  *
  * @author Sam Brannen
+ * @author Vedran Pavic
  * @since 3.2
  */
 public class MockHttpSessionTests {
 
-	private final MockHttpSession session = new MockHttpSession();
+	private MockHttpSession session = new MockHttpSession();
 
 
 	@Test
@@ -143,4 +148,70 @@ public class MockHttpSessionTests {
 		session.isNew();
 	}
 
+	@Test
+	public void bindingListenerBindListener() {
+		String bindingListenerName = "bindingListener";
+		CountingHttpSessionBindingListener bindingListener = new CountingHttpSessionBindingListener();
+
+		session.setAttribute(bindingListenerName, bindingListener);
+
+		assertEquals(bindingListener.getCounter(), 1);
+	}
+
+	@Test
+	public void bindingListenerBindListenerThenUnbind() {
+		String bindingListenerName = "bindingListener";
+		CountingHttpSessionBindingListener bindingListener = new CountingHttpSessionBindingListener();
+
+		session.setAttribute(bindingListenerName, bindingListener);
+		session.removeAttribute(bindingListenerName);
+
+		assertEquals(bindingListener.getCounter(), 0);
+	}
+
+	@Test
+	public void bindingListenerBindSameListenerTwice() {
+		String bindingListenerName = "bindingListener";
+		CountingHttpSessionBindingListener bindingListener = new CountingHttpSessionBindingListener();
+
+		session.setAttribute(bindingListenerName, bindingListener);
+		session.setAttribute(bindingListenerName, bindingListener);
+
+		assertEquals(bindingListener.getCounter(), 1);
+	}
+
+	@Test
+	public void bindingListenerBindListenerOverwrite() {
+		String bindingListenerName = "bindingListener";
+		CountingHttpSessionBindingListener bindingListener1 = new CountingHttpSessionBindingListener();
+		CountingHttpSessionBindingListener bindingListener2 = new CountingHttpSessionBindingListener();
+
+		session.setAttribute(bindingListenerName, bindingListener1);
+		session.setAttribute(bindingListenerName, bindingListener2);
+
+		assertEquals(bindingListener1.getCounter(), 0);
+		assertEquals(bindingListener2.getCounter(), 1);
+	}
+
+	private static class CountingHttpSessionBindingListener
+			implements HttpSessionBindingListener {
+
+		private final AtomicInteger counter = new AtomicInteger(0);
+
+		@Override
+		public void valueBound(HttpSessionBindingEvent event) {
+			this.counter.incrementAndGet();
+		}
+
+		@Override
+		public void valueUnbound(HttpSessionBindingEvent event) {
+			this.counter.decrementAndGet();
+		}
+
+		int getCounter() {
+			return this.counter.get();
+		}
+
+	}
+
 }

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

@@ -41,6 +41,7 @@ import org.springframework.util.StringUtils;
  * @author Rod Johnson
  * @author Mark Fisher
  * @author Sam Brannen
+ * @author Vedran Pavic
  * @since 1.0.2
  */
 @SuppressWarnings("deprecation")
@@ -176,9 +177,14 @@ public class MockHttpSession implements HttpSession {
 		assertIsValid();
 		Assert.notNull(name, "Attribute name must not be null");
 		if (value != null) {
-			this.attributes.put(name, value);
-			if (value instanceof HttpSessionBindingListener) {
-				((HttpSessionBindingListener) value).valueBound(new HttpSessionBindingEvent(this, name, value));
+			Object oldValue = this.attributes.put(name, value);
+			if (value != oldValue) {
+				if (oldValue instanceof HttpSessionBindingListener) {
+					((HttpSessionBindingListener) value).valueUnbound(new HttpSessionBindingEvent(this, name, oldValue));
+				}
+				if (value instanceof HttpSessionBindingListener) {
+					((HttpSessionBindingListener) value).valueBound(new HttpSessionBindingEvent(this, name, value));
+				}
 			}
 		}
 		else {