INT-1387 added 'read' method to MessageHistory and committed some unit tests

spring-integration-core/src/main/java/org/springframework/integration/history/MessageHistory.java

@@ -49,6 +49,11 @@ public class MessageHistory implements List<Properties> {
 	private final List<Properties> components;
 
 
+	public static MessageHistory read(Message<?> message) {
+		return (message != null) ?
+				message.getHeaders().get(HEADER_NAME, MessageHistory.class) : null;
+	}
+
 	public static <T> Message<T> addComponentToHistory(Message<T> message, NamedComponent component) {
 		Assert.notNull(message, "Message must not be null");
 		Assert.notNull(component, "Component must not be null");

spring-integration-core/src/test/java/org/springframework/integration/core/MessageHistoryTests.java

@@ -0,0 +1,76 @@
+/*
+ * Copyright 2002-2010 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.integration.core;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+
+import java.util.Properties;
+
+import org.junit.Test;
+
+import org.springframework.integration.Message;
+import org.springframework.integration.context.NamedComponent;
+import org.springframework.integration.history.MessageHistory;
+
+/**
+ * @author Mark Fisher
+ * @since 2.0
+ */
+public class MessageHistoryTests {
+
+	@Test
+	public void addComponents() {
+		StringMessage original = new StringMessage("foo");
+		assertNull(MessageHistory.read(original));
+		Message<String> result1 = MessageHistory.addComponentToHistory(original, new TestComponent(1));
+		MessageHistory history1 = MessageHistory.read(result1);
+		assertNotNull(history1);
+		assertEquals("testComponent-1", history1.toString());
+		Message<String> result2 = MessageHistory.addComponentToHistory(result1, new TestComponent(2));
+		MessageHistory history2 = MessageHistory.read(result2);
+		assertNotNull(history2);
+		assertEquals("testComponent-1,testComponent-2", history2.toString());
+	}
+
+	@Test(expected = UnsupportedOperationException.class)
+	public void verifyImmutability() {
+		Message<?> message = MessageHistory.addComponentToHistory(MessageBuilder.withPayload("test").build(), new TestComponent(1));
+		MessageHistory history = MessageHistory.read(message);
+		history.add(new Properties());
+	}
+
+
+	private static class TestComponent implements NamedComponent {
+
+		private final int id;
+
+		private TestComponent(int id) {
+			this.id = id;
+		}
+
+		public String getComponentName() {
+			return "testComponent-" + this.id;
+		}
+
+		public String getComponentType() {
+			return "type-" + this.id;
+		}
+	}
+
+}