BATCH-1566: fix dirty flag on ExecutionContext

spring-batch-infrastructure/src/main/java/org/springframework/batch/item/ExecutionContext.java

@@ -125,12 +125,13 @@ public class ExecutionContext implements Serializable {
 	public void put(String key, Object value) {
 		if (value != null) {
 			Assert.isInstanceOf(Serializable.class, value, "Value: [ " + value + "must be serializable.");
-			map.put(key, value);
+			Object result = map.put(key, value);
+			dirty = result==null || result!=null && !result.equals(value);
 		}
 		else {
-			map.remove(key);
+			Object result = map.remove(key);
+			dirty = result!=null;
 		}
-		dirty = true;
 	}
 
 	/**

spring-batch-infrastructure/src/test/java/org/springframework/batch/item/ExecutionContextTests.java

@@ -89,6 +89,25 @@ public class ExecutionContextTests {
 		assertFalse(context.isDirty());
 	}
 
+	@Test
+	public void testNotDirtyWithDuplicate() {
+		context.putString("1", "test");
+		assertTrue(context.isDirty());
+		context.clearDirtyFlag();
+		context.putString("1", "test");
+		assertFalse(context.isDirty());
+	}
+
+	@Test
+	public void testNotDirtyWithRemoveMissing() {
+		context.putString("1", "test");
+		assertTrue(context.isDirty());
+		context.putString("1", null); // remove an item that was present
+		assertTrue(context.isDirty());
+		context.putString("1", null); // remove a non-existent item
+		assertFalse(context.isDirty());
+	}
+
 	@Test
 	public void testContains() {
 		context.putString("1", "testString");