Add builder for CompositeItemProcessor

resolves #BATCH-2617

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

@@ -67,8 +67,14 @@ public class CompositeItemProcessor<I, O> implements ItemProcessor<I, O>, Initia
 		Assert.notEmpty(delegates, "The 'delegates' may not be empty");
 	}
 
+	/**
+	 * Establishes the {@link ItemProcessor} delegates that will work on the item to be
+	 * processed.
+	 * @param delegates list of {@link ItemProcessor} delegates that will work on the
+	 * item.
+	 */
 	public void setDelegates(List<? extends ItemProcessor<?, ?>> delegates) {
 		this.delegates = delegates;
-	}	
+	}
 
 }

spring-batch-infrastructure/src/main/java/org/springframework/batch/item/support/builder/CompositeItemProcessorBuilder.java

@@ -0,0 +1,60 @@
+/*
+ * Copyright 2017 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.batch.item.support.builder;
+
+import java.util.List;
+
+import org.springframework.batch.item.ItemProcessor;
+import org.springframework.batch.item.support.CompositeItemProcessor;
+import org.springframework.util.Assert;
+
+/**
+ * Creates a fully qualified {@link CompositeItemProcessorBuilder}.
+ *
+ * @author Glenn Renfro
+ *
+ * @since 4.0
+ */
+public class CompositeItemProcessorBuilder<I, O> {
+	private List<? extends ItemProcessor<?, ?>> delegates;
+
+	/**
+	 * Establishes the {@link ItemProcessor} delegates that will work on the item to be processed.
+	 * @param delegates list of {@link ItemProcessor} delegates that will work on the item.
+	 * @return this instance for method chaining.
+	 * @see CompositeItemProcessor#setDelegates(List)
+	 */
+	public CompositeItemProcessorBuilder<I, O> delegates(List<? extends ItemProcessor<?, ?>> delegates) {
+		this.delegates = delegates;
+
+		return this;
+	}
+
+	/**
+	 * Returns a fully constructed {@link CompositeItemProcessor}.
+	 *
+	 * @return a new {@link CompositeItemProcessor}
+	 */
+	public CompositeItemProcessor<I, O> build() {
+		Assert.notNull(delegates, "A list of delegates is required.");
+		Assert.notEmpty(delegates, "The delegates list must have one or more delegates.");
+
+		CompositeItemProcessor<I, O> processor = new CompositeItemProcessor<>();
+		processor.setDelegates(this.delegates);
+		return processor;
+	}
+}

spring-batch-infrastructure/src/test/java/org/springframework/batch/item/support/builder/CompositeItemProcessorBuilderTests.java

@@ -0,0 +1,89 @@
+/*
+ * Copyright 2017 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.batch.item.support.builder;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+
+import org.springframework.batch.item.ItemProcessor;
+import org.springframework.batch.item.support.CompositeItemProcessor;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.fail;
+import static org.mockito.Mockito.when;
+
+/**
+ * @author Glenn Renfro
+ */
+public class CompositeItemProcessorBuilderTests {
+
+	@Mock
+	private ItemProcessor<Object, Object> processor1;
+
+	@Mock
+	private ItemProcessor<Object, Object> processor2;
+
+	private List<ItemProcessor<Object, Object>> processors;
+
+	@Before
+	public void setup() {
+		MockitoAnnotations.initMocks(this);
+
+		this.processors = new ArrayList<>();
+		this.processors.add(processor1);
+		this.processors.add(processor2);
+	}
+
+	@Test
+	public void testTransform() throws Exception {
+		Object item = new Object();
+		Object itemAfterFirstTransfromation = new Object();
+		Object itemAfterSecondTransformation = new Object();
+		CompositeItemProcessor<Object, Object> composite = new CompositeItemProcessorBuilder<>()
+				.delegates(this.processors).build();
+
+		when(processor1.process(item)).thenReturn(itemAfterFirstTransfromation);
+		when(processor2.process(itemAfterFirstTransfromation)).thenReturn(itemAfterSecondTransformation);
+
+		assertSame(itemAfterSecondTransformation, composite.process(item));
+	}
+
+	@Test
+	public void testNullOrEmptyDelegates() throws Exception {
+		validateExceptionMessage(new CompositeItemProcessorBuilder<>().delegates(new ArrayList<>()),
+				"The delegates list must have one or more delegates.");
+		validateExceptionMessage(new CompositeItemProcessorBuilder<>(),
+				"A list of delegates is required.");
+	}
+
+	private void validateExceptionMessage(CompositeItemProcessorBuilder<?, ?> builder, String message) {
+		try {
+			builder.build();
+			fail("IllegalArgumentException should have been thrown");
+		}
+		catch (IllegalArgumentException iae) {
+			assertEquals("IllegalArgumentException message did not match the expected result.", message,
+					iae.getMessage());
+		}
+	}
+}