add new SynchronizedItemStreamReader

Decorator for an ItemStreamReader

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

@@ -0,0 +1,70 @@
+/*
+ * Copyright 2015 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;
+
+import org.springframework.batch.item.ExecutionContext;
+import org.springframework.batch.item.ItemReader;
+import org.springframework.batch.item.ItemStream;
+import org.springframework.batch.item.ItemStreamReader;
+import org.springframework.batch.item.NonTransientResourceException;
+import org.springframework.batch.item.ParseException;
+import org.springframework.batch.item.UnexpectedInputException;
+
+/**
+ * 
+ * This is a simple ItemStreamReader decorator with a synchronized ItemReader.read() 
+ * method - which makes a non-thread-safe ItemReader thread-safe.
+ * 
+ * However, if reprocessing an item is problematic then using this will make a job not 
+ * restartable.  If a restartable job is desired in that case, then further co-ordination 
+ * between the read and close methods needs to be implemented.
+ * 
+ * Here are some links about the motivation behind this class:
+ * - http://projects.spring.io/spring-batch/faq.html#threading-reader}
+ * - http://stackoverflow.com/a/20002493/2910265}
+ * 
+ * @author Matthew Ouyang
+ * @since 3.0
+ *
+ * @param <T>
+ */
+public class SynchronizedItemStreamReader<T> implements ItemStream, ItemReader<T> {
+
+	ItemStreamReader<T> itemStreamReader;
+
+	public void setItemStreamReader(ItemStreamReader<T> itemStreamReader) {
+		this.itemStreamReader = itemStreamReader;
+	}
+
+	/**
+	 * This delegates to the read method of the <code>itemStreamReader</code>
+	 */
+	public synchronized T read() throws Exception, UnexpectedInputException, ParseException, NonTransientResourceException {
+		return this.itemStreamReader.read();
+	}
+
+	public void close() {
+		this.itemStreamReader.close();
+	}
+
+	public void open(ExecutionContext executionContext) {
+		this.itemStreamReader.open(executionContext);
+	}
+
+	public void update(ExecutionContext executionContext) {
+		this.itemStreamReader.update(executionContext);
+	}
+}