BATCHADM-49: Use a ChannelInterceptor to turn a ThreadLocalChannel into a pass-thru channel. Keeps JMS receive in the caller's transaction.

spring-batch-integration/src/main/java/org/springframework/batch/integration/chunk/MessageSourcePollerInterceptor.java

@@ -0,0 +1,76 @@
+package org.springframework.batch.integration.chunk;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.springframework.beans.factory.InitializingBean;
+import org.springframework.integration.channel.ChannelInterceptor;
+import org.springframework.integration.channel.ThreadLocalChannel;
+import org.springframework.integration.channel.interceptor.ChannelInterceptorAdapter;
+import org.springframework.integration.core.Message;
+import org.springframework.integration.core.MessageChannel;
+import org.springframework.integration.message.MessageSource;
+import org.springframework.util.Assert;
+
+/**
+ * A {@link ChannelInterceptor} that turns a pollable channel into a "pass-thru channel": if a client calls
+ * <code>receive()</code> on the channel it will delegate to a {@link MessageSource} to pull the message directly from
+ * an external source. This is particularly useful in combination with a {@link ThreadLocalChannel}, in which case the
+ * <code>receive()</code> can join a transaction which was started by the caller.
+ * 
+ * @author Dave Syer
+ * 
+ */
+public class MessageSourcePollerInterceptor extends ChannelInterceptorAdapter implements InitializingBean {
+
+	private static Log logger = LogFactory.getLog(MessageSourcePollerInterceptor.class);
+
+	private MessageSource<?> source;
+
+	/**
+	 * Convenient default constructor for configuration purposes.
+	 */
+	public MessageSourcePollerInterceptor() {
+	}
+
+	/**
+	 * @param source a message source to poll for messages on receive.
+	 */
+	public MessageSourcePollerInterceptor(MessageSource<?> source) {
+		this.source = source;
+	}
+
+	/**
+	 * Asserts that mandatory properties are set.
+	 * @see InitializingBean#afterPropertiesSet()
+	 */
+	public void afterPropertiesSet() throws Exception {
+		Assert.state(source != null, "A MessageSource must be provided");
+	}
+
+	/**
+	 * @param source a message source to poll for messages on receive.
+	 */
+	public void setMessageSource(MessageSource<?> source) {
+		this.source = source;
+	}
+
+	/**
+	 * Receive from the {@link MessageSource} and send immediately to the input channel, so that the call that we are
+	 * intercepting always a message to receive.
+	 * 
+	 * @see ChannelInterceptorAdapter#preReceive(MessageChannel)
+	 */
+	@Override
+	public boolean preReceive(MessageChannel channel) {
+		Message<?> message = source.receive();
+		if (message != null) {
+			channel.send(message);
+			if (logger.isDebugEnabled()) {
+				logger.debug("Sent " + message + " to channel " + channel.getName());
+			}
+			return true;
+		}
+		return true;
+	}
+
+}