spring-batch MessageSourcePollerInterceptor 源码
spring-batch MessageSourcePollerInterceptor 代码
文件路径：/spring-batch-integration/src/main/java/org/springframework/batch/integration/chunk/MessageSourcePollerInterceptor.java
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.core.MessageSource;
import org.springframework.messaging.Message;
import org.springframework.messaging.MessageChannel;
import org.springframework.messaging.support.ChannelInterceptor;
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 message channel in thread scope, in which
* case the <code>receive()</code> can join a transaction which was started by the caller.
*
* @author Dave Syer
*
*/
public class MessageSourcePollerInterceptor implements ChannelInterceptor, InitializingBean {
private static Log logger = LogFactory.getLog(MessageSourcePollerInterceptor.class);
private MessageSource<?> source;
private MessageChannel channel;
/**
* 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;
}
/**
* Optional MessageChannel for injecting the message received from the source
* (defaults to the channel intercepted in {@link #preReceive(MessageChannel)}).
* @param channel the channel to set
*/
public void setChannel(MessageChannel channel) {
this.channel = channel;
}
/**
* 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 ChannelInterceptor#preReceive(MessageChannel)
*/
@Override
public boolean preReceive(MessageChannel channel) {
Message<?> message = source.receive();
if (message != null) {
if (this.channel != null) {
channel = this.channel;
}
channel.send(message);
if (logger.isDebugEnabled()) {
logger.debug("Sent " + message + " to channel " + channel);
}
return true;
}
return true;
}
}
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