RabbitExceptionTranslator异常转换

外部异常转换为框架内部异常的实例：
RabbitExceptionTranslator把IOException、UnsupportedEncodingException、ConnectException和TimeoutException等转换为Rabbit框架内部异常

package org.springframework.amqp.rabbit.support;

import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.net.ConnectException;
import java.util.concurrent.TimeoutException;

import org.springframework.amqp.AmqpAuthenticationException;
import org.springframework.amqp.AmqpConnectException;
import org.springframework.amqp.AmqpException;
import org.springframework.amqp.AmqpIOException;
import org.springframework.amqp.AmqpTimeoutException;
import org.springframework.amqp.AmqpUnsupportedEncodingException;
import org.springframework.amqp.UncategorizedAmqpException;
import org.springframework.util.Assert;

import com.rabbitmq.client.ConsumerCancelledException;
import com.rabbitmq.client.PossibleAuthenticationFailureException;
import com.rabbitmq.client.ShutdownSignalException;

/**
 * Translates Rabbit Exceptions to the {@link AmqpException} class
 * hierarchy.
 * This functionality was previously in RabbitUtils, but that
 * caused a package tangle.
 *
 * @author Gary Russell
 * @since 1.2
 *
 */
public final class RabbitExceptionTranslator {

	private RabbitExceptionTranslator() {
	}

	public static RuntimeException convertRabbitAccessException(Throwable ex) {
		Assert.notNull(ex, "Exception must not be null");
		if (ex instanceof AmqpException) {
			return (AmqpException) ex;
		}
		if (ex instanceof ShutdownSignalException) {
			return new AmqpConnectException((ShutdownSignalException) ex);
		}
		if (ex instanceof ConnectException) {
			return new AmqpConnectException((ConnectException) ex);
		}
		if (ex instanceof PossibleAuthenticationFailureException) {
			return new AmqpAuthenticationException(ex);
		}
		if (ex instanceof UnsupportedEncodingException) {
			return new AmqpUnsupportedEncodingException(ex);
		}
		if (ex instanceof IOException) {
			return new AmqpIOException((IOException) ex);
		}
		if (ex instanceof TimeoutException) {
			return new AmqpTimeoutException(ex);
		}
		if (ex instanceof ConsumerCancelledException) {
			return new org.springframework.amqp.rabbit.support.ConsumerCancelledException(ex);
		}
		if (ex instanceof org.springframework.amqp.rabbit.support.ConsumerCancelledException) {
			return (org.springframework.amqp.rabbit.support.ConsumerCancelledException) ex;
		}
		// fallback
		return new UncategorizedAmqpException(ex);
	}

}

另外一个问题，为什么要这样转换呢？
下面找几个引用convertRabbitAccessException方法的地方看看。

org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer#stop()

@Override
	public void stop() {
		try {
			doStop();
		}
		catch (Exception ex) {
			throw convertRabbitAccessException(ex);
		}
		finally {
			synchronized (this.lifecycleMonitor) {
				this.running = false;
				this.lifecycleMonitor.notifyAll();
			}
		}
	}

org.springframework.amqp.rabbit.core.RabbitTemplate#doExecute

try {
			return invokeAction(action, connectionFactory, channel);
		}
		catch (Exception ex) {
			if (isChannelLocallyTransacted(channel)) {
				resourceHolder.rollbackAll();
			}
			throw convertRabbitAccessException(ex);
		}

原来是为了方便异常的捕获，都是同一抛出Exception，然后调用convertRabbitAccessException方法统一转换对应的异常。实现代码的复用。