場景：

使用rabbitmq時報錯，異常棧如下：

Exception in thread "main" com.rabbitmq.client.AlreadyClosedException: channel is already closed due to channel error; protocol method: #method<channel.close>(reply-code=406, reply-text=PRECONDITION_FAILED - unknown delivery tag 1, class-id=60, method-id=80)

    at com.rabbitmq.client.impl.AMQChannel.ensureIsOpen(AMQChannel.java:195)
    at com.rabbitmq.client.impl.AMQChannel.transmit(AMQChannel.java:309)
    at com.rabbitmq.client.impl.AMQChannel.transmit(AMQChannel.java:303)
    at com.rabbitmq.client.impl.ChannelN.basicAck(ChannelN.java:1031)
    at com.mj.rabbitmquse.demo.task.TaskHandler.main(TaskHandler.java:37)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)

    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)

解決：

當使用channel的basicAck方法時，定義了channel的basicConsume方法的第二個引數，autoAck為true。

@param autoAck true if the server should consider messages
* acknowledged once delivered; false if the server should expect
* explicit acknowledgements

將autoAck設為false就OK了。