默认情况下如果一个 Message 被消费者所正确接收则会被从 Queue 中移除
如果一个 Queue 没被任何消费者订阅，那么这个 Queue 中的消息会被 Cache（缓存），当有消费者订阅时则会立即发送，当 Message 被消费者正确接收时，就会被从 Queue 中移除
消息发送确认
发送的消息怎么样才算失败或成功？如何确认？
- 当消息无法路由到队列时，确认消息路由失败。消息成功路由时，当需要发送的队列都发送成功后，进行确认消息，对于持久化队列意味着写入磁盘，对于镜像队列意味着所有镜像接收成功
ConfirmCallback
- 通过实现 ConfirmCallback 接口，消息发送到 Broker 后触发回调，确认消息是否到达 Broker 服务器，也就是只确认是否正确到达 Exchange 中
@Component public class RabbitTemplateConfig implements RabbitTemplate.ConfirmCallback{<span class="token annotation punctuation">@Autowired</span> <span class="token keyword">private</span> <span class="token class-name">RabbitTemplate</span> rabbitTemplate<span class="token punctuation">;</span><span class="token annotation punctuation">@PostConstruct</span> <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">init</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span>rabbitTemplate<span class="token punctuation">.</span><span class="token function">setConfirmCallback</span><span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//指定 ConfirmCallback</span> <span class="token punctuation">}</span><span class="token annotation punctuation">@Override</span> <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">confirm</span><span class="token punctuation">(</span><span class="token class-name">CorrelationData</span> correlationData<span class="token punctuation">,</span> <span class="token keyword">boolean</span> ack<span class="token punctuation">,</span> <span class="token class-name">String</span> cause<span class="token punctuation">)</span> <span class="token punctuation">{</span><span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"消息唯一标识："</span><span class="token operator">+</span>correlationData<span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"确认结果："</span><span class="token operator">+</span>ack<span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"失败原因："</span><span class="token operator">+</span>cause<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span>