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<?xml version="1.0" encoding="utf-8"?>
<search>
<entry>
<title>使用@Async注解报错提示没有返回值</title>
<link href="/2024/02/10/%E4%BD%BF%E7%94%A8@Async%E6%B3%A8%E8%A7%A3%E6%8A%A5%E9%94%99%E6%8F%90%E7%A4%BA%E6%B2%A1%E6%9C%89%E8%BF%94%E5%9B%9E%E5%80%BC/"/>
<url>/2024/02/10/%E4%BD%BF%E7%94%A8@Async%E6%B3%A8%E8%A7%A3%E6%8A%A5%E9%94%99%E6%8F%90%E7%A4%BA%E6%B2%A1%E6%9C%89%E8%BF%94%E5%9B%9E%E5%80%BC/</url>
<content type="html"><![CDATA[<h2 id="使用-Async注解报错提示没有返回值"><a href="#使用-Async注解报错提示没有返回值" class="headerlink" title="使用@Async注解报错提示没有返回值"></a>使用@Async注解报错提示没有返回值</h2><h4 id="问题描述"><a href="#问题描述" class="headerlink" title="问题描述"></a>问题描述</h4><p>报错信息如下：</p><p><img src="http://www.kdocs.cn/api/v3/office/copy/bFFKUytlZEZkMUhNeGRUSytoQkx5c25XNTNabjVFS3Z6cHhXNkZCRjVMZmEyNnlCU2N3OC9ReDA0WVFGY1VLSGxjcTJ6b3BKWjRhcmMwVTdlc0c1aiszaWprVHNlR2VUb1N6YUdDWmtyZUsxU0Zja3k5TDdvOGZ3Zk5qMncrT3RPczQ4MWtTekZJWDk5RlhCbjIxTVh2MXF5RUpJUkQwQStDbURzU2huUlJnV2I0dk5BSFpDL1hRT3hKMzM3N2FZYWRRN3MxRUF6b0w4aVlNWUdiVU4vbjdKVURwZFcvbklUL2JlVlhZRXJBRmFiaDRHTWtJeFNKWlVOVWZPbmdza0tjK3NsRFI1QzZVPQ==/attach/object/PYZM2BIBOA" alt="img"></p><p>我是代码里用了异步线程，AOP做了一层切面处理，底层是通过jdk动态代理cglib实现。</p><h4 id="解决方案"><a href="#解决方案" class="headerlink" title="解决方案"></a>解决方案</h4><p><img src="http://www.kdocs.cn/api/v3/office/copy/bFFKUytlZEZkMUhNeGRUSytoQkx5c25XNTNabjVFS3Z6cHhXNkZCRjVMZmEyNnlCU2N3OC9ReDA0WVFGY1VLSGxjcTJ6b3BKWjRhcmMwVTdlc0c1aiszaWprVHNlR2VUb1N6YUdDWmtyZUsxU0Zja3k5TDdvOGZ3Zk5qMncrT3RPczQ4MWtTekZJWDk5RlhCbjIxTVh2MXF5RUpJUkQwQStDbURzU2huUlJnV2I0dk5BSFpDL1hRT3hKMzM3N2FZYWRRN3MxRUF6b0w4aVlNWUdiVU4vbjdKVURwZFcvbklUL2JlVlhZRXJBRmFiaDRHTWtJeFNKWlVOVWZPbmdza0tjK3NsRFI1QzZVPQ==/attach/object/EQ2M2BIA5M" alt="img"></p><p>为什么一定要Integer不能用Int类型</p><p>查了一下，如果代理的方法返回值类型为void，就return null；否则就return method.invoke(my, args);</p><p>也就是说，动态代理在没有返回值的情况下，会返回null值。</p><p>我使用的@Asyn就是没有返回值的，所以会返回null</p><p>null值必须用包装类Integer去接收。</p><p>修改前</p><p><img src="http://www.kdocs.cn/api/v3/office/copy/bFFKUytlZEZkMUhNeGRUSytoQkx5c25XNTNabjVFS3Z6cHhXNkZCRjVMZmEyNnlCU2N3OC9ReDA0WVFGY1VLSGxjcTJ6b3BKWjRhcmMwVTdlc0c1aiszaWprVHNlR2VUb1N6YUdDWmtyZUsxU0Zja3k5TDdvOGZ3Zk5qMncrT3RPczQ4MWtTekZJWDk5RlhCbjIxTVh2MXF5RUpJUkQwQStDbURzU2huUlJnV2I0dk5BSFpDL1hRT3hKMzM3N2FZYWRRN3MxRUF6b0w4aVlNWUdiVU4vbjdKVURwZFcvbklUL2JlVlhZRXJBRmFiaDRHTWtJeFNKWlVOVWZPbmdza0tjK3NsRFI1QzZVPQ==/attach/object/Y42M2BIAF4" alt="img"></p><p>修改后</p><p><img src="http://www.kdocs.cn/api/v3/office/copy/bFFKUytlZEZkMUhNeGRUSytoQkx5c25XNTNabjVFS3Z6cHhXNkZCRjVMZmEyNnlCU2N3OC9ReDA0WVFGY1VLSGxjcTJ6b3BKWjRhcmMwVTdlc0c1aiszaWprVHNlR2VUb1N6YUdDWmtyZUsxU0Zja3k5TDdvOGZ3Zk5qMncrT3RPczQ4MWtTekZJWDk5RlhCbjIxTVh2MXF5RUpJUkQwQStDbURzU2huUlJnV2I0dk5BSFpDL1hRT3hKMzM3N2FZYWRRN3MxRUF6b0w4aVlNWUdiVU4vbjdKVURwZFcvbklUL2JlVlhZRXJBRmFiaDRHTWtJeFNKWlVOVWZPbmdza0tjK3NsRFI1QzZVPQ==/attach/object/RE242BIAWU" alt="img"></p><p>参考链接</p><p><a href="https://stackoverflow.com/questions/56497893/org-springframework-aop-aopinvocationexception-null-return-value-from-advice-do">https://stackoverflow.com/questions/56497893/org-springframework-aop-aopinvocationexception-null-return-value-from-advice-do</a></p>]]></content>
<categories>
<category> java </category>
</categories>
<tags>
<tag> java </tag>
</tags>
</entry>
<entry>
<title>记一次RabbitMQ踩坑</title>
<link href="/2024/01/19/%E8%AE%B0%E4%B8%80%E6%AC%A1RabbitMQ%E8%B8%A9%E5%9D%91/"/>
<url>/2024/01/19/%E8%AE%B0%E4%B8%80%E6%AC%A1RabbitMQ%E8%B8%A9%E5%9D%91/</url>
<content type="html"><![CDATA[<h3 id="记一次RabbitMQ踩坑"><a href="#记一次RabbitMQ踩坑" class="headerlink" title="记一次RabbitMQ踩坑"></a>记一次RabbitMQ踩坑</h3><h4 id="1-问题描述"><a href="#1-问题描述" class="headerlink" title="1. 问题描述"></a>1. 问题描述</h4><p>前段时间写消费端代码的时候遇到个mq确认机制的问题，消费端接收消息消费的过程，如果发生异常并且没有被捕获，这个时候会抛到源码层面去catch异常，由于rabbitmq有消息ack确认机制，消费端因为发生异常没有被捕获导致一直回不了ack,所以会一直重复消费某条消息。</p><h4 id="2-错误案例"><a href="#2-错误案例" class="headerlink" title="2. 错误案例"></a>2. 错误案例</h4><p>消费端代码如下：</p><pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token annotation punctuation">@RabbitHandler</span><span class="token annotation punctuation">@SneakyThrows</span><span class="token annotation punctuation">@RabbitListener</span><span class="token punctuation">(</span>queues <span class="token operator">=</span> <span class="token string">"${spring.rabbitmq.first.queue}"</span><span class="token punctuation">,</span> containerFactory <span class="token operator">=</span> <span class="token string">"firstFactory"</span><span class="token punctuation">)</span><span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">onMessageOne</span><span class="token punctuation">(</span><span class="token class-name">Message</span> message<span class="token punctuation">,</span> <span class="token class-name">Channel</span> channel<span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token class-name">String</span> msg <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">String</span><span class="token punctuation">(</span>message<span class="token punctuation">.</span><span class="token function">getBody</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token constant">ENCODING</span><span class="token punctuation">)</span><span class="token punctuation">;</span> log<span class="token punctuation">.</span><span class="token function">info</span><span class="token punctuation">(</span><span class="token string">"[RabbitListener 监听的消息-ONE] - [{}]"</span><span class="token punctuation">,</span> msg<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token class-name">JSONObject</span> jsonObject <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">JSONObject</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> jsonObject<span class="token punctuation">.</span><span class="token function">put</span><span class="token punctuation">(</span><span class="token string">"queue"</span><span class="token punctuation">,</span> firstQueue<span class="token punctuation">)</span><span class="token punctuation">;</span> jsonObject<span class="token punctuation">.</span><span class="token function">put</span><span class="token punctuation">(</span><span class="token string">"message"</span><span class="token punctuation">,</span> msg<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//此处代码出现异常，并未被捕获</span> <span class="token class-name">ServiceMQInvoke</span> invokeGroovy <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token class-name">ServiceMQInvoke</span><span class="token punctuation">)</span> groovyProcess<span class="token punctuation">.</span><span class="token function">getGroovyClass</span><span class="token punctuation">(</span>groovyUrl<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">newInstance</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> invokeGroovy<span class="token punctuation">.</span><span class="token function">consumer</span><span class="token punctuation">(</span>eliteBean<span class="token punctuation">,</span> jsonObject<span class="token punctuation">)</span><span class="token punctuation">;</span> channel<span class="token punctuation">.</span><span class="token function">basicAck</span><span class="token punctuation">(</span>message<span class="token punctuation">.</span><span class="token function">getMessageProperties</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">getDeliveryTag</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token boolean">true</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token punctuation">}</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre><p>由于在执行channel.basicAck()方法前出现了异常，RabbitMQ没有收到ack确认机制，所以会出现消费重复消息的情况。如下图</p><p></p><p>打印三条日志后，就结束了。为什么只打印三条？是因为rabbitmq 有重试机制。配置如下：</p><pre class="line-numbers language-yaml" data-language="yaml"><code class="language-yaml"><span class="token comment">#RabbitMQ配置</span><span class="token key atrule">rabbitmq</span><span class="token punctuation">:</span> <span class="token key atrule">listener</span><span class="token punctuation">:</span> <span class="token key atrule">simple</span><span class="token punctuation">:</span> <span class="token key atrule">acknowledge-mode</span><span class="token punctuation">:</span> manual <span class="token comment">#手动 ack</span> <span class="token key atrule">default-requeue-rejected</span><span class="token punctuation">:</span> <span class="token boolean important">true</span> <span class="token key atrule">retry</span><span class="token punctuation">:</span> <span class="token key atrule">enabled</span><span class="token punctuation">:</span> <span class="token boolean important">true</span> <span class="token key atrule">max-attempts</span><span class="token punctuation">:</span> <span class="token number">3</span> <span class="token comment">#重试3次</span> <span class="token key atrule">direct</span><span class="token punctuation">:</span> <span class="token key atrule">acknowledge-mode</span><span class="token punctuation">:</span> manual <span class="token key atrule">retry</span><span class="token punctuation">:</span> <span class="token key atrule">enabled</span><span class="token punctuation">:</span> <span class="token boolean important">true</span> <span class="token key atrule">max-attempts</span><span class="token punctuation">:</span> <span class="token number">3</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre><p>是因为max-attempts参数配置重试次数为3。</p><h4 id="3-正确案例"><a href="#3-正确案例" class="headerlink" title="3. 正确案例"></a>3. 正确案例</h4><p>加上try catch捕获异常，让程序出现异常后继续往下执行。代码如下：</p><pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token annotation punctuation">@RabbitHandler</span><span class="token annotation punctuation">@SneakyThrows</span><span class="token annotation punctuation">@RabbitListener</span><span class="token punctuation">(</span>queues <span class="token operator">=</span> <span class="token string">"${spring.rabbitmq.first.queue}"</span><span class="token punctuation">,</span> containerFactory <span class="token operator">=</span> <span class="token string">"firstFactory"</span><span class="token punctuation">)</span><span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">onMessageOne</span><span class="token punctuation">(</span><span class="token class-name">Message</span> message<span class="token punctuation">,</span> <span class="token class-name">Channel</span> channel<span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token class-name">String</span> msg <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">String</span><span class="token punctuation">(</span>message<span class="token punctuation">.</span><span class="token function">getBody</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token constant">ENCODING</span><span class="token punctuation">)</span><span class="token punctuation">;</span> log<span class="token punctuation">.</span><span class="token function">info</span><span class="token punctuation">(</span><span class="token string">"[RabbitListener 监听的消息-ONE] - [{}]"</span><span class="token punctuation">,</span> msg<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token keyword">try</span> <span class="token punctuation">{</span> <span class="token class-name">JSONObject</span> jsonObject <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">JSONObject</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> jsonObject<span class="token punctuation">.</span><span class="token function">put</span><span class="token punctuation">(</span><span class="token string">"queue"</span><span class="token punctuation">,</span> firstQueue<span class="token punctuation">)</span><span class="token punctuation">;</span> jsonObject<span class="token punctuation">.</span><span class="token function">put</span><span class="token punctuation">(</span><span class="token string">"message"</span><span class="token punctuation">,</span> msg<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token class-name">ServiceMQInvoke</span> invokeGroovy <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token class-name">ServiceMQInvoke</span><span class="token punctuation">)</span> groovyProcess<span class="token punctuation">.</span><span class="token function">getGroovyClass</span><span class="token punctuation">(</span>groovyUrl<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">newInstance</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> invokeGroovy<span class="token punctuation">.</span><span class="token function">consumer</span><span class="token punctuation">(</span>eliteBean<span class="token punctuation">,</span> jsonObject<span class="token punctuation">)</span><span class="token punctuation">;</span> channel<span class="token punctuation">.</span><span class="token function">basicAck</span><span class="token punctuation">(</span>message<span class="token punctuation">.</span><span class="token function">getMessageProperties</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">getDeliveryTag</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token boolean">true</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">Exception</span> e<span class="token punctuation">)</span> <span class="token punctuation">{</span> log<span class="token punctuation">.</span><span class="token function">error</span><span class="token punctuation">(</span><span class="token string">"[RabbitListener 监听的消息异常-ONE] - [{}]"</span><span class="token punctuation">,</span> e<span class="token punctuation">.</span><span class="token function">getMessage</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span><span class="token punctuation">}</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre><p>加了异常捕获后消息能正常消费了。</p>]]></content>
<categories>
<category> rabbitMQ </category>
</categories>
<tags>
<tag> java </tag>
</tags>
</entry>
<entry>
<title>记一次sql字符排序规则不统一导致的报错</title>
<link href="/2023/11/14/%E8%AE%B0%E4%B8%80%E6%AC%A1sql%E5%AD%97%E7%AC%A6%E6%8E%92%E5%BA%8F%E8%A7%84%E5%88%99%E4%B8%8D%E7%BB%9F%E4%B8%80%E5%AF%BC%E8%87%B4%E7%9A%84%E6%8A%A5%E9%94%99/"/>
<url>/2023/11/14/%E8%AE%B0%E4%B8%80%E6%AC%A1sql%E5%AD%97%E7%AC%A6%E6%8E%92%E5%BA%8F%E8%A7%84%E5%88%99%E4%B8%8D%E7%BB%9F%E4%B8%80%E5%AF%BC%E8%87%B4%E7%9A%84%E6%8A%A5%E9%94%99/</url>
<content type="html"><![CDATA[<h2 id="记一次sql字符排序规则不统一导致的报错"><a href="#记一次sql字符排序规则不统一导致的报错" class="headerlink" title="记一次sql字符排序规则不统一导致的报错"></a>记一次sql字符排序规则不统一导致的报错</h2><h3 id="问题"><a href="#问题" class="headerlink" title="问题"></a>问题</h3><p>left join表会出现 Illegal mix of collations (utf8_general_ci,IMPLICIT) and (utf8_croatian_ci,IMPLICIT) for operation ‘=’错误.</p><p>这是由于表的编码格式不一致 例如 某个表的排序规则字符编码为utf8_general_ci而关联表的排序规则字符编码为utf8_croatian_ci导致当前错误！</p><p>排查问题发现，只要涉及到作为关联条件的字段都要统一字符编码，要么都设置为一样的编码，要么都设置。出现上面的问题是因为a表中的关联字段设置了字符编码，b表这的关联字段未设置字符编码。关联查询也会报错。</p><h3 id="解决方案"><a href="#解决方案" class="headerlink" title="解决方案"></a>解决方案</h3><ol><li>修改表中字段的字符编码</li></ol><pre class="line-numbers language-sql" data-language="sql"><code class="language-sql">ALTERTABLE 表名 CONVERTTOCHARACTERSET utf8mb4 <span class="token keyword">COLLATE</span> utf8_general_ci<span class="token punctuation">;</span> <span aria-hidden="true" class="line-numbers-rows"><span></span></span></code></pre><ol><li>删除掉字段后面的字符编码</li></ol><pre class="line-numbers language-sql" data-language="sql"><code class="language-sql">ALTERTABLE 表名 DEFAULTCHARACTERSET utf8mb4 <span class="token keyword">COLLATE</span> utf8_general_ci<span class="token punctuation">;</span><span aria-hidden="true" class="line-numbers-rows"><span></span></span></code></pre><ol><li>删除每个字段后面的字符编码</li></ol><p>最终采用了第三种方案，为了适配以后各个项目数据库设置的编码不一样问题，如果不设置字段后面的字符编码会默认采用数据库的字符编码。避免了以后出现同样的问题。</p>]]></content>
<categories>
<category> 数据库 </category>
</categories>
<tags>
<tag> sql </tag>
</tags>
</entry>
<entry>
<title>TransmittableThreadLocal 的使用指南</title>
<link href="/2023/10/16/TransmittableThreadLocal-%E7%9A%84%E4%BD%BF%E7%94%A8%E6%8C%87%E5%8D%97/"/>
<url>/2023/10/16/TransmittableThreadLocal-%E7%9A%84%E4%BD%BF%E7%94%A8%E6%8C%87%E5%8D%97/</url>
<content type="html"><![CDATA[<h1 id="TransmittableThreadLocal-的使用指南"><a href="#TransmittableThreadLocal-的使用指南" class="headerlink" title="TransmittableThreadLocal 的使用指南"></a>TransmittableThreadLocal 的使用指南</h1><h2 id="简介"><a href="#简介" class="headerlink" title="简介"></a>简介</h2><p><code>TransmittableThreadLocal</code> 是一种用于多线程环境下的数据传递的工具。它是 <code>ThreadLocal</code> 的增强版本，能够在不同线程之间有效传递数据，尤其适用于线程池、异步任务等场景。</p><h2 id="如何使用-TransmittableThreadLocal"><a href="#如何使用-TransmittableThreadLocal" class="headerlink" title="如何使用 TransmittableThreadLocal"></a>如何使用 TransmittableThreadLocal</h2><h3 id="1-引入依赖"><a href="#1-引入依赖" class="headerlink" title="1. 引入依赖"></a>1. 引入依赖</h3><p>项目中引入了 <code>TransmittableThreadLocal</code> 相关的依赖。可以使用阿里巴巴的 Transmittable-Thread-Local，具体依赖可以在 Maven 中配置：</p><p>Maven:</p><pre class="line-numbers language-markup" data-language="markup"><code class="language-markup"><span class="token tag"><span class="token tag"><span class="token punctuation"><</span>dependency</span><span class="token punctuation">></span></span> <span class="token tag"><span class="token tag"><span class="token punctuation"><</span>groupId</span><span class="token punctuation">></span></span>com.alibaba<span class="token tag"><span class="token tag"><span class="token punctuation"></</span>groupId</span><span class="token punctuation">></span></span> <span class="token tag"><span class="token tag"><span class="token punctuation"><</span>artifactId</span><span class="token punctuation">></span></span>transmittable-thread-local<span class="token tag"><span class="token tag"><span class="token punctuation"></</span>artifactId</span><span class="token punctuation">></span></span> <span class="token tag"><span class="token tag"><span class="token punctuation"><</span>version</span><span class="token punctuation">></span></span>2.14.1<span class="token tag"><span class="token tag"><span class="token punctuation"></</span>version</span><span class="token punctuation">></span></span> <span class="token tag"><span class="token tag"><span class="token punctuation"></</span>dependency</span><span class="token punctuation">></span></span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span></span></code></pre><h3 id="2-创建-TransmittableThreadLocal-变量"><a href="#2-创建-TransmittableThreadLocal-变量" class="headerlink" title="2. 创建 TransmittableThreadLocal 变量"></a>2. 创建 TransmittableThreadLocal 变量</h3><p>在你的 Java 代码中，创建 <code>TransmittableThreadLocal</code> 类型的变量，定义需要在线程间传递的数据类型。</p><pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token keyword">import</span> <span class="token import"><span class="token namespace">com<span class="token punctuation">.</span>alibaba<span class="token punctuation">.</span>ttl<span class="token punctuation">.</span></span><span class="token class-name">TransmittableThreadLocal</span></span><span class="token punctuation">;</span><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">SecurityContextHolder</span> <span class="token punctuation">{</span> <span class="token keyword">private</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">TransmittableThreadLocal</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Map</span><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">,</span> <span class="token class-name">Object</span><span class="token punctuation">></span><span class="token punctuation">></span></span> <span class="token constant">THREAD_LOCAL</span> <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">TransmittableThreadLocal</span><span class="token generics"><span class="token punctuation"><</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">set</span><span class="token punctuation">(</span><span class="token class-name">String</span> key<span class="token punctuation">,</span> <span class="token class-name">Object</span> value<span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token class-name">Map</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">,</span> <span class="token class-name">Object</span><span class="token punctuation">></span></span> map <span class="token operator">=</span> <span class="token function">getLocalMap</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> map<span class="token punctuation">.</span><span class="token function">put</span><span class="token punctuation">(</span>key<span class="token punctuation">,</span> value <span class="token operator">==</span> <span class="token keyword">null</span> <span class="token operator">?</span> <span class="token class-name">StringUtils</span><span class="token punctuation">.</span><span class="token constant">EMPTY</span> <span class="token operator">:</span> value<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">remove</span><span class="token punctuation">(</span><span class="token class-name">String</span> key<span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token class-name">Map</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">,</span> <span class="token class-name">Object</span><span class="token punctuation">></span></span> map <span class="token operator">=</span> <span class="token function">getLocalMap</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> map<span class="token punctuation">.</span><span class="token function">remove</span><span class="token punctuation">(</span>key<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token class-name">String</span> <span class="token function">get</span><span class="token punctuation">(</span><span class="token class-name">String</span> key<span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token class-name">Map</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">,</span> <span class="token class-name">Object</span><span class="token punctuation">></span></span> map <span class="token operator">=</span> <span class="token function">getLocalMap</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token keyword">return</span> <span class="token class-name">Convert</span><span class="token punctuation">.</span><span class="token function">toStr</span><span class="token punctuation">(</span>map<span class="token punctuation">.</span><span class="token function">getOrDefault</span><span class="token punctuation">(</span>key<span class="token punctuation">,</span> <span class="token class-name">StringUtils</span><span class="token punctuation">.</span><span class="token constant">EMPTY</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token generics"><span class="token punctuation"><</span><span class="token class-name">T</span><span class="token punctuation">></span></span> <span class="token class-name">T</span> <span class="token function">get</span><span class="token punctuation">(</span><span class="token class-name">String</span> key<span class="token punctuation">,</span> <span class="token class-name">Class</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">T</span><span class="token punctuation">></span></span> clazz<span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token class-name">Map</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">,</span> <span class="token class-name">Object</span><span class="token punctuation">></span></span> map <span class="token operator">=</span> <span class="token function">getLocalMap</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token keyword">return</span> <span class="token class-name">StringUtils</span><span class="token punctuation">.</span><span class="token function">cast</span><span class="token punctuation">(</span>map<span class="token punctuation">.</span><span class="token function">getOrDefault</span><span class="token punctuation">(</span>key<span class="token punctuation">,</span> <span class="token keyword">null</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token class-name">Map</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">,</span> <span class="token class-name">Object</span><span class="token punctuation">></span></span> <span class="token function">getLocalMap</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token class-name">Map</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">,</span> <span class="token class-name">Object</span><span class="token punctuation">></span></span> map <span class="token operator">=</span> <span class="token constant">THREAD_LOCAL</span><span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token keyword">if</span> <span class="token punctuation">(</span>map <span class="token operator">==</span> <span class="token keyword">null</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> map <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ConcurrentHashMap</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">String</span><span class="token punctuation">,</span> <span class="token class-name">Object</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token constant">THREAD_LOCAL</span><span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span>map<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token keyword">return</span> map<span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token punctuation">}</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre><h3 id="3-设置和获取数据"><a href="#3-设置和获取数据" class="headerlink" title="3. 设置和获取数据"></a>3. 设置和获取数据</h3><p>在你的应用程序中，你可以使用 <code>TransmittableThreadLocal</code> 来设置和获取数据。例如，将当前登录的用户信息放在ThreadLocal中：</p><pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token class-name">SecurityContextHolder</span><span class="token punctuation">.</span><span class="token function">set</span><span class="token punctuation">(</span><span class="token class-name">SecurityConstants<span class="token punctuation">.</span>Details</span><span class="token punctuation">.</span><span class="token constant">LOGIN_USER</span><span class="token punctuation">.</span><span class="token function">getCode</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token class-name">JSONObject</span><span class="token punctuation">.</span><span class="token function">parseObject</span><span class="token punctuation">(</span>loginUserStr<span class="token punctuation">,</span> <span class="token class-name">LoginUser</span><span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span aria-hidden="true" class="line-numbers-rows"><span></span></span></code></pre><p>然后在另一个线程中，你可以获取该数据：</p><pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token class-name">String</span> user <span class="token operator">=</span> <span class="token class-name">SecurityContextHolder</span><span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span><span class="token class-name">SecurityConstants<span class="token punctuation">.</span>Details</span><span class="token punctuation">.</span><span class="token constant">LOGIN_USER</span><span class="token punctuation">.</span><span class="token function">getCode</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span aria-hidden="true" class="line-numbers-rows"><span></span></span></code></pre><h2 id="注意事项"><a href="#注意事项" class="headerlink" title="注意事项"></a>注意事项</h2><p>使用 <code>TransmittableThreadLocal</code> 时需要注意以下事项：</p><ol><li><p><strong>依赖包版本</strong>：确保你的项目使用了兼容版本的 <code>TransmittableThreadLocal</code> 依赖。通常，你应该使用最新版本以获取最新功能和修复。</p></li><li><p><strong>线程池和异步任务</strong>：主要用途是支持在线程池和异步任务中传递数据，确保你的线程池配置和异步任务调用兼容 <code>TransmittableThreadLocal</code>。</p></li><li><p><strong>清理数据</strong>：一定要在不再需要数据时及时清理，以避免内存泄漏。</p></li><li><p><strong>线程安全性</strong>：<code>TransmittableThreadLocal</code> 本身是线程安全的，但要确保你存储在其中的数据是线程安全的，以避免并发问题。</p></li><li><p><strong>性能影响</strong>：尽管 <code>TransmittableThreadLocal</code> 是为了解决线程池和异步任务中的问题而设计的，但在一般多线程应用中使用时，可能会带来轻微的性能开销。请根据应用需求进行权衡。</p></li></ol><h2 id="总结"><a href="#总结" class="headerlink" title="总结"></a>总结</h2><p><code>TransmittableThreadLocal</code> 是一个用于多线程环境下数据传递的有用工具，特别适用于线程池和异步任务。通过引入依赖，创建变量，设置和获取数据，以及及时清理数据，你可以在多线程应用中安全地传递上下文数据。</p><h2 id="参考资料"><a href="#参考资料" class="headerlink" title="参考资料"></a>参考资料</h2><ul><li><a href="https://github.com/alibaba/transmittable-thread-local">Transmittable-Thread-Local GitHub</a></li><li><a href="https://github.com/alibaba/transmittable-thread-local/wiki">阿里巴巴 Transmittable-Thread-Local 文档</a></li></ul>]]></content>
<categories>
<category> java </category>
</categories>
<tags>
<tag> 多线程 </tag>
</tags>
</entry>
<entry>
<title>CountDownLatch和Future用法</title>
<link href="/2023/08/30/CountDownLatch%E5%92%8CFuture%E7%94%A8%E6%B3%95/"/>
<url>/2023/08/30/CountDownLatch%E5%92%8CFuture%E7%94%A8%E6%B3%95/</url>
<content type="html"><![CDATA[<h2 id="1-CountDownLatch-概念"><a href="#1-CountDownLatch-概念" class="headerlink" title="1. CountDownLatch 概念"></a><strong>1. CountDownLatch 概念</strong></h2><p><code>CountDownLatch</code> 可以用于控制线程的同步等待。<code>CountDownLatch</code> 通常用于一个或多个线程等待其他线程的操作完成后再继续执行。</p><p><code>CountDownLatch</code> 可以用于很多场景，例如等待多个子任务完成后再执行主任务，控制并发测试中的线程同步，或者等待多个服务初始化完成后再启动应用程序等。</p><p>CountDownLatch 定义了一个<strong>计数器</strong>，和一个<strong>阻塞队列</strong>， 当计数器的值递减为0之前，阻塞队列里面的线程处于挂起状态，直到所有线程执行完毕。</p><p><strong>要点</strong>：</p><ol><li>初始化计数：<code>CountDownLatch</code> 的实例通过指定一个初始计数来初始化，该计数表示需要等待的线程数量。</li><li>线程等待：线程可以通过 <code>await()</code> 方法来等待计数器归零。当调用 <code>await()</code> 方法时，如果计数器不为零，则线程将进入等待状态，直到计数器变为零。</li><li>计数减少：通过 <code>countDown()</code> 方法可以将计数器减少1。每次调用 <code>countDown()</code> 方法都会使计数器减少1，直到计数器达到零。</li><li>等待阻塞：<code>await()</code> 方法调用后，当前线程会被阻塞，直到满足以下任一条件：计数器归零，或者当前线程被中断。</li><li>倒计时完成后：当计数器归零时，所有被阻塞的线程将被释放，可以继续执行后续操作。</li></ol><p><strong>示例代码：</strong></p><pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">CountDownLatchDemo</span> <span class="token punctuation">{</span> <span class="token keyword">private</span> <span class="token keyword">static</span> <span class="token class-name">Map</span> map <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">HashMap</span><span class="token generics"><span class="token punctuation"><</span><span class="token punctuation">></span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token keyword">private</span> <span class="token keyword">static</span> <span class="token class-name">CountDownLatch</span> countDownLatch <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">CountDownLatch</span><span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token comment">//记录开始时间</span> <span class="token keyword">long</span> start <span class="token operator">=</span> <span class="token class-name">System</span><span class="token punctuation">.</span><span class="token function">currentTimeMillis</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token class-name">Thread</span> thread1 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Thread</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">Runnable</span><span class="token punctuation">(</span><span class="token punctuation">)</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">run</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token keyword">try</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">"线程1任务开始执行"</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token class-name">Thread</span><span class="token punctuation">.</span><span class="token function">sleep</span><span class="token punctuation">(</span><span class="token number">6000</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//任务执行需要6秒</span> map<span class="token punctuation">.</span><span class="token function">put</span><span class="token punctuation">(</span><span class="token string">"thread1"</span><span class="token punctuation">,</span> <span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//保存结果值</span> countDownLatch<span class="token punctuation">.</span><span class="token function">countDown</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//标记已经完成一个任务</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">"线程1任务执行完毕"</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">InterruptedException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{</span> e<span class="token punctuation">.</span><span class="token function">printStackTrace</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token punctuation">}</span> <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span> thread1<span class="token punctuation">.</span><span class="token function">start</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token class-name">Thread</span> thread2 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Thread</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">Runnable</span><span class="token punctuation">(</span><span class="token punctuation">)</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">run</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token keyword">try</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">"线程2任务开始执行"</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token class-name">Thread</span><span class="token punctuation">.</span><span class="token function">sleep</span><span class="token punctuation">(</span><span class="token number">3000</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//任务执行需要3秒</span> map<span class="token punctuation">.</span><span class="token function">put</span><span class="token punctuation">(</span><span class="token string">"thread2"</span><span class="token punctuation">,</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//保存结果值</span> countDownLatch<span class="token punctuation">.</span><span class="token function">countDown</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//标记已经完成一个任务</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">"线程2任务执行完毕"</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">InterruptedException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{</span> e<span class="token punctuation">.</span><span class="token function">printStackTrace</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token punctuation">}</span> <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span> thread2<span class="token punctuation">.</span><span class="token function">start</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token keyword">try</span> <span class="token punctuation">{</span> countDownLatch<span class="token punctuation">.</span><span class="token function">await</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//等待所有任务执行完毕</span> <span class="token keyword">long</span> endTime <span class="token operator">=</span> <span class="token class-name">System</span><span class="token punctuation">.</span><span class="token function">currentTimeMillis</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//记录结束时间</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">"------统计所有线程全部完成--------"</span><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">"统计结果为："</span> <span class="token operator">+</span> map<span class="token punctuation">.</span><span class="token function">toString</span><span class="token punctuation">(</span><span class="token punctuation">)</span><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">"任务总执行时间为"</span> <span class="token operator">+</span> <span class="token punctuation">(</span>endTime <span class="token operator">-</span> start<span class="token punctuation">)</span> <span class="token operator">/</span> <span class="token number">1000</span> <span class="token operator">+</span> <span class="token string">"秒"</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">Exception</span> e<span class="token punctuation">)</span> <span class="token punctuation">{</span> e<span class="token punctuation">.</span><span class="token function">printStackTrace</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token punctuation">}</span><span class="token punctuation">}</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre><p>输出结果：</p><pre class="line-numbers language-java" data-language="java"><code class="language-java">线程<span class="token number">1</span>任务开始执行线程<span class="token number">2</span>任务开始执行线程<span class="token number">2</span>任务执行完毕线程<span class="token number">1</span>任务执行完毕<span class="token operator">--</span><span class="token operator">--</span><span class="token operator">--</span>统计所有线程全部完成<span class="token operator">--</span><span class="token operator">--</span><span class="token operator">--</span><span class="token operator">--</span>统计结果为：<span class="token punctuation">{</span>thread1<span class="token operator">=</span><span class="token number">1</span><span class="token punctuation">,</span> thread2<span class="token operator">=</span><span class="token number">2</span><span class="token punctuation">}</span>任务总执行时间为<span class="token number">6</span>秒<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre><h3 id="1-1-源码分析"><a href="#1-1-源码分析" class="headerlink" title="1.1 源码分析"></a>1.1 源码分析</h3><h4 id="1-1-1-创建计数器"><a href="#1-1-1-创建计数器" class="headerlink" title="1.1.1 创建计数器"></a>1.1.1 创建计数器</h4><p>当我们调用CountDownLatch countDownLatch=new CountDownLatch(2) 时候，此时会创建一个AQS的同步队列，并把创建CountDownLatch 传进来的计数器赋值给AQS队列的 state，所以state的值也代表CountDownLatch所剩余的计数次数；</p><pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token keyword">public</span> <span class="token class-name">CountDownLatch</span><span class="token punctuation">(</span><span class="token keyword">int</span> count<span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token keyword">if</span> <span class="token punctuation">(</span>count <span class="token operator"><</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token keyword">throw</span> <span class="token keyword">new</span> <span class="token class-name">IllegalArgumentException</span><span class="token punctuation">(</span><span class="token string">"count < 0"</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token keyword">this</span><span class="token punctuation">.</span>sync <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Sync</span><span class="token punctuation">(</span>count<span class="token punctuation">)</span><span class="token punctuation">;</span><span class="token comment">//创建同步队列，并设置初始计数器值</span> <span class="token punctuation">}</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span></span></code></pre><h4 id="1-1-2-countDown-方法"><a href="#1-1-2-countDown-方法" class="headerlink" title="1.1.2 countDown()方法"></a>1.1.2 countDown()方法</h4><p>调用 countDownLatch.countDown()方法，会对计数器进行减一，AQS（阻塞队列）内部是通过释放锁的方式，对state进行减1操作，当state=0的时候证明计数器已经递减完毕，此时会将AQS阻塞队列里的节点线程全部唤醒。</p><pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">countDown</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token keyword">this</span><span class="token punctuation">.</span>sync<span class="token punctuation">.</span><span class="token function">releaseShared</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//Sync extends AbstractQueuedSynchronizer </span><span class="token punctuation">}</span><span class="token keyword">public</span> <span class="token keyword">final</span> <span class="token keyword">boolean</span> <span class="token function">releaseShared</span><span class="token punctuation">(</span><span class="token keyword">int</span> var1<span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">tryReleaseShared</span><span class="token punctuation">(</span>var1<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span><span class="token comment">//当计数器为0时，</span> <span class="token keyword">this</span><span class="token punctuation">.</span><span class="token function">doReleaseShared</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//唤醒线程</span> <span class="token keyword">return</span> <span class="token boolean">true</span><span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span> <span class="token keyword">return</span> <span class="token boolean">false</span><span class="token punctuation">;</span> <span class="token punctuation">}</span><span class="token punctuation">}</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre><h2 id="2-线程池使用Future-get"><a href="#2-线程池使用Future-get" class="headerlink" title="2. 线程池使用Future.get()"></a>2. 线程池使用Future.get()</h2><p><code>Future</code> 它表示一个异步计算的结果。通过 <code>Future</code> 接口，我们可以提交任务给线程池进行异步执行，并在未来某个时间获取任务的执行结果。</p><p>future的核心思想是异步调用，当我们需要调用一个函数方法时，如果这个函数执行得很慢，那么我们就要进行等待。因此，我们可以让被调者立即返回，让它在后台慢慢处理这个请求。对于调用者来说，则可以先处理一些其他任务，在真正需要数据的场合再去尝试获得需要的数据。</p><p><strong>要点：</strong></p><ol><li>提交任务：通过将任务提交给线程池的执行器（<code>Executor</code>）的 <code>submit()</code> 或 <code>submit(Callable)</code> 方法，可以获得一个 <code>Future</code> 对象来表示任务的执行。</li><li>异步执行：任务被线程池接受后，线程池会在后台使用一个线程或线程池中的多个线程来执行任务。任务的执行不会阻塞当前线程，可以继续进行其他操作。</li><li>获取结果：通过调用 <code>Future</code> 对象的 <code>get()</code> 方法，可以阻塞当前线程，直到任务执行完成并返回结果。<code>get()</code> 方法会返回任务的执行结果，如果任务还没有完成，则会阻塞等待。</li><li>取消任务：可以通过调用 <code>Future</code> 对象的 <code>cancel(boolean)</code> 方法来取消任务的执行。传递参数为 <code>true</code> 表示尝试取消正在执行的任务，传递参数为 <code>false</code> 表示不尝试取消正在执行的任务。</li><li>判断任务状态：可以通过调用 <code>isDone()</code> 方法来判断任务是否已经完成，或通过 <code>isCancelled()</code> 方法判断任务是否被取消。</li><li>阻塞超时：<code>get()</code> 方法还支持设置阻塞超时时间，如果任务在指定的时间内没有完成，则抛出超时异常。</li></ol><p><strong>示例代码</strong></p><pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">FutureDemo</span> <span class="token punctuation">{</span> <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token comment">// 初始化线程池</span> <span class="token class-name">ExecutorService</span> threadPool <span class="token operator">=</span> <span class="token class-name">Executors</span><span class="token punctuation">.</span><span class="token function">newFixedThreadPool</span><span class="token punctuation">(</span><span class="token number">5</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 初始化线程任务</span> <span class="token class-name">MyTask</span> myTask <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">MyTask</span><span class="token punctuation">(</span><span class="token number">5</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token class-name">MyTask2</span> myTask2 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">MyTask2</span><span class="token punctuation">(</span><span class="token number">5</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 向线程池递交线程任务</span> <span class="token class-name">Future</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Integer</span><span class="token punctuation">></span></span> future <span class="token operator">=</span> threadPool<span class="token punctuation">.</span><span class="token function">submit</span><span class="token punctuation">(</span>myTask<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token class-name">Future</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Integer</span><span class="token punctuation">></span></span> future2 <span class="token operator">=</span> threadPool<span class="token punctuation">.</span><span class="token function">submit</span><span class="token punctuation">(</span>myTask2<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 主线程休眠5秒，模拟主线程在做其他的事情</span> <span class="token keyword">try</span> <span class="token punctuation">{</span> <span class="token class-name">Thread</span><span class="token punctuation">.</span><span class="token function">sleep</span><span class="token punctuation">(</span><span class="token number">5000</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">InterruptedException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{</span> e<span class="token punctuation">.</span><span class="token function">printStackTrace</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token comment">// 主线程获取异步任务的执行结果</span> <span class="token keyword">try</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">"异步线程任务执行结果1 "</span> <span class="token operator">+</span> future<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span><span class="token punctuation">)</span><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">"检查异步线程任务是否执行完毕1 "</span> <span class="token operator">+</span> future<span class="token punctuation">.</span><span class="token function">isDone</span><span class="token punctuation">(</span><span class="token punctuation">)</span><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">"异步线程任务执行结果2 "</span> <span class="token operator">+</span> future2<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span><span class="token punctuation">)</span><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">"检查异步线程任务是否执行完毕2 "</span> <span class="token operator">+</span> future2<span class="token punctuation">.</span><span class="token function">isDone</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">InterruptedException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{</span> e<span class="token punctuation">.</span><span class="token function">printStackTrace</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">ExecutionException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{</span> e<span class="token punctuation">.</span><span class="token function">printStackTrace</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token punctuation">}</span> <span class="token comment">// 静态内部类，实现Callable接口的任务类</span> <span class="token keyword">static</span> <span class="token keyword">class</span> <span class="token class-name">MyTask</span> <span class="token keyword">implements</span> <span class="token class-name">Callable</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Integer</span><span class="token punctuation">></span></span> <span class="token punctuation">{</span> <span class="token keyword">private</span> <span class="token keyword">int</span> num<span class="token punctuation">;</span> <span class="token keyword">public</span> <span class="token class-name">MyTask</span><span class="token punctuation">(</span><span class="token keyword">int</span> num<span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token keyword">this</span><span class="token punctuation">.</span>num <span class="token operator">=</span> num<span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token annotation punctuation">@Override</span> <span class="token keyword">public</span> <span class="token class-name">Integer</span> <span class="token function">call</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">Exception</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 class-name">Thread</span><span class="token punctuation">.</span><span class="token function">currentThread</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">getName</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">+</span> <span class="token string">" 正在执行异步任务"</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token keyword">this</span><span class="token punctuation">.</span>num <span class="token operator">+=</span> <span class="token number">1</span><span class="token punctuation">;</span> <span class="token keyword">return</span> <span class="token keyword">this</span><span class="token punctuation">.</span>num<span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token punctuation">}</span> <span class="token keyword">static</span> <span class="token keyword">class</span> <span class="token class-name">MyTask2</span> <span class="token keyword">implements</span> <span class="token class-name">Callable</span><span class="token generics"><span class="token punctuation"><</span><span class="token class-name">Integer</span><span class="token punctuation">></span></span> <span class="token punctuation">{</span> <span class="token keyword">private</span> <span class="token keyword">int</span> num<span class="token punctuation">;</span> <span class="token keyword">public</span> <span class="token class-name">MyTask2</span><span class="token punctuation">(</span><span class="token keyword">int</span> num<span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token keyword">this</span><span class="token punctuation">.</span>num <span class="token operator">=</span> num<span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token annotation punctuation">@Override</span> <span class="token keyword">public</span> <span class="token class-name">Integer</span> <span class="token function">call</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">Exception</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 class-name">Thread</span><span class="token punctuation">.</span><span class="token function">currentThread</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">getName</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">+</span> <span class="token string">" 正在执行异步任务"</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token keyword">this</span><span class="token punctuation">.</span>num <span class="token operator">*=</span> <span class="token number">2</span><span class="token punctuation">;</span> <span class="token keyword">return</span> <span class="token keyword">this</span><span class="token punctuation">.</span>num<span class="token punctuation">;</span> <span class="token punctuation">}</span> <span class="token punctuation">}</span><span class="token punctuation">}</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre><p><strong>输出结果</strong></p><pre class="line-numbers language-java" data-language="java"><code class="language-java">pool<span class="token operator">-</span><span class="token number">1</span><span class="token operator">-</span>thread<span class="token operator">-</span><span class="token number">1</span> 正在执行异步任务pool<span class="token operator">-</span><span class="token number">1</span><span class="token operator">-</span>thread<span class="token operator">-</span><span class="token number">2</span> 正在执行异步任务异步线程任务执行结果<span class="token number">1</span> <span class="token number">6</span>检查异步线程任务是否执行完毕<span class="token number">1</span> <span class="token boolean">true</span>异步线程任务执行结果<span class="token number">2</span> <span class="token number">10</span>检查异步线程任务是否执行完毕<span class="token number">2</span> <span class="token boolean">true</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>]]></content>
<categories>
<category> 多线程 </category>
</categories>
<tags>
<tag> java </tag>
</tags>
</entry>
<entry>
<title>HEXO常用命令</title>
<link href="/2023/08/29/HEXO%E5%B8%B8%E7%94%A8%E5%91%BD%E4%BB%A4/"/>
<url>/2023/08/29/HEXO%E5%B8%B8%E7%94%A8%E5%91%BD%E4%BB%A4/</url>
<content type="html"><![CDATA[<h3 id="常用命令"><a href="#常用命令" class="headerlink" title="常用命令"></a>常用命令</h3><table><thead><tr><th>命令</th><th>描述</th></tr></thead><tbody><tr><td>hexo new post “title”</td><td>新建文章</td></tr><tr><td>hexo new page “title”</td><td>新建页面</td></tr><tr><td>hexo generate/g</td><td>生成静态页面至public目录</td></tr><tr><td>hexo server/s</td><td>开启本地预览访问端口</td></tr><tr><td>hexo deploy/d</td><td>将.deploy目录部署到GitHub</td></tr><tr><td>hexo clean</td><td>清除缓存文件等</td></tr></tbody></table>]]></content>
<categories>
<category> 默认 </category>
</categories>
<tags>
<tag> 默认 </tag>
</tags>
</entry>
<entry>
<title>Spring中的@ConditionalOnExpression注解</title>
<link href="/2023/07/26/Spring%E4%B8%AD%E7%9A%84@ConditionalOnExpression%E6%B3%A8%E8%A7%A3/"/>
<url>/2023/07/26/Spring%E4%B8%AD%E7%9A%84@ConditionalOnExpression%E6%B3%A8%E8%A7%A3/</url>
<content type="html"><![CDATA[<h2 id="ConditionalOnExpression"><a href="#ConditionalOnExpression" class="headerlink" title="@ConditionalOnExpression"></a>@ConditionalOnExpression</h2><p><code>@ConditionalOnExpression</code> 是 Spring提供的一个条件注解。</p><p>该注解用于根据指定的条件表达式来决定是否启用或禁用一个 Spring 组件。</p><h2 id="使用示例"><a href="#使用示例" class="headerlink" title="使用示例"></a>使用示例</h2><p>在配置类、Bean 方法或自定义注解上标记 <code>@ConditionalOnExpression</code> 注解，以基于特定条件来决定是否创建或装配相关的 Bean。</p><p>示例代码：</p><pre class="line-numbers language-none"><code class="language-none">@Configurationpublic class MyConfiguration { @Bean @ConditionalOnExpression("${config.face.enabled:true}") public MyBean myBean() { return new MyBean(); }}<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre><p>在上述示例中，<code>@ConditionalOnExpression("${config.face.enabled:true}")</code> 表示当条件表达式 <code>${config.face.enabled:true}</code> 的结果为真时，才会创建并注册名为 <code>myBean</code> 的 Bean。</p><p>配置文件：</p><pre class="line-numbers language-none"><code class="language-none">config: face: enabled: true<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span></span></code></pre><p><code>${config.face.enabled:true}</code> 是一个条件表达式，它可以是任意的 SpEL（Spring Expression Language）表达式。在这个表达式中，<code>${config.face.enabled}</code> 是一个占位符，表示从配置文件<code>ymal</code>获取一个属性值，如果该属性不存在，则使用默认值 <code>true</code>。</p><p>通过使用 <code>@ConditionalOnExpression</code> 注解，可以根据条件表达式动态控制 Bean 的创建和装配。这使得应用在不同的环境或配置下具有灵活的行为。</p><p>需要注意的是，条件表达式的结果类型必须为布尔值。如果条件表达式的结果为 <code>true</code>，则相应的 Bean 将被创建和装配；如果结果为 <code>false</code>，则该 Bean 将被忽略。</p><h2 id="总结"><a href="#总结" class="headerlink" title="总结"></a>总结</h2><p><code>@ConditionalOnExpression</code> 注解是一个在 Spring中非常有用的条件注解之一。它使得根据特定条件来控制组件的创建和装配成为可能。通过编写条件表达式，并将其与 <code>@ConditionalOnExpression</code> 注解结合使用，可以在应用程序中实现更灵活的配置和条件性的行为。</p>]]></content>
<categories>
<category> Spring </category>
</categories>
<tags>
<tag> java </tag>
</tags>
</entry>
</search>