spring项目启动完成后，自动执行一次某个特定方法。

Myth丶恋晨 2024-02-18 16:33 142阅读 0赞

在做web项目开发中，尤其是企业级应用开发的时候，往往会在工程启动的时候做许多的前置检查。

比如检查是否使用了我们组禁止使用的Mysql的group\_concat函数，如果使用了项目就不能启动，并指出哪个文件的xml文件使用了这个函数。

而在Spring的web项目中，我们可以介入Spring的启动过程。我们希望在Spring容器将所有的Bean都初始化完成之后，做一些操作，这个时候我们就可以实现一个接口：

<table> 
 <tbody> 
  <tr> 
   <td> 
    <div> 
     <div> 
      <code>package</code> 
      <code> com.yk.test.executor.processor</code> 
     </div> 
     <div> 
      <code>public</code> 
      <code> class</code> 
      <code>InstantiationTracingBeanPostProcessor </code> 
      <code>implements</code> 
      <code>ApplicationListener&lt;ContextRefreshedEvent&gt; { </code> 
     </div> 
     <div> 
      <code>@Override</code> 
     </div> 
     <div> 
      <code>public</code> 
      <code> void</code> 
      <code>onApplicationEvent(ContextRefreshedEvent event) { </code> 
     </div> 
     <div> 
      <code>//需要执行的逻辑代码，当spring容器初始化完成后就会执行该方法。</code> 
     </div> 
     <div> 
      <code>}</code> 
     </div> 
     <div> 
      <code>}</code> 
     </div> 
    </div> </td> 
  </tr> 
 </tbody> 
</table>

同时在Spring的配置文件中，添加注入：

<table> 
 <tbody> 
  <tr> 
   <td> 
    <div> 
     <div> 
      <code>&lt;!-- 当Spring容器启动完成后执行下面的这个Bean --&gt;</code> 
     </div> 
     <div> 
      <code>&lt;bean </code> 
      <code>class</code> 
      <code>=</code> 
      <code>"com.yk.test.executor.processor.InstantiationTracingBeanPostProcessor"</code> 
      <code>/&gt;</code> 
     </div> 
    </div> </td> 
  </tr> 
 </tbody> 
</table>

但是这个时候，会存在一个问题，在web 项目中（spring mvc），系统会存在两个容器，一个是root application context ,另一个就是我们自己的 projectName-servlet context（作为root application context的子容器）。

这种情况下，就会造成onApplicationEvent方法被执行两次。为了避免上面提到的问题，我们可以只在root application context初始化完成后调用逻辑代码，其他的容器的初始化完成，则不做任何处理，修改后代码

如下：

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 <tbody> 
  <tr> 
   <td> 
    <div> 
     <div> 
      <code>@Override</code> 
     </div> 
     <div> 
      <code>public</code> 
      <code> void</code> 
      <code>onApplicationEvent(ContextRefreshedEvent event) { </code> 
     </div> 
     <div> 
      <code>if</code> 
      <code>(event.getApplicationContext().getParent() == </code> 
      <code>null</code> 
      <code>){ </code> 
      <code>//root application context 没有parent，他就是老大.</code> 
     </div> 
     <div> 
      <code>//需要执行的逻辑代码，当spring容器初始化完成后就会执行该方法。</code> 
     </div> 
     <div> 
      <code>}</code> 
     </div> 
     <div> 
      <code>}</code> 
     </div> 
    </div> </td> 
  </tr> 
 </tbody> 
</table>

**其实更简单的方法是使用注解：\`@PostConstruct\`，只需要在需要启动的时候执行的方法上标注这个注解就搞定了。**

注解描述如下：

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 <tbody> 
  <tr> 
   <td> 
    <div> 
     <div> 
      <code>/*</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* Copyright (c) 2005, 2013, Oracle and/or its affiliates. All rights reserved.</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>*</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>*</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>*</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>*</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>*</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>*</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>*</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>*</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>*</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>*</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>*</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>*</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>*</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>*</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>*</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>*</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>*</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>*</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>*</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>*</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>*/</code> 
     </div> 
     <div>
       &nbsp; 
     </div> 
     <div> 
      <code>package</code> 
      <code>javax.annotation;</code> 
     </div> 
     <div>
       &nbsp; 
     </div> 
     <div> 
      <code>import</code> 
      <code> java.lang.annotation.*;</code> 
     </div> 
     <div> 
      <code>import</code> 
      <code> static</code> 
      <code>java.lang.annotation.ElementType.*;</code> 
     </div> 
     <div> 
      <code>import</code> 
      <code> static</code> 
      <code>java.lang.annotation.RetentionPolicy.*;</code> 
     </div> 
     <div>
       &nbsp; 
     </div> 
     <div> 
      <code>/**</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* The PostConstruct annotation is used on a method that needs to be executed</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* after dependency injection is done to perform any initialization. This</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* method MUST be invoked before the class is put into service. This</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* annotation MUST be supported on all classes that support dependency</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* injection. The method annotated with PostConstruct MUST be invoked even</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* if the class does not request any resources to be injected. Only one</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* method can be annotated with this annotation. The method on which the</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* PostConstruct annotation is applied MUST fulfill all of the following</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* criteria:</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* &lt;p&gt;</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* &lt;ul&gt;</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* &lt;li&gt;The method MUST NOT have any parameters except in the case of</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* interceptors in which case it takes an InvocationContext object as</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* defined by the Interceptors specification.&lt;/li&gt;</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* &lt;li&gt;The method defined on an interceptor class MUST HAVE one of the</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* following signatures:</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* &lt;p&gt;</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* void &lt;METHOD&gt;(InvocationContext)</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* &lt;p&gt;</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* Object &lt;METHOD&gt;(InvocationContext) throws Exception</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* &lt;p&gt;</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* &lt;i&gt;Note: A PostConstruct interceptor method must not throw application</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* exceptions, but it may be declared to throw checked exceptions including</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* the java.lang.Exception if the same interceptor method interposes on</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* business or timeout methods in addition to lifecycle events. If a</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* PostConstruct interceptor method returns a value, it is ignored by</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* the container.&lt;/i&gt;</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* &lt;/li&gt;</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* &lt;li&gt;The method defined on a non-interceptor class MUST HAVE the</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* following signature:</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* &lt;p&gt;</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* void &lt;METHOD&gt;()</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* &lt;/li&gt;</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* &lt;li&gt;The method on which PostConstruct is applied MAY be public, protected,</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* package private or private.&lt;/li&gt;</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* &lt;li&gt;The method MUST NOT be static except for the application client.&lt;/li&gt;</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* &lt;li&gt;The method MAY be final.&lt;/li&gt;</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* &lt;li&gt;If the method throws an unchecked exception the class MUST NOT be put into</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* service except in the case of EJBs where the EJB can handle exceptions and</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* even recover from them.&lt;/li&gt;&lt;/ul&gt;</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* @since Common Annotations 1.0</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* @see javax.annotation.PreDestroy</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>* @see javax.annotation.Resource</code> 
     </div> 
     <div> 
      <code>&nbsp;</code> 
      <code>*/</code> 
     </div> 
     <div> 
      <code>@Documented</code> 
     </div> 
     <div> 
      <code>@Retention</code> 
      <code>(RUNTIME)</code> 
     </div> 
     <div> 
      <code>@Target</code> 
      <code>(METHOD)</code> 
     </div> 
     <div> 
      <code>public</code> 
      <code> @interface</code> 
      <code>PostConstruct { </code> 
     </div> 
     <div> 
      <code>}</code> 
     </div> 
     <div> 
      <code><br> </code> 
     </div> 
     <div> 
      <code><br> </code> 
     </div> 
     <div> 
      <code>转载：<a href="https://www.cnblogs.com/rollenholt/p/3612440.html" rel="nofollow">https://www.cnblogs.com/rollenholt/p/3612440.html</a><br> </code> 
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