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：

方法一、

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package  com.leadsoft.test.executor.processor public  class  InstantiationTracingBeanPostProcessor  implements  ApplicationListener<ContextRefreshedEvent> { @Override public  void  onApplicationEvent(ContextRefreshedEvent event) { //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。 } }

　　

　　同时在Spring的配置文件中，添加注入：

1 2	<!-- 当Spring容器启动完成后执行下面的这个Bean --> <bean  class = "com.leadsoft.test.executor.processor.InstantiationTracingBeanPostProcessor" />

　　

　　

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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@Override public  void  onApplicationEvent(ContextRefreshedEvent event) { //root application context 没有parent，他就是老大. if (event.getApplicationContext().getParent() ==  null ){ //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。 } }

方法二、　　

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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/*   * Copyright (c) 2005, 2013, Oracle and/or its affiliates. All rights reserved.   * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.   *   *   *   *   *   *   *   *   *   *   *   *   *   *   *   *   *   *   *   *   */   package  javax.annotation;   import  java.lang.annotation.*; import  static  java.lang.annotation.ElementType.*; import  static  java.lang.annotation.RetentionPolicy.*;   /**   * The PostConstruct annotation is used on a method that needs to be executed   * after dependency injection is done to perform any initialization. This   * method MUST be invoked before the class is put into service. This   * annotation MUST be supported on all classes that support dependency   * injection. The method annotated with PostConstruct MUST be invoked even   * if the class does not request any resources to be injected. Only one   * method can be annotated with this annotation. The method on which the   * PostConstruct annotation is applied MUST fulfill all of the following   * criteria:   * <p>   * <ul>   * <li>The method MUST NOT have any parameters except in the case of   * interceptors in which case it takes an InvocationContext object as   * defined by the Interceptors specification.</li>   * <li>The method defined on an interceptor class MUST HAVE one of the   * following signatures:   * <p>   * void <METHOD>(InvocationContext)   * <p>   * Object <METHOD>(InvocationContext) throws Exception   * <p>   * <i>Note: A PostConstruct interceptor method must not throw application   * exceptions, but it may be declared to throw checked exceptions including   * the java.lang.Exception if the same interceptor method interposes on   * business or timeout methods in addition to lifecycle events. If a   * PostConstruct interceptor method returns a value, it is ignored by   * the container.</i>   * </li>   * <li>The method defined on a non-interceptor class MUST HAVE the   * following signature:   * <p>   * void <METHOD>()   * </li>   * <li>The method on which PostConstruct is applied MAY be public, protected,   * package private or private.</li>   * <li>The method MUST NOT be static except for the application client.</li>   * <li>The method MAY be final.</li>   * <li>If the method throws an unchecked exception the class MUST NOT be put into   * service except in the case of EJBs where the EJB can handle exceptions and   * even recover from them.</li></ul>   * @since Common Annotations 1.0   * @see javax.annotation.PreDestroy   * @see javax.annotation.Resource   */ @Documented @Retention  (RUNTIME) @Target (METHOD) public  @interface  PostConstruct { } 方法三、 方法实现InitializingBean或者ServletContextAware