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：

package com.yk.test.executor.processorpublic class InstantiationTracingBeanPostProcessor implements ApplicationListener
     
       {@Overridepublic 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：

　　

　　

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：

 

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

　　

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：

 

/* * 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: * 
 * 
     
       * 
      
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.
 * 
      
The method defined on an interceptor class MUST HAVE one of the * following signatures: * 
 * void 
        
         (InvocationContext) * 
        
 * Object 
        
         (InvocationContext) throws Exception * 
        
 * 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. * 
 * 
      
The method defined on a non-interceptor class MUST HAVE the * following signature: * 
 * void 
        
         () * 
        
 * 
      
The method on which PostConstruct is applied MAY be public, protected, * package private or private.
 * 
      
The method MUST NOT be static except for the application client.
 * 
      
The method MAY be final.
 * 
      
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.
     
 * @since Common Annotations 1.0 * @see javax.annotation.PreDestroy * @see javax.annotation.Resource */@Documented@Retention (RUNTIME)@Target(METHOD)public @interface PostConstruct {}