当spring 容器初始化完成后执行某个方法


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.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:

<!-- 当Spring容器启动完成后执行下面的这个Bean -->
<bean class="com.yk.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:

 

@Override
public 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:
 * <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 {
}

  

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