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 { }