spring 容器初始化完成后执行某个特定方法

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、

package  com.bosssoft.nontax.agency
public  class  InstantiationTracingBeanPostProcessor  implements   ApplicationListener {
    @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：

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：

@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：

 

 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 {
}