【spring源碼學習】Spring @PostConstruct和@PreDestroy執行個體

在Spring中，既可以實作 InitializingBean和DisposableBean接口或在bean配置檔案中指定 init-method 和 destroy-method 在初始化和銷毀回調函數。在這篇文章中，我們将介紹如何使用 @PostConstruct 和 @PreDestroy 注解來做同樣的事情。

注：@PostConstruct和@PreDestroy 标注不屬于 Spring，它是在J2EE庫- common-annotations.jar。

@PostConstruct 和 @PreDestroy

一個 CustomerService Bean使用 @PostConstruct 和 @PreDestroy 注釋

package com.yiibai.customer.services;

import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;

public class CustomerService
{
	String message;
	
	public String getMessage() {
	  return message;
	}

	public void setMessage(String message) {
	  this.message = message;
	}
	
	@PostConstruct
	public void initIt() throws Exception {
	  System.out.println("Init method after properties are set : " + message);
	}
	
	@PreDestroy
	public void cleanUp() throws Exception {
	  System.out.println("Spring Container is destroy! Customer clean up");
	}
	
}      

預設情況下，Spring不會意識到@PostConstruct和@PreDestroy注解。要啟用它，要麼注冊“CommonAnnotationBeanPostProcessor”，要麼在bean配置檔案的<context:annotation-config />‘ 指定，

1. CommonAnnotationBeanPostProcessor

<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://www.springframework.org/schema/beans
	http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">

	<bean class="org.springframework.context.annotation.CommonAnnotationBeanPostProcessor" />

	<bean id="customerService" class="com.yiibai.customer.services.CustomerService">
		<property name="message" value="i'm property message" />
	</bean>
		
</beans>      

2. <context:annotation-config />

<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:context="http://www.springframework.org/schema/context"
	xsi:schemaLocation="http://www.springframework.org/schema/beans
	http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
	http://www.springframework.org/schema/context
	http://www.springframework.org/schema/context/spring-context-2.5.xsd">

	<context:annotation-config />

	<bean id="customerService" class="com.yiibai.customer.services.CustomerService">
		<property name="message" value="i'm property message" />
	</bean>
		
</beans>      

執行結果

package com.yiibai.common;

import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.yiibai.customer.services.CustomerService;

public class App 
{
    public static void main( String[] args )
    {
    	ConfigurableApplicationContext context = 
    	  new ClassPathXmlApplicationContext(new String[] {"Spring-Customer.xml"});
	
    	CustomerService cust = (CustomerService)context.getBean("customerService");
    	
    	System.out.println(cust);
    	
    	context.close();
    }
}      

輸出結果

Init method after properties are set : im property message
com.yiibai.customer.services.CustomerService@47393f
...
INFO: Destroying singletons in org.springframework.beans.factory.
support.DefaultListableBeanFactory@77158a: 
defining beans [customerService]; root of factory hierarchy
Spring Container is destroy! Customer clean up      

initIt()方法(@PostConstruct)被調用時，消息屬性設定後 cleanUp() 方法(@PreDestroy)是在context.close()執行後被調用;