Spring注解之@PostConstruct

一、注解解释

Spring的@PostConstruct注解在方法上，表示此方法是在Spring实例化该Bean之后马上执行此方法，之后才会去实例化其他Bean，并且一个Bean中@PostConstruct注解的方法可以有多个。

二、示例代码

1. spring配置文件

<?xml version="1.0" encoding="UTF-8"?>
<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-3.0.xsd 
http://www.springframework.org/schema/context 
http://www.springframework.org/schema/context/spring-context-3.0.xsd
">

	<!-- 引入属性文件 -->
	<context:property-placeholder location="classpath:config.properties" />

	<!-- 自动扫描dao和service包(自动注入) -->
	<context:component-scan base-package="com.wbf.bean" />

</beans>

2. Bean1.java

package com.wbf.bean;

import javax.annotation.PostConstruct;

import org.apache.log4j.Logger;
import org.springframework.stereotype.Service;

@Service("bean1")
public class Bean1 {
	
	private static final Logger log = Logger.getLogger(Bean1.class);
	
	public Bean1() {
		log.info(System.currentTimeMillis() + ": Bean1 Constructor");
	}
	
	@PostConstruct
	public void test() {
		log.info(System.currentTimeMillis() + ": bean1-->test()");
		Bean2.uniqueInstance().test();
		
	}
	
	@PostConstruct
	public void print() {
		log.info(System.currentTimeMillis() + ": bean1-->print()");
	}
}

3. Bean2.java

package com.wbf.bean;

import org.apache.log4j.Logger;

public class Bean2 {
	
	private static final Logger log = Logger.getLogger(Bean2.class);
	
	private static Bean2 instance = uniqueInstance();
	
	public static Bean2 uniqueInstance() {
		if (instance == null)
			instance = new Bean2();
		
		return instance;
	}
	
	public Bean2() {
		log.info(System.currentTimeMillis() + ": Bean2 Construtor");
	}
	
	public void test() {
		log.info(System.currentTimeMillis() + ": bean2-->test()");
	}
}

4. Bean3.java

package com.wbf.bean;

import org.apache.log4j.Logger;
import org.springframework.stereotype.Service;

@Service("bean3")
public class Bean3 {
	
	private static final Logger log = Logger.getLogger(Bean3.class);
	
	public Bean3() {
		log.info(System.currentTimeMillis() + ": Bean3 Construtor");
	}
	
}

5. SpringTest.java

package com.wbf.bean;

import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class SpringTest {
	
	@Test
	public void test() {
		//加载/解析spring.xml, 得到BeanFactory, 实例化所有IOC容器中的Bean
		//在实例化每一个Bean之后，如果当前Bean包含@PostConstruct注解的方法则会马上执行该方法，之后才会去实例化其他的Bean
		//每一个Bean中可以有多个包含@PostConstruct注解的方法
		ApplicationContext ac = new ClassPathXmlApplicationContext(new String[]{"classpath:spring.xml"});
	}
	
}

运行结果：

[org.springframework.context.support.ClassPathXmlApplicationContext]Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@b0f2b2: startup date [Thu Jun 11 11:51:17 CST 2015]; root of context hierarchy
[org.springframework.beans.factory.xml.XmlBeanDefinitionReader]Loading XML bean definitions from class path resource [spring.xml]
[org.springframework.beans.factory.config.PropertyPlaceholderConfigurer]Loading properties file from class path resource [config.properties]
[org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor]JSR-330 'javax.inject.Inject' annotation found and supported for autowiring
[org.springframework.beans.factory.support.DefaultListableBeanFactory]Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@1b8dc93: defining beans [org.springframework.beans.factory.config.PropertyPlaceholderConfigurer#0,bean1,bean3,org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,org.springframework.context.annotation.internalPersistenceAnnotationProcessor,org.springframework.context.annotation.ConfigurationClassPostProcessor.importAwareProcessor]; root of factory hierarchy
[com.wbf.bean.Bean1]1433994678340: Bean1 Constructor
[com.wbf.bean.Bean1]1433994678347: bean1-->print()
[com.wbf.bean.Bean1]1433994678347: bean1-->test()
[com.wbf.bean.Bean2]1433994678348: Bean2 Construtor
[com.wbf.bean.Bean2]1433994678348: bean2-->test()
[com.wbf.bean.Bean3]1433994678348: Bean3 Construtor

从运行结果可以看出Spring在实例化Bean1之后马上执行了它的@PostConstruct注解的方法print()和test()，之后才去实例化Bean3。其中Bean2没有被Spring IOC容器管理。

三、补充说明

@PostConstruct注解Bean中的某些方法，可以用在服务器启动时的做一些初始化工作。

Spring注解之@PostConstruct

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