实例化，执行，初始化，销毁bean对象

最新推荐文章于 2023-03-04 16:12:28 发布

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本文介绍如何在Spring框架中实现懒加载功能，通过配置文件设置属性lazy-init=true来延迟实例化对象，仅在需要使用时创建。同时展示了ExampleBean类实例化、初始化及销毁的过程，并通过测试案例验证懒加载的效果。

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1.修改applicationContext.xml，通过设置配置文件属性lazy-init="true"，可以改变Spring容器创建对象的时机。
2.在顶级的<beans/>元素中的default-lazy-init属性，可以为容器所有<bean>指定延迟实例化特性

3.从输出结果可以看出，当使用ExampleBean对象时，才被创建，即，设置lazy-init="true"属性后，对象不使用不创建。

package org.spring.dao;

public class ExampleBean {
	
	public ExampleBean() {
		System.out.println("实例化ExampleBean");
	}

	public void execute() {
		System.out.println("执行ExampleBean处理");
	}

	public void init() {
		System.out.println("初始化ExampleBean对象");
	}

	public void destroy() {
		System.out.println("销毁ExampleBean对象");
	}

}

package org.spring.dao;

public class ExampleBean1 {
	public ExampleBean1() {
		System.out.println("实例化ExampleBean1");
	}
}

<?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"
	xmlns:jdbc="http://www.springframework.org/schema/jdbc" xmlns:jee="http://www.springframework.org/schema/jee"
	xmlns:tx="http://www.springframework.org/schema/tx" xmlns:jpa="http://www.springframework.org/schema/data/jpa"
	xsi:schemaLocation="
		http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
		http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.2.xsd
		http://www.springframework.org/schema/jdbc http://www.springframework.org/schema/jdbc/spring-jdbc-3.2.xsd
		http://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee-3.2.xsd
		http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.2.xsd
		http://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa-1.3.xsd"
	default-lazy-init="true" 
	default-init-method="init"
	default-destroy-method="destroy">


	<bean id="exampleBean" class="org.spring.dao.ExampleBean" scope="singleton"
		init-method="init" destroy-method="destroy" depends-on="bean1" />
		
	<bean id="bean1" class="org.spring.dao.ExampleBean1" lazy-init="true" />

</beans>

package org.spring.test;

import org.junit.Test;
import org.spring.dao.ExampleBean;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.AbstractApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class testCase {

	@Test
	public void testExampleBean() {
		// 实例化Spring容器示例
		String conf = "applicationContext.xml";
		ApplicationContext ac = new ClassPathXmlApplicationContext(conf);
		//System.out.println(ac);
		// 获取ExampleBean对象
		ExampleBean bean1 = ac.getBean("exampleBean", ExampleBean.class);
		ExampleBean bean2 = ac.getBean("exampleBean", ExampleBean.class);
		System.out.println(bean1 == bean2);
		// 关闭Spring容器, 注意AbstractApplicationContext类型定义了 close()方法
		AbstractApplicationContext ctx = (AbstractApplicationContext) ac;
		ctx.close();
	}
}