spring容器的懒加载lazy-init设置

默认情况下，spring的IOC容器中lazy-init是false的，即没有打开懒加载模式。

如果你没有看到这个lazy-init 的参数设置就说明是false啦。

那么什么是懒加载？

懒加载---就是我们在spring容器启动的是先不把所有的bean都加载到spring的容器中去，而是在当需要用的时候，才把这个对象实例化到容器中。

例如我有如下的代码：

package com.luch.spring.demo;  

import org.springframework.beans.factory.annotation.Autowired;  

import com.luch.spring.bean.Person;  

public class NewPerson {  

    @Autowired  
    private Person person;  

    public NewPerson(){  
        System.out.println("lazy loading...");  
    }  
    public void printMsg(){  
        if(person !=null) {  
            System.out.println(person.getName());  
        } else {  
            System.out.println("no person initialize!");  
        }  
    }  

    public void setPerson(Person person) {  
        //this.person = person;  
    }  


}  

在无惨构造器里输出一句话，然后我先不设置懒加载模式：我有一个beans.xml的配置文件：

<?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.xsd  
            http://www.springframework.org/schema/context    
            http://www.springframework.org/schema/context/spring-context.xsd">  

           <context:annotation-config/>  
           <bean id="person" class="com.luch.spring.bean.Person">  
               <property name="id" value="22"></property>  
               <property name="name" value="Jack"></property>  
           </bean>  

           <bean id="newPerson" class="com.luch.spring.demo.NewPerson">  
               <property name="person" ref="person"></property>  
           </bean>  

</beans>  

然后我用一个junit来做测试：

package junit.test;  

import static org.junit.Assert.*;  

import org.junit.Test;  

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

import com.luch.spring.demo.NewPerson;  

public class JunitTest {  

    @Test  
    public void printMsg(){  
        AbstractApplicationContext ctx = new ClassPathXmlApplicationContext("/beans.xml");  
        //NewPerson test = (NewPerson) ctx.getBean("newPerson");  
        //test.printMsg();  
    }  
}  

这个时候输出的结果为：
[color=orange]四月 17, 2014 9:26:41 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@762efe5d: startup date [Thu Apr 17 21:26:41 CST 2014]; root of context hierarchy
四月 17, 2014 9:26:42 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [beans.xml]
四月 17, 2014 9:26:42 下午 org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
信息: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@77caeb3e: defining beans [org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,person,newPerson,org.springframework.context.annotation.ConfigurationClassPostProcessor$ImportAwareBeanPostProcessor#0]; root of factory hierarchy
lazy loading..[/color]
即对象被实例化了，也就是被加载到spring的容器中去了。


然后我们设置一下懒加载模式：我们beans.xml的配置文件. lazy-init="true"即

<?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.xsd  
            http://www.springframework.org/schema/context    
            http://www.springframework.org/schema/context/spring-context.xsd">  

           <context:annotation-config/>  
           <bean id="person" class="com.luch.spring.bean.Person">  
               <property name="id" value="22"></property>  
               <property name="name" value="Jack"></property>  
           </bean>  

           <bean id="newPerson" lazy-init="true" class="com.luch.spring.demo.NewPerson">  
               <property name="person" ref="person"></property>  
           </bean>  

</beans>

再重新跑一次junit：结果为：
[color=orange]四月 17, 2014 9:33:54 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@762efe5d: startup date [Thu Apr 17 21:33:54 CST 2014]; root of context hierarchy四月 17, 2014 9:33:54 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions信息: Loading XML bean definitions from class path resource [beans.xml]四月 17, 2014 9:33:54 下午 org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons信息: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@77caeb3e: defining beans [org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,person,newPerson,org.springframework.context.annotation.ConfigurationClassPostProcessor$ImportAwareBeanPostProcessor#0]; root of factory hierarchy[/color]
即没有了实例化的过程，这个时候只有在你需要它的时候，它才会出现。比如你执行了：
NewPerson test = (NewPerson) ctx.getBean("newPerson"); 这个时候你的bean就实例化出来了。
那么是不是我如果很多的bean都不想在IOC容器启动的时候就加载，而是要beans.xml的每个bean里都加上lazy-init属性呢。
不用的，spring提供了default-lazy-init方法来实现这个业务。
我们只要在beans的头里面加上这个就ok 了

< beans default-lazy-init ="true" >

以上代码本人亲测，可用

csdn博客真的垃圾，真心用不下去了