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Sring容器的懒加载lazy-init设置

分类: IT文章 • 2023-11-06 19:11:47

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： 

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..

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： 

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

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" >

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