spring容器的懒加载lazy-init设置

时间:2022-11-01 20:30:15
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: 
Java代码  spring容器的懒加载lazy-init设置
  1. package com.luch.spring.demo;    
  2.     
  3. import org.springframework.beans.factory.annotation.Autowired;    
  4.     
  5. import com.luch.spring.bean.Person;    
  6.     
  7. public class NewPerson {    
  8.         
  9.     @Autowired    
  10.     private Person person;    
  11.         
  12.     public NewPerson(){    
  13.         System.out.println("lazy loading...");    
  14.     }    
  15.     public void printMsg(){    
  16.         if(person !=null) {    
  17.             System.out.println(person.getName());    
  18.         } else {    
  19.             System.out.println("no person initialize!");    
  20.         }    
  21.     }    
  22.     
  23.     public void setPerson(Person person) {    
  24.         //this.person = person;    
  25.     }    
  26.         
  27.     
  28. }    

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代码  spring容器的懒加载lazy-init设置
  1. <?xml version="1.0" encoding="UTF-8"?>    
  2. <beans xmlns="http://www.springframework.org/schema/beans"    
  3.        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"    
  4.        xmlns:context="http://www.springframework.org/schema/context"     
  5.        xsi:schemaLocation="http://www.springframework.org/schema/beans    
  6.            http://www.springframework.org/schema/beans/spring-beans.xsd    
  7.             http://www.springframework.org/schema/context      
  8.             http://www.springframework.org/schema/context/spring-context.xsd">    
  9.                
  10.            <context:annotation-config/>    
  11.            <bean id="person" class="com.luch.spring.bean.Person">    
  12.                <property name="id" value="22"></property>    
  13.                <property name="name" value="Jack"></property>    
  14.            </bean>    
  15.                
  16.            <bean id="newPerson" class="com.luch.spring.demo.NewPerson">    
  17.                <property name="person" ref="person"></property>    
  18.            </bean>    
  19.                
  20. </beans>    


然后我用一个junit来做测试: 
Java代码  spring容器的懒加载lazy-init设置
  1. package junit.test;    
  2.     
  3. import static org.junit.Assert.*;    
  4.     
  5. import org.junit.Test;    
  6.     
  7. import org.springframework.context.support.AbstractApplicationContext;    
  8. import org.springframework.context.support.ClassPathXmlApplicationContext;    
  9.     
  10. import com.luch.spring.demo.NewPerson;    
  11.     
  12. public class JunitTest {    
  13.     
  14.     @Test    
  15.     public void printMsg(){    
  16.         AbstractApplicationContext ctx = new ClassPathXmlApplicationContext("/beans.xml");    
  17.         //NewPerson test = (NewPerson) ctx.getBean("newPerson");    
  18.         //test.printMsg();    
  19.     }    
  20. }    



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代码  spring容器的懒加载lazy-init设置
  1. <?xml version="1.0" encoding="UTF-8"?>    
  2. <beans xmlns="http://www.springframework.org/schema/beans"    
  3.        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"    
  4.        xmlns:context="http://www.springframework.org/schema/context"     
  5.        xsi:schemaLocation="http://www.springframework.org/schema/beans    
  6.            http://www.springframework.org/schema/beans/spring-beans.xsd    
  7.             http://www.springframework.org/schema/context      
  8.             http://www.springframework.org/schema/context/spring-context.xsd">    
  9.                
  10.            <context:annotation-config/>    
  11.            <bean id="person" class="com.luch.spring.bean.Person">    
  12.                <property name="id" value="22"></property>    
  13.                <property name="name" value="Jack"></property>    
  14.            </bean>    
  15.                
  16.            <bean id="newPerson" lazy-init="true" class="com.luch.spring.demo.NewPerson">    
  17.                <property name="person" ref="person"></property>    
  18.            </bean>    
  19.                
  20. </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" > 

以上代码本人亲测,可用