Spring点滴九：Spring bean的延迟初始化

Spring bean延迟初始化：

官网API:

By default, ApplicationContext implementations eagerly create and configure all singleton beans as part of the initialization process. Generally, this pre-instantiation is desirable, because errors in the configuration or surrounding environment are discovered immediately, as opposed to hours or even days later. When this behavior is not desirable, you can prevent pre-instantiation of a singleton bean by marking the bean definition as lazy-initialized. A lazy-initialized bean tells the IoC container to create a bean instance when it is first requested, rather than at startup.

译文：默认情况下，Spring 容器在初始化过程中会创建和配置所有单例的bean。这种提前实例化是可取的，因为配置环境错误会被立即发现而不需要过多的时间。如果不采取这种行为，可以将单例的bean标记为延迟初始化。一个延迟初始化的bean告诉Spring IoC容器去创建这个bean实例化对象当它第一次被调用时而不是在容器启动时立即创建。

在Spring Bean声明周期这篇文档中http://www.cnblogs.com/sishang/p/6575839.html

将beanLifecycle定义添加lazy-init="true"属性

  <bean id="beanLifecycle" class="com.test.spring.BeanLifecycle" init-method="init" destroy-method="close" lazy-init="true">
        <property name="name" value="张三"></property>
        <property name="sex" value="男"></property>
  </bean>

测试：

package com.test.spring;

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

public class T {
    ApplicationContext applicationcontext=null;
    @Before
    public void before() {
        System.out.println("》》》Spring ApplicationContext容器开始初始化了......");
        applicationcontext= new ClassPathXmlApplicationContext(new String[]{"test1-service.xml"});
        System.out.println("》》》Spring ApplicationContext容器初始化完毕了......");
    }
    @Test
    public void  test() {
        String [] beans=applicationcontext.getBeanDefinitionNames();
        for(String beanName:beans){
            System.out.println(beanName);
        }
        //BeanLifecycle beanLifecycle =applicationcontext.getBean("beanLifecycle",BeanLifecycle.class);
    }
}

测试结果：

》》》Spring ApplicationContext容器开始初始化了......
2017-03-19 16:43:58  INFO:ClassPathXmlApplicationContext-Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@18c92ff9: startup date [Sun Mar 19 16:43:58 CST 2017]; root of context hierarchy
2017-03-19 16:43:59  INFO:XmlBeanDefinitionReader-Loading XML bean definitions from class path resource [test1-service.xml]
》》》Spring ApplicationContext容器初始化完毕了......
org.springframework.context.annotation.CommonAnnotationBeanPostProcessor#0
beanLifecycle
postProcessor

***********

发现Spring IoC容器中虽然有beanLifecycle ID,但是容器并没有实例化它，因为beanLifecycle的创建信息没有被执行

**********

将测试中BeanLifecycle beanLifecycle =applicationcontext.getBean("beanLifecycle",BeanLifecycle.class)这段代码解除注释，beanLifecycle被第一次请求，容器会立即创建它。

------------------------------------------------------------------------------------------------------------------------------------------------

测试结果：

》》》Spring ApplicationContext容器开始初始化了......
2017-03-19 16:49:21  INFO:ClassPathXmlApplicationContext-Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@406c9125: startup date [Sun Mar 19 16:49:21 CST 2017]; root of context hierarchy
2017-03-19 16:49:21  INFO:XmlBeanDefinitionReader-Loading XML bean definitions from class path resource [test1-service.xml]
》》》Spring ApplicationContext容器初始化完毕了......
narCodeService
org.springframework.context.annotation.CommonAnnotationBeanPostProcessor#0
beanLifecycle
postProcessor
》》》调用无参构造方法了
》》》调用BeanLifecycle对象null属性set方法，设值为:张三
》》》调用BeanLifecycle对象null属性set方法，设值为:男
》》》调用BeanNameAware接口setBenaName方法: beanLifecycle
》》》调用BeanFactoryAware接口setBeanFactory方法:org.springframework.beans.factory.support.DefaultListableBeanFactory@5ccc995c: defining beans [narCodeService,org.springframework.context.annotation.CommonAnnotationBeanPostProcessor#0,beanLifecycle,postProcessor]; root of factory hierarchy
》》》调用ApplicationContextAware接口setApplicationContext方法:org.springframework.context.support.ClassPathXmlApplicationContext@406c9125: startup date [Sun Mar 19 16:49:21 CST 2017]; root of context hierarchy
后置处理器处理bean=【beanLifecycle】开始
》》》注解初始化方法被调用
》》》BeanLifecycle调用了InitailizingBean的afterPorpertiesSet方法了.....
》》》init方法被调用
后置处理器处理bean=【beanLifecycle】完毕!

但是有一点需要注意就是：当一个非延迟初始化单例bean需要依赖注入一个延迟初始化bean，Spring 容器会立即创建这个延迟初始化的bean。因为它要满足单例的相关性

官网API:

However, when a lazy-initialized bean is a dependency of a singleton bean that is not lazy-initialized, the ApplicationContext creates the lazy-initialized bean at startup, because it must satisfy the singleton’s dependencies. The lazy-initialized bean is injected into a singleton bean elsewhere that is not lazy-initialized.

示例：

在Spring配置文件中添加如下bean定义(基于Spring Bean声明周期这篇文档中http://www.cnblogs.com/sishang/p/6575839.html)：

<bean id="test" class="com.test.spring.Test" >
     <property name="beanLifecycle" ref="beanLifecycle"></property>
</bean>

新建Test类：

package com.test.spring;


public class Test {

    private  BeanLifecycle beanLifecycle;

    public BeanLifecycle getBeanLifecycle() {
        return beanLifecycle;
    }

    public void setBeanLifecycle(BeanLifecycle beanLifecycle) {
        this.beanLifecycle = beanLifecycle;
    }
    
}

测试：

package com.test.spring;

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

public class T {
    ApplicationContext applicationcontext=null;
    @Before
    public void before() {
        System.out.println("》》》Spring ApplicationContext容器开始初始化了......");
        applicationcontext= new ClassPathXmlApplicationContext(new String[]{"test1-service.xml"});
        System.out.println("》》》Spring ApplicationContext容器初始化完毕了......");
    }
    @Test
    public void  test() {
        //BeanLifecycle beanLifecycle =applicationcontext.getBean("beanLifecycle",BeanLifecycle.class);
        String [] beans=applicationcontext.getBeanDefinitionNames();
        for(String beanName:beans){
            System.out.println(beanName);
        }
       //applicationcontext.getBean(BeanLifecycle.class);
    }
}

测试结果：

》》》Spring ApplicationContext容器开始初始化了......
2017-03-19 17:06:19  INFO:ClassPathXmlApplicationContext-Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@406c9125: startup date [Sun Mar 19 17:06:19 CST 2017]; root of context hierarchy
2017-03-19 17:06:19  INFO:XmlBeanDefinitionReader-Loading XML bean definitions from class path resource [test1-service.xml]
》》》调用无参构造方法了
》》》调用BeanLifecycle对象null属性set方法，设值为:张三
》》》调用BeanLifecycle对象null属性set方法，设值为:男
》》》调用BeanNameAware接口setBenaName方法: beanLifecycle
》》》调用BeanFactoryAware接口setBeanFactory方法:org.springframework.beans.factory.support.DefaultListableBeanFactory@76e9e1a0: defining beans [narCodeService,org.springframework.context.annotation.CommonAnnotationBeanPostProcessor#0,beanLifecycle,postProcessor,test]; root of factory hierarchy
》》》调用ApplicationContextAware接口setApplicationContext方法:org.springframework.context.support.ClassPathXmlApplicationContext@406c9125: startup date [Sun Mar 19 17:06:19 CST 2017]; root of context hierarchy
后置处理器处理bean=【beanLifecycle】开始
》》》注解初始化方法被调用
》》》BeanLifecycle调用了InitailizingBean的afterPorpertiesSet方法了.....
》》》init方法被调用
后置处理器处理bean=【beanLifecycle】完毕!
后置处理器处理bean=【test】开始
后置处理器处理bean=【test】完毕!
》》》Spring ApplicationContext容器初始化完毕了......
org.springframework.context.annotation.CommonAnnotationBeanPostProcessor#0
beanLifecycle
postProcessor
test

从输出信息看到：beanLifecycle被容器创建了。

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原文地址：https://www.cnblogs.com/sishang/p/6580945.html