Spring中xml标签lazy-init使用

1. 引言

bean的初始化有两种方式

• 实时初始化。Spring容器启用以后，即刻初始化
• 延迟初始化。代码中调用的时候，才会创建

Spring默认情况下，所有的bean都会被实时初始化。但是大量的bean实时初始化，会导致启动变慢。因此对于需要延迟初始化的bean，可以通过xml进行设置。

2. 延迟创建bean

修改springid.xml，如下

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

    <bean id="school" class="com.liwl.dev.SchoolImpl" lazy-init="true">
        <property name="name" value="jiangnan"/>
        <property name="address" value="江苏省无锡市滨湖区蠡湖大道1800号"/>
    </bean>

    <bean id="company" class="com.liwl.dev.CompanyImpl" lazy-init="true">
        <property name="name" value="nsccwx"/>
        <property name="address" value="江苏省无锡市滨湖区吟白路1号"/>
    </bean>

    <bean id="liwl001" class="com.liwl.dev.LiwanLiangImpl" depends-on="school,company" autowire="byType" lazy-init="true">
        <property name="name" value="liwl" />
        <property name="age" value="30"/>
    </bean>

</beans>

修改LiwlTest.java

package com.liwl.dev;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class LiwlTest {
    public static void main(String[] args) {
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("springdi.xml");
        SchoolImpl school = (SchoolImpl) context.getBean("school");
        System.out.println("school:"+school);
        context.close();
    }
}

运行结果

调用SchoolImpl bean 无参构造方法
school:[SchoolImpl bean],name:jiangnan,address:江苏省无锡市滨湖区蠡湖大道1800号
SchoolImpl bean 销毁

从结果看出，并没有创建LiwanLiangImpl的bean，说明是被延迟创建的

3. 依赖注入情况下的bean

修改springdi.xml

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

    <bean id="school" class="com.liwl.dev.SchoolImpl" lazy-init="true">
        <property name="name" value="jiangnan"/>
        <property name="address" value="江苏省无锡市滨湖区蠡湖大道1800号"/>
    </bean>

    <bean id="company" class="com.liwl.dev.CompanyImpl" lazy-init="true">
        <property name="name" value="nsccwx"/>
        <property name="address" value="江苏省无锡市滨湖区吟白路1号"/>
    </bean>

    <bean id="liwl001" class="com.liwl.dev.LiwanLiangImpl" depends-on="school,company" autowire="byType">
        <property name="name" value="liwl" />
        <property name="age" value="30"/>
    </bean>

</beans>

运行结果

调用SchoolImpl bean 无参构造方法
调用CompanyImpl bean 无参构造方法
调用LiwanLiangImpl bean 无参构造方法
school:[SchoolImpl bean],name:jiangnan,address:江苏省无锡市滨湖区蠡湖大道1800号
LiwanLiangImpl bean 销毁
CompanyImpl bean 销毁
SchoolImpl bean 销毁

说明此种情况，即便是被依赖的bean，school和company标注了lasy-init，也还是因为被实时创建的beanliwanliang依赖而实时创建