Spring Bean 延迟加载

港控/mmm° 2022-11-02 11:42 410阅读 0赞

Spring 中可以

*  在 xml <bean> 中配置参数 lazy-init="true"
 *  可以使用 @Lazy 注解标记 Bean 需要延迟加载

延迟加载的优缺点很明显：

*  提升系统的启动速度，按需要加载 Bean 节约了内存
 *  但不符合 fast-fail 原则，如果系统已经启动完成，在后期的使用过程加载 Bean 出现异常情况比如内存不够，那对系统后期的正常使用影响很大

所以需酌情使用。

示例代码：

spring xml 配置

<?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">
    
        <bean id="user1" class="constxiong.User">
            <constructor-arg name="id" value="1"></constructor-arg>
            <property name="name" value="constxiong"/>
        </bean>
    
        <bean id="user2" class="constxiong.User" lazy-init="true">
            <constructor-arg name="id" value="2"></constructor-arg>
            <property name="name" value="user2"/>
        </bean>
        
        <context:component-scan base-package="constxiong"/>
    
    </beans>

User 类

public class User {
    
    	private Integer id;
    
    	private String name;
    
    	public User(Integer id) {
    		this.id = id;
    		System.out.println("init id:" + id);
    	}
    
    	public void setId(Integer id) {
    		this.id = id;
    	}
    
    	public String getName() {
    		return name;
    	}
    
    	public void setName(String name) {
    		this.name = name;
    	}
    
    	@Override
    	public String toString() {
    		return "User{" +
    				"id=" + id +
    				", name='" + name + ''' +
    				"}
    " + super.toString();
    	}
    }

测试代码

/**
     * 测试 Bean 延迟加载及区别
     * @author ConstXiong
     */
    @Configuration
    public class Test {
    	
    	public static void main(String[] args) {
    		ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("META-INF/spring-bean-lazy-init.xml");
    //		User user1 = context.getBean("user1", User.class);
    //		System.out.println(user1);
    //		User user2 = context.getBean("user2", User.class);
    //		System.out.println(user2);
    //		User user3 = context.getBean("user3", User.class);
    //		System.out.println(user3);
    	}
    
    	@Bean(name = "user3")
    	@Lazy
    	static User getUser() {
    		User user = new User(3);
    		return user;
    	}
    }

打印结果

init id:1

从打印结果看，user1、user2、user3 获取的代码都被注释掉了，系统启动时会自动实例化 user1，其余两个 Bean user2 user3 都未自动实例化。

[完整代码：010-spring-bean-lazy-init][010-spring-bean-lazy-init]

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

### 【Java学习资源】整理推荐 ###

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[010-spring-bean-lazy-init]: https://github.com/ConstXiong/toy/tree/master/spring-study/010-spring-bean-lazy-init
[Bean]: https://www.javanav.com/val/3fdc7ac3bd034a5ab7040e23f37153fa.html
[Bean 1]: https://www.javanav.com/val/59101a7207864f4aa971e5c48b592c77.html
[maven _ tomcat _ jar _ web]: https://www.javanav.com/val/b1f4691bd6ba488a80e3bdfcefdec33c.html
[Spring]: https://www.javanav.com/val/a9569837e1bc4df9aeac0e6cbf96bf06.html
[Spring _ DependencyDescriptor]: https://www.javanav.com/val/152161d266a94fd38efb365a78d8f9a3.html
[Spring _ Aware]: https://www.javanav.com/val/089b3993c8bc4dec891ea677c104c5e4.html
[Spring Bean _ Exception]: https://www.javanav.com/val/2b31b7061b3342c0a67f8d7fc7373ed3.html
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[BeanDefinition]: https://www.javanav.com/val/e82279480ec24184bcaf723a50ef08b3.html
[Spring IoC]: https://www.javanav.com/val/d382c8380fc2480788a35a7e671b5e9b.html
[BeanFactory _ FactoryBean]: https://www.javanav.com/val/173e873a2c98499a8a08a13b4f88ae10.html
[BeanFactory _ ApplicationContext]: https://www.javanav.com/val/bbc2c9580b7045e583855925d5f1a50b.html
[Spring IoC 1]: https://www.javanav.com/val/a835e6c709ea439ebb21a80f1bf77926.html
[Spring IoC 2]: https://www.javanav.com/val/e377beac22644c2c85308079b239a0fd.html
[Spring bean]: https://www.javanav.com/val/7f8c2e1f24db46e79bc4b9b04f9ad715.html
[Spring-IoC]: https://www.javanav.com/val/a412668efda74412a13f6df9a6d2c714.html
[Spring 1]: https://www.javanav.com/val/6eac12a548ea40c68ff64b1af307563a.html
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[Link 10]: https://www.javanav.com/interview/67a50996c28f418e83b109ea42fc3eff.html
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[MySQL]: https://www.javanav.com/interview/d311e78502a845f1a4bb307bd6aec2b3.html
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