📫作者简介：zhz小白
公众号：小白的Java进阶之路
专业技能：
1、Java基础，并精通多线程的开发，熟悉JVM原理
2、熟悉Java基础，并精通多线程的开发，熟悉JVM原理，具备⼀定的线上调优经验
3、熟悉MySQL数据库调优，索引原理等，⽇志原理等，并且有出过⼀篇专栏
4、了解计算机⽹络，对TCP协议，滑动窗⼝原理等有⼀定了解
5、熟悉Spring，Spring MVC，Mybatis，阅读过部分Spring源码
6、熟悉SpringCloud Alibaba体系，阅读过Nacos，Sentinel，Seata，Dubbo，Feign，Gateway核⼼源码与设计，⼆次开发能⼒
7、熟悉消息队列（Kafka，RocketMQ）的原理与设计
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9、熟悉分布式缓存中间件Redis，对其的核⼼数据结构，部署架构，⾼并发问题解决⽅案有⼀定的积累
10、熟悉常⽤设计模式，并运⽤于实践⼯作中
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12、了解K8s，Jekins，GitLab
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文章目录

• 1、@PostConstruct
• • 1.1、源码分析
• 2、@PreDestroy
• • 2.1、源码分析
• 3、使用
• • 3.1、创建对象
  • 3.2、创建配置类
  • 3.3、测试类
  • 3.4、运行结果

1、@PostConstruct

1.1、源码分析

首先我们看一下@PostConstruct注解他是Java原生的，并不是Spring的，让我们看一下其源码，代码如下所示

/** Copyright (c) 2005, 2013, Oracle and/or its affiliates. All rights reserved.* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.*/package javax.annotation;import java.lang.annotation.*;
import static java.lang.annotation.ElementType.*;
import static java.lang.annotation.RetentionPolicy.*;/*** The PostConstruct annotation is used on a method that needs to be executed* after dependency injection is done to perform any initialization. This* method MUST be invoked before the class is put into service. This* annotation MUST be supported on all classes that support dependency* injection. The method annotated with PostConstruct MUST be invoked even* if the class does not request any resources to be injected. Only one* method can be annotated with this annotation. The method on which the* PostConstruct annotation is applied MUST fulfill all of the following* criteria:* 
* 
* 
The method MUST NOT have any parameters except in the case of* interceptors in which case it takes an InvocationContext object as* defined by the Interceptors specification.
* 
The method defined on an interceptor class MUST HAVE one of the* following signatures:* 
* void <METHOD>(InvocationContext)* 
* Object <METHOD>(InvocationContext) throws Exception* 
* Note: A PostConstruct interceptor method must not throw application* exceptions, but it may be declared to throw checked exceptions including* the java.lang.Exception if the same interceptor method interposes on* business or timeout methods in addition to lifecycle events. If a* PostConstruct interceptor method returns a value, it is ignored by* the container.* 
* 
The method defined on a non-interceptor class MUST HAVE the* following signature:* 
* void <METHOD>()* 
* 
The method on which PostConstruct is applied MAY be public, protected,* package private or private.
* 
The method MUST NOT be static except for the application client.
* 
The method MAY be final.
* 
If the method throws an unchecked exception the class MUST NOT be put into* service except in the case of EJBs where the EJB can handle exceptions and* even recover from them.
* @since Common Annotations 1.0* @see javax.annotation.PreDestroy* @see javax.annotation.Resource*/
@Documented
@Retention (RUNTIME)
@Target(METHOD)
public @interface PostConstruct {
}

• @PostConstruct是Java中的注解，不是Spring的注解。
• @PostConstruct注解被用来修饰一个非静态的void()方法。被@PostConstruct注解修饰的方法会在服务器加载Servlet的时候运行，并且只会被服务器执行一次。被@PostConstruct注解修饰的方法通常在构造函数之后，init()方法之前执行。
• 通常我们是会在Spring框架中使用到@PostConstruct注解的，该注解的方法在整个bean初始化中的执行顺序如下：

• Constructor（构造方法）→@Autowired（依赖注入）→@PostConstruct（注释的方法）

2、@PreDestroy

2.1、源码分析

@PreDestroy注解也并不是Spring的注解，也是Java提供的注解，只不过Spring内部会兼容。我们来看一下其源码：

/** Copyright (c) 2005, 2013, Oracle and/or its affiliates. All rights reserved.* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.*/package javax.annotation;import java.lang.annotation.*;
import static java.lang.annotation.ElementType.*;
import static java.lang.annotation.RetentionPolicy.*;/*** The PreDestroy annotation is used on methods as a callback notification to* signal that the instance is in the process of being removed by the* container. The method annotated with PreDestroy is typically used to* release resources that it has been holding. This annotation MUST be* supported by all container managed objects that support PostConstruct* except the application client container in Java EE 5. The method on which* the PreDestroy annotation is applied MUST fulfill all of the following* criteria:* 
* 
* 
The method MUST NOT have any parameters except in the case of* interceptors in which case it takes an InvocationContext object as* defined by the Interceptors specification.
* 
The method defined on an interceptor class MUST HAVE one of the* following signatures:* 
* void <METHOD>(InvocationContext)* 
* Object <METHOD>(InvocationContext) throws Exception* 
* Note: A PreDestroy interceptor method must not throw application* exceptions, but it may be declared to throw checked exceptions including* the java.lang.Exception if the same interceptor method interposes on* business or timeout methods in addition to lifecycle events. If a* PreDestroy interceptor method returns a value, it is ignored by* the container.* 
* 
The method defined on a non-interceptor class MUST HAVE the* following signature:* 
* void <METHOD>()* 
* 
The method on which PreDestroy is applied MAY be public, protected,* package private or private.
* 
The method MUST NOT be static.
* 
The method MAY be final.
* 
If the method throws an unchecked exception it is ignored except in the* case of EJBs where the EJB can handle exceptions.
* 
** @see javax.annotation.PostConstruct* @see javax.annotation.Resource* @since Common Annotations 1.0*/@Documented
@Retention (RUNTIME)
@Target(METHOD)
public @interface PreDestroy {
}

• 被@PreDestroy注解修饰的方法会在服务器卸载Servlet的时候运行，并且只会被服务器调用一次，类似于Servlet的destroy()方法。被@PreDestroy注解修饰的方法会在destroy()方法之后，Servlet被彻底卸载之前执行。执行顺序如下所示：

• 调用destroy()方法→@PreDestroy→destroy()方法→bean销毁

3、使用

3.1、创建对象

package com.zhz.bean;import lombok.Data;
import org.springframework.beans.factory.DisposableBean;
import org.springframework.beans.factory.InitializingBean;import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;/*** @author zhouhengzhe* @date 2022/11/23*/
public class PostPerson implements InitializingBean, DisposableBean {// 在对象创建完成并且属性赋值完成之后调用@PostConstructpublic void init() {System.out.println("构造之后");}// 在容器销毁（移除）对象之前调用@PreDestroypublic void preDestroy() {System.out.println("销毁之前");}@Overridepublic void afterPropertiesSet() throws Exception {System.out.println("属性赋值");}@Overridepublic void destroy() throws Exception {System.out.println("销毁");}
}

3.2、创建配置类

package com.zhz.config;import com.zhz.bean.Person;
import com.zhz.bean.PostPerson;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Scope;/*** 生命周期相关配置* @author zhouhengzhe* @date 2022/11/21*/
@Configuration
public class MainConfigByLifeCycle {@Beanpublic PostPerson personPerson() {return new PostPerson();}
}

3.3、测试类

@Testpublic void test4ByPostConstruct(){AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(MainConfigByLifeCycle.class);System.out.println("容器创建完成");PostPerson postPerson = applicationContext.getBean(PostPerson.class);applicationContext.close();}

3.4、运行结果

我们可以看出：

• 被@PostConstruct注解修饰的方法是在bean创建完成并且属性赋值完成之后才执行的，
• 而被@PreDestroy注解修饰的方法是在容器销毁bean之前执行的，通常是进行一些清理工作。