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Spring bean lifecycle
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‎MD/spring/spring-bean-lifecycle.md

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## Spring Bean 生命周期
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Spring Bean 的生命周期在整个 Spring 中占有很重要的位置，掌握这些可以加深对 Spring 的理解。
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首先看下生命周期图：
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![](https://ws3.sinaimg.cn/large/006tNc79gy1fpjsamy6uoj30nt0cqq4i.jpg)
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再谈生命周期之前有一点需要先明确：
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> Spring 只帮我们管理单例模式 Bean 的**完整**生命周期，对于 prototype 的 bean ，Spring 在创建好交给使用者之后则不会再管理后续的生命周期。
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### 注解方式
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在 bean 初始化时会经历几个阶段，首先可以使用注解 `@PostConstruct`, `@PreDestroy` 来在 bean 的创建和销毁阶段进行调用:
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```java
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@Component
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public class AnnotationBean {
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private final static Logger LOGGER = LoggerFactory.getLogger(AnnotationBean.class);
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@PostConstruct
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public void start(){
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LOGGER.info("AnnotationBean start");
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}
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@PreDestroy
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public void destroy(){
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LOGGER.info("AnnotationBean destroy");
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}
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}
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```
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### InitializingBean, DisposableBean 接口
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还可以实现 `InitializingBean,DisposableBean` 这两个接口，也是在初始化以及销毁阶段调用：
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```java
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@Service
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public class SpringLifeCycleService implements InitializingBean,DisposableBean{
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private final static Logger LOGGER = LoggerFactory.getLogger(SpringLifeCycleService.class);
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@Override
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public void afterPropertiesSet() throws Exception {
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LOGGER.info("SpringLifeCycleService start");
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}
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@Override
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public void destroy() throws Exception {
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LOGGER.info("SpringLifeCycleService destroy");
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}
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}
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```
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### 自定义初始化和销毁方法
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也可以自定义方法用于在初始化、销毁阶段调用:
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```java
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@Configuration
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public class LifeCycleConfig {
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@Bean(initMethod = "start", destroyMethod = "destroy")
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public SpringLifeCycle create(){
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SpringLifeCycle springLifeCycle = new SpringLifeCycle() ;
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return springLifeCycle ;
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}
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}
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public class SpringLifeCycle{
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private final static Logger LOGGER = LoggerFactory.getLogger(SpringLifeCycle.class);
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public void start(){
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LOGGER.info("SpringLifeCycle start");
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}
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public void destroy(){
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LOGGER.info("SpringLifeCycle destroy");
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}
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}
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```
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以上是在 SpringBoot 中可以这样配置，如果是原始的基于 XML 也是可以使用:
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```xml
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<bean class="com.crossoverjie.spring.SpringLifeCycle" init-method="start" destroy-method="destroy">
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</bean>
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```
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来达到同样的效果。
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### 实现 *Aware 接口
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`*Aware` 接口可以用于在初始化 bean 时获得 Spring 中的一些对象，如获取 `Spring 上下文`等。
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```java
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@Component
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public class SpringLifeCycleAware implements ApplicationContextAware {
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private final static Logger LOGGER = LoggerFactory.getLogger(SpringLifeCycleAware.class);
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private ApplicationContext applicationContext ;
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@Override
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public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
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this.applicationContext = applicationContext ;
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LOGGER.info("SpringLifeCycleAware start");
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}
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}
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```
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这样在 `springLifeCycleAware` 这个 bean 初始化会就会调用 `setApplicationContext` 方法，并可以获得 `applicationContext` 对象。
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### BeanPostProcessor 增强处理器
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实现 BeanPostProcessor 接口，Spring 中所有 bean 在做初始化时都会调用该接口中的两个方法，可以用于对一些特殊的 bean 进行处理：
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```java
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@Component
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public class SpringLifeCycleProcessor implements BeanPostProcessor {
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private final static Logger LOGGER = LoggerFactory.getLogger(SpringLifeCycleProcessor.class);
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/**
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* 预初始化 初始化之前调用
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* @param bean
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* @param beanName
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* @return
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* @throws BeansException
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*/
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@Override
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public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
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if ("annotationBean".equals(beanName)){
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LOGGER.info("SpringLifeCycleProcessor start beanName={}",beanName);
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}
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return bean;
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}
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/**
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* 后初始化 bean 初始化完成调用
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* @param bean
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* @param beanName
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* @return
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* @throws BeansException
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*/
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@Override
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public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
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if ("annotationBean".equals(beanName)){
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LOGGER.info("SpringLifeCycleProcessor end beanName={}",beanName);
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}
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return bean;
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}
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}
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```
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执行之后观察结果：
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```
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018-03-21 00:40:24.856 [restartedMain] INFO c.c.s.p.SpringLifeCycleProcessor - SpringLifeCycleProcessor start beanName=annotationBean
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2018-03-21 00:40:24.860 [restartedMain] INFO c.c.spring.annotation.AnnotationBean - AnnotationBean start
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2018-03-21 00:40:24.861 [restartedMain] INFO c.c.s.p.SpringLifeCycleProcessor - SpringLifeCycleProcessor end beanName=annotationBean
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2018-03-21 00:40:24.864 [restartedMain] INFO c.c.s.aware.SpringLifeCycleAware - SpringLifeCycleAware start
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2018-03-21 00:40:24.867 [restartedMain] INFO c.c.s.service.SpringLifeCycleService - SpringLifeCycleService start
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2018-03-21 00:40:24.887 [restartedMain] INFO c.c.spring.SpringLifeCycle - SpringLifeCycle start
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2018-03-21 00:40:25.062 [restartedMain] INFO o.s.b.d.a.OptionalLiveReloadServer - LiveReload server is running on port 35729
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2018-03-21 00:40:25.122 [restartedMain] INFO o.s.j.e.a.AnnotationMBeanExporter - Registering beans for JMX exposure on startup
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2018-03-21 00:40:25.140 [restartedMain] INFO com.crossoverjie.Application - Started Application in 2.309 seconds (JVM running for 3.681)
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2018-03-21 00:40:25.143 [restartedMain] INFO com.crossoverjie.Application - start ok!
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2018-03-21 00:40:25.153 [Thread-8] INFO o.s.c.a.AnnotationConfigApplicationContext - Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@3913adad: startup date [Wed Mar 21 00:40:23 CST 2018]; root of context hierarchy
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2018-03-21 00:40:25.155 [Thread-8] INFO o.s.j.e.a.AnnotationMBeanExporter - Unregistering JMX-exposed beans on shutdown
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2018-03-21 00:40:25.156 [Thread-8] INFO c.c.spring.SpringLifeCycle - SpringLifeCycle destroy
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2018-03-21 00:40:25.156 [Thread-8] INFO c.c.s.service.SpringLifeCycleService - SpringLifeCycleService destroy
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2018-03-21 00:40:25.156 [Thread-8] INFO c.c.spring.annotation.AnnotationBean - AnnotationBean destroy
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```
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直到 Spring 上下文销毁时则会调用自定义的销毁方法以及实现了 `DisposableBean` 的 `destroy()` 方法。
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‎src/main/java/com/crossoverjie/design/pattern/factorymethod/Animal.java

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package com.crossoverjie.design.pattern.factorymethod;
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/**
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* Function:
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*
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* @author crossoverJie
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* Date: 19/03/2018 14:29
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* @since JDK 1.8
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*/
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public abstract class Animal {
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private String name ;
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public String getName() {
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return name;
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}
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public void setName(String name) {
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this.name = name;
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}
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/**
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* 描述抽象方法
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*/
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protected abstract void desc() ;
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}

‎src/main/java/com/crossoverjie/design/pattern/factorymethod/AnimalFactory.java

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package com.crossoverjie.design.pattern.factorymethod;
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/**
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* Function:工厂方法模式
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*
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* @author crossoverJie
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* Date: 19/03/2018 14:29
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* @since JDK 1.8
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*/
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public interface AnimalFactory {
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Animal createAnimal() ;
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}

‎src/main/java/com/crossoverjie/design/pattern/factorymethod/Cat.java

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package com.crossoverjie.design.pattern.factorymethod;
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/**
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* Function:
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*
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* @author crossoverJie
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* Date: 19/03/2018 14:33
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* @since JDK 1.8
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*/
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public class Cat extends Animal {
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@Override
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protected void desc() {
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System.out.println("Cat name is=" + this.getName());
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}
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}

‎src/main/java/com/crossoverjie/design/pattern/factorymethod/CatFactory.java

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package com.crossoverjie.design.pattern.factorymethod;
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/**
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* Function:
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*
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* @author crossoverJie
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* Date: 19/03/2018 15:21
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* @since JDK 1.8
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*/
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public class CatFactory implements AnimalFactory {
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@Override
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public Animal createAnimal() {
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return new Cat();
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}
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}

‎src/main/java/com/crossoverjie/design/pattern/factorymethod/Fish.java

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package com.crossoverjie.design.pattern.factorymethod;
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/**
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* Function:
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*
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* @author crossoverJie
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* Date: 19/03/2018 14:32
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* @since JDK 1.8
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*/
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public class Fish extends Animal {
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@Override
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protected void desc() {
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System.out.println("fish name is=" + this.getName());
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}
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}

‎src/main/java/com/crossoverjie/design/pattern/factorymethod/FishFactory.java

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package com.crossoverjie.design.pattern.factorymethod;
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/**
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* Function:
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*
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* @author crossoverJie
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* Date: 19/03/2018 15:21
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* @since JDK 1.8
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*/
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public class FishFactory implements AnimalFactory {
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@Override
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public Animal createAnimal() {
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return new Fish() ;
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}
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}

‎src/main/java/com/crossoverjie/design/pattern/factorymethod/Main.java

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package com.crossoverjie.design.pattern.factorymethod;
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/**
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* Function:
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*
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* @author crossoverJie
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* Date: 19/03/2018 14:34
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* @since JDK 1.8
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*/
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public class Main {
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public static void main(String[] args) {
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AnimalFactory factory = new CatFactory() ;
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Animal animal = factory.createAnimal();
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animal.setName("猫咪");
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animal.desc();
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}
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}

‎src/main/java/com/crossoverjie/spring/LifeCycleConfig.java

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package com.crossoverjie.spring;
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import com.crossoverjie.concurrent.Singleton;
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import org.springframework.context.annotation.Bean;
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import org.springframework.context.annotation.ComponentScan;
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import org.springframework.context.annotation.Configuration;
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/**
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* Function:使用 initMethod 和 destroyMethod 的方式
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*
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* @author crossoverJie
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* Date: 19/03/2018 22:37
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* @since JDK 1.8
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*/
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@Configuration
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public class LifeCycleConfig {
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@Bean(initMethod = "start", destroyMethod = "destroy")
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public SpringLifeCycle create(){
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SpringLifeCycle springLifeCycle = new SpringLifeCycle() ;
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return springLifeCycle ;
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}
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}

‎src/main/java/com/crossoverjie/spring/SpringLifeCycle.java

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package com.crossoverjie.spring;
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import com.crossoverjie.Application;
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import org.slf4j.Logger;
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import org.slf4j.LoggerFactory;
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import org.springframework.beans.BeansException;
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import org.springframework.context.ApplicationContext;
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import org.springframework.context.ApplicationContextAware;
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/**
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* Function:
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*
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* @author crossoverJie
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* Date: 20/03/2018 18:23
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* @since JDK 1.8
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*/
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public class SpringLifeCycle{
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private final static Logger LOGGER = LoggerFactory.getLogger(SpringLifeCycle.class);
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public void start(){
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LOGGER.info("SpringLifeCycle start");
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}
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public void destroy(){
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LOGGER.info("SpringLifeCycle destroy");
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}
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}

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