《RabbitMQ》《Spring》《SpringMVC》
前言
上篇文章详细讲诉了Bean的生命周期和作用域，在生命周期中提到了如何自定义初始化Bean，可能很多人不知道如何自定义初始化，这里详细补充讲解一下：使用@Bean注解指定初始化和销毁方法、实现InitializingBean接口和DisposableBean接口自定义初始化和销毁、@PostConstruct(初始化逻辑)和@PreDestroy(销毁逻辑)注解、使用BeanPostProcessor接口。
一、@Bean注解指定初始化和销毁方法
- 创建BeanTest类，自定义初始化方法和销毁方法。
- 在@Bean注解的参数中指定BeanTest自定义的初始化和销毁方法：
- 销毁方法只有在IOC容器关闭的时候才调用。
代码如下：
/**
* @Version: 1.0.0
* @Author: Dragon_王
* @ClassName: dog
* @Description: TODO描述
* @Date: 2024/1/21 22:55
*/
public class BeanTest {
public BeanTest(){
System.out.println("BeanTest被创建");
}
public void init(){
System.out.println("BeanTest被初始化");
}
public void destory(){
System.out.println("BeanTest被销毁");
}
}
/**
* @Version: 1.0.0
* @Author: Dragon_王
* @ClassName: MyConfig
* @Description: TODO描述
* @Date: 2024/1/21 22:59
*/
@Configuration
@ComponentScan(("com.dragon.restart1"))
public class MyConfig {
@Bean(initMethod = "init",destroyMethod = "destory")
public BeanTest beanTest(){
return new BeanTest();
}
}
//测试代码
AnnotationConfigApplicationContext ct = new AnnotationConfigApplicationContext(MyConfig.class);
System.out.println("IoC容器创建完成");
- 可以看到调用的是自定义的方法，这里解释一下，测试时，运行完代码块程序就结束了，所哟IoC容器就被关闭，所以调用了IoC销毁方法。同时可以看到初始化方法在对象创建完成后调用。
- 当组件的作用域为单例时在容器启动时即创建对象，而当作用域为原型（PROTOTYPE）时在每次获取对象的时候才创建对象。并且当作用域为原型（PROTOTYPE）时，IOC容器只负责创建Bean但不会管理Bean，所以IOC容器不会调用销毁方法。
二、实现InitializingBean接口和DisposableBean接口
看一下两接口的方法：
public interface InitializingBean {
/**
* Invoked by the containing {@code BeanFactory} after it has set all bean properties
* and satisfied {@link BeanFactoryAware}, {@code ApplicationContextAware} etc.
* <p>This method allows the bean instance to perform validation of its overall
* configuration and final initialization when all bean properties have been set.
* @throws Exception in the event of misconfiguration (such as failure to set an
* essential property) or if initialization fails for any other reason
* Bean都装配完成后执行初始化
*/
void afterPropertiesSet() throws Exception;
}
====================================================================
public interface DisposableBean {
/**
* Invoked by the containing {@code BeanFactory} on destruction of a bean.
* @throws Exception in case of shutdown errors. Exceptions will get logged
* but not rethrown to allow other beans to release their resources as well.
*/
void destroy() throws Exception;
}
代码如下：
/**
* @Version: 1.0.0
* @Author: Dragon_王
* @ClassName: BeanTest1
* @Description: TODO描述
* @Date: 2024/1/21 23:25
*/
public class BeanTest1 implements InitializingBean, DisposableBean {
@Override
public void destroy() throws Exception {
System.out.println("BeanTest1销毁");
}
@Override
public void afterPropertiesSet() throws Exception {
System.out.println("BeanTest1初始化");
}
public BeanTest1() {
System.out.println("BeanTest1被创建");
}
}
=========================
@Configuration
@ComponentScan(("com.dragon.restart1"))
public class MyConfig {
@Bean
public BeanTest1 beanTest1(){
return new BeanTest1();
}
}
三、@PostConstruct(初始化逻辑)和@PreDestroy(销毁逻辑)注解
- 被@PostConstruct修饰的方法会在服务器加载Servlet的时候运行，并且只会被服务器调用一次，类似于Serclet的inti()方法。
- 被@PostConstruct修饰的方法会在构造函数之后，init()方法之前运行。
- 被@PreDestroy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修饰的方法会在destroy()方法之后运行，在Servlet被彻底卸载之前。
代码如下：
/**
* @Version: 1.0.0
* @Author: Dragon_王
* @ClassName: BeanTest2
* @Description: TODO描述
* @Date: 2024/1/21 23:32
*/
public class BeanTest2 {
public BeanTest2(){
System.out.println("BeanTest2被创建");
}
@PostConstruct
public void init(){
System.out.println("BeanTest2被初始化");
}
@PreDestroy
public void destory(){
System.out.println("BeanTest2被销毁");
}
}
========================
//
@Configuration
@ComponentScan(("com.dragon.restart1"))
public class MyConfig {
@Bean
public BeanTest2 beanTest2(){
return new BeanTest2();
}
}
四、BeanPostProcessor接口
BeanPostProcessor又叫Bean的后置处理器，是Spring框架中IOC容器提供的一个扩展接口，在Bean初始化的前后进行一些处理工作。
BeanPostProcessor的源码如下：
public interface BeanPostProcessor {
/**
* Apply this BeanPostProcessor to the given new bean instance <i>before</i> any bean
* initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
* or a custom init-method). The bean will already be populated with property values.
* The returned bean instance may be a wrapper around the original.
* <p>The default implementation returns the given {@code bean} as-is.
* @param bean the new bean instance
* @param beanName the name of the bean
* @return the bean instance to use, either the original or a wrapped one;
* if {@code null}, no subsequent BeanPostProcessors will be invoked
* @throws org.springframework.beans.BeansException in case of errors
* @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
*/
@Nullable
//bean初始化方法调用前被调用
default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
return bean;
}
/**
* Apply this BeanPostProcessor to the given new bean instance <i>after</i> any bean
* initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
* or a custom init-method). The bean will already be populated with property values.
* The returned bean instance may be a wrapper around the original.
* <p>In case of a FactoryBean, this callback will be invoked for both the FactoryBean
* instance and the objects created by the FactoryBean (as of Spring 2.0). The
* post-processor can decide whether to apply to either the FactoryBean or created
* objects or both through corresponding {@code bean instanceof FactoryBean} checks.
* <p>This callback will also be invoked after a short-circuiting triggered by a
* {@link InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation} method,
* in contrast to all other BeanPostProcessor callbacks.
* <p>The default implementation returns the given {@code bean} as-is.
* @param bean the new bean instance
* @param beanName the name of the bean
* @return the bean instance to use, either the original or a wrapped one;
* if {@code null}, no subsequent BeanPostProcessors will be invoked
* @throws org.springframework.beans.BeansException in case of errors
* @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
* @see org.springframework.beans.factory.FactoryBean
*/
@Nullable
//bean初始化方法调用后被调用
default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
return bean;
}
代码如下：
/**
* @Version: 1.0.0
* @Author: Dragon_王
* @ClassName: MyBeanPostProcess
* @Description: TODO描述
* @Date: 2024/1/21 23:40
*/
@Component
public class MyBeanPostProcess implements BeanPostProcessor {
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
System.out.println("postProcessBeforeInitialization..."+beanName+"=>"+bean);
return bean;
}
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
System.out.println("postProcessAfterInitialization..."+beanName+"=>"+bean);
return bean;
}
}
============================
@Configuration
@ComponentScan(("com.dragon.restart1"))
public class MyConfig {
@Bean
public BeanTest1 beanTest1(){
return new BeanTest1();
}
@Bean
public BeanTest2 beanTest2(){
return new BeanTest2();
}
}
运行结果如下：
BeanTest1被创建
postProcessBeforeInitialization...beanTest1=>com.dragon.restart1.BeanTest1@111d5c97
BeanTest1初始化
postProcessAfterInitialization...beanTest1=>com.dragon.restart1.BeanTest1@111d5c97
BeanTest2被创建
postProcessBeforeInitialization...beanTest2=>com.dragon.restart1.BeanTest2@29c17c3d
BeanTest2被初始化
postProcessAfterInitialization...beanTest2=>com.dragon.restart1.BeanTest2@29c17c3d
IoC容器创建完成
BeanTest2被销毁
BeanTest1销毁
通过上述运行结果可以发现使用BeanPostProcessor的运行顺序为：
IOC容器实例化Bean---->调用BeanPostProcessor的postProcessBeforeInitialization方法---->调用bean实例的初始化方法---->调用BeanPostProcessor的postProcessAfterInitialization方法。
总结
以上就是Bean生命周期自定义初始化和销毁的讲解。
