网站建设服务代理商/网络营销的好处

时隔一年多，在掌握了Spring、SpringBoot、SpringCloud之后

我再次回头，重新学习Spring框架

 

Bean的生命周期学习：

在传统的XML配置中，可以这样自定义初始化和销毁方法：

init-method="" destroy-method=""

 

注解方式的简单使用：

@Configuration
public class LifeCircleConfig {@Bean(initMethod = "init",destroyMethod = "destroy")public Car car(){return new Car();}
}

public class Car {public Car(){System.out.println("Construct Car!");}public void init(){System.out.println("Car init!");}public void destroy(){System.out.println("Car destroy!");}
}

public class LifeCircleTest {private static AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(LifeCircleConfig.class);@Testpublic void test(){applicationContext.close();}
}

注意：要有close方法，否则不会打印Car销毁方法

 

打印如下：

Construct Car!
Car init!
Car destroy!

 

这里默认的是单实例Bean

如果是多实例的话，按照以上的测试代码是不会打印的，因为多实例情况下，在获取Bean的情况下才会创建对象

而且在多例情况下，只会调用初始化和构造方法，不会调用销毁方法

以上测试代码只完成了初始化IOC容器，所以什么都不打印

 

实现Spring中接口方式：这时候不需要在@Bean中进行配置

public class Car implements InitializingBean, DisposableBean {public Car() {System.out.println("Construct Car!");}public void afterPropertiesSet() throws Exception {System.out.println("Car init!");}public void destroy() {System.out.println("Car destroy!");}}

 

使用Java原生注解：

public class Car {public Car() {System.out.println("Construct Car!");}@PostConstructpublic void init() {System.out.println("Car init!");}@PreDestroypublic void destroy() {System.out.println("Car destroy!");}}

 

使用Spring中Bean的后置处理器：

@Component
public class MyBeanPostProcessor implements BeanPostProcessor {/*** 初始化前调用*/public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {System.out.println("postProcessBeforeInitialization " + bean + " " + beanName);return bean;}/*** 初始化后调用*/public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {System.out.println("postProcessAfterInitialization " + bean + " " + beanName);return bean;}
}

@Configuration
@ComponentScan("org.dreamtech.bean")
public class LifeCircleConfig {@Beanpublic Car car(){return new Car();}
}

 

测试后部分打印如下：

Construct Car!
postProcessBeforeInitialization org.dreamtech.bean.Car@2d9d4f9d car
postProcessAfterInitialization org.dreamtech.bean.Car@2d9d4f9d car

 

BeanPostProcessor原理：

查看这一段源码：

initializeBean(beanName, exposedObject, mbd)方法中：

        Object wrappedBean = bean;if (mbd == null || !mbd.isSynthetic()) {wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);}try {invokeInitMethods(beanName, wrappedBean, mbd);}catch (Throwable ex) {throw new BeanCreationException((mbd != null ? mbd.getResourceDescription() : null),beanName, "Invocation of init method failed", ex);}if (mbd == null || !mbd.isSynthetic()) {wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);}

在invokeInitMethods初始化方法之前

调用了applyBeanPostProcessorsBeforeInitialization，也就是调用了所有PostProcessor的Before方法

在invokeInitMethods初始化方法之后

调用了applyBeanPostProcessorsAfterInitialization，也就是调用了所有PostProcessor的After方法

 

进入applyBeanPostProcessorsBeforeInitialization方法查看源码：

遍历所有的Processor，一旦返回null，就会跳出循环

    @Overridepublic Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)throws BeansException {Object result = existingBean;for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {result = beanProcessor.postProcessBeforeInitialization(result, beanName);if (result == null) {return result;}}return result;}

 

在initializeBean方法之前，调用的是populateBean方法

作用：给属性赋值

        // Initialize the bean instance.Object exposedObject = bean;try {populateBean(beanName, mbd, instanceWrapper);if (exposedObject != null) {exposedObject = initializeBean(beanName, exposedObject, mbd);}}

 

所以：BeanPostProcessor是在Bean赋值之后，初始化的过程前后执行的

 

BeanPostProcessor在Spring底层的使用：

获取IOC容器的接口：

public interface ApplicationContextAware extends Aware {void setApplicationContext(ApplicationContext var1) throws BeansException;
}

而它就是基于BeanPostProcessor的，代码过长就不截取了

class ApplicationContextAwareProcessor implements BeanPostProcessor

 

或者是参数校验：也使用到了BeanPostProcessor

public class BeanValidationPostProcessor implements BeanPostProcessor, InitializingBean

部分代码如下：

    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {if (!this.afterInitialization) {this.doValidate(bean);}return bean;}public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {if (this.afterInitialization) {this.doValidate(bean);}return bean;}