Spring Bean 后置处理器BeanPostProcessor-蒲公英云

文章目录

- Spring Bean 后置处理器BeanPostProcessor
- BeanPostProcessor实现类代码演示
- BeanPostProcessor生成代理对象

Spring Bean 后置处理器BeanPostProcessor

Spring 提供一种机制，只要实现此接口BeanPostProcessor，并将实现类提供给spring容器，spring容器将自动执行，在初始化方法前执行before()，在初始化方法后执行after()

可以配置多个 BeanPostProcessor 接口，通过设置 BeanPostProcessor 实现的 Ordered 接口提供的 order 属性来控制这些 BeanPostProcessor 接口的执行顺序。

ApplicationContext 会自动检测由 BeanPostProcessor 接口的实现定义的 bean，注册这些 bean 为后置处理器，然后通过在容器中创建 bean，在适当的时候调用它。

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Factory hook(勾子) that allows for custom modification of new bean instances, e.g. checking for marker interfaces or wrapping them with proxies.
spring提供工厂勾子，用于修改实例对象，可以生成代理对象，是AOP底层。

模拟
A a =new A();
a = B.before(a) —> 将a的实例对象传递给后处理bean，可以生成代理对象并返回。
a.init();
a = B.after(a);
a.addUser(); //生成代理对象，目的在目标方法前后执行（例如：开启事务、提交事务）
a.destroy()

BeanPostProcessor实现类代码演示

BeanPostProcessor实现类1，同时实现getOrder方法来控制这些执行顺序

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.core.Ordered;

public class PostProcessor implements BeanPostProcessor,Ordered {

//可以在初始化 bean 的之前和之后实现更复杂的逻辑。
//在Init-method的前后执行
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
    System.out.println("postProcessBeforeInitialization1:" + beanName);
    ((InitHelloWorld)bean).getMessage();
    return bean;
}
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
    System.out.println("postProcessAfterInitialization1:" + beanName);
    ((InitHelloWorld)bean).getMessage();
    return bean;
}
@Override
public int getOrder() {
    return 0;
}

}

BeanPostProcessor实现类2

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.core.Ordered;

public class PostProcessor2 implements BeanPostProcessor,Ordered {

//可以在初始化 bean 的之前和之后实现更复杂的逻辑。
//在Init-method的前后执行
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
    System.out.println("postProcessBeforeInitialization2:" + beanName);
    ((InitHelloWorld)bean).getMessage();
    return bean;
}
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
    System.out.println("postProcessAfterInitialization2:" + beanName);
    ((InitHelloWorld)bean).getMessage();
    return bean;
}
@Override
public int getOrder() {
    return 1;
}

}

配置

<?xml version=”1.0” encoding=”UTF-8”?>

    <bean id="initHelloWorld" class="com.cc.study.lifecycle.InitHelloWorld"
          init-method="init" destroy-method="destroy">
        <property name="message" value="Hello World!"></property>
    </bean>
    <bean id="postProcessor" class="com.cc.study.lifecycle.PostProcessor"></bean>
    <bean id="postProcessor2" class="com.cc.study.lifecycle.PostProcessor2"></bean>
</beans>

InitHelloWorld

public class InitHelloWorld{

private String message;
public void setMessage(String message){
    this.message  = message;
}
public void getMessage(){
    System.out.println("Your Message : " + message);
}
public void init(){
    System.out.println("Bean is going through init.");
}
public void destroy(){
    System.out.println("Bean will destroy now.");
}

}

测试

@Test

public void demo(){
    String xmlPath = "lifecycle2.xml";
    AbstractApplicationContext applicationContext = new ClassPathXmlApplicationContext(xmlPath);
    InitHelloWorld initHelloWorld = applicationContext.getBean("initHelloWorld",InitHelloWorld.class);
    initHelloWorld.getMessage();
    applicationContext.registerShutdownHook();
}

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BeanPostProcessor生成代理对象

MyBeanPostProcessor

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

public class MyBeanPostProcessor implements BeanPostProcessor {

@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
    System.out.println("前方法 ： " + beanName);
    return bean;
}
@Override
public Object postProcessAfterInitialization(final Object bean, String beanName) throws BeansException {
    System.out.println("后方法 ： " + beanName);
    // bean 目标对象
    // 生成 jdk 代理
    return Proxy.newProxyInstance(
                MyBeanPostProcessor.class.getClassLoader(), 
                bean.getClass().getInterfaces(), 
                new InvocationHandler(){
                    @Override
                    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                        System.out.println("------开启事务");
                        System.out.println("调用方法：" + method.getName());
                        //执行目标方法
                        Object obj = method.invoke(bean, args);
                        System.out.println("------提交事务");
                        return obj;
                    }});
}

}

配置

<?xml version=”1.0” encoding=”UTF-8”?>

BookDaoImpl

public class BookDaoImpl implements BookDao {

@Override
public void addBook() {
    System.out.println("di add book");
}

}

测试

@Test

public void demo(){
    String xmlPath = "lifecycle3.xml";
    AbstractApplicationContext applicationContext = new ClassPathXmlApplicationContext(xmlPath);
    BookDao bookDao = applicationContext.getBean("bookDaoId",BookDao.class);
    bookDao.addBook();
}