Spring Bean前置后置处理器的使用

Z时代
2024-01-10
分类：综合

本文内容纲要：Spring Bean前置后置处理器的使用

Spirng中BeanPostProcessor和InstantiationAwareBeanPostProcessorAdapter两个接口都可以实现对bean前置后置处理的效果，那这次先讲解一下BeanPostProcessor处理器的使用

先看一下BeanPostProcessor接口的源码，它定义了两个方法，一个在bean初始化之前，一个在bean初始化之后

public interface BeanPostProcessor {
    @Nullable
    default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }
    @Nullable
    default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }
}

下面，我们来实现这个类，测试一下Spring中的前置后置处理器吧

首先是pom.xml,增加Spring相关的依赖

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.myspring</groupId>
  <artifactId>myspring</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>jar</packaging>
  <name>myspring</name>
  <url>http://maven.apache.org</url>
  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>
  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
    <!-- Spring 5.0 核心工具包 -->
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-core</artifactId>
        <version>5.0.7.RELEASE</version>
    </dependency>
    <!-- Spring 5.0 Bean管理工具包 -->
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-beans</artifactId>
        <version>5.0.7.RELEASE</version>
    </dependency>
    <!-- Spring 5.0 context管理工具包 -->
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context</artifactId>
        <version>5.0.7.RELEASE</version>
    </dependency>
    <!-- Spring 5.0 aop支持包 -->
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-aop</artifactId>
        <version>5.0.7.RELEASE</version>
    </dependency>
  </dependencies>
</project>

定义一个测试接口：

public interface BaseService {
    String doSomething();
    String eat();
}
定义接口实现类：
public class ISomeService implements BaseService {
    public String doSomething() {
        // 增强效果：返回内容全部大写
        return "Hello i am kxm";
    }
    public String eat() {
        return "eat food";
    }
}

实现BeanPostProcessor接口

public class MyBeanPostProcessor implements BeanPostProcessor  {
    // 前置处理器
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        Class beanClass = bean.getClass();
        if (beanClass == ISomeService.class) {
            System.out.println("bean 对象初始化之前······");
        }
        return bean;
    }
    // 后置处理器 --- 此处具体的实现用的是Java中的动态代理
    public Object postProcessAfterInitialization(final Object beanInstance, String beanName) throws BeansException {
        // 为当前 bean 对象注册监控代理对象，负责增强 bean 对象方法的能力
        Class beanClass = beanInstance.getClass();
        if (beanClass == ISomeService.class) {
            Object proxy = Proxy.newProxyInstance(beanInstance.getClass().getClassLoader(),beanInstance.getClass().getInterfaces(), new InvocationHandler() {
                public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                    System.out.println("ISomeService 中的 doSome() 被拦截了···");
                    String result = (String) method.invoke(beanInstance, args);
                    return result.toUpperCase(); 
                }
            });     
            return proxy;
        }
        return beanInstance;
    }
}

Spring的配置文件如下：

<!-- 注册 bean：被监控的实现类 -->
<bean id="iSomeService" class="com.my.spring.beanprocessor.ISomeService"></bean>
<!-- 注册代理实现类 -->
<bean class="com.my.spring.beanprocessor.MyBeanPostProcessor"></bean>
测试类如下：
public class TestBeanPostProcessor {
    public static void main(String[] args) {
        /**
         * BeanPostProcessor 前置后置处理器
         */
        ApplicationContext factory = new ClassPathXmlApplicationContext("spring_config.xml");
        BaseService serviceObj = (BaseService) factory.getBean("iSomeService");
        System.out.println(serviceObj.doSomething());
    }
}