「2020最新」Spring最易学习教程 3— 代理设计模式 Spring AOP 动态代理原理

web.xml 在tomcat启动应用时，创建Spring工厂
<context-param>
 <param-name>contextConfigLocation</param-name>
 <param-value>classpath:applicationContext.xml</param-value>
</context-param>

<listener>
 <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>

public interface UserService {
    public boolean login(String username,String password);
    public void removeUser(Integer id);
}

public class UserServiceImpl implements UserService {
    @Override
    public boolean login(String username, String password) {
        System.out.println("username = [" + username + "], password = [" + password + "]");
        return false;
    }

    @Override
    public void removeUser(Integer id) {
        System.out.println("id = [" + id + "]");
    }
}

public class UserServiceProxy implements UserService {
    private UserService userService = new UserServiceImpl();
    @Override
    public boolean login(String username, String password) {
        System.out.println("开启事务");
        boolean result = userService.login(username,password);
        System.out.println("结束事务");
        return result;
    }

    @Override
    public void removeUser(Integer id) {
        System.out.println("开启事务");
        userService.removeUser(id);
        System.out.println("结束事务");
    }
}

public class UserAction {
    private UserService userService = new UserServiceProxy();
    public String login(){
        userService.login("xiaohei", "123456");
        return "success";
    }
    public String removeUser(){
        userService.removeUser(1);
        return "success";
    }
}

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-aop</artifactId>
    <version>4.3.26.RELEASE</version>
</dependency>
<dependency>
    <groupId>org.aspectj</groupId>
    <artifactId>aspectjweaver</artifactId>
    <version>1.9.5</version>
</dependency>

创建原始类型对象
<bean id="标识" class="原始（目标）类全类名"></bean>

定义额外功能。实现Spring的特定接口
public class MyMethodBeforeAdvice implements MethodBeforeAdvice {
 @Override
 /*
        method: 原始类型中方法
        args: 参数
        target: 原始对象
     */
 public void before(Method method, Object[] args, Object target) throws Throwable {
        System.out.println("before...");
    }
}

配置额外功能类
 <!-- 配置功能增强类 -->
 <bean id="myBeforeAdvice" class="com.bcl.advice.MyMethodBeforeAdvice"/>

组装
<aop:config>
 <!-- 定义切入点-->
 <aop:pointcut id="myPointCut" expression="execution(* com.bcl.service.*.*(..))"/>

 <!-- 组装 -->
 <aop:advisor advice-ref="myBeforeAdvice" pointcut-ref="myPointCut"/>
</aop:config>

public class MyMethodBeforeAdvice implements MethodBeforeAdvice {
    @Override
    /*
        method: 原始方法
        args: 调用方法时的实参列表
        target: 原始对象
     */
    public void before(Method method, Object[] args, Object target) throws Throwable {
        System.out.println("method = [" + method + "], args = [" + Arrays.toString(args) + "], target = [" + target + "]");
        System.out.println("target.getClass() = " + target.getClass());
        System.out.println("前置增强");
    }
}

public class MyAfterReturningAdvice implements AfterReturningAdvice {
    /*
        returnValue: 原始方法正常结束后的返回值
        method: 原始方法
        args: 实参列表
        target: 原始对象
     */
    @Override
    public void afterReturning(Object returnValue, Method method, Object[] args, Object target) throws Throwable {
        System.out.println("后置增强");
    }
}

public class MyThrowsAdvice implements ThrowsAdvice {
    /*
        method: 原始方法
        args: 实参列表
        target: 原始对象
        throwable: 原始方法运行时的异常
     */
    public void afterThrowing(Method method, Object[] args,Object target, Throwable throwable){
        System.out.println("异常增强");
    }
}

public class MyRoundAdvice implements MethodInterceptor {
    @Override
    public Object invoke(MethodInvocation pj) throws Throwable {
        System.out.println("前置增强");

        Object result = null;
        try {
            //放行：调用原始方法
            result = pj.proceed();

            System.out.println("后置增强");
        }catch(Exception e){
            System.out.println("异常增强");
            throw e;
        }finally{
            System.out.println("最终增强");
        }
        return result;
    }
}

自定义一个注解
public @interface MyAnnotation {
}

使用自定义注解描述方法（实现类中的方法）
public class UserServiceImpl implements UserService {
 @Override
 @MyAnnotation
 public boolean login(String username, String password) {
        System.out.println("username = [" + username + "], password = [" + password + "]");
 return false;
    }

 @Override
 public void removeUser(Integer id) {
        System.out.println("id = [" + id + "]");
 //int i = 10/0;
    }
}

切入点配置为 @annotation(自定义注解类型)
<aop:pointcut id="myPointCut" expression="@annotation(com.bcl.annotation.MyAnnotation)"/>