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概述

AOP（Aspect Orient Programming），我们一般称为面向方面（切面）编程，作为面向对象的一种补充，用于处理系统中分布于各个模块的横切关注点，比如事务管理、日志、缓存等等。 Spring AOP采用的是动态代理，在运行期间对业务方法进行增强，所以不会生成新类，Spring AOP提供了对JDK动态代理的支持以及CGLib的支持。本章我们不关注aop代理类的实现，我简单实现一个指定次序的链式调用。

实现链式调用的

MethodInterceptor定义拦截器链,MethodInvocation 递归进入下一个拦截器链中。类图如下：

MethodInterceptor

public interface MethodInterceptor {    Object invoke(MethodInvocation invocation) throws Throwable;}

MethodInvocation

public interface MethodInvocation {    Object proceed() throws Throwable;}

AbstractAspectJAdvice

抽象类,实现MethodInterceptor

public abstract class AbstractAspectJAdvice implements MethodInterceptor{    private Method adviceMethod;    private Object adviceObject;    public AbstractAspectJAdvice(Method adviceMethod, Object adviceObject) {        this.adviceMethod = adviceMethod;        this.adviceObject = adviceObject;    }    public Method getAdviceMethod() {        return this.adviceMethod;    }    public void invokeAdviceMethod() throws Throwable {        adviceMethod.invoke(adviceObject);    }}

AspectJBeforeAdvice

前置通知

public class AspectJBeforeAdvice extends AbstractAspectJAdvice {    public AspectJBeforeAdvice(Method method, Object adviceObject) {        super(method, adviceObject);    }    @Override    public Object invoke(MethodInvocation invocation) throws Throwable{        this.invokeAdviceMethod();        Object o = invocation.proceed();        return o;    }}

AspectJAfterReturningAdvice

后置通知

public class AspectJAfterReturningAdvice extends AbstractAspectJAdvice {    public AspectJAfterReturningAdvice(Method method, Object adviceObject) {        super(method, adviceObject);    }    @Override    public Object invoke(MethodInvocation invocation) throws Throwable{        Object o = invocation.proceed();        this.invokeAdviceMethod();        return o;    }}

ReflectiveMethodInvocation

实现MethodInvocation，proceed()方法递归实现链式调用。

public class ReflectiveMethodInvocation implements MethodInvocation {    private final Object targetObject;    private final Method targetMethod;    private final List
    
      interceptorList;    private int currentInterceptorIndex = -1;    public ReflectiveMethodInvocation(Object targetObject, Method targetMethod, List
     
       interceptorList) {        this.targetObject = targetObject;        this.targetMethod = targetMethod;        this.interceptorList = interceptorList;    }    @Override    public Object proceed() throws Throwable {        if (this.currentInterceptorIndex == this.interceptorList.size() - 1) {            return invokeJoinPoint();        }        this.currentInterceptorIndex++;        MethodInterceptor interceptor =                this.interceptorList.get(this.currentInterceptorIndex);        return interceptor.invoke(this);    }    private Object invokeJoinPoint() throws Throwable {        return this.targetMethod.invoke(this.targetObject);    }}
     
    

NioCoderService

模拟service类

public class NioCoderService {    public void testAop() {        System.out.println("http://niocoder.com/");    }}

TransactionManager

模拟通知类

public class TransactionManager {    public void start() {        System.out.println("start tx");    }    public void commit() {        System.out.println("commit tx");    }    public void rollback() {        System.out.println("rollback tx");    }}

ReflectiveMethodInvocationTest

beforeAdvice->afterReturningAdvice

测试类，测试通知

public class ReflectiveMethodInvocationTest {    private AspectJBeforeAdvice beforeAdvice = null;    private AspectJAfterReturningAdvice afterReturningAdvice = null;    private NioCoderService nioCoderService;    private TransactionManager tx;    public void setUp() throws Exception {        nioCoderService = new NioCoderService();        tx = new TransactionManager();        beforeAdvice = new AspectJBeforeAdvice(TransactionManager.class.getMethod("start"), tx);        afterReturningAdvice = new AspectJAfterReturningAdvice(TransactionManager.class.getMethod("commit"), tx);    }    public void testMethodInvocation() throws Throwable {        Method method = NioCoderService.class.getMethod("testAop");        List
    
      interceptorList = new ArrayList<>();        interceptorList.add(beforeAdvice);        interceptorList.add(afterReturningAdvice);                ReflectiveMethodInvocation mi = new ReflectiveMethodInvocation(nioCoderService, method, interceptorList);        mi.proceed();    }    public static void main(String[] args) throws Throwable {        ReflectiveMethodInvocationTest reflectiveMethodInvocationTest = new ReflectiveMethodInvocationTest();        reflectiveMethodInvocationTest.setUp();        reflectiveMethodInvocationTest.testMethodInvocation();    }}
    

输出:

start txhttp://niocoder.com/commit tx

时序图 beforeAdvice->afterReturningAdvice

afterReturningAdvice->beforeAdvice

修改interceptorList的顺序

public void testMethodInvocation() throws Throwable {        Method method = NioCoderService.class.getMethod("testAop");        List
    
      interceptorList = new ArrayList<>();        interceptorList.add(afterReturningAdvice);         interceptorList.add(beforeAdvice);        ReflectiveMethodInvocation mi = new ReflectiveMethodInvocation(nioCoderService, method, interceptorList);        mi.proceed();    }
    

输出:

start txhttp://niocoder.com/commit tx

时序图 afterReturningAdvice->beforeAdvice

代码下载

• github:

代码下载

• github: