spring aop之链式调用的实现

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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<MethodInterceptor> interceptorList;

  private int currentInterceptorIndex = -1;

  public ReflectiveMethodInvocation(Object targetObject, Method targetMethod, List<MethodInterceptor> 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<MethodInterceptor> 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 tx
http://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<MethodInterceptor> interceptorList = new ArrayList<>();
    interceptorList.add(afterReturningAdvice);
     interceptorList.add(beforeAdvice);

    ReflectiveMethodInvocation mi = new ReflectiveMethodInvocation(nioCoderService, method, interceptorList);

    mi.proceed();
  }

输出: