spring aop 之鏈式調用

關關雎鳩，在河之洲。窈窕淑女，君子好逑。

概述

AOP（Aspect Orient Programming），我們一般稱爲面向方面（切面）編程，作爲面向對象的一種補充，用於處理系統中分佈於各個模塊的橫切關注點，比如事務管理、日誌、緩存等等。 Spring AOP採用的是動態代理，在運行期間對業務方法進行增強，所以不會生成新類，Spring AOP提供了對JDK動態代理的支持以及CGLib的支持。本章我們不關注aop代理類的實現，我簡單實現一個指定次序的鏈式調用。

實現鏈式調用的

MethodInterceptor定義攔截器鏈,MethodInvocation 遞歸進入下一個攔截器鏈中。類圖如下：

MethodInterceptor

public interface MethodInterceptor {

    Object invoke(MethodInvocation invocation) throws Throwable;
}

MethodInvocation

public interface MethodInvocation {

    Object proceed() throws Throwable;
}

AbstractAspectJAdvice

抽象類,實現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

後置通知

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

實現MethodInvocation，proceed()方法遞歸實現鏈式調用。

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

模擬service類

public class NioCoderService {

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

TransactionManager

模擬通知類

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

測試類，測試通知

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();
    }
}

輸出:

start tx
http://niocoder.com/
commit tx

時序圖 beforeAdvice->afterReturningAdvice

afterReturningAdvice->beforeAdvice

修改interceptorList的順序

  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();
    }

輸出:

start tx
http://niocoder.com/
commit tx

時序圖 afterReturningAdvice->beforeAdvice

代碼下載

• github:https://github.com/longfeizheng/data-structure-java/blob/master/src/main/java/cn/merryyou/aop

代碼下載

• github:https://github.com/longfeizheng/data-structure-java