spring aop之鏈?zhǔn)秸{(diào)用的實現(xiàn)

更新時間：2019年02月20日 10:18:19 作者：niocoder

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概述

AOP（Aspect Orient Programming），我們一般稱為面向方面（切面）編程，作為面向?qū)ο蟮囊环N補(bǔ)充，用于處理系統(tǒng)中分布于各個模塊的橫切關(guān)注點(diǎn)，比如事務(wù)管理、日志、緩存等等。 Spring AOP采用的是動態(tài)代理，在運(yùn)行期間對業(yè)務(wù)方法進(jìn)行增強(qiáng)，所以不會生成新類，Spring AOP提供了對JDK動態(tài)代理的支持以及CGLib的支持。本章我們不關(guān)注aop代理類的實現(xiàn)，我簡單實現(xiàn)一個指定次序的鏈?zhǔn)秸{(diào)用。

實現(xiàn)鏈?zhǔn)秸{(diào)用的

MethodInterceptor定義攔截器鏈,MethodInvocation 遞歸進(jìn)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(xiàn)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

實現(xiàn)MethodInvocation，proceed()方法遞歸實現(xiàn)鏈?zhǔn)秸{(diào)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: