spring aop之链式调用的实现

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:

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

时序图 afterreturningadvice->beforeadvice

代码下载

github:

代码下载

github:

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