Spring AOP从原理到源码(二)

接着上一节:Spring AOP从原理到源码(一)

手写一个简单AOP

  1. 配置Interceptor
  2. 创建代理对象
  3. 调用过程封装调用链,然后逐个调用

解剖AOP,从简单到复杂

再次重复,要完成一个AOP,核心就两部分:

  1. 代理对象的创建
  2. 调用过程的拦截
    为了完成一个简单的AOP组件,我们大致需要以下一些组件:
  • 用于创建代理对象的工厂;
  • 用于动态拦截方法的拦截器;
  • 推荐拦截器链执行的MethodInvocation(叫方法调用者?)。

1. 方法拦截器

抽象类:

public abstract class MethodBeforeInterceptor implements MethodInterceptor {
    /**
     * 在方法调用前执行
     * @param method
     * @param args
     * @param target
     * @throws Throwable
     */
    public abstract void before(Method method, Object[] args, Object target) throws Throwable;

    @Override
    public Object invoke(MethodInvocation invocation) throws Throwable {
        // 先调用before方法
        this.before(invocation.getMethod(), invocation.getArguments(), invocation.getThis());
        // 继续执行调用链
        return invocation.proceed();
    }
}

public abstract class AfterReturningInteceptor implements MethodInterceptor {
    public abstract void afterReturning(Object returnValue, Method method, Object[] args, Object target) throws Throwable;

    @Override
    public Object invoke(MethodInvocation invocation) throws Throwable {
        // 先执行目标方法获取到返回值
        Object retVal = invocation.proceed();
        this.afterReturning(retVal, invocation.getMethod(), invocation.getArguments(), invocation.getThis());
        // 返回
        return retVal;
    }
}

具体实现:

public class FirstMethodBeforeInteceptor extends MethodBeforeInterceptor {
    @Override
    public void before(Method method, Object[] args, Object target) throws Throwable {
        System.out.println(String.format("这是FirstMethodBeforeInteceptor#before,正在拦截%s方法", method.getName()));
    }
}

public class FirstAfterReturningInterceptor extends AfterReturningInteceptor {
    @Override
    public void afterReturning(Object returnValue, Method method, Object[] args, Object target) throws Throwable {
        System.out.println(String.format("这是FirstAfterReturningInterceptor#afterReturning,正在拦截%s方法,它的返回值是%s", method.getName(), returnValue));
    }
}

2. MethodInvocation

public class ProxyMethodInvocation implements MethodInvocation {
    private Method method;
    private Object[] args;
    private Object target;
    private List interceptorList;
    int currentIndex = -1;

    public ProxyMethodInvocation(Method method, Object[] args, Object target, List interceptorList) {
        this.method = method;
        this.args = args;
        this.target = target;
        this.interceptorList = interceptorList;
    }

    @Override
    public Method getMethod() {
        return this.method;
    }

    @Override
    public Object[] getArguments() {
        return this.args;
    }

    @Override
    public Object proceed() throws Throwable {
        if (currentIndex == interceptorList.size() -1) {
            return method.invoke(target, args);
        }

        MethodInterceptor nextInteceptor = interceptorList.get(++currentIndex);
        return nextInteceptor.invoke(this);
    }

    @Override
    public Object getThis() {
        return this.target;
    }

    @Override
    public AccessibleObject getStaticPart() {
        return this.method;
    }
}

3. 创建代理的工厂

public class ProxyFactory implements InvocationHandler {
    // 被代理的对象
    private Object target;
    // 被代理对象的所有拦截器
    List interceptorList = new ArrayList<>();

    public ProxyFactory(Object target) {
        this.target = target;
    }

    public Object getProxy() {
        Class[] allInterfaces = ClassUtils.getAllInterfaces(target);
        return Proxy.newProxyInstance(Thread.currentThread().getContextClassLoader(), allInterfaces, this);
    }

    public void addInterceptor(MethodInterceptor interceptor) {
        interceptorList.add(interceptor);
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        ProxyMethodInvocation invocation = new ProxyMethodInvocation(method, args, target, interceptorList);
        return invocation.proceed();
    }
}

4. 测试

写一个Service,作为被代理对象。

public interface IService {
    String doService(String msg);
}

public class MyServiceImpl implements IService {
    @Override
    public String doService(String msg) {
        System.out.println("正在执行MyServiceImpl#doService");
        return "Hello " + msg;
    }
}

以下代码比较简单。

public class ProxyFactoryTest {

    @Test
    public void test() {
        MyServiceImpl target = new MyServiceImpl();
        ProxyFactory factory = new ProxyFactory(target);
        IService proxy = (IService) factory.getProxy();

        Assert.assertTrue(Proxy.isProxyClass(proxy.getClass()));
    }

    @Test
    public void test1() {
        MyServiceImpl target = new MyServiceImpl();
        ProxyFactory factory = new ProxyFactory(target);

        factory.addInterceptor(new FirstMethodBeforeInteceptor());

        IService proxy = (IService) factory.getProxy();
        proxy.doService("myaop");

    }

    @Test
    public void test2() {
        MyServiceImpl target = new MyServiceImpl();
        ProxyFactory factory = new ProxyFactory(target);

        factory.addInterceptor(new FirstAfterReturningInterceptor());

        IService proxy = (IService) factory.getProxy();
        proxy.doService("myaop");
    }

    @Test
    public void test3() {
        MyServiceImpl target = new MyServiceImpl();
        ProxyFactory factory = new ProxyFactory(target);

        factory.addInterceptor(new FirstAfterReturningInterceptor());
        factory.addInterceptor(new FirstMethodBeforeInteceptor());

        IService proxy = (IService) factory.getProxy();
        proxy.doService("myaop");
    }

    @Test
    public void test4() {
        MyServiceImpl target = new MyServiceImpl();
        ProxyFactory factory = new ProxyFactory(target);

        factory.addInterceptor(new FirstMethodBeforeInteceptor());
        factory.addInterceptor(new SecondMethodBeforeInteceptor());


        IService proxy = (IService) factory.getProxy();
        proxy.doService("myaop");
    }

    @Test
    public void test5() {
        MyServiceImpl target = new MyServiceImpl();
        ProxyFactory factory = new ProxyFactory(target);

        factory.addInterceptor(new FirstMethodBeforeInteceptor());
        factory.addInterceptor(new SecondMethodBeforeInteceptor());
        factory.addInterceptor(new FirstAfterReturningInterceptor());
        factory.addInterceptor(new SecondAfterReturningInterceptor());


        IService proxy = (IService) factory.getProxy();
        proxy.doService("myaop");
    }
}

解释一下ProxyMethodInvocation#procedd方法,它就是一个递归调用的方法,很简单。

简单的例子,表达的是比较核心的一些东西。还有很多东西没有表达出来,如:

  1. 为什么创建代理的时候spring添加的是Advisor而不是直接添加MethodInterceptor
    答:一个Advisor(准确说是Advice)可以对应多个MethodInterceptor。

参考DefaultAdvisorAdapterRegistry#getInterceptors

  1. 如果不是目标对象没有实现任何接口怎么办?如果让ProxyFactory更具通用性,支持在任何情况下都能生成代理对象,完成目标对象的生产?

源码

源码地址

小结

本节模仿Spring AOP的核心过程实现一个简单的AOP,大致上说明了spring aop的核心过程,如果大家能理解的话,对于spring aop的理解也就不难了。后面将从代理对象的创建方法调用的拦截过程两部分对spring aop的核心ProxyFactory进行讲解。下一节一起先看看spring aop是怎么创建代理对象的。
转载请说明出处!

你可能感兴趣的:(Spring AOP从原理到源码(二))