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Spring AOP从原理到源码(二)

Spring AOP从原理到源码(二)

作者: 李不言被占用了 | 来源:发表于2020-04-20 09:13 被阅读0次

    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:
    3. 用于创建代理对象的工厂;
    4. 用于动态拦截方法的拦截器;
    5. 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<MethodInterceptor> interceptorList;
        int currentIndex = -1;
    
        public ProxyMethodInvocation(Method method, Object[] args, Object target, List<MethodInterceptor> 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<MethodInterceptor> 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");
        }
    }
    

    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

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