AOP原理与应用

1. AOP概述
2. Test Code
3. AOP原理与实现
    3.1 原理分析
    3.2 设计实现
4. 总结

public class AdvisorChainTest extends BaseTest{

    static class ProxyBuilder{
        public static Object buildProxy(Class<?> interfaces, Object target, List<MethodInterceptor> list){
            return Proxy.newProxyInstance(ProxyBuilder.class.getClassLoader(), 
                    new Class<?>[]{interfaces},  new DefaultInvocationHandler(target, list));
        }
    }

    @Test
    public void testAOP() {
        
        Set<String> exclusionMethodNames = new HashSet<String>();
        exclusionMethodNames.add("delete");//拦截delete方法
        
        //过滤方法的拦截器
        MethodFilterInterceptor filter = new MethodFilterInterceptor(exclusionMethodNames);
        
        //记录方法执行时间拦截器
        TimeLogInterceptor time = new TimeLogInterceptor();
        
        List<MethodInterceptor> list = Arrays.asList(filter,time);
        
        UserService user = new UserServiceImpl();
        UserService proxy = (UserService)ProxyBuilder.buildProxy(UserService.class,user,list);

        proxy.update(null);
        assertTrue(time.msg.contains("update execute time:"));
        
        try{
            proxy.delete(null);
            fail("method delete is not allowed!");
        }catch(Exception e){
            assertEquals(MethodNotAllowedException.class, e.getClass());
        }
    }
}

/**
 * MethodInvocation代表方法的执行
 * 
 * @author wqx
 *
 */
public interface MethodInvocation {
    
    /**
     * 获取方法对象
     * 
     * @return
     */
    public Method getMethod();
    
    /**
     *  获取参数
     * 
     * @return
     */
    public Object[] getParameters();
    
    /**
     * 执行下一个方法
     * 
     * @return
     * @throws Exception
     */
    Object executeNext() throws Exception;
    
}

public interface MethodInterceptor {
    
    Object invoke(MethodInvocation invocation) throws Exception;
    
}

/**
 * MethodInvocation的默认实现
 * 
 * @author wqx
 *
 */
public class DefaultMethodInvocation implements MethodInvocation {

    //目标对象
    private Object target;
    //代理
    private Object proxy;
    //目标方法
    private Method method;
    //参数
    private Object[] parameters;
    
    //拦截器链
    private List<?> interceptors;
    //当前执行的Interceptor的索引（范围：0-interceptors.size()-1），初始为-1
    private int currentIndex = -1;
    
    public DefaultMethodInvocation(Object target,Object proxy,Method method,Object[] parameters, List<?> interceptors){
        this.target = target;
        this.proxy = proxy;
        this.method = method;
        this.parameters = parameters;
        this.interceptors = interceptors;
    }
    
    @Override
    public Object executeNext() throws Exception {
        //判断拦截器链是否执行完
        if(this.currentIndex == this.interceptors.size() - 1){
            //如果执行完，直接执行目标方法
            method.setAccessible(true);
            return method.invoke(target, parameters);
        }
        Object interceptor = this.interceptors.get(++this.currentIndex);
        MethodInterceptor methodInterceptor = (MethodInterceptor)interceptor;
        return methodInterceptor.invoke(this);
    }
    
    //getter and seter
}

public class DefaultInvocationHandler implements InvocationHandler {

    private Object target;
    
    private List<MethodInterceptor> interceptorsChain;
    
    public DefaultInvocationHandler(Object target, List<MethodInterceptor> interceptorsChain){
        this.target = target;
        this.interceptorsChain = interceptorsChain;
    }
    
    @Override
    public Object invoke(Object proxy, Method method, Object[] args)
            throws Throwable {
        MethodInvocation methodInvocation;
        
        List<MethodInterceptor> chain = interceptorsChain;
        
        Object relVal;
        if(chain != null && !chain.isEmpty()){
            methodInvocation = new DefaultMethodInvocation(target,proxy,method,args,chain);
            relVal = methodInvocation.executeNext();
        }else{//直接调用目标方法
            relVal = method.invoke(target, args);
        }
        return relVal;
    }
}

//获取下一个拦截器
Object interceptor = this.interceptors.get(++this.currentIndex);
MethodInterceptor methodInterceptor = (MethodInterceptor)interceptor;
//执行拦截器的invoke方法
return methodInterceptor.invoke(this);