通过JDK动态代理实现拦截器

拦截器

拦截器是我们开发中接触比较多的。今天使用JDK动态代理模式来实现拦截器。实现过程我们通过代码来展示，代码中有相应的解释：

//拦截器接口
public interface Interceptor {
    /**
     * 调用真实方法之前执行，写调用真实方法的前提逻辑
     * @param proxy 代理对象
     * @param obj 真实对象
     * @param method 方法
     * @param args 方法参数
     * @return
     */
    public boolean before(Object proxy,Object obj,Method method,Object[] args);
    /**
     * 当before方法结果是false时，调用此方法
     * @param proxy
     * @param obj
     * @param method
     * @param args
     */
    public void around(Object proxy,Object obj,Method method,Object[] args);
    /**
     * 调用完真实对象或者执行完around方法之后执行此方法
     * @param proxy
     * @param obj
     * @param method
     * @param args
     */
    public void after(Object proxy,Object obj,Method method,Object[] args);
    
}

//拦截器实现类
public class InterceptorImpl implements Interceptor {

    @Override
    public boolean before(Object proxy, Object obj, Method method, Object[] args) {
        System.out.println("反射方法执行之前的逻辑~~");
        return false;
    }

    @Override
    public void around(Object proxy, Object obj, Method method, Object[] args) {
        System.out.println("执行around方法~~~");
    }

    @Override
    public void after(Object proxy, Object obj, Method method, Object[] args) {
        System.out.println("反射方法之后的逻辑~~");
    }
}

//JDK动态代理所需要的接口
public interface ISayHello {
    public void say();
}

//JDK动态代理接口实现类
public class SayHelloImpl implements ISayHello {

    @Override
    public void say() {
        System.out.println("真实对象逻辑~Hello World!");    
    }

}

//jdk动态代理实现拦截器
public class InterceptorJdkProxy implements InvocationHandler {
    //真实对象
    private Object obj;
    //拦截器权限定名
    private String interceptorClass = null;
    
    public Object bind(Object obj,String interceptorClas) {
        this.obj = obj;
        this.interceptorClass = interceptorClas;
        Object proxy = Proxy.newProxyInstance(obj.getClass().getClassLoader(), 
                obj.getClass().getInterfaces(), this);
        return proxy;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        //如果没有拦截器，直接走原逻辑
        if(interceptorClass == null) {
            return method.invoke(obj, args);
        }
        //接收真实对象方法
        Object result = null;
        //反射生成拦截器对象
        Interceptor interceptor = (Interceptor) Class.forName(interceptorClass).newInstance();
        if(interceptor.before(proxy, obj, method, args)) {
            result = method.invoke(obj, args);
        } else {
            interceptor.around(proxy, obj, method, args);
        }
        interceptor.after(proxy, obj, method, args);
        return result;
    }
}

//测试代码
public class TestInterceptor {
    public static void main(String[] args) {
        InterceptorJdkProxy interceptorJdkProxy = new InterceptorJdkProxy();
        ISayHello bind = (ISayHello) interceptorJdkProxy.bind(new SayHelloImpl(), "interceptor.InterceptorImpl");
        bind.say();
    }
}

测试结果展示

当执行before方法返回为true

当执行before方法返回为false