gistfile1.java

package interceptor;

import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

/**
 * @author Gabriel Francisco - [email protected]
 */
@Retention(RetentionPolicy.RUNTIME)
@Inherited
public @interface Interceptor {
    Class<?> interceptorClazz();
}


package interceptor;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

/**
 * @author Gabriel Francisco - [email protected]
 */
@Retention(RetentionPolicy.RUNTIME)
public @interface After {
}


package interceptor;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

/**
 * @author Gabriel Francisco - [email protected]
 */
@Retention(RetentionPolicy.RUNTIME)
public @interface Before {
}


package interceptor;

import java.lang.reflect.Method;

/**
 * @author Gabriel Francisco - [email protected]
 */
public class InvocationContext {
    private Object target;
    private Object result;
    private Method method;

    public InvocationContext(Object target, Method method) {
        this.target = target;
        this.method = method;
    }

    public InvocationContext(Object target, Object result, Method method) {
        this.target = target;
        this.result = result;
        this.method = method;
    }

    public Object getTarget() {
        return target;
    }

    public Method getMethod() {
        return method;
    }

    public Object getResult() {
        return result;
    }
    
    public void setResult(Object result) {
        this.result = result;
    }
}


package interceptor;

import java.lang.annotation.Annotation;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;

/**
 * @author Gabriel Francisco - [email protected]
 */
public class InterceptorInvocationHandler implements InvocationHandler {
    private Object instance;

    public InterceptorInvocationHandler(Object instance) {
        this.instance = instance;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        Interceptor interceptor = null;

        for (Annotation annotation : instance.getClass().getDeclaredAnnotations()) {
            if (annotation.annotationType().isAnnotationPresent(Interceptor.class)) {
                interceptor = annotation.annotationType().getAnnotation(Interceptor.class);
            }
        }

        if (interceptor == null) {
            throw new IllegalArgumentException("There is no interceptor to invoke");
        }

        Object o = interceptor.interceptorClazz().newInstance();

        Method[] methods = interceptor.interceptorClazz().getDeclaredMethods();

        Method before = null;
        Method after = null;

        for (Method m : methods) {
            if (m.isAnnotationPresent(Before.class)) {
                before = m;
            }

            if (m.isAnnotationPresent(After.class)) {
                after = m;
            }
        }

        InvocationContext invocationContext = new InvocationContext(instance, method);

        if (before != null) {
            before.invoke(o, invocationContext);
        }

        invocationContext.setResult(method.invoke(instance, args));

        if (after != null) {
            after.invoke(o, invocationContext);
        }

        return invocationContext.getResult();
    }
}


package interceptor;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Proxy;

/**
 * @author Gabriel Francisco - [email protected]
 */
public class InterceptorProxy {

    public static <T> T createProxy(Object instance, Class<?> interfaceClazz) {
        InvocationHandler handler = new InterceptorInvocationHandler(instance);
        return (T) Proxy.newProxyInstance(interfaceClazz.getClassLoader(), new Class[]{interfaceClazz}, handler);
    }
}



//EXEMPLO
//EXEMPLO
//EXEMPLO

package sample;

import interceptor.Interceptor;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

/**
 * @author Gabriel Francisco - [email protected]
 */
@Retention(RetentionPolicy.RUNTIME)
@Interceptor(interceptorClazz = LoggerInterceptor.class)
public @interface Logger {
}

package sample;

import interceptor.After;
import interceptor.Before;
import interceptor.InvocationContext;

/**
 * @author Gabriel Francisco - [email protected]
 */
public class LoggerInterceptor {

    @Before
    public void before(InvocationContext invocationContext){
        System.out.println("before method: " + invocationContext.getMethod().getName());
    }

    @After
    public void after(InvocationContext invocationContext){
        System.out.println("after method: " + invocationContext.getMethod().getName());
    }
}

package sample;

/**
 * @author Gabriel Francisco - [email protected]
 */
public interface SampleClass {
    void doSomething();
}


package sample;

import interceptor.InterceptorProxy;

/**
 * @author Gabriel Francisco - [email protected]
 */
@Logger
public class SampleClassImpl implements SampleClass {

    @Override
    public void doSomething(){
        System.out.println("doSomething method!");
    }

    public static void main(String[] args) {
        SampleClass sampleClass = new InterceptorProxy().createProxy(new SampleClassImpl(), SampleClass.class);
        sampleClass.doSomething();
    }
}