动态代理实践(一)

叁歲伎倆 2022-04-25 09:56 140阅读 0赞

### cglib动态代理 ###

![20190531110957189.png][]

导入两个jar包

![20190531111048223.png][]

很多java字节码操作和分析的第三方类库都引用了**[asm.jar][]**文件，由于工程不是Maven管理的，无法解决以来传递问题，所以要手动引入asm.jar文件。

否则会报异常 :

Exception in thread "main" java.lang.NoClassDefFoundError: org/objectweb/asm/Type\
    Caused by: java.lang.ClassNotFoundException: org.objectweb.asm.Type

package com.itheima.dao;
    
    public class DogDao {
    	public void food (Object obj) {
    	System.out.println("dog eat :"+obj);
    }
    public void bark (Object obj) {
    	System.out.println("dog say :"+obj);
    }
    public void sleep (Object obj) {
    	System.out.println("dog sleep :"+obj);
    }
    	
    }

package com.itheima.proxy;
    
    import java.lang.reflect.Method;
    
    import net.sf.cglib.proxy.MethodInterceptor;
    import net.sf.cglib.proxy.MethodProxy;
    
    public class MethodInterceporImpl implements MethodInterceptor{
    
    
    @Override
    public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
    	System.out.println("dog do what ? : dog ~"+method);
    	Object result = proxy.invokeSuper(obj, args);
    	System.out.println("dog stop doing what ? : dog stop~"+method);
    	return result;
    }
    }

package com.itheima.proxy;
    import com.itheima.dao.DogDao;
    
    import net.sf.cglib.proxy.Enhancer;
    
    public class DaoFactory {
    public static DogDao create() {
    	Enhancer enhancer = new Enhancer();
    	enhancer.setSuperclass(DogDao.class);
    	enhancer.setCallback(new MethodInterceporImpl());
    	DogDao dogDao = (DogDao)enhancer.create();
    	return dogDao;
    }
    }

package com.itheima.proxy;
    
    import com.itheima.dao.DogDao;
    
    public class TestMain {
    
    	public static void main(String[] args) {
    		DogDao dogDao = DaoFactory.create();
    		dogDao.sleep("zzz");
    		dogDao.bark("wawoo~");
    		dogDao.food("生肉");
    
    	}
    
    }

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zOTU5Mzk4NQ_size_16_color_FFFFFF_t_70][]

# **回调过滤器CallbackFilter** #

net.sf.cglib.proxy.CallbackFilter有选择的对一些方法使用回调。

CallbackFilter可以实现不同的方法使用不同的回调方法。所以CallbackFilter称为"回调选择器"更合适一些。

CallbackFilter中的accept方法，根据不同的method返回不同的值i，这个值是在callbacks中callback对象的序号，就是调用了callbacks\[i\]。

package com.itheima.proxy;
    import com.itheima.dao.DogDao;
    
    import net.sf.cglib.proxy.Callback;
    import net.sf.cglib.proxy.Enhancer;
    import net.sf.cglib.proxy.NoOp;
    
    public class DaoFactory {
    public static DogDao create() {
    
    	MethodInterceporAnotherImpl m1 = new MethodInterceporAnotherImpl();
    	MethodInterceporImpl m0 = new MethodInterceporImpl();
    	Enhancer enhancer = new Enhancer();
    	enhancer.setSuperclass(DogDao.class);
    	enhancer.setCallbacks(new Callback[] {m0,m1,NoOp.INSTANCE});
    	enhancer.setCallbackFilter(new CallbackFilterImpl());
    	DogDao dogDao = (DogDao)enhancer.create();
    	return dogDao;
    }
    }

package com.itheima.proxy;
    
    import java.lang.reflect.Method;
    
    import net.sf.cglib.proxy.MethodInterceptor;
    import net.sf.cglib.proxy.MethodProxy;
    
    public class MethodInterceporAnotherImpl implements MethodInterceptor{
    
    
    @Override
    public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
    	System.out.println("狗子咋啦 : dog ~"+method);
    	Object result = proxy.invokeSuper(obj, args);
    	System.out.println("狗子 : dog stop~"+method);
    	return result;
    }
    }

package com.itheima.proxy;
    
    import java.lang.reflect.Method;
    
    import net.sf.cglib.proxy.CallbackFilter;
    
    public class CallbackFilterImpl implements CallbackFilter {
    
    	@Override
    	public int accept(Method method) {
    		String methodName =  method.getName();
    		if("bark".equals(methodName)) {
    			return 0;//使用 callbacks[1]对象拦截
    		}else {
    			return 1;
    		}
    	}
    
    }

package com.itheima.proxy;
    
    import com.itheima.dao.DogDao;
    
    public class TestMain {
    
    	public static void main(String[] args) {
    		DogDao dogDao = DaoFactory.create();
    		dogDao.sleep("做梦了");
    		dogDao.bark("wawoo~");
    		dogDao.food("饿了");
    
    	}
    
    }

![20190531124643394.png][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zOTU5Mzk4NQ_size_16_color_FFFFFF_t_70 1][]

[20190531110957189.png]: /images/20220125/2b4156edc3854c26877a660003e70b48.png
[20190531111048223.png]: /images/20220125/9d07106d9e8044e78913fcaf7b595b06.png
[asm.jar]: http://asm.ow2.org/
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zOTU5Mzk4NQ_size_16_color_FFFFFF_t_70]: /images/20220125/c5780ed97c86402888fceff79d8e1e00.png
[20190531124643394.png]: /images/20220125/d4b109f944184ba689730956a2528080.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zOTU5Mzk4NQ_size_16_color_FFFFFF_t_70 1]: /images/20220125/626ff31bcd7a4576a8335b18c99fb2b4.png