1.示例需要代码

1.接口代码

public interface People { 
    public String workAndGetReward();
    public String reward();
}

2.接口实现类代码

public class Programmer implements People { 
    @Override
    public String workAndGetReward() { 
        System.out.println("Programmer works hard under 996.");
        return reward();
    }
    @Override
    public String reward() { 
        return "Then he goes icu.";
    }
}

3.动态代理处理类代码

import java.lang.reflect.Method;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import net.sf.cglib.proxy.Enhancer;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;
public class CglibProxy implements MethodInterceptor { 
    private static Logger logger = LoggerFactory.getLogger(Programmer.class);
    @Override
    public Object intercept(Object proxy, Method method, Object[] params, MethodProxy methodProxy) throws Throwable { 
        logger.info("before invoke:" + method.getName() + " - " + System.currentTimeMillis());
        Object retObj = methodProxy.invokeSuper(proxy, params);
        logger.info("after invoke:" + method.getName() + " - " + System.currentTimeMillis());
        return retObj;
    }
    // 返回目标对象的代理对象
    public Object newProxy(Object target) { 
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(target.getClass());
        enhancer.setCallback(this);
        enhancer.setClassLoader(target.getClass().getClassLoader());
        return enhancer.create();
    }
}

4.main代码

public class App { 
    public static void main(String[] args) { 
        // 要代理的真实对象
        Programmer programmer = new Programmer();
        // 生成MethodInterceptor对象
        CglibProxy proxy = new CglibProxy();
        // 根据真实对象生成代理对象
        Programmer proxyProgrammer = (Programmer) proxy.newProxy(programmer);
        System.out.println(proxyProgrammer.workAndGetReward() + " - " + System.currentTimeMillis());
    }
}

2.代码分析

cglib动态代理的核心是
Enhancer对象
我们可以通过以下步骤实现动态代理

创建Enhancer实例
通过setSuperclass方法来设置目标类
通过setCallback 方法来设置拦截对象
create方法生成Target的代理类，并返回代理类的相应代理对象实例

通过这个方法和三个参数我们得到传入类型的代理对象,然后在调用方法时,会经过我们自定义的代理方法增强了,如以下输出:

[main] INFO 反射.cglib动态代理.v1.Programmer - before invoke:workAndGetReward - 1554827985920
[main] INFO 反射.cglib动态代理.v1.Programmer - before invoke:reward - 1554827985929
[main] INFO 反射.cglib动态代理.v1.Programmer - after invoke:reward - 1554827985929
[main] INFO 反射.cglib动态代理.v1.Programmer - after invoke:workAndGetReward - 1554827985929
Programmer works hard under 996.
Then he goes icu. - 1554827985929

从控制台的输出可以看出来workAndGetReward()方法受到了动态代理的增强
在workAndGetReward()里调用的reward()方法也受到增强

3.代码修改一

cglib也可以不用实现接口来进行动态代理
修改后的真实对象类代码:

public class Programmer { 
    public String workAndGetReward() { 
        System.out.println("Programmer works hard under 996.");
        return reward();
    }
    public String reward() { 
        return "Then he goes icu.";
    }
}

输出:

[main] INFO 反射.cglib动态代理.v1.Programmer - before invoke:workAndGetReward - 1554828540025
[main] INFO 反射.cglib动态代理.v1.Programmer - before invoke:reward - 1554828540034
Programmer works hard under 996.
[main] INFO 反射.cglib动态代理.v1.Programmer - after invoke:reward - 1554828540034
[main] INFO 反射.cglib动态代理.v1.Programmer - after invoke:workAndGetReward - 1554828540034
Then he goes icu. - 1554828540034

可以看到输出顺序略有不同,猜测还会产生其他影响

4.代码修改二

如果我们把内部调用的方法改为final(private方法也会被隐形标记为final)
修改后的真实对象类代码:

public class Programmer { 
    public String workAndGetReward() { 
        System.out.println("Programmer works hard under 996.");
        return reward();
    }
    private String reward() { 
        return "Then he goes icu.";
    }
}

输出:

[main] INFO 反射.cglib动态代理.v1.Programmer - before invoke:workAndGetReward - 1554828701583
[main] INFO 反射.cglib动态代理.v1.Programmer - after invoke:workAndGetReward - 1554828701592
Programmer works hard under 996.
Then he goes icu. - 1554828701592