1、 Reflection

1. Get class object

2. Common methods of class

// 此段代码为公共代码
interface People {
    int parentAge = 18;
    public void sayHi(String name);
}
class PeopleImpl implements People {
    private String privSex = "男";
    public String race = "汉族";
    @Override
    public void sayHi(String name) {
        System.out.println("hello," + name);
    }
    private void prvSayHi() {
        System.out.println("prvSayHi~");
    }
    public static void getSex() {
        System.out.println("18岁");
    }
}

3.1 static method call

// 核心代码（省略了抛出异常的声明）
public static void main(String[] args) {
    Class myClass = Class.forName("example.PeopleImpl");
    // 调用静态（static）方法
    Method getSex = myClass.getmethod("getSex");
    getSex.invoke(myClass);
}

3.2 general method call

Class myClass = Class.forName("example.PeopleImpl");
Object object = myClass.newInstance();
Method method = myClass.getmethod("sayHi",String.class);
method.invoke(object,"老王");

3.3 calling private methods

Class myClass = Class.forName("example.PeopleImpl");
Object object = myClass.newInstance();
Method privSayHi = myClass.getDeclaredMethod("privSayHi");
privSayHi.setAccessible(true); // 修改访问限制
privSayHi.invoke(object);

4. Summary

2、 Dynamic agent

1. JDK proxy dynamic proxy

interface Animal {
    void eat();
}
class Dog implements Animal {
    @Override
    public void eat() {
        System.out.println("The dog is eating");
    }
}
class Cat implements Animal {
    @Override
    public void eat() {
        System.out.println("The cat is eating");
    }
}

// JDK 代理类
class AnimalProxy implements InvocationHandler {
    private Object target; // 代理对象
    public Object getInstance(Object target) {
        this.target = target;
        // 取得代理对象
        return Proxy.newProxyInstance(target.getClass().getClassLoader(),target.getClass().getInterfaces(),this);
    }
    @Override
    public Object invoke(Object proxy,Method method,Object[] args) throws Throwable {
        System.out.println("调用前");
        Object result = method.invoke(target,args); // 方法调用
        System.out.println("调用后");
        return result;
    }
}

public static void main(String[] args) {
    // JDK 动态代理调用
    AnimalProxy proxy = new AnimalProxy();
    Animal dogProxy = (Animal) proxy.getInstance(new Dog());
    dogProxy.eat();
}

@CallerSensitive
public static Object newProxyInstance(ClassLoader loader,Class<?>[] interfaces,InvocationHandler h)
    throws IllegalArgumentException
{
// 省略其他代码

* @param   loader the class loader to define the proxy class
* @param   interfaces the list of interfaces for the proxy class to implement

2. Cglib dynamic proxy

<dependency>
    <groupId>cglib</groupId>
    <artifactId>cglib</artifactId>
    <version>3.2.9</version>
</dependency>

class Panda {
    public void eat() {
        System.out.println("The panda is eating");
    }
}
class cglibProxy implements MethodInterceptor {
    private Object target; // 代理对象
    public Object getInstance(Object target) {
        this.target = target;
        Enhancer enhancer = new Enhancer();
        // 设置父类为实例类
        enhancer.setSuperclass(this.target.getClass());
        // 回调方法
        enhancer.setCallback(this);
        // 创建代理对象
        return enhancer.create();
    }
    @Override
    public Object intercept(Object o,Object[] objects,MethodProxy methodProxy) throws Throwable {
        System.out.println("调用前");
        Object result = methodProxy.invokeSuper(o,objects); // 执行方法调用
        System.out.println("调用后");
        return result;
    }
}

public static void main(String[] args) {
    // cglib 动态代理调用
    cglibProxy proxy = new cglibProxy();
    Panda panda = (Panda)proxy.getInstance(new Panda());
    panda.eat();
}

3、 JDK proxy vs cglib

4、 Reference documents