Java学习路线-32：ClassLoader类加载器反射与代理设计模式

JVM -> ClassLoader -> CLASSPATH -> .class

Bootstrap 系统类加载器
PlatformClassLoader 平台类加载器
AppClassLoader 应用程序加载器
自定义类加载器（磁盘、网络）

public class Person {
    public void sayHello(){
        System.out.println("hello");
    }
}

import java.io.*;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
class MyClassLoader extends ClassLoader {
    private static final String PERSON_CLASS_PATH = "/demo" + File.separator + "Person.class";
    public Class<?> loadMyClass(String className) throws IOException {
        byte[] data = this.loadClassData();
        if (data != null) {
            return super.defineClass(className, data, 0, data.length);
        }
        return null;
    }
    public byte[] loadClassData() throws IOException {
        InputStream input = null;
        ByteArrayOutputStream bos = new ByteArrayOutputStream(); // 将数据加载到内存
        byte[] data = null;
        byte[] temp = new byte[1024];
        int len = 0;
        try {
            input = new FileInputStream(PERSON_CLASS_PATH);
            while ((len = input.read(temp)) != -1) {
                bos.write(temp, 0, len);
            }
            // 读取所有的字节
            data = bos.toByteArray();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (input != null) {
                input.close();
            }
            if (bos != null) {
                bos.close();
            }
        }
        return data;
    }
}
class Demo {
    public static void main(String[] args) throws Exception{
        MyClassLoader loader = new MyClassLoader();
        Class<?> cls = loader.loadMyClass("Person");
        Object obj = cls.getDeclaredConstructor().newInstance();
        Method method = cls.getDeclaredMethod("sayHello");
        method.invoke(obj);
        // hello
    }
}

// 接口标准
interface IMessage {
    void send();
}
// 业务实现类
class MessageImpl implements IMessage {
    @Override
    public void send() {
        System.out.println("发送");
    }
}
// 代理类
class MessageProxy implements IMessage {
    private IMessage message;
    public MessageProxy(IMessage message) {
        this.message = message;
    }
    @Override
    public void send() {
        if (this.isConnect()) {
            this.message.send();
        }
    }
    public void close() {
    }
    public boolean isConnect() {
        return true;
    }
}
class Demo {
    public static void main(String[] args) {
        IMessage message = new MessageProxy(new MessageImpl());
        message.send();
    }
}

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
// 接口标准
interface IMessage {
    void send();
}
// 业务实现类
class MessageImpl implements IMessage {
    @Override
    public void send() {
        System.out.println("发送");
    }
}
// 动态代理类
class MyProxy implements InvocationHandler{
    private Object target; // 保存真实业务对象
    // 真实业务对象与代理业务对象之间的绑定
    public Object bind(Object target){
        this.target = target;
        Class cls = target.getClass();
        return Proxy.newProxyInstance(cls.getClassLoader(), cls.getInterfaces(), this);
    }
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        Object obj = null;
        if (this.isConnect()) {
            obj = method.invoke(this.target, args);
            this.close();
        }
        return obj;
    }
    public void close() {
    }
    public boolean isConnect() {
        return true;
    }
}
class Demo {
    public static void main(String[] args) {
        IMessage message =(IMessage)new MyProxy().bind(new MessageImpl());
        message.send();
    }
}

pom.xml 引入
<dependencies>
    <dependency>
        <groupId>cglib</groupId>
        <artifactId>cglib</artifactId>
        <version>2.2.2</version>
    </dependency>
</dependencies>

import net.sf.cglib.proxy.Enhancer;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;
import java.lang.reflect.Method;
// 业务实现类
class Message {
    public void send() {
        System.out.println("发送");
    }
}
// 动态代理类
class MyProxy implements MethodInterceptor {
    private Object target; // 保存真实业务对象
    // 真实业务对象与代理业务对象之间的绑定
    public MyProxy(Object target) {
        this.target = target;
    }
    @Override
    public Object intercept(Object o, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
        Object obj = null;
        if (this.isConnect()) {
            obj = method.invoke(this.target, args);
            this.close();
        }
        return obj;
    }
    public void close() {
    }
    public boolean isConnect() {
        return true;
    }
}
class Demo {
    public static void main(String[] args) {
        Message message = new Message(); // 真实主体
        Enhancer enhancer = new Enhancer(); // 负责代理操作的程序类
        enhancer.setSuperclass(message.getClass()); // 假定一个父类
        enhancer.setCallback(new MyProxy(message));
        Message proxyMessage = (Message) enhancer.create();
        proxyMessage.send();
    }
}