代理模式的作用：AOP、拦截器、解耦 ...

1. 静态代理：

2. 动态代理:

3. 自己手写动态代理：

• 结构

  
  结构图

• 代理类Proxy

package xin.zero2one.proxy.myproxy;

import javax.tools.JavaCompiler;
import javax.tools.JavaFileObject;
import javax.tools.StandardJavaFileManager;
import javax.tools.ToolProvider;
import java.io.File;
import java.io.FileWriter;
import java.io.InputStream;
import java.lang.reflect.Constructor;
import java.lang.reflect.Method;

/**
 * Created by jundo on 2018/5/30.
 */
public class MyProxy {

    private final static String ln = "\r\n";

    public static Object newProxyInstance(MyClassLoader loader, Class<?>[] interfaces, MyInvocationHandler h){

        try {
            //生成$Proxy.java文件，只针对Car对象
            String src = generateSrc(interfaces);

            //将$Proxy.java保存到classpath
            String classpath = MyProxy.class.getResource("").getPath();
            File proxyFile = new File(classpath + "$Proxy0.java");
            FileWriter fw = new FileWriter(proxyFile);
            fw.write(src);
            fw.flush();
            fw.close();

            //编译$Proxy.java
            JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
            StandardJavaFileManager manager = compiler.getStandardFileManager(null, null, null);
            Iterable<? extends JavaFileObject> iterable = manager.getJavaFileObjects(proxyFile);
            JavaCompiler.CompilationTask task = compiler.getTask(null, manager, null, null, null, iterable);
            task.call();
            manager.close();

            //将$Proxy.java加载到内存中
            System.out.println("find class");
            Class<?> proxy0 = loader.findClass("$Proxy0");
            System.out.println("find ok");
            Constructor<?> constructor = proxy0.getConstructor(MyInvocationHandler.class);
            return constructor.newInstance(h);
        }catch (Exception e){
            e.printStackTrace();
        }
        return null;
    }

    private static String generateSrc(Class<?>[] interfaces){
        StringBuffer sb = new StringBuffer();
        sb.append("package xin.zero2one.proxy.myproxy;" + ln);
        sb.append("import xin.zero2one.bean.Car;" + ln);
        sb.append("import xin.zero2one.proxy.myproxy.MyInvocationHandler;" + ln);
        sb.append("import java.lang.reflect.Method;" + ln);
        sb.append("public class $Proxy0 implements " + interfaces[0].getName() + "{" + ln);
        sb.append("MyInvocationHandler h;" + ln);
        sb.append("public $Proxy0(MyInvocationHandler h) { " + ln);
        sb.append("this.h = h;");
        sb.append("}" + ln);
        for (Method m : interfaces[0].getMethods()){
            sb.append("public " + m.getReturnType().getName() + " " + m.getName() + "() {" + ln);
            sb.append("try{" + ln);
            sb.append("Method m = " + interfaces[0].getName() + ".class.getMethod(\"" + m.getName() + "\",new Class[]{});" + ln);
            sb.append("this.h.invoke(this,m,null);" + ln);
            sb.append("}catch(Throwable e){" + ln);
            sb.append("e.printStackTrace();" + ln);
            sb.append("}");
            sb.append("}");
        }
        sb.append("}" + ln);
        return sb.toString();
    }
}

• MyInvocationHandler

package xin.zero2one.proxy.myproxy;

import java.lang.reflect.Method;

/**
 * Created by jundo on 2018/5/30.
 */
public interface MyInvocationHandler {
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable;
}

• MyClassLoader

package xin.zero2one.proxy.myproxy;

import java.io.*;

/**
 * Created by jundo on 2018/5/30.
 */
public class MyClassLoader extends ClassLoader{

    @Override
    protected Class<?> findClass(String name) throws ClassNotFoundException {
        String classpath = MyClassLoader.class.getResource("").getPath();
        String className = MyClassLoader.class.getPackage().getName() + "." + name;
        String filePath = name.replaceAll("\\.", "/");
        File classFile = new File(classpath, filePath + ".class");
        if (classFile.exists()) {
            FileInputStream fis = null;
            ByteArrayOutputStream out = null;
            try {
                fis = new FileInputStream(classFile);
                out = new ByteArrayOutputStream();
                byte[] bytes = new byte[1024];
                int len;
                while ((len = fis.read(bytes)) != -1) {
                    out.write(bytes, 0, len);
                }
                return defineClass(className, out.toByteArray(), 0, out.size());
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                if (fis != null) {
                    try {
                        fis.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
                if (out != null) {
                    try {
                        out.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }

        }
        return null;
    }
}

• 被代理接口Car

package xin.zero2one.bean;

/**
 * Created by jundo on 2018/5/29.
 */
public interface Car {

    void getCar();
}

• Car实现类

package xin.zero2one.bean;

/**
 * Created by jundo on 2018/5/29.
 */
public class Tesla implements Car{
    @Override
    public void getCar() {
        System.out.println("get tesla");
    }
}

• Car代理类

package xin.zero2one.proxy;

import xin.zero2one.bean.Car;

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

/**
 * Created by jundo on 2018/5/29.
 */
public class CarProxy implements InvocationHandler{

    private Car car;

    public Object getInstance(Car car){
        this.car = car;
        Class<?> clazz = car.getClass();
        Class<?>[] interfaces = clazz.getInterfaces();
        Car obj = (Car) Proxy.newProxyInstance(clazz.getClassLoader(), interfaces, this);
        return obj;
    }


    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("找车子啦");
        System.out.println(method == null);
        method.invoke(this.car,args);
        System.out.println("就决定是你了");
        return null;
    }
}

• 测试类

package xin.zero2one.proxy.myproxy;

import xin.zero2one.bean.Car;
import xin.zero2one.bean.Tesla;

/**
 * Created by jundo on 2018/5/30.
 */
public class MyProxyTest {

    public static void main(String[] args) {
        MyCarProxy proxy = new MyCarProxy();
        Car car = (Car)proxy.getInstance(new Tesla());
        car.getCar();
    }
}