整个过程中用到了手写类加载器，
手写动态生成java代码
手写编译代码
最后实现动态代理

手写Proxy示例代码：

package com.example.demo.proxy.custom;import javax.tools.JavaCompiler;
import javax.tools.JavaFileObject;
import javax.tools.StandardJavaFileManager;
import javax.tools.ToolProvider;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Parameter;public class GPProxy {public static final String ln = "\r\n";public static Object newProxyInstance(GPClassLoader classLoader,Class<?>[] interfaces,GPInvocationHandler h){//生成java代码String s = generateSrc(interfaces);//将代码写入到本地String path = GPProxy.class.getResource("").getPath();System.out.println(path);File file = new File(path + "$Proxy0.java");FileOutputStream fileOutputStream = null;try {fileOutputStream = new FileOutputStream(file);fileOutputStream.write(s.getBytes());fileOutputStream.close();} catch (FileNotFoundException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();}finally {if(fileOutputStream != null){try {fileOutputStream.close();} catch (IOException e) {e.printStackTrace();}}}//编译代码JavaCompiler javaCompiler = ToolProvider.getSystemJavaCompiler();StandardJavaFileManager manager = javaCompiler.getStandardFileManager(null, null, null);Iterable<? extends JavaFileObject> javaFileObjects = manager.getJavaFileObjects(file);JavaCompiler.CompilationTask task = javaCompiler.getTask(null, manager, null, null, null, javaFileObjects);task.call();try {manager.close();} catch (IOException e) {e.printStackTrace();}//删除.java文件file.delete();//将代码读取到jvm，并生成对应的类Object o = null;try {Class<?> clazz = classLoader.findClass("$Proxy0");Constructor<?> constructor = clazz.getConstructor(GPInvocationHandler.class);o = constructor.newInstance(h);} catch (ClassNotFoundException | NoSuchMethodException e) {e.printStackTrace();} catch (IllegalAccessException e) {e.printStackTrace();} catch (InstantiationException e) {e.printStackTrace();} catch (InvocationTargetException e) {e.printStackTrace();}//返回字节码重组以后的新的代理对象return o;}private static String generateSrc(Class<?>[] interfaces ) {StringBuffer sb = new StringBuffer();sb.append(GPProxy.class.getPackage() + ";" + ln);sb.append("import " + interfaces[0].getPackage().toString().substring(8) + "." + interfaces[0].getSimpleName() +";" + ln);sb.append("import java.lang.reflect.*;" + ln);sb.append("public class $Proxy0 implements " + interfaces[0].getSimpleName() + "{" + ln);sb.append("GPInvocationHandler h;" + ln);//初始化GPInvocationHandlersb.append("public $Proxy0(GPInvocationHandler h){" + ln);sb.append("this.h = h;" + ln);sb.append("}" + ln);//循环调用方法for (Method m : interfaces[0].getMethods()) {sb.append("public final " + 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("}" + ln);sb.append("}" + ln);}sb.append("}" + ln);return sb.toString();}
}

手写ClassLoader示例代码：

package com.example.demo.proxy.custom;import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;public class GPClassLoader extends ClassLoader{private File classPathFile;public GPClassLoader(){String classPath = GPClassLoader.class.getResource("").getPath();this.classPathFile = new File(classPath);}@Overrideprotected Class<?> findClass(String name) throws ClassNotFoundException {String className = GPClassLoader.class.getPackage().getName() + "." + name;if(classPathFile != null){File classFile = new File(classPathFile, name.replaceAll("\\.", "/") + ".class");if(classFile.exists()){FileInputStream in = null;ByteArrayOutputStream out = null;try{in = new FileInputStream(classFile);out = new ByteArrayOutputStream();byte[] buff = new byte[1024];int len = 0;while ((len = in.read(buff)) != -1){out.write(buff,0,len);}return defineClass(className,out.toByteArray(),0,out.size());}catch (Exception e){e.printStackTrace();}finally {try {if(in != null)in.close();} catch (IOException e) {e.printStackTrace();}try {if(out != null)out.close();} catch (IOException e) {e.printStackTrace();}}}}return null;}
}

手写InvocationHandler

package com.example.demo.proxy.custom;import java.lang.reflect.Method;@FunctionalInterface
public interface GPInvocationHandler {public Object invoke(Object proxy, Method method, Object[] args);
}

动态代理类的示例代码：

package com.example.demo.proxy.custom;import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;public class GPMeipo implements GPInvocationHandler{Object object;public Object getInstance(Object object){this.object = object;Object o = GPProxy.newProxyInstance(new GPClassLoader(), object.getClass().getInterfaces(), this);return o;}@Overridepublic Object invoke(Object proxy, Method method, Object[] args) {System.out.println("媒婆拿到需求");System.out.println("媒婆匹配姑娘！");Object invoke = null;try {invoke = method.invoke(object, args);} catch (IllegalAccessException e) {e.printStackTrace();} catch (InvocationTargetException e) {e.printStackTrace();}System.out.println("媒婆安排婚事");return invoke;}
}

测试接口的代码:

package com.example.demo.proxy;public interface Person {void findLove();void zufangzi();
}

测试被代理类的代码：

package com.example.demo.proxy;public class ZH implements Person {@Overridepublic void findLove() {System.out.println("肤白貌美大长腿！");}@Overridepublic void zufangzi() {}
}

测试手写代理类：

package com.example.demo.proxy.custom;import com.example.demo.proxy.Person;
import com.example.demo.proxy.ZH;public class CustomProxyTest {public static void main(String[] args) {Person zh = (Person) new GPMeipo().getInstance(new ZH());zh.findLove();}
}