纯手写轻量级JDK动态代理

纯手写JDK动态代理

 

JDK动态代理原理分析

1. 在使用jdk动态代理的时候，必须要实现InvocationHandler接口，invoke方法

Invoke 方法中该三个参数分别表示为: 代理对象、被代理执行的方法、参数

 

 

1. 使用jdk动态代理获取代理类对象（JDK自动生成代理类） $Proxy0.class

 

纯手写动态代理原理分析

1. 创建代理类$Proxy0源代码文件实现被代理的接口。

public final class $Proxy0 extends java.lang.reflect.Proxy implements com.cx.service.OrderService {

 

1.  使用JavaCompiler技术编译该$Proxy0文件获取到$Proxy0.class
2.  使用ClassLoader将该$Proxy0.class加入到当前JVM内存中

 

 

ClassLoader 顾名思义就是类加载器,ClassLoader 作用：

负责将 Class 加载到 JVM 中

审查每个类由谁加载（父优先的等级加载机制）

将 Class 字节码重新解析成 JVM 统一要求的对象格式

 

Jdk动态代理的简单实现

 

public interface MyExtInvocationHandler {     /**      * 纯手写模拟 jdk动态模拟 InvocationHandler接口      *      * @param proxy      * @param method      * @param args      * @return      * @throws Throwable      */     public Object invoke(Object proxy, Method method, Object[] args) throws InvocationTargetException, IllegalAccessException; } public class ExtJdkInvocationHandler implements MyExtInvocationHandler {     /**      * 目标执行对象 (被代理的对象)      */     private Object target;     public ExtJdkInvocationHandler(Object target) {         this.target = target;     }     @Override     public Object invoke(Object proxy, Method method, Object[] args) throws InvocationTargetException, IllegalAccessException {         System.out.println("纯手写JDK动态代理日志拦截开始>>>>>");         Object result = method.invoke(target, args);// 执行代理对象的方法         System.out.println("纯手写JDK动态代理日志拦截结束>>>>>");         return result;     }     //    /** //     * 获取代理对象 //     * //     * @param //     * @return //     */     public <T> T getProxy() {         return (T) new $Proxy0(this);     } }   public class $Proxy0 implements OrderService {     private MyExtInvocationHandler h;     /**      * 使用构造函数传递myExtInvocationHandler      *      * @param myExtInvocationHandler      */     public $Proxy0(MyExtInvocationHandler myExtInvocationHandler) {         this.h = myExtInvocationHandler;     }     @Override     public void order() throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {         //传递被代理对象的方法         Method orderMethod = OrderService.class.getMethod("order", new Class[]{});         this.h.invoke(this, orderMethod, null);     } }   ExtJdkInvocationHandler extJdkInvocationHandler = new ExtJdkInvocationHandler(new OrderServiceImpl()); OrderService proxy = extJdkInvocationHandler.getProxy(); proxy.order();

 

完全逼真模拟Jdk动态代理

public interface MyExtInvocationHandler {     /**      * 纯手写模拟 jdk动态模拟 InvocationHandler接口      *      * @param proxy      * @param method      * @param args      * @return      * @throws Throwable      */     public Object invoke(Object proxy, Method method, Object[] args) throws InvocationTargetException, IllegalAccessException; }   public class JavaClassLoader extends ClassLoader {     private File classPathFile;     public JavaClassLoader(){ //        String classPath=JavaClassLoader.class.getResource("").getPath();         String classPath="D:\\code";         this.classPathFile=new File(classPath);     }     @Override     public Class findClass(String name) throws ClassNotFoundException {         String className= JavaClassLoader.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;                   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 {                   if(in!=null){                       try {                           in.close();                       } catch (IOException e) {                           e.printStackTrace();                       }                   }                   if(out!=null){                       try {                           out.close();                       } catch (IOException e) {                           e.printStackTrace();                       }                   }               }           }         }         return null;     } }   public class ExtJdkInvocationHandler implements MyExtInvocationHandler {     /**      * 目标执行对象 (被代理的对象)      */     private Object target;     public ExtJdkInvocationHandler(Object target) {         this.target = target;     }     @Override     public Object invoke(Object proxy, Method method, Object[] args) throws InvocationTargetException, IllegalAccessException {         System.out.println("纯手写JDK动态代理日志拦截开始>>>>>");         Object result = method.invoke(target, args);// 执行代理对象的方法         System.out.println("纯手写JDK动态代理日志拦截结束>>>>>");         return result;     }     //    /** //     * 获取代理对象 //     * //     * @param //     * @return //     */     public <T> T getProxy() {         return (T) MyProxy.newProxyInstance(new JavaClassLoader(), OrderService.class, this);     } }   public class MyProxy {     static String rt = "\r\t";     /**      * @param classInfo 被代理实现的接口信息      * @param h      * @return      */     public static Object newProxyInstance(JavaClassLoader javaClassLoader, Class classInfo, MyExtInvocationHandler h) {         try {             // 1.创建代理类java源码文件,写入到硬盘中..             Method[] methods = classInfo.getMethods();             String proxyClass = "package com.cx.ext.jdk.proxy;" + rt                     + "import java.lang.reflect.Method;" + rt                     + "import com.cx.ext.jdk.proxy.MyExtInvocationHandler;" + rt                     + "public class $Proxy0 implements " + classInfo.getName() + "{" + rt                     + "MyExtInvocationHandler h;" + rt                     + "public $Proxy0(MyExtInvocationHandler h)" + "{" + rt                     + "this.h= h;" + rt + "}"                     + getMethodString(methods, classInfo) + rt + "}";             // 2. 将代理类源码文件写入硬盘中             String filename = "d:/code/$Proxy0.java";             File f = new File(filename);             FileWriter fw = new FileWriter(f);             fw.write(proxyClass);             fw.flush();             fw.close();             // 3.使用JavaJavaCompiler 编译该$Proxy0源代码 获取class文件             JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();             StandardJavaFileManager fileMgr = compiler.getStandardFileManager(null, null, null);             Iterable units = fileMgr.getJavaFileObjects(filename);             JavaCompiler.CompilationTask t = compiler.getTask(null, fileMgr, null, null, null, units);             t.call();             fileMgr.close();             //4.使用classClassLoader 将$Proxy0.class读取到内存中...             Class proxy0Class = javaClassLoader.findClass("$Proxy0");             //5.使用java反射机制给函数中赋值             Constructor m = proxy0Class.getConstructor(MyExtInvocationHandler.class);             Object o = m.newInstance(h);             return o;         } catch (Exception e) {             e.printStackTrace();             ;         }         return null;     }     public static String getMethodString(Method[] methods, Class intf) {         String proxyMe = "";         for (Method method : methods) {             proxyMe += "public void " + method.getName() + "() throws Throwable {" + rt                     + "Method md= " + intf.getName() + ".class.getMethod(\"" + method.getName()                     + "\",new Class[]{});" + rt                     + "this.h.invoke(this,md,null);" + rt + "}" + rt;         }         return proxyMe;     } }

github地址：https://github.com/919337588/cxDynamicProxy