纯手写JDK动态代理【深入了解Proxy类底层实现】

一、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

public class JdkInvocationHandler implements InvocationHandler { /** * 被代理对象，目标对象 */ private Object target; public JdkInvocationHandler(Object target){ this.target = target; } /** * * @param proxy 代理类对象 * @param method 被代理执行的方法 * @param args 目标方法参数 * @return 防止执行的返回值 * @throws Throwable */ public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { System.out.println("日志收集开始。。。"); Object result = method.invoke(target, args); System.out.println("日志收集结束。。。"); return result; } /** * 生成代理类对象 * @param <T> * @return */ public <T> T getProxy(){ return (T) Proxy.newProxyInstance(target.getClass().getClassLoader(),target.getClass().getInterfaces() , this); } }

2、使用jdk动态代理获取代理类对象（JDK自动生成代理类） $Proxy0.class，使用反编译工具

二、纯手写JDK动态代理原理分析

创建代理类$Proxy0源代码文件实现被代理的接口。 public final class $Proxy0 extends java.lang.reflect.Proxy implements com.xwhy.service.OrderService { 使用JavaCompiler技术编译该$Proxy0文件获取到$Proxy0.class使用ClassLoader将该$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

三、纯手写JDK动态代理V1.0

1.自定义MyExtJdkInvocationHandler接口 ——相当于InvocationHandler

public interface MyExtJdkInvocationHandler { /** * * @param proxy 代理类 * @param method 被代理执行的方法 * @param args 参数 * @return * @throws Throwable */ Object invoke(Object proxy, Method method,Object[] args) throws Throwable; }

2.写一个MyJdkInvocationHandler实现MyJdkInvocationHandler接口

public class MyJdkInvocationHandler implements MyExtJdkInvocationHandler { private Object target; public MyJdkInvocationHandler(Object target){ this.target = target; } public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { System.out.println("纯手写jdk动态代理开始。。。"); Object result = method.invoke(target,args); System.out.println("纯手写jdk动态代理开始。。。"); return result; } }

service层

public interface OrderService { void order() throws Throwable; } public class OrderServiceImpl implements OrderService { public void order() { System.out.println("执行订单操作。。。"); } }

3.对比反编译$Proxy0.class来写$Proxy0

public class $Proxy0 implements OrderService { private MyExtJdkInvocationHandler handler; public $Proxy0(MyExtJdkInvocationHandler handler){ this.handler = handler; } public void order() throws Throwable { Method orderMethod = OrderService.class.getMethod("order", new Class[]{}); this.handler.invoke(this, orderMethod, null); } }

4、测试

public class TestClient { public static void main(String[] args) throws Throwable { $Proxy0 proxy = new $Proxy0(new MyJdkInvocationHandler(new OrderServiceImpl())); proxy.order(); } }

5、打印结果

纯手写jdk动态代理开始。。。 执行订单操作。。。 纯手写jdk动态代理开始。。。

四、纯手写JDK动态代理V2.0

我们只需要将V1.0中的$Proxy0类变成动态生成就可以了。

1.看Proxy怎么实现的newProxyInstance

2.实现自己的MyProxy

package com.xwhy; import com.xwhy.ext.proxy.JavaClassLoader; import com.xwhy.ext.proxy.MyExtJdkInvocationHandler; import com.xwhy.service.OrderService; import javax.tools.JavaCompiler; import javax.tools.StandardJavaFileManager; import javax.tools.ToolProvider; import java.io.File; import java.io.FileWriter; import java.lang.reflect.Constructor; import java.lang.reflect.Method; /** * @description: ${description} * @author: Mark * @create: 2019-05-26 16:02:40 **/ public class MyProxy { private static String rt = "\r\t"; public static Object newProxyInstance(JavaClassLoader javaClassLoader, Class<?> classInfo, MyExtJdkInvocationHandler h) { try { //1、拼接代理类源代码 Method[] methods = classInfo.getMethods(); String proxyClass = "package com.xwhy.ext.proxy;" + rt + "import java.lang.reflect.Method;" + rt + "import com.xwhy.ext.proxy.MyExtJdkInvocationHandler;" + rt + "public class $Proxy0 implements " + classInfo.getName() + "{" + rt + "MyExtJdkInvocationHandler h;" + rt + "public $Proxy0(MyExtJdkInvocationHandler h)" + "{" + rt + "this.h= h;" + rt + "}" + getMethodString(methods, classInfo) + rt + "}"; // 2. 写入到到本地文件中.. String filename = "/Users/mark/$Proxy0.java"; File f = new File(filename); FileWriter fw = new FileWriter(f); fw.write(proxyClass); fw.flush(); fw.close(); // 3. 将源代码编译成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ClassLoader加载到内存 Class<?> $Proxy0 = javaClassLoader.findClass("$Proxy0"); // 5.执行初始化又参构造函数 Constructor<?> constructor = $Proxy0.getConstructor(MyExtJdkInvocationHandler.class); Object o = constructor.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; } public static void main(String[] args) { newProxyInstance(null, OrderService.class, null); } }

3.实现自己的ClassLoader

package com.xwhy.ext.proxy; import java.io.ByteArrayOutputStream; import java.io.File; import java.io.FileInputStream; import java.io.IOException; public class JavaClassLoader extends ClassLoader { private File classPathFile; public JavaClassLoader(){ // String classPath=JavaClassLoader.class.getResource("").getPath(); String classPath="/Users/mark"; 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; } }

4.测试

public class TestClient { public static void main(String[] args) throws Throwable { OrderService orderService = (OrderService) MyProxy.newProxyInstance(new JavaClassLoader(),OrderService.class, new MyJdkInvocationHandler(new OrderServiceImpl())); orderService.order(); } }

生成的$Proxy0.class文件如下： 运行时生成的$Proxy0.java文件如下：

package com.xwhy; import java.lang.reflect.Method; import com.xwhy.ext.proxy.MyExtJdkInvocationHandler; public class $Proxy0 implements com.xwhy.service.OrderService { MyExtJdkInvocationHandler h; public $Proxy0(MyExtJdkInvocationHandler h) { this.h = h; } public void order() throws Throwable { Method md = com.xwhy.service.OrderService.class.getMethod("order", new Class[]{}); this.h.invoke(this, md, null); } }

5.运行结果

纯手写jdk动态代理开始。。。 执行订单操作。。。 纯手写jdk动态代理开始。。。

五、JDK动态代理Proxy.newProxyInstance源码分析

public class Proxy implements java.io.Serializable { //【3】缓存，这里有个ProxyClassFactory，代理类工厂初始化 private static final WeakCache<ClassLoader, Class<?>[], Class<?>> proxyClassCache = new WeakCache<>(new KeyFactory(), new ProxyClassFactory()); private static final class ProxyClassFactory implements BiFunction<ClassLoader, Class<?>[], Class<?>> { // prefix for all proxy class names private static final String proxyClassNamePrefix = "$Proxy"; // next number to use for generation of unique proxy class names private static final AtomicLong nextUniqueNumber = new AtomicLong(); //【4】将源代码编译成class文件，帮助我们初始化，创建class文件 @Override public Class<?> apply(ClassLoader loader, Class<?>[] interfaces) { Map<Class<?>, Boolean> interfaceSet = new IdentityHashMap<>(interfaces.length); for (Class<?> intf : interfaces) { /* * Verify that the class loader resolves the name of this * interface to the same Class object. */ Class<?> interfaceClass = null; try { interfaceClass = Class.forName(intf.getName(), false, loader); } catch (ClassNotFoundException e) { } if (interfaceClass != intf) { throw new IllegalArgumentException( intf + " is not visible from class loader"); } /* * Verify that the Class object actually represents an * interface. */ if (!interfaceClass.isInterface()) { throw new IllegalArgumentException( interfaceClass.getName() + " is not an interface"); } /* * Verify that this interface is not a duplicate. */ if (interfaceSet.put(interfaceClass, Boolean.TRUE) != null) { throw new IllegalArgumentException( "repeated interface: " + interfaceClass.getName()); } } //代理类的包名，可以自定义 String proxyPkg = null; // package to define proxy class in int accessFlags = Modifier.PUBLIC | Modifier.FINAL; /* * Record the package of a non-public proxy interface so that the * proxy class will be defined in the same package. Verify that * all non-public proxy interfaces are in the same package. */ for (Class<?> intf : interfaces) { int flags = intf.getModifiers(); if (!Modifier.isPublic(flags)) { accessFlags = Modifier.FINAL; String name = intf.getName(); int n = name.lastIndexOf('.'); String pkg = ((n == -1) ? "" : name.substring(0, n + 1)); if (proxyPkg == null) { proxyPkg = pkg; } else if (!pkg.equals(proxyPkg)) { throw new IllegalArgumentException( "non-public interfaces from different packages"); } } } if (proxyPkg == null) { // if no non-public proxy interfaces, use com.sun.proxy package proxyPkg = ReflectUtil.PROXY_PACKAGE + "."; } /* * Choose a name for the proxy class to generate. */ //使用原子类自增保证代理类的名称自增的线程安全问题 long num = nextUniqueNumber.getAndIncrement(); String proxyName = proxyPkg + proxyClassNamePrefix + num; /* * Generate the specified proxy class. */ //将代理类的原代理生成字节码文件 byte[] proxyClassFile = ProxyGenerator.generateProxyClass( proxyName, interfaces, accessFlags); try { //【5】使用ClassLoader将代理类的class文件加载到内存中 return defineClass0(loader, proxyName, proxyClassFile, 0, proxyClassFile.length); } catch (ClassFormatError e) { /* * A ClassFormatError here means that (barring bugs in the * proxy class generation code) there was some other * invalid aspect of the arguments supplied to the proxy * class creation (such as virtual machine limitations * exceeded). */ throw new IllegalArgumentException(e.toString()); } } } /** * Generate a proxy class. Must call the checkProxyAccess method * to perform permission checks before calling this. */ private static Class<?> getProxyClass0(ClassLoader loader, Class<?>... interfaces) { if (interfaces.length > 65535) { throw new IllegalArgumentException("interface limit exceeded"); } //【2】获取代理类，写入到本地文件 return proxyClassCache.get(loader, interfaces); } public static Object newProxyInstance(ClassLoader loader, Class<?>[] interfaces, InvocationHandler h) { ... //【1】创建代理类java源代码，写入到硬盘 Class<?> cl = getProxyClass0(loader, intfs); ... } }