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
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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
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使用jdk动态代理获取代理类对象（JDK自动生成代理类） $Proxy0.class
纯手写动态代理原理分析
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创建代理类$Proxy0源代码文件实现被代理的接口。 public final class $Proxy0 extends java.lang.reflect.Proxy implements com.cx.service.OrderService {
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使用JavaCompiler技术编译该$Proxy0文件获取到$Proxy0.class
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使用ClassLoader将该$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 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 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 <br>
* @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;
}
}
csdn地址：https://blog.csdn.net/qq_28056571/article/details/90452643