Spring杂谈 | 自己动手模拟JDK动态代理

public interface MyService {
 void test01();
 void test02(String s);
}

public class MyServiceImpl implements MyService {

 @Override
 public void test01() {
  System.out.println("test01");
 }

 @Override
 public void test02(String s) {
  System.out.println(s);
 }
}

public class Main {
 public static void main(String[] args) {
  MyServiceImpl target = new MyServiceImpl();
    }
}

package com.dmz.proxy;

import com.dmz.proxy.target.MyService;

/**
 * 静态代理
 */
public class StaticProxy implements MyService {

 private MyService target;

 public StaticProxy(MyService target) {
 this.target = target;
 }

 @Override
 public void test01() {
  System.out.println("proxy print log for test01");
  target.test01();
 }

 @Override
 public void test02(String s) {
  System.out.println("proxy print log for test02");
  target.test02(s);
 }
}

public class ProxyUtil {
 /**
  * @param target 目标对象
  * @return 代理对象
  */
 public static Object newInstance(Object target) {
  Object proxy = null;
        // 开始拼接字符串
  Class targetInf = target.getClass().getInterfaces()[0];
  Method[] methods = targetInf.getDeclaredMethods();
  String line = System.lineSeparator();
  String tab = "\t";
  String infName = targetInf.getSimpleName();
  String content = "";
  String packageContent = "package com.dmz.proxy;" + line;
  String importContent = "import " + targetInf.getName() + ";" + line;
  String clazzFirstLineContent = "public class $Proxy implements " + infName + "{" + line;
  String filedContent = tab + "private " + infName + " target;" + line;
  String constructorContent = tab + "public $Proxy (" + infName + " target){" + line
    + tab + tab + "this.target =target;"
    + line + tab + "}" + line;
  String methodContent = "";
  for (Method method : methods) {
   String returnTypeName = method.getReturnType().getSimpleName();
   String methodName = method.getName();
   // Sting.class String.class
   Class args[] = method.getParameterTypes();
   String argsContent = "";
   String paramsContent = "";
   int flag = 0;
   for (Class arg : args) {
    String temp = arg.getSimpleName();
    //String
    //String p0,Sting p1,
    argsContent += temp + " p" + flag + ",";
    paramsContent += "p" + flag + ",";
    flag++;
   }
   if (argsContent.length() > 0) {
    argsContent = argsContent.substring(0, argsContent.lastIndexOf(",") - 1);
    paramsContent = paramsContent.substring(0, paramsContent.lastIndexOf(",") - 1);
   }

   methodContent += tab + "public " + returnTypeName + " " + methodName + "(" + argsContent + ") {" + line
     + tab + tab + "System.out.println(\"proxy print log for " + methodName + "\");" + line
     + tab + tab + "target." + methodName + "(" + paramsContent + ");" + line
     + tab + "}" + line;

  }

  content = packageContent + importContent + clazzFirstLineContent + filedContent + constructorContent + methodContent + "}";
  //字符串拼接结束
        
        
        // 开始生成.java文件
  File file = new File("g:\\com\\dmz\\proxy\\$Proxy.java");
  try {
   if (!file.exists()) {
    file.createNewFile();
   }
   FileWriter fw = new FileWriter(file);
   fw.write(content);
   fw.flush();
   fw.close();
  // .java文件生成结束
                     
            
        // 开始进行编译   
   JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();

   StandardJavaFileManager fileMgr = compiler.getStandardFileManager(null, null, null);
   Iterable units = fileMgr.getJavaFileObjects(file);

   JavaCompiler.CompilationTask t = compiler.getTask(null, fileMgr, null, null, null, units);
   t.call();
   fileMgr.close();
  // 编译结束，生成.class文件
            
   // 从G盘中加载class文件
   URL[] urls = new URL[]{new URL("file:G:\\\\")};
   URLClassLoader urlClassLoader = new URLClassLoader(urls);
   // 加载
   Class clazz = urlClassLoader.loadClass("com.dmz.proxy.$Proxy");
            // 加载结束
            
            // 构造代理对象
   Constructor constructor = clazz.getConstructor(targetInf);
   proxy = constructor.newInstance(target);

  } catch (Exception e) {
   e.printStackTrace();
  }
  return proxy;
 }
}

public class Main {
 public static void main(String[] args) {
        MyServiceImpl target = new MyServiceImpl();
        MyService o = ((MyService) ProxyUtil.newInstance(target));
        o.test01();
        o.test02("test02");
    }
}