深入理解java虚拟机（14）：手写动态生成一个代理类

通过java动态生成一个代理类的代码如下

package aop.proxyutil;

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;
import java.lang.reflect.Parameter;
import java.net.URL;
import java.net.URLClassLoader;

/**
 * @author: yangchun
 * @description:
 * @date: Created in 2019-09-24 16:09
 */
public class ProxyUtil {
    /**
     * .java
     * .class
     * .new
     * @return
     */
    public static Object newInstance(Class targeInf, CustomInvocationHandler h) throws NoSuchMethodException{
        Object proxy=null;
        String infName = targeInf.getSimpleName();
        String line ="\n";
        String tab = "\t";
        Method[] methods=targeInf.getMethods();
        String content ="";
        String packageContent = "package aop.proxyutil;"+line;
        String importContent = "import "+targeInf.getName()+";"+line
                +"import java.lang.reflect.Method;"+line
                +"import java.lang.reflect.Parameter;"+line;
        String clazzFirstLineContent = "public class $Proxy implements " +infName +" {"+line;
        String fieldContent = tab+"private CustomInvocationHandler h;"+line;
        String constructContent = tab+"public $Proxy(CustomInvocationHandler h){"+line
                +tab+tab+"this.h = h;"+line+
                tab+"}"+line;
        String methodContent ="";
        for(Method method:methods){
            String returnType=method.getReturnType().getSimpleName();
            String methodName = method.getName();
            Class<?>[] paramsTypes= method.getParameterTypes();
            Class[] args = method.getParameterTypes();
            String argsContent ="";
            String paramContent ="";
            String param ="";
            int flag =0;
            for(Class arg:args){
                String temp =  arg.getSimpleName();
                argsContent += temp +" p"+ flag+",";
                paramContent += arg.getTypeName()+".class,";
                param +="p"+flag+",";
                flag++;
            }
            if(argsContent.length()>0){
                argsContent = argsContent.substring(0,argsContent.lastIndexOf(","));
                paramContent = paramContent.substring(0,paramContent.lastIndexOf(","));
                param = param.substring(0,param.lastIndexOf(","));
            }
            methodContent+=tab+"public "+returnType+" "+methodName+"("+argsContent+"){"+line+
                    tab+tab+"try{"+line+
                    tab+tab+tab+"Method method = Class.forName(\""+targeInf.getName()+"\").getDeclaredMethod(\""+methodName+"\","+paramContent+");"+line;
                    //tab+tab+tab+"Parameter[] parameters=method.getParameters();"+line;
            if(returnType.equals("void")){
                methodContent +=tab+tab+tab+"h.invoke(method,"+param+");"+line+
                        tab+tab+"}"+"catch(Exception e){"+line+
                 tab+tab+tab+"e.printStackTrace();"+line+
                 tab+tab+"}"+line+
                 tab+"}";
            }else {
                methodContent +=tab+tab+"return h.invoke(method,parameters);"+line+
                        tab+"}"+line;
            }
        }
        content = packageContent+importContent+clazzFirstLineContent+fieldContent+constructContent+methodContent+line+"}";
        File file = new File("e:/backup/chubao/chubao/java/src/aop/proxyutil/$Proxy.java");
        try {
            if(!file.exists()){
                file.createNewFile();
            }
            FileWriter fw = new FileWriter(file);
            fw.write(content);
            fw.flush();
            fw.close();
            JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
            StandardJavaFileManager fileManager = compiler.getStandardFileManager(null,null,null);
            Iterable units = fileManager.getJavaFileObjects(file);
            JavaCompiler.CompilationTask t = compiler.getTask(null,fileManager,null,null,null,units);
            t.call();
            fileManager.close();
            URL[] urls = new URL[]{new URL("file:E:/backup/chubao/chubao/java/src/")};
            URLClassLoader urlClassLoader = new URLClassLoader(urls);
            Class clazz = urlClassLoader.loadClass("aop.proxyutil.$Proxy");
            Constructor constructor = clazz.getConstructor(CustomInvocationHandler.class);
            proxy = constructor.newInstance(h);

        }catch (Exception e){
            e.printStackTrace();
        }
        return  proxy;
    }
}
测试代码如下

package aop.proxy;

import aop.proxyutil.ProxyUtil;
import aop.proxyutil.TestCustomInvocationHandler;

/**
 * @author: yangchun
 * @description:
 * @date: Created in 2019-09-24 13:25
 */
public class Test {
    public static void main(String[] args)throws Exception{
        UserDaoImpl userDao = new UserDaoLogImpl();
       // userDao.query();
       UserDaoImpl  $proxy =(UserDaoImpl) ProxyUtil.newInstance(UserDaoImpl.class,new TestCustomInvocationHandler(userDao));
//        UserDaoImpl  $proxy =new $Proxy(new TestCustomInvocationHandler(userDao));
        $proxy.query(1);
    }
}