手写JAVA动态代理

╰半夏微凉° 2022-04-04 15:53 191阅读 0赞

代码目录：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dmbG92ZWphdmE_size_16_color_FFFFFF_t_70][]

具体类：

public interface UserDao {
    
        public void query(String s);
    }

public class UserDaoImpl implements UserDao{
    
        private UserDao userDao;
    
        public UserDaoImpl(){
    
        }
    
        public UserDaoImpl( UserDao userDao){
            this.userDao = userDao;
        }
    
        public void query(String s){
            System.out.println("query");
        }
    }

/**
     * @author wufei
     * @create 2018-12-17 15:51
     **/
    public class ProxyUtil
    {
        public static   Object newInstance(Class targetInfo) throws IOException, IllegalAccessException, InstantiationException, ClassNotFoundException {
            StringBuilder context  = new StringBuilder();
    
            String line = "\n";
            String tab = "";
            //包名
            String packageContext = "package com.wf.springdemo.proxy;"+line;
            //导入包名
            String importContext = "import "+targetInfo.getName()+";"+line;
    
            String targetNameInfo = targetInfo.getSimpleName();
            //代理类名
            String proxyClassName = "public class $Proxy implements "+targetNameInfo+"{"+line;
    
            String fieldContext = "private "+targetNameInfo+" target;"+line;
            //构造函数
            String constructorContext = "public  $Proxy  ("+targetNameInfo+" target){" +line+
                    "this.target = target; "+line+"}"+line;
    
            //方法
            String methodContext = "";
            Method[] methods = targetInfo.getDeclaredMethods();
            for (Method method : methods) {
                //方法返回值类型
                String methodReturnType = method.getReturnType().getName();
                //方法名
                String methodName = method.getName();
    
                //参数类型
                Class[] parameterTypes = method.getParameterTypes();
                String argsContext = "";
                //参数名称
                String parameterName="p";
                int p =1;
                for (Class parameterType : parameterTypes) {
                    //String p1, String p2
                    parameterName = parameterName+p;
                    argsContext=parameterType.getSimpleName()+" "+parameterName+"";
                    p++;
                }
                //取出逗号,
                System.out.println("argsContext = [" + argsContext + "]");
    
                String argsContext1 = "";
    //            if(argsContext.length()>0){
    //                argsContext1=   argsContext.substring(0,argsContext.lastIndexOf(",")-1);
    //            }
    
                methodContext +="public "+ methodReturnType+" "+methodName+"("+argsContext+"){"+line
                             +"System.out.println(\"query\");"+line  //业务逻辑比较复杂了 不处理了
                              +"target."+methodName+"("+parameterName+");"+line+"}"+line;
            }
    
    
            context.append(packageContext);
            context.append(importContext);
            context.append(proxyClassName);
            context.append(fieldContext);
            context.append(constructorContext);
            context.append(methodContext);
            context.append(line+"}");
            System.out.println("result: \n"+context.toString());
    
            //输出到磁盘，jdk是内存上
            File file = new File("D:\\test\\$Proxy.java");
            if(file.exists()){
                file.createNewFile();
            }
            FileWriter fileWriter = new FileWriter(file);
            fileWriter.write(context.toString());
            fileWriter.flush();
            fileWriter.close();
    
    
            JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
            StandardJavaFileManager standardJavaFileManager =  compiler.getStandardFileManager(null,null,null);
            Iterable units = standardJavaFileManager.getJavaFileObjects(file);
            JavaCompiler.CompilationTask t = compiler.getTask(null,standardJavaFileManager,null,null,null,units);
            t.call();
            standardJavaFileManager.close();
    
            URL[] urls = new URL[]{new URL("file:d\\\\")};
    
            URLClassLoader urlClassLoader = new URLClassLoader(urls);
            Class aClass = urlClassLoader.loadClass("com.wf.springdemo.proxy.$Proxy");
            return    aClass.newInstance();
        }
    
    }

public class Main {
        public static void main(String[] args) {
            try {
                UserDao userDao = null;
                try {
                    userDao = (UserDao) ProxyUtil.newInstance(UserDao.class);
                    userDao.query("ok");
    
                } catch (IllegalAccessException e) {
                    e.printStackTrace();
                } catch (InstantiationException e) {
                    e.printStackTrace();
                } catch (ClassNotFoundException e) {
                    e.printStackTrace();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
    
        }
    }

生成的代理类：

package com.wf.springdemo.proxy;
    import com.wf.springdemo.proxy.UserDao;
    public class $Proxy implements UserDao{
    private UserDao target;
    public  $Proxy  (UserDao target){
    this.target = target; 
    }
    public void query(String p1){
    System.out.println("query");
    target.query(p1);
    }
    
    }

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