不能直接用   File file = new File("http://127.0.0.1:8080/aa.txt") 来读取，因为网络上的传输协议为HTTP,与
        本地不同，要用URL来读取

       String output="";
        File file = new File("E://bb.txt");     

        URL MyURL = new URL("http://127.0.0.1:8080/aa.txt");
        URLConnection uc=MyURL.openConnection();
        uc.connect();

        InputStreamReader _Input=new InputStreamReader(uc.getInputStream(),"UTF-8");
        BufferedReader br=new BufferedReader(_Input);

        String s="";
        while((s=br.readLine())!=null){
        output+=s;
        }

        FileWriter fw=new FileWriter(file);
        fw.write(output);
        fw.flush();
        fw.close();