套接字InputStream出现故障，同时读取块中的字节

Question

我正在通过套接字连接编写简单的文件传输，在以字节为单位下载文件时遇到问题。 当我一次读取一个字节时，一切正常，但是当我尝试以512字节的块为单位进行读取时，在下载文件的所有字节后（由于头文件，我知道了长度）后，套接字开始接收一些随机字节最终导致崩溃，因为发现2x“％”，并且服务器开始尝试计算传入消息的长度时（没有开始时）。

 @Override
  public void run() {

      while (client.isConnected() && !client.isClosed() && !client.isInputShutdown()){
          try {
                readResponse();
                clientWriter.write("0%"); /// IF IT CATCHES EXCEPTION SOCKET CLOSED ON THE OTHER SIDE(DON'T KNOW HOW TO CHECK IT IN ANOTHER WAY)
           } 
          catch (IOException e) {
               System.out.println(e.toString());
               return;
           } 
          catch (InterruptedException e) {
               System.out.println(e.toString());
               return;
           } 
      }

   }

private void readResponse() throws IOException, InterruptedException {

       int length = 0;
       int ch;
       FileOutputStream file = new FileOutputStream("holder");
       boolean bWrite = false;
       StringBuilder name = new StringBuilder();
       int percentageCount = 0;
       String filename="";
       length = 0;
       int l = 0;
       int old = 0;
       while ((ch=client.getInputStream().read())!=-1){
           if (!bWrite) {
               name.append(Character.toChars(ch));
           }
           if (ch==37 && !bWrite){
               if (percentageCount<1){
                   percentageCount++;
               } else {
                filename = name.toString();
                length = Integer.parseInt(filename.substring(0,filename.indexOf("%")));
                l = length;
                filename = filename.substring(filename.indexOf("%")+1);
                filename = filename.substring(0,filename.indexOf("%"));
               file = new FileOutputStream(filename);
               bWrite = true;
               break;
               }
           }
       }
       byte[] bytes = new byte[512];
       while (length>=512){
           client.getInputStream().read(bytes, 0, 512);
           file.write(bytes, 0, 512);
           length-=512;
       }
       if (length>0){
           bytes = new byte[length];
           client.getInputStream().read(bytes,0,length);
           file.write(bytes,0,length);
           length = 0;
       }
       file.flush();
       file.close();
    }

Answer 1

可以将代码的最后一部分更改为（未测试）：

   byte[] bytes = new byte[512];
   InputStream is = client.getInputStream();
   while (length>0) {
       int read = is.read(bytes, 0, Math.min(bytes.length, length));
       if (read > 0) {
         file.write(bytes, 0, read);
         length-=read;
       }
       if (read < 0)
         throw new IOException("end reached before all data read"; 
   }

这样可以正确检查返回的大小，避免两个循环并检查流的结尾。

BTW2： getInputStream()是相当沉重的重量，它应该只进行一次（的is从我的例子应该在方法开始进行检索，尤其是读循环之前）。