从套接字通道读取字符串

Posted 2023-03-14

【中文标题】从套接字通道读取字符串

【英文标题】：Read string from socket channel

【发布时间】：2015-03-07 18:08:08

【问题描述】：

喂，

我有以下代码：

    public AppThread(SocketChannel socketChannel)
    this.socketChannel=socketChannel;
  

      public void run()
            try
              ByteBuffer bb = ByteBuffer.allocate(11);    
              socketChannel.read(bb);
              //byte[] b = new byte[bb.capacity()];
             // bb.get(b, 0, 11);
              System.out.println(bb.toString());
              byte[] a = new byte[11];
              CharBuffer cb = bb.asCharBuffer();
              System.out.println(cb);
              bb.get(a);

              App app=new App();
             // String an = new String(b);
              //String zodie = Zodie.getZodie(an);
              //b = new byte[zodie.length()];
              //b = zodie.getBytes();
              bb.clear();
              //bb.put(b);
              socketChannel.write(bb);
              socketChannel.close(); 
            
            catch(IOException e)
               System.err.println("Server comunication error : "+e.getMessage());
              
          

还有接收字符串并返回字符串的zodie静态方法。

如何将字符串写入 SocketChannel 以将其作为参数传递给 zodiac 静态方法。

我提到在客户端我发送了一个字节数组，我已经检查过了，没关系。

客户端：

  byte[] a = an.getBytes();
        System.out.println(new String(a));
    ByteBuffer bb=ByteBuffer.allocate(11);
    // Varianta 1
    bb.put(a);
    // Varianta 2
    // LongBuffer lb=bb.asLongBuffer();
    // lb.put(0,m).put(1,n);
    try
      sc.write(bb);
      bb.clear();
      sc.read(bb);
      // Varianta 1
      //a = new byte[bb.remaining()];
      zodie=bb.toString();
      // Varianta 2
      // r=lb.get(0);
      System.out.println("Zodia : "+ zodie);
      sc.close();

此致，

我收到服务器错误：

Server ready... 
    java.nio.HeapByteBuffer[pos=1 lim=11 cap=11]

    Exception in thread "pool-1-thread-1" java.nio.BufferUnderflowException
        at java.nio.HeapByteBuffer.get(Unknown Source)
        at java.nio.ByteBuffer.get(Unknown Source)
        at server.AppThread.run(AppThread.java:27)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)

【参考方案1】：

你的问题在 bb.get(a);

您将 11 个字符的数组指定为参数，因此 get() 方法期望 bb 包含 11 个字符，但它只包含 1 个。

原因是当您向套接字写入 11 个字符时，它们不能保证一次全部到达。他们可以分成小组到达，例如 1 和 10 或 5 和 6 等。

您需要查看和读取套接字并检查 read() 调用的结果。类似的东西：

for (;;) 
   int numberOfBytesRead =socket.read(buf);
   if (numberOfBytesRead < 0)  break; 

【讨论】：

我为 (;;) System.out.println("xxx @@@ "); 插入了以下行int numberOfBytesRead =socketChannel.read(bb); System.out.println(numberOfBytesRead); if (numberOfBytesRead

我的错。客户端关闭连接时返回 -1。它可能会返回零，但您需要使用阻塞。更多信息：docs.oracle.com/javase/7/docs/api/java/nio/channels/…

【参考方案2】：

问题出在客户端。我使用了一个字符缓冲区作为包装器

Scanner scanner=new Scanner(System.in);
String m;
System.out.println("Enter the date (yyyy-mm-dd) :");
m=scanner.next()+" ";

CharBuffer  c = CharBuffer.wrap(m);
System.out.println("Sending date ...: " + c);
ByteBuffer b = Charset.forName("ISO-8859-1").encode(c);
 b.compact();
System.out.println("Bytebuffer has the capacity of "+ 
b.capacity() + "pointer position on bytebuffer is on: "+ b.position() + " and the limit is:" + b.limit());
b.flip();

在服务器端：

CharBuffer  c;
    ByteBuffer bb = ByteBuffer.allocate(11);    
     System.out.println("Server allocated a number of 11 octets to ByteBuffer");

    socketChannel.read(bb);
    bb.flip();//sets the Position to 0 and limit to the number of bytes to be read.
    CharBuffer c = Charset.forName("ISO-8859-1").decode(bb);
           System.out.println("Got " + c);

    byte[] byteArray = new byte[11];
    bb.get(byteArray);
    System.out.println("Server got from client the string: " +new String(byteArray));
    String an = new String(byteArray);
     bb.clear();