从套接字通道读取字符串

Question

Hy,

I have the following code:

    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());
            }  
          }
}

and the zodie static method which receive a string and return a string.

How can I get the string written into SocketChannel to pass it as argument to zodiac static method.

I mention that in the client side I send an array of bytes and I have checked and it's ok.

Client side:

  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();

Sincerely,

I get the server error:

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)

Answer 1

The issue was on the client side. I have used a charbuffer as a wraper

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();

On the server side:

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();

Answer 2

You problem is in line bb.get(a);

You specify 11 characters array as a parameter and thus method get() expects bb to contain 11 characters but it only contains 1.

The reason is that when you write 11 characters to the socket they are not guaranteed to arrive all at once. They can arrive in small groups like 1 and than 10 or 5 and 6 etc.

You need to look and read from socket and check result of read() call. Something along the lines:

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