Java NIO - UDP packets
I'm curious as to the rationale behind having a DatagramPacket class and just using ByteBuffers for TCP connections. I can see the logic, but I'm trying to write a Java framework wrapping NIO with TCP and UDP connections. In my C++ version I have one packet class that I use for both types of connections. I'm stuck with what to implement for Java as I'm going to need two classes, NIO's DatagramPacket and a new TCPPacket. Ideally I would like both to implement an interface or derive from a parent class so I can pass them to all class methods that deal with packets, be they UDP or TCP based. But this won't work. I could wrap DatagramPacket into a new class, and have it and the TCPPacket class implement a Packet interface. But when I'm sending UDP packets I'll be creating two objects for the price of one.
Any suggestions?
Thanks
Remember that in UDP case you can easily lose packets and never know. In TCP you would receive an exception, but UDP can silently discard your packages while in transit.
My point is, you probably should use a different package class for UDP anyway, maybe adding some stuff like a package ID that would enable re-sending and additional processing in order to ensure a successful communication.
If you already have this information and some procedures for retrying in your package, then I agree with the previous poster in that you can use bytebuffer for both.
Similar Messages
-
Sending udp packets using java and receiving it using c
hi,
Is it possible to send udp packets using java and receive the same using c??????? if yes.... plz help immediately.The biggest issue is data format. The JVM is big endian, with 16-bit characters. The machine running 'C' could be almost anything. A (signed!) byte array is probably the easiest unit of exchange.
The Java program has its own techniques for storing/retrieving data to/from the byte array - and the C program has its own techniques. ASCII Strings are often the easiest to exchange - just convert the java String objects to byte array and send them.
apaliwal1 has already given the UDP calls to send/receive the data. -
Hi,
I'm in a case where I have to send an empty UDP packet.
When i send datas i use: DatagramChannel.send(...)
This method is supposed to return the number of bytes sent (0 or the size of the buffer).
However when I'm sending an empty buffer, In case of both success or failure, the returned value is 0.
I can capture my empty packet, no problem, but if my socket output buffer is full, how do I know if I sent my empty datagram package or not ?
Thanks in advance.DrClap wrote:
I don't see the problem. In one case the server received a packet, but there wasn't anything in it. In the other case the server didn't receive a packet. In both cases the server received nothing, so there is no difference between the two cases.I'm talking about UDP, not TCP, so at receiver side there is a difference between receiving an empty packet and receiving no packet at all. However, the receiver is able to receive an empty packet so there is no problem.
ejp wrote:
I can capture my empty packet, no problem, but if my socket output buffer is full, how do I know if I sent my empty datagram package or not ?You don't.The problem is in fact at the sender side. And that answer is what i was afraid of ;-)
The probability of this happening is quite thin, however in any NIO Reactor you're supposed to handle the case where you could not send the datas and send them later again.
I wonder if this problem could be considered as a lack/bug of the nio classes. -
Socket seems too slow...maybe java.nio?
Hello
In our system I have to receive Multicast Packets repeats very quick(1-5 ms). I have to link them one after an other in the order they sent. And if I miss a packet, something will go wrong...
I have to listen to different IPs and I use different threads for different IPs. If I use only one thread (and listens to only one IP) everything seems ok.
But if I starts listening to an other ip too, I miss 2 packets in a row, or only one if I turn off parsing the message (XML).
Here is the code I use in the Threads:
try{
socket = new MulticastSocket(port);
socket.setSoTimeout(1000);
inetAddress = InetAddress.getByName(ip);
NetworkInterface nInterface=
NetworkInterface.getByName(networkInterface);
if(nInterface!=null)socket.setNetworkInterface(nInterface);
socket.joinGroup(inetAddress);
catch(IOException ioe){
logger.error(ioe.getMessage(), ioe);
return;
try{
while (!interrupted()) {
try{
byte[] buffer = new byte[1480];
packet = new DatagramPacket(buffer, buffer.length);
socket.receive(packet);
parse(buffer);
}catch(SocketTimeoutException stoe){
// DO NOTHING
}catch(IOException ioe){
logger.error(ioe.getMessage(), ioe);
}finally{
try {
if(socket!=null){
socket.leaveGroup(inetAddress);
} catch (IOException ioe) {}
Every Thread has its own parsing object.
Any tips, what is wrong?
Maybe java.nio could solve the problem somehow. There is a sample server in [Java Home]/sample/nio/server and it suggest that there are quicker methods to receive messages from different IPs (maybe Blocking/Pooled-Thread Server). But I can't understand the API and the Sample while I was reading it (20-30 minutes).
Could it be quicker? Does it worth toying with the idea?
Thanks:
BenceIn our system I have to receive Multicast Packets
repeats very quick(1-5 ms). I have to link them one
after an other in the order they sent. And if I miss
a packet, something will go wrong...There is no guarantee anywhere in the system that you won't miss a datagram. UDP doesn't make such guarantees. If you need all the packets you will have to build ACK or NACK into your protocol.
You can alleviate the problem by running a very large socket receive buffer. But you can't eliminate it. Rethink this.
NIO is not significantly quicker for applications like this, it is more scalable. -
Hello,
Ive been looking for implementation of nio udp sockets with selectors all over the internet but i didnt get much. Does anyone here know of any websites with simple examples on nio udp sockets with selectors? (server + client),
thanks.
PaulJGroups supports UDP but only old IO.
However Grizzly Messaging uses NIO UDP. [https://grizzly.dev.java.net/nonav/xref/index.html] e.g. [https://grizzly.dev.java.net/nonav/xref/com/sun/grizzly/UDPConnectorHandler.html]
I would be interested if you get UDP working over the internet. I would have thought the packet loss rate would be too high and too unpredictable to make it worth using (compared with TCP). So if you can prove me wrong please let me know! -
JMF How to stream rtp from udp packet
I implemented an rtsp client and use the client to setup two rtp session(audio, vedio). But when I use the example pramgram "AVReceive3" to stream the udp packet, it doesn't work.
When the AVReceive3 receive the udp packet from the rtp port, it will call the update(ReceiveStreamEvent evt) function, and the event type is StreamMappedEvent, and the call to evt.getReceiveStream().getDataSource() return null.
I thought the first event should be NewReceiveStreamEvent. Please help to solve the problem.
What's rtp packet will cause the event StreamMappedEvent.
Following is the code of AVReceive3.java:
* AVReceive3.java
* Created on 2007年10月30日, 下午4:11
* To change this template, choose Tools | Template Manager
* and open the template in the editor.
package PlayerTest;
import java.io.*;
import java.awt.*;
import java.net.*;
import java.awt.event.*;
import java.util.Vector;
import javax.media.*;
import javax.media.rtp.*;
import javax.media.rtp.event.*;
import javax.media.rtp.rtcp.*;
import javax.media.protocol.*;
import javax.media.protocol.DataSource;
import javax.media.format.AudioFormat;
import javax.media.format.VideoFormat;
import javax.media.Format;
import javax.media.format.FormatChangeEvent;
import javax.media.control.BufferControl;
* AVReceive3 to receive RTP transmission using the RTPConnector.
public class AVReceive3 extends Thread implements ReceiveStreamListener, SessionListener,
ControllerListener
String sessions[] = null;
RTPManager mgrs[] = null;
Vector playerWindows = null;
boolean dataReceived = false;
Object dataSync = new Object();
public AVReceive3(String sessions[])
this.sessions = sessions;
public void run()
initialize();
public boolean initialize() {
try {
mgrs = new RTPManager[sessions.length];
playerWindows = new Vector();
SessionLabel session;
// Open the RTP sessions.
for (int i = 0; i < sessions.length; i++) {
// Parse the session addresses.
try {
session = new SessionLabel(sessions);
} catch (IllegalArgumentException e) {
System.err.println("Failed to parse the session address given: " + sessions[i]);
return false;
System.err.println(" - Open RTP session for: addr: " + session.addr + " port: " + session.port + " ttl: " + session.ttl);
mgrs[i] = (RTPManager) RTPManager.newInstance();
mgrs[i].addSessionListener(this);
mgrs[i].addReceiveStreamListener(this);
// Initialize the RTPManager with the RTPSocketAdapter
mgrs[i].initialize(new RTPSocketAdapter(
InetAddress.getByName(session.addr),
session.port, session.ttl));
// You can try out some other buffer size to see
// if you can get better smoothness.
BufferControl bc = (BufferControl)mgrs[i].getControl("javax.media.control.BufferControl");
if (bc != null)
bc.setBufferLength(350);
} catch (Exception e){
System.err.println("Cannot create the RTP Session: " + e.getMessage());
return false;
// Wait for data to arrive before moving on.
long then = System.currentTimeMillis();
long waitingPeriod = 30000; // wait for a maximum of 30 secs.
try{
synchronized (dataSync) {
while (!dataReceived &&
System.currentTimeMillis() - then < waitingPeriod) {
if (!dataReceived)
System.err.println(" - Waiting for RTP data to arrive");
dataSync.wait(1000);
} catch (Exception e) {}
if (!dataReceived) {
System.err.println("No RTP data was received.");
close();
return false;
return true;
public boolean isDone() {
return playerWindows.size() == 0;
* Close the players and the session managers.
protected void close() {
for (int i = 0; i < playerWindows.size(); i++) {
try {
((PlayerWindow)playerWindows.elementAt(i)).close();
} catch (Exception e) {}
playerWindows.removeAllElements();
// close the RTP session.
for (int i = 0; i < mgrs.length; i++) {
if (mgrs[i] != null) {
mgrs[i].removeTargets( "Closing session from AVReceive3");
mgrs[i].dispose();
mgrs[i] = null;
PlayerWindow find(Player p) {
for (int i = 0; i < playerWindows.size(); i++) {
PlayerWindow pw = (PlayerWindow)playerWindows.elementAt(i);
if (pw.player == p)
return pw;
return null;
PlayerWindow find(ReceiveStream strm) {
for (int i = 0; i < playerWindows.size(); i++) {
PlayerWindow pw = (PlayerWindow)playerWindows.elementAt(i);
if (pw.stream == strm)
return pw;
return null;
* SessionListener.
public synchronized void update(SessionEvent evt) {
if (evt instanceof NewParticipantEvent) {
Participant p = ((NewParticipantEvent)evt).getParticipant();
System.err.println(" - A new participant had just joined: " + p.getCNAME());
* ReceiveStreamListener
public synchronized void update( ReceiveStreamEvent evt) {
System.out.println("\nReceive an receiveStreamEvent:"+evt.toString());
RTPManager mgr = (RTPManager)evt.getSource();
Participant participant = evt.getParticipant(); // could be null.
ReceiveStream stream = evt.getReceiveStream(); // could be null.
System.out.println("The RTPManager is:");
if (evt instanceof RemotePayloadChangeEvent) {
System.err.println(" - Received an RTP PayloadChangeEvent.");
System.err.println("Sorry, cannot handle payload change.");
System.exit(0);
else if (evt instanceof NewReceiveStreamEvent) {
try {
stream = ((NewReceiveStreamEvent)evt).getReceiveStream();
DataSource ds = stream.getDataSource();
// Find out the formats.
RTPControl ctl = (RTPControl)ds.getControl("javax.media.rtp.RTPControl");
if (ctl != null){
System.err.println(" - Recevied new RTP stream: " + ctl.getFormat());
} else
System.err.println(" - Recevied new RTP stream");
if (participant == null)
System.err.println(" The sender of this stream had yet to be identified.");
else {
System.err.println(" The stream comes from: " + participant.getCNAME());
// create a player by passing datasource to the Media Manager
Player p = javax.media.Manager.createPlayer(ds);
if (p == null)
return;
p.addControllerListener(this);
p.realize();
PlayerWindow pw = new PlayerWindow(p, stream);
playerWindows.addElement(pw);
pw.setVisible(true);
// Notify intialize() that a new stream had arrived.
synchronized (dataSync) {
dataReceived = true;
dataSync.notifyAll();
} catch (Exception e) {
System.err.println("NewReceiveStreamEvent exception " + e.getMessage());
return;
else if (evt instanceof StreamMappedEvent) {
if (stream != null)
if(stream.getDataSource()!=null)
DataSource ds = stream.getDataSource();
// Find out the formats.
RTPControl ctl = (RTPControl)ds.getControl("javax.media.rtp.RTPControl");
System.err.println(" - The previously unidentified stream ");
if (ctl != null)
System.err.println(" " + ctl.getFormat());
System.err.println(" had now been identified as sent by: " + participant.getCNAME());
else if (evt instanceof ByeEvent) {
System.err.println(" - Got \"bye\" from: " + participant.getCNAME());
PlayerWindow pw = find(stream);
if (pw != null) {
pw.close();
playerWindows.removeElement(pw);
* ControllerListener for the Players.
public synchronized void controllerUpdate(ControllerEvent ce) {
Player p = (Player)ce.getSourceController();
if (p == null)
return;
// Get this when the internal players are realized.
if (ce instanceof RealizeCompleteEvent) {
PlayerWindow pw = find(p);
if (pw == null) {
// Some strange happened.
System.err.println("Internal error!");
System.exit(-1);
pw.initialize();
pw.setVisible(true);
p.start();
if (ce instanceof ControllerErrorEvent) {
p.removeControllerListener(this);
PlayerWindow pw = find(p);
if (pw != null) {
pw.close();
playerWindows.removeElement(pw);
System.err.println("AVReceive3 internal error: " + ce);
* A utility class to parse the session addresses.
class SessionLabel {
public String addr = null;
public int port;
public int ttl = 1;
SessionLabel(String session) throws IllegalArgumentException {
int off;
String portStr = null, ttlStr = null;
if (session != null && session.length() > 0) {
while (session.length() > 1 && session.charAt(0) == '/')
session = session.substring(1);
// Now see if there's a addr specified.
off = session.indexOf('/');
if (off == -1) {
if (!session.equals(""))
addr = session;
} else {
addr = session.substring(0, off);
session = session.substring(off + 1);
// Now see if there's a port specified
off = session.indexOf('/');
if (off == -1) {
if (!session.equals(""))
portStr = session;
} else {
portStr = session.substring(0, off);
session = session.substring(off + 1);
// Now see if there's a ttl specified
off = session.indexOf('/');
if (off == -1) {
if (!session.equals(""))
ttlStr = session;
} else {
ttlStr = session.substring(0, off);
if (addr == null)
throw new IllegalArgumentException();
if (portStr != null) {
try {
Integer integer = Integer.valueOf(portStr);
if (integer != null)
port = integer.intValue();
} catch (Throwable t) {
throw new IllegalArgumentException();
} else
throw new IllegalArgumentException();
if (ttlStr != null) {
try {
Integer integer = Integer.valueOf(ttlStr);
if (integer != null)
ttl = integer.intValue();
} catch (Throwable t) {
throw new IllegalArgumentException();
* GUI classes for the Player.
class PlayerWindow extends Frame {
Player player;
ReceiveStream stream;
PlayerWindow(Player p, ReceiveStream strm) {
player = p;
stream = strm;
public void initialize() {
add(new PlayerPanel(player));
public void close() {
player.close();
setVisible(false);
dispose();
public void addNotify() {
super.addNotify();
pack();
* GUI classes for the Player.
class PlayerPanel extends Panel {
Component vc, cc;
PlayerPanel(Player p) {
setLayout(new BorderLayout());
if ((vc = p.getVisualComponent()) != null)
add("Center", vc);
if ((cc = p.getControlPanelComponent()) != null)
add("South", cc);
public Dimension getPreferredSize() {
int w = 0, h = 0;
if (vc != null) {
Dimension size = vc.getPreferredSize();
w = size.width;
h = size.height;
if (cc != null) {
Dimension size = cc.getPreferredSize();
if (w == 0)
w = size.width;
h += size.height;
if (w < 160)
w = 160;
return new Dimension(w, h);
public static void main(String argv[]) {
//if (argv.length == 0)
// prUsage();
String sessions[]= new String[] {"127.0.0.1/6670","127.0.0.1/6672"};
AVReceive3 avReceive = new AVReceive3(sessions);
if (!avReceive.initialize()) {
System.err.println("Failed to initialize the sessions.");
System.exit(-1);
// Check to see if AVReceive3 is done.
try {
while (!avReceive.isDone())
Thread.sleep(1000);
} catch (Exception e) {}
System.err.println("Exiting AVReceive3");
static void prUsage() {
System.err.println("Usage: AVReceive3 <session> <session> ");
System.err.println(" <session>: <address>/<port>/<ttl>");
System.exit(0);
}// end of AVReceive3
Following is the code of RTPSocketAdapter.java:
* RTPSocketAdapter.java
* Created on 2007年10月30日, 下午4:13
* To change this template, choose Tools | Template Manager
* and open the template in the editor.
package PlayerTest;
import java.io.IOException;
import java.net.InetAddress;
import java.net.DatagramSocket;
import java.net.MulticastSocket;
import java.net.DatagramPacket;
import java.net.SocketException;
import javax.media.protocol.DataSource;
import javax.media.protocol.PushSourceStream;
import javax.media.protocol.ContentDescriptor;
import javax.media.protocol.SourceTransferHandler;
import javax.media.rtp.RTPConnector;
import javax.media.rtp.OutputDataStream;
* An implementation of RTPConnector based on UDP sockets.
public class RTPSocketAdapter implements RTPConnector {
DatagramSocket dataSock;
DatagramSocket ctrlSock;
InetAddress addr;
int port;
SockInputStream dataInStrm = null;
SockInputStream ctrlInStrm = null;
SockOutputStream dataOutStrm = null;
SockOutputStream ctrlOutStrm = null;
public RTPSocketAdapter(InetAddress addr, int port) throws IOException {
this(addr, port, 1);
public RTPSocketAdapter(InetAddress addr, int port, int ttl) throws IOException {
try {
if (addr.isMulticastAddress()) {
dataSock = new MulticastSocket(port);
ctrlSock = new MulticastSocket(port+1);
((MulticastSocket)dataSock).joinGroup(addr);
((MulticastSocket)dataSock).setTimeToLive(ttl);
((MulticastSocket)ctrlSock).joinGroup(addr);
((MulticastSocket)ctrlSock).setTimeToLive(ttl);
} else {
dataSock = new DatagramSocket(port, InetAddress.getLocalHost());
ctrlSock = new DatagramSocket(port+1, InetAddress.getLocalHost());
} catch (SocketException e) {
throw new IOException(e.getMessage());
this.addr = addr;
this.port = port;
* Returns an input stream to receive the RTP data.
public PushSourceStream getDataInputStream() throws IOException {
if (dataInStrm == null) {
dataInStrm = new SockInputStream(dataSock, addr, port);
dataInStrm.start();
return dataInStrm;
* Returns an output stream to send the RTP data.
public OutputDataStream getDataOutputStream() throws IOException {
if (dataOutStrm == null)
dataOutStrm = new SockOutputStream(dataSock, addr, port);
return dataOutStrm;
* Returns an input stream to receive the RTCP data.
public PushSourceStream getControlInputStream() throws IOException {
if (ctrlInStrm == null) {
ctrlInStrm = new SockInputStream(ctrlSock, addr, port+1);
ctrlInStrm.start();
return ctrlInStrm;
* Returns an output stream to send the RTCP data.
public OutputDataStream getControlOutputStream() throws IOException {
if (ctrlOutStrm == null)
ctrlOutStrm = new SockOutputStream(ctrlSock, addr, port+1);
return ctrlOutStrm;
* Close all the RTP, RTCP streams.
public void close() {
if (dataInStrm != null)
dataInStrm.kill();
if (ctrlInStrm != null)
ctrlInStrm.kill();
dataSock.close();
ctrlSock.close();
* Set the receive buffer size of the RTP data channel.
* This is only a hint to the implementation. The actual implementation
* may not be able to do anything to this.
public void setReceiveBufferSize( int size) throws IOException {
dataSock.setReceiveBufferSize(size);
* Get the receive buffer size set on the RTP data channel.
* Return -1 if the receive buffer size is not applicable for
* the implementation.
public int getReceiveBufferSize() {
try {
return dataSock.getReceiveBufferSize();
} catch (Exception e) {
return -1;
* Set the send buffer size of the RTP data channel.
* This is only a hint to the implementation. The actual implementation
* may not be able to do anything to this.
public void setSendBufferSize( int size) throws IOException {
dataSock.setSendBufferSize(size);
* Get the send buffer size set on the RTP data channel.
* Return -1 if the send buffer size is not applicable for
* the implementation.
public int getSendBufferSize() {
try {
return dataSock.getSendBufferSize();
} catch (Exception e) {
return -1;
* Return the RTCP bandwidth fraction. This value is used to
* initialize the RTPManager. Check RTPManager for more detauls.
* Return -1 to use the default values.
public double getRTCPBandwidthFraction() {
return -1;
* Return the RTCP sender bandwidth fraction. This value is used to
* initialize the RTPManager. Check RTPManager for more detauls.
* Return -1 to use the default values.
public double getRTCPSenderBandwidthFraction() {
return -1;
* An inner class to implement an OutputDataStream based on UDP sockets.
class SockOutputStream implements OutputDataStream {
DatagramSocket sock;
InetAddress addr;
int port;
public SockOutputStream(DatagramSocket sock, InetAddress addr, int port) {
this.sock = sock;
this.addr = addr;
this.port = port;
public int write(byte data[], int offset, int len) {
try {
sock.send(new DatagramPacket(data, offset, len, addr, port));
} catch (Exception e) {
return -1;
return len;
* An inner class to implement an PushSourceStream based on UDP sockets.
class SockInputStream extends Thread implements PushSourceStream {
DatagramSocket sock;
InetAddress addr;
int port;
boolean done = false;
boolean dataRead = false;
SourceTransferHandler sth = null;
public SockInputStream(DatagramSocket sock, InetAddress addr, int port) {
this.sock = sock;
this.addr = addr;
this.port = port;
public int read(byte buffer[], int offset, int length) {
DatagramPacket p = new DatagramPacket(buffer, offset, length, addr, port);
try {
sock.receive(p);
} catch (IOException e) {
return -1;
synchronized (this) {
dataRead = true;
notify();
System.out.println("RTPSocketAdapter receive RTP packet from port:"+port);
System.out.println("The received RTP packet:"+new String(buffer));
return p.getLength();
public synchronized void start() {
super.start();
if (sth != null) {
dataRead = true;
notify();
public synchronized void kill() {
done = true;
notify();
public int getMinimumTransferSize() {
return 2 * 1024; // twice the MTU size, just to be safe.
public synchronized void setTransferHandler(SourceTransferHandler sth) {
this.sth = sth;
dataRead = true;
notify();
// Not applicable.
public ContentDescriptor getContentDescriptor() {
return null;
// Not applicable.
public long getContentLength() {
return LENGTH_UNKNOWN;
// Not applicable.
public boolean endOfStream() {
return false;
// Not applicable.
public Object[] getControls() {
return new Object[0];
// Not applicable.
public Object getControl(String type) {
return null;
* Loop and notify the transfer handler of new data.
public void run() {
while (!done) {
synchronized (this) {
while (!dataRead && !done) {
try {
wait();
} catch (InterruptedException e) { }
dataRead = false;
if (sth != null && !done) {
sth.transferData(this);
Thanks.The error of No format has been registered for RTP Payload type 96
is caused by the dynamic payload mapping, when I add the dynamic mapping between dynamic payload and format. The Player cann't work yet. I think it because JMF doesn't support the format of my clips. For example:
video: a=rtpmap:96 H263-2000/90000
audio:a=rtpmap:97 MP4A-LATM/12000/1
Is there some available plugin to support these format?
Thanks -
Now i'm doing socket programming using UDP and TCP/IP and now again i
need your help.
1. Can UDP packet in Java put into data structure like C? or packet map to a java object but sender is not using Java program or serialize object.
2. What is the easiest way to extract the UDP packet in Java?
assume the structure like this.
sampleMessageHeader
MessageCode UInt 16
TimeStamp UInt 32
Message Char(12)1. Serialisation - no problem. However, if the other end doesn't have a Java serialisation library (i.e. isn't using Java) then you'll have to serialise manually. (Well - it may be possible to find documentation on the serialisation format and strip the headers before you put the bytes into a UDP packet, but such a mechanism would be a mess and a headache).
2. packet.getData() gives you a byte[]. Wrap a ByteArrayInputStream round it, and a DataInputStream around that. Then assuming appropriate byte-ordering you'll be able to read ints and shorts. Of course, Java doesn't have a UInt type, and the meaning of Char depends on your C header files. -
Not receiving UDP packet with Windows
Using a Windows 2000 Professional system I send a UDP packet (DatagramSocket()/DatagramPacket()) to a server, which returns a UDP packet on the same socket. Simple textbook stuff! The Java application works fine on a Linux machine, but catches an SocketException with "socket closed" message from the receive() method when run on a Windows 2000 machine. What gives? I have disabled the security checks and still can't get the packet. Any suggestions? (other than ditch Windows)
I got the same problem. I ran the identical program on WinXP and no exception! What's the cause for this? How to avoid it?
Thanks, -
Java.nio select() method return 0 in my client application
Hello,
I'm developing a simple chat application who echo messages
But my client application loop because the select() method return 0
This is my code
// SERVER
package test;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.Iterator;
import java.util.Set;
public class Server {
private int port = 5001;
public void work() {
try {
ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
serverSocketChannel.configureBlocking(false);
InetSocketAddress isa = new InetSocketAddress(port);
serverSocketChannel.socket().bind(isa);
Selector selector = Selector.open();
serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
System.out.println("Listing on "+port);
while(selector.select()>0) {
Set keys = selector.selectedKeys();
for(Iterator i = keys.iterator(); i.hasNext();) {
SelectionKey key = (SelectionKey) i.next();
i.remove();
if (key.isAcceptable()) {
ServerSocketChannel keyChannel = (ServerSocketChannel)key.channel();
SocketChannel channel = keyChannel.accept();
channel.configureBlocking(false);
channel.register(selector, SelectionKey.OP_READ );
} else if (key.isReadable()) {
SocketChannel keyChannel = (SocketChannel) key.channel();
String m = Help.read(keyChannel );
Help.write(m.toUpperCase(), keyChannel );
} catch (IOException e) {
e.printStackTrace();
public static void main(String[] args) {
Server s = new Server();
s.work();
// CLIENT
package test;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;
import java.util.Iterator;
import java.util.Set;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
public class Client extends JFrame {
private String host = "localhost";
private int port = 5001;
private SocketChannel socketChannel;
private Selector selector;
public void work() {
try {
socketChannel = SocketChannel.open();
socketChannel.configureBlocking(false);
InetSocketAddress isa = new InetSocketAddress(host, port);
socketChannel.connect(isa);
selector = Selector.open();
socketChannel.register(selector, SelectionKey.OP_CONNECT | SelectionKey.OP_READ );
while(true) {
selector.select();
Set keys = selector.selectedKeys();
for(Iterator i = keys.iterator(); i.hasNext();) {
SelectionKey key = (SelectionKey) i.next();
i.remove();
if (key.isConnectable()) {
SocketChannel keyChannel = (SocketChannel) key.channel();
if (keyChannel.isConnectionPending()) {
System.out.println("Connected "+keyChannel.finishConnect());
} else if (key.isReadable()) {
SocketChannel keyChannel = (SocketChannel) key.channel();
String m = Help.read(keyChannel);
display(m);
} catch (IOException e) {
e.printStackTrace();
private void display(final String m) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
area.append(m+"\n");
textFieed.setText("");
private void sendMessage(final String m) {
Thread t = new Thread(new Runnable() {
public void run() {
try {
Help.write(m, socketChannel);
} catch (IOException e) {
e.printStackTrace();
t.start();
public Client() {
addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(1);
textFieed.addKeyListener(new KeyAdapter() {
public void keyPressed(KeyEvent e) {
if (e.getKeyCode()== KeyEvent.VK_ENTER) {
String m = textFieed.getText();
sendMessage(m);
area.setEditable(false);
getContentPane().add(textFieed, "North");
getContentPane().add(new JScrollPane(area));
setBounds(200, 200, 400, 300);
show();
private String messageToSend;
private JTextArea area = new JTextArea();
JTextField textFieed = new JTextField();
public static void main(String[] args) {
Client s = new Client();
s.work();
// HELPER CLASS
package test;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.channels.SocketChannel;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CharsetEncoder;
public class Help {
private static Charset charset = Charset.forName("us-ascii");
private static CharsetEncoder enc = charset.newEncoder();
private static CharsetDecoder dec = charset.newDecoder();
private static void log(String m) {
System.out.println(m);
public static String read(SocketChannel channel) throws IOException {
log("*** start READ");
int n;
ByteBuffer buffer = ByteBuffer.allocate(1024);
while((n = channel.read(buffer)) > 0) {
System.out.println(" adding "+n+" bytes");
log(" BUFFER REMPLI : "+buffer);
buffer.flip();
CharBuffer cb = dec.decode(buffer);
log(" CHARBUFFER : "+cb);
String m = cb.toString();
log(" MESSAGE : "+m);
log("*** end READ");
//buffer.clear();
return m;
public static void write(String m, SocketChannel channel) throws IOException {
log("xxx start WRITE");
CharBuffer cb = CharBuffer.wrap(m);
log(" CHARBUFFER : "+cb);
ByteBuffer buffer = enc.encode(cb);
log(" BUFFER ALLOUE REMPLI : "+buffer);
int n;
while(buffer.hasRemaining()) {
n = channel.write(buffer);
System.out.println(" REMAINING : "+buffer.hasRemaining());
log("xxx end WRITE");Here's the fix for that old problem. Change the work method to do the following
- don't register interest in things that can't happen
- when you connect register based on whether the connection is complete or pending.
- add the OP_READ interest once the connection is complete.
This doesn't fix all the other problems this code will have,
eg.
- what happens if a write is incomplete?
- why does my code loop if I add OP_WRITE interest?
- why does my interestOps or register method block?
For code that answers all those questions see my obese post Taming the NIO Circus
Here's the fixed up Client code
// CLIENT
package test
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;
import java.util.Iterator;
import java.util.Set;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
public class Client extends JFrame {
private String host = "localhost";
private int port = 5001;
private SocketChannel socketChannel;
private Selector selector;
public void work() {
try {
socketChannel = SocketChannel.open();
socketChannel.configureBlocking(false);
InetSocketAddress isa = new InetSocketAddress(host, port);
socketChannel.connect(isa);
selector = Selector.open();
int interest = 0;
if(socketChannel.isConnected())interest = SelectionKey.OP_READ;
else if(socketChannel.isConnectionPending())interest = SelectionKey.OP_CONNECT;
socketChannel.register(selector, interest);
while(true)
int nn = selector.select();
System.out.println("nn="+nn);
Set keys = selector.selectedKeys();
for(Iterator i = keys.iterator(); i.hasNext();)
SelectionKey key = (SelectionKey) i.next();
i.remove();
if (key.isConnectable())
SocketChannel keyChannel = (SocketChannel) key.channel();
System.out.println("Connected "+keyChannel.finishConnect());
key.interestOps(SelectionKey.OP_READ);
if (key.isReadable())
SocketChannel keyChannel = (SocketChannel) key.channel();
String m = Help.read(keyChannel);
display(m);
} catch (IOException e) {
e.printStackTrace();
private void display(final String m) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
area.append(m+"\n");
textFieed.setText("");
private void sendMessage(final String m) {
Thread t = new Thread(new Runnable() {
public void run() {
try {
Help.write(m, socketChannel);
} catch (IOException e) {
e.printStackTrace();
t.start();
public Client() {
addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(1);
textFieed.addKeyListener(new KeyAdapter() {
public void keyPressed(KeyEvent e) {
if (e.getKeyCode()== KeyEvent.VK_ENTER) {
String m = textFieed.getText();
sendMessage(m);
area.setEditable(false);
getContentPane().add(textFieed, "North");
getContentPane().add(new JScrollPane(area));
setBounds(200, 200, 400, 300);
show();
private String messageToSend;
private JTextArea area = new JTextArea();
JTextField textFieed = new JTextField();
public static void main(String[] args) {
Client s = new Client();
s.work(); -
Problematic frame: # J java.nio.MappedByteBuffer.load()
Helo all...
I'm getting an error when generating a PDF using BIRT Framework in Eclipse. Nothing fancy, just compiling a simple report to pdf.
The problem is, the JVM crashes with the following error:
# A fatal error has been detected by the Java Runtime Environment:
# EXCEPTION_IN_PAGE_ERROR (0xc0000006) at pc=0x0190f0be, pid=5848, tid=2392
# JRE version: 7.0_09-b05
# Java VM: Java HotSpot(TM) Client VM (23.5-b02 mixed mode, sharing windows-x86 )
**# Problematic frame:
# J java.nio.MappedByteBuffer.load()Ljava/nio/MappedByteBuffer;**
# Failed to write core dump. Minidumps are not enabled by default on client versions of Windows
# An error report file with more information is saved as:
# C:\Users\luis\Desktop\teste\birt\hs_err_pid5848.log
# If you would like to submit a bug report, please visit:
# http://bugreport.sun.com/bugreport/crash.jsp
I already tried:
1. Run the program in another computers - it worked
2. Reinstall Java on the computer - It did nothing
3. I check the integrity of the disk C: - Nothing
I already spent two days trying to fix this and I don't have any progress. I can't find a solution on the web either.
Thanks in advanceThanks for the help.
But it can not be related to BIRT because it works in every other computer that I tried so far. There is only one computer that not works properly.
If it were BIRT's fault, it wouldn't work in any computer.
Thanks again -
Java NIO locking and NTFS network resources
Hi all - just ran into a really nasty situation and I was wondering if anyone else has hit it and might have some suggestions.
Platform: JRE 1.4_02 on a Win XP machine
The following test code locks a file, then copies it to another location using NIO.
When I run it with source path on my local drives (C), it works fine. If I run it with source path on a network shared resource, it fails with an IOException with description 'Error performing inpage operation'.
If I disable the lock immediately before the copy operation, it works fine.
My conclusion is that there is something about the NIO locking implementation that prevents it from working properly with NTFS volumes on other hosts. Can this be right? I've found the following bug report:
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4774175
but this seems like a huge problem that would prevent folks from using NIO in many, many applications. Maybe I'm wrong on something here...
Anyway, here's the test code:
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
* Created on May 28, 2004
* (c) 2004 Trumpet, Inc.
* @author kevin
public class test {
private void createFile(File f) throws IOException{
FileOutputStream os = new FileOutputStream(f);
for(int i = 0; i < 10; i++){
os.write(i);
os.close();
public test() {
boolean testWithReleasingLockPriorToCopy = false;
final File f1= new File("w:/temp/test2.lok");
final File f2 = new File("w:/temp/test.lok");
f1.delete();
f2.delete();
try {
createFile(f1);
RandomAccessFile raf1 = new RandomAccessFile(f1, "rw");
RandomAccessFile raf2 = new RandomAccessFile(f1, "rw");
FileChannel ch1 = raf1.getChannel();
FileChannel ch2 = raf2.getChannel();
FileLock flock1 = ch1.lock();
if (!f2.getParentFile().exists() && !f2.getParentFile().mkdirs())
throw new IOException("Unable to create directories for destination file '" + f2 + "'");
if (testWithReleasingLockPriorToCopy)
flock1.release();
ch1.transferTo(0, raf1.length(), ch2);
raf1.close();
raf2.close();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
public static void main(String[] args) {
test t = new test();
}Does anyone have any pointers here? I need to be able to exclusively lock a file on a network drive (preventing any other applications from opening it), then make a copy of it. I can't use regular stream operations, because the lock prevents them from working properly (it appears that, once you grab a file lock using NIO, the only way your application can use the file is via the NIO operations - using stream operations fails...).
Thanks in advance for any help!
- Kevini've run into the same problem recently, channels working fine for local file locking, but when you turn to the network, they fail to accurately handle locks.
i ended up writing a jni utility to ship with my java application that locks files using native windows calls.
my .c file ends up looking something like this:
JNIEXPORT jint JNICALL Java_Mapper_NativeUtils_LockFile
(JNIEnv *env, jobject obj, jstring filename)
const char* ntvFilename = (*env)->GetStringUTFChars(env, filename, 0);
int retVal = (int)CreateFile
ntvFilename
, GENERIC_WRITE
, FILE_SHARE_READ
, 0
, OPEN_EXISTING
, FILE_FLAG_SEQUENTIAL_SCAN
, 0
//add code to throw java exceptions based on retVal
if (retVal == (int)INVALID_HANDLE_VALUE)
return retVal;
(*env)->ReleaseStringUTFChars(env, filename, ntvFilename);
return retVal;
JNIEXPORT jboolean JNICALL Java_Mapper_NativeUtils_UnlockFile
(JNIEnv *env, jobject obj, jint handle)
CloseHandle((void *)handle);
return 1;
it's a little shy on the error checking side, but it provides support for network file locking that java seems to lack. -
Converting from CP1252 (Windows) to ISO 8859-1 doesn't work with java.nio?
Hi
I'm trying to write some code that checks whether an InputStream contains only characters with a given encoding. I'm using java.nio for that. For tests, I downloaded some character set examples from http://www.columbia.edu/kermit/csettables.html
When creating the CharsetDecoder, I want to get all errors:
Charset charset = Charset.forName( encoding );
CharsetDecoder decoder = charset.newDecoder();
decoder.onMalformedInput( CodingErrorAction.REPORT );
decoder.onUnmappableCharacter( CodingErrorAction.REPORT );I then read an InputStream and try to convert it. If that fails, it can't contain the desired encoding:
boolean isWellEncoded = true;
ByteBuffer inBuffer = ByteBuffer.allocate( 1024 );
ReadableByteChannel channel = Channels.newChannel( inputStream );
while ( channel.read( inBuffer ) != -1 )
CharBuffer decoded = null;
try
inBuffer.flip();
decoded = decoder.decode( inBuffer );
catch ( MalformedInputException ex )
isWellEncoded = false;
catch ( UnmappableCharacterException ex )
isWellEncoded = false;
catch ( CharacterCodingException ex )
isWellEncoded = false;
if ( decoded != null )
LOG.debug( decoded.toString() );
if ( !isWellEncoded )
break;
inBuffer.compact();
channel.close();
return isWellEncoded;Now I want to check whether a file containing Windows 1252 characters is ISO-8859-1. From my point of view, the code above should fail when it gets to the Euro symbol (decimal 128), since that's not defined in ISO-8859-1.
But all I get is a ? character instead:
(}) 125 07/13 175 7D RIGHT CURLY BRACKET, RIGHT BRACE
(~) 126 07/14 176 7E TILDE
[?] 128 08/00 200 80 EURO SYMBOL
[?] 130 08/02 202 82 LOW 9 SINGLE QUOTEI also tried to replace the faulty character, using
decoder.onUnmappableCharacter( CodingErrorAction.REPLACE );
decoder.replaceWith("!");but I still get the question marks.
I'm probably doing something fundamentally wrong, but I dont get it :-)
Any help is greatly appreciated!
EricAs a suggestion....create a complete example demonstrating the problem. It shouldn't have channel in it since that wouldn't appear to be the problem (decoding is.) You should create the byte array in the example code - populate it with the byte sequence that you think should work. And your code should then demonstrate that it doesn't. Then post that.
-
Cannot access class java.nio.ByteBuffer
Hi All -
I'm trying to compile a java sample code.
I keep getting the error described in the subject line
cannot access class java.nio.ByteBuffer; file java\nio\ByteBuffer.class not found
I have un-ziped the java sdk 1.4.1 src.zip to a directory under c:\ and added the java\nio directory to the project setting and compile with jdk runtime 1.4.1 and yet get the same error....
I've tried by redirecting to src.zip and didn't work either....
I would appreciate your feedbacks and sorry for the lame question, consider it as a newcomer to Java world.
thanks in advanceYou test it by running the following line....
java java.nio.ByteBuffer
If it says "main not found" then your problem has nothing to do with the java install nor the classpath. The code you are trying to compile is wrong.
If it says class not found then you use this line next....
java -version
If this returns nothing then you are not using the Sun VM (you are using the MS one.) If it returns a version below 1.4 then your PATH statement is wrong (and you should uninstall all sun versions then reinstall.) You can fix the MS VM problem by altering the path so the java path is first.
If it does say 1.4 then you need to uninstall and reinstall because something is messed up. -
DNS after reducing the advertised EDNS UDP packet size to 512 octets
hello
There is something wrong with my DNS server, it open internet webs so slow,and i have no idea with this .
04-Mar-2011 14:31:57.264 zone 0.0.127.in-addr.arpa/IN/com.apple.ServerAdmin.DNS.public: loaded serial 1997022700
04-Mar-2011 14:31:57.264 zone 15.0.168.192.in-addr.arpa/IN/com.apple.ServerAdmin.DNS.public: loaded serial 2011030204
04-Mar-2011 14:31:57.265 zone ******/IN/com.apple.ServerAdmin.DNS.public: loaded serial 2011030404
04-Mar-2011 14:31:57.265 zone localhost/IN/com.apple.ServerAdmin.DNS.public: loaded serial 42
04-Mar-2011 14:31:57.265 running
04-Mar-2011 14:32:00.066 host unreachable resolving 'b.dns-sd.udp.0.0.168.192.in-addr.arpa/PTR/IN': 2001:7fd::1#53
04-Mar-2011 14:32:00.261 host unreachable resolving 'r.dns-sd.udp.0.0.168.192.in-addr.arpa/PTR/IN': 2001:500:2f::f#53
04-Mar-2011 14:32:00.261 host unreachable resolving 'r.dns-sd.udp.0.0.168.192.in-addr.arpa/PTR/IN': 2001:503:c27::2:30#53
04-Mar-2011 14:32:00.261 host unreachable resolving 'r.dns-sd.udp.0.0.168.192.in-addr.arpa/PTR/IN': 2001:503:ba3e::2:30#53
04-Mar-2011 14:32:00.261 host unreachable resolving 'r.dns-sd.udp.0.0.168.192.in-addr.arpa/PTR/IN': 2001:7fd::1#53
04-Mar-2011 14:32:00.261 host unreachable resolving 'r.dns-sd.udp.0.0.168.192.in-addr.arpa/PTR/IN': 2001:dc3::35#53
04-Mar-2011 14:32:00.361 host unreachable resolving 'dr.dns-sd.udp.0.0.168.192.in-addr.arpa/PTR/IN': 2001:500:1::803f:235#53
04-Mar-2011 14:32:00.361 host unreachable resolving 'dr.dns-sd.udp.0.0.168.192.in-addr.arpa/PTR/IN': 2001:7fd::1#53
04-Mar-2011 14:32:00.361 host unreachable resolving 'dr.dns-sd.udp.0.0.168.192.in-addr.arpa/PTR/IN': 2001:dc3::35#53
04-Mar-2011 14:32:00.361 host unreachable resolving 'dr.dns-sd.udp.0.0.168.192.in-addr.arpa/PTR/IN': 2001:503:ba3e::2:30#53
04-Mar-2011 14:32:00.866 host unreachable resolving './NS/IN': 2001:7fd::1#53
04-Mar-2011 14:32:01.005 success resolving './NS' (in '.'?) after reducing the advertised EDNS UDP packet size to 512 octets
04-Mar-2011 14:32:01.408 success resolving 'local/SOA' (in '.'?) after disabling EDNS
04-Mar-2011 14:32:01.533 host unreachable resolving 't.arin.net/AAAA/IN': 2001:503:ba3e::2:30#53
04-Mar-2011 14:32:01.534 host unreachable resolving 'v.arin.net/AAAA/IN': 2001:500:1::803f:235#53
04-Mar-2011 14:32:01.534 host unreachable resolving 'v.arin.net/AAAA/IN': 2001:7fd::1#53
04-Mar-2011 14:32:01.534 host unreachable resolving 'v.arin.net/AAAA/IN': 2001:503:ba3e::2:30#53
04-Mar-2011 14:32:01.534 host unreachable resolving 'w.arin.net/A/IN': 2001:500:1::803f:235#53
anyone help!! Thanks a lot.
Message was edited by: leo.xuealso interesting, when setting DNS servers IPs in Network Settings for your host,
it is important that the IPs are not doubled.
in example if you have Networksettings like
automatic DHCP given from router or server.
IP-Adress: 192.168.2.2
Subnetmask: 255.255.255.0
Router IP: 192.168.2.1
DNS-Server: 127.0.0.1, 192.168.2.2
wich means localhost and again same machine, just different IP..
then your lookup mechanism has to walk thru this steps to know if there is nothing inside to resolve adresses.
which means in this example it would take double the time if DNS-Server would be just 127.0.0.1
you can see if there is a lot to work thru in your logs.
look for something like "sizing zone task pool based on 9 zones".
this mount of zones will change if you set the correct DNS server IP.
more zones are slower than less, very logical!
but this will not solve your problem with packet size at all, it just reduces circles after dns resolves not known adresses even with packet size change. -
I'm not sure which forum this should go in so applogies if I got it wrong.
I would like to use the java.nio package from JDK1.4 with the J2ME. Is this possible in any way?
cheers
AndrewI'm not sure which forum this should go in so
applogies if I got it wrong.
I would like to use the java.nio package from JDK1.4
with the J2ME. Is this possible in any way?this topic should be post at
CLDC and MIDP
http://forum.java.sun.com/forum.jsp?forum=76
or
K Virtual Machine (KVM)
http://forum.java.sun.com/forum.jsp?forum=50
CLDC 1.0 and MIDP 1.0 doesn't include java.nio
please go to
http://java.sun.com/j2me/docs/
two documents will be useful
CLDC Specification, V1.0
MIDP 1.0 Specification, Final (JSR 37)
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