Java.nio.bytebuffer question.
I have a piece of code that copies data from one byte buffer to another for continuous 20 bytes. However after the loop the destination buffer is still empty.
ByteBuffer respBuffer = ByteBuffer.allocate(20, false);
respBuffer.order(ByteOrder.LITTLE_ENDIAN);
for(int i=0; i<(Constants.wrapperSize + Constants.headerSize); i++){
respBuffer.put(requestBuffer.get());
the respBuffer is empty after this loop.The current position in both the buffers is set to 0. And the source buffer is not empty as I have printed the hexDump of it .
Help appreciated.
Edited by: tys on Aug 15, 2008 12:41 PM
Byte order makes no difference if you are working with bytes.
I don't see how the position could be 0 and the get() method always moves the position unless a BufferOverrun has occured.
Have a look at the buffer before you copy it.
A debugger is good for this.
Similar Messages
-
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. -
A few general java.nio.* questions
Hi,
I've been reading up on selectors and channels for networking programming. During my reading I came across this website, http://www.javaworld.com/javaworld/jw-09-2001/jw-0907-merlin.html
It's kind of dated (3 years ago) but the example they provide on non-blocking I/O still compiles.
Further in the article (http://www.javaworld.com/javaworld/jw-09-2001/jw-0907-merlin-p4.html) they mention a few "gotcha's" with using selectors. One in particular that caught my attention was "a selector can have only 63 channels registered, which is probably not a big deal."
So only 63 channels max can be registered to a selector ? I searched around the web and the java API looking to confirm this. Does anyone know this to be true or if the max 63 registered channels was dropped before java 1.4 beta became the stable release of java 1.4? The article was written when java 1.4 was in beta.
Lastly, do selectors weed out dropped socket connections? For example. Say I have 500 socket (TCP/IP) connections to a server of mine. Of those 500 , 100 are now closed by the client by the time the server comes around to send them data. As the server loops through the 500 connections using a selector, will there be a delay because 100 connections are dropped and the server must wait for a timeout before proceeding to send the data to the next connection or does the selector detect these 100 dropped connections and only use the 400 still connected?
I hope this last question makes sense.
Thanks in advance,
NickHi,
I've been reading up on selectors and channels for
networking programming. During my reading I came
across this website,
http://www.javaworld.com/javaworld/jw-09-2001/jw-0907-m
rlin.html
It's kind of dated (3 years ago) but the example they
provide on non-blocking I/O still compiles.
Further in the article
(http://www.javaworld.com/javaworld/jw-09-2001/jw-0907-
erlin-p4.html) they mention a few "gotcha's" with
using selectors. One in particular that caught my
attention was "a selector can have only 63 channels
registered, which is probably not a big deal."
So only 63 channels max can be registered to a
selector ? I searched around the web and the java API
looking to confirm this. Does anyone know this to be
true or if the max 63 registered channels was dropped
before java 1.4 beta became the stable release of java
1.4? The article was written when java 1.4 was in
beta.I don't know if that limit of 63 is still there, but it probably makes sense to use a pool of threads each supporting a Selector if the number of connections gets that high.
Lastly, do selectors weed out dropped socket
connections? For example. Say I have 500 socket
(TCP/IP) connections to a server of mine. Of those 500
, 100 are now closed by the client by the time the
server comes around to send them data. As the server
loops through the 500 connections using a selector,
will there be a delay because 100 connections are
dropped and the server must wait for a timeout before
proceeding to send the data to the next connection or
does the selector detect these 100 dropped connections
and only use the 400 still connected?closed channels are removed by the select statement. When using non-blocking IO, nothing waits anyway.
I hope this last question makes sense.
Thanks in advance,
Nick -
Using ByteBuffer from java.nio package
Hi,
I have a java.nio.ByteBuffer object that is returned from the C++ code, created using NewDirectByteBuffer. I would like to use this ByteBuffer object in my java code to create a WritableRaster object. I would like to avoid an array copy here as the data may be huge.
Could someone please let me know if there is a solution to this?
Thanks in advance for any help.Warning: I know almost nothing about the java.awt.image package - so please take what Im going to suggest as the throw away, off the top of my head random rambling that it is......
Could you implement a custom DataBuffer which sits on top of a NIO ByteBuffer? Already, custom DataBuffers provide access for certain data types (e.g. theres a DataBufferByte, DataBufferDouble which wrap arrays) - so I guess you could write a NIODataBufferByte - or what ever - which sits on top of a ByteBuffer.
Im not sure how this would tie in with the SampleModel though (again, I dont know anything about this area).
Hopefully someone who knows this stuff will come across this thread and actually give you some decent advice :o)
~D -
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(); -
I need to make the server is able to hold about 500 connections and operates on a single thread. The server itself should make all the connections. Where can I find examples of finished implementations?
I have an example, but it does not work
import java.io.IOException;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.SocketChannel;
import java.nio.channels.spi.SelectorProvider;
import java.util.*;
public class NioClient implements Runnable {
// The host:port combination to connect to
private InetAddress hostAddress;
private String host;
private int port;
// The selector we'll be monitoring
private Selector selector;
// The buffer into which we'll read data when it's available
private ByteBuffer readBuffer = ByteBuffer.allocate(8192);
// A list of PendingChange instances
private List pendingChanges = new LinkedList();
// Maps a SocketChannel to a list of ByteBuffer instances
private Map pendingData = new HashMap();
// Maps a SocketChannel to a RspHandler
private Map rspHandlers = Collections.synchronizedMap(new HashMap());
public NioClient() {
try {this.selector = this.initSelector();} catch(IOException e){}
public void connect(String host, int port, RspHandler handler) throws IOException {
this.hostAddress = hostAddress;
this.host = host;
this.port = port;
this.send("$Hello |".getBytes(), handler);
public void send(byte[] data, RspHandler handler) throws IOException {
// Start a new connection
SocketChannel socket = this.initiateConnection();
// Register the response handler
this.rspHandlers.put(socket, handler);
// And queue the data we want written
synchronized (this.pendingData) {
List queue = (List) this.pendingData.get(socket);
if (queue == null) {
queue = new ArrayList();
this.pendingData.put(socket, queue);
queue.add(ByteBuffer.wrap(data));
// Finally, wake up our selecting thread so it can make the required changes
this.selector.wakeup();
handler.waitForResponse();
public void run() {
while (true) {
try {
// Process any pending changes
synchronized (this.pendingChanges) {
Iterator changes = this.pendingChanges.iterator();
while (changes.hasNext()) {
ChangeRequest change = (ChangeRequest) changes.next();
switch (change.type) {
case ChangeRequest.CHANGEOPS:
SelectionKey key = change.socket.keyFor(this.selector);
key.interestOps(change.ops);
break;
case ChangeRequest.REGISTER:
change.socket.register(this.selector, change.ops);
break;
this.pendingChanges.clear();
// Wait for an event one of the registered channels
this.selector.select();
// Iterate over the set of keys for which events are available
Iterator selectedKeys = this.selector.selectedKeys().iterator();
while (selectedKeys.hasNext()) {
SelectionKey key = (SelectionKey) selectedKeys.next();
selectedKeys.remove();
if (!key.isValid()) {
continue;
// Check what event is available and deal with it
if (key.isConnectable()) {
this.finishConnection(key);
} else if (key.isReadable()) {
this.read(key);
} else if (key.isWritable()) {
this.write(key);
} catch (Exception e) {
e.printStackTrace();
private void read(SelectionKey key) throws IOException {
SocketChannel socketChannel = (SocketChannel) key.channel();
// Clear out our read buffer so it's ready for new data
this.readBuffer.clear();
// Attempt to read off the channel
int numRead;
try {
numRead = socketChannel.read(this.readBuffer);
} catch (IOException e) {
// The remote forcibly closed the connection, cancel
// the selection key and close the channel.
key.cancel();
socketChannel.close();
return;
System.out.println("READ");
if (numRead == -1) {
// Remote entity shut the socket down cleanly. Do the
// same from our end and cancel the channel.
key.channel().close();
key.cancel();
return;
// Handle the response
this.handleResponse(socketChannel, this.readBuffer.array(), numRead);
private void handleResponse(SocketChannel socketChannel, byte[] data, int numRead) throws IOException {
// Make a correctly sized copy of the data before handing it
// to the client
byte[] rspData = new byte[numRead];
System.arraycopy(data, 0, rspData, 0, numRead);
// Look up the handler for this channel
RspHandler handler = (RspHandler) this.rspHandlers.get(socketChannel);
// And pass the response to it
if (handler.handleResponse(rspData)) {
// The handler has seen enough, close the connection
socketChannel.close();
socketChannel.keyFor(this.selector).cancel();
private void write(SelectionKey key) throws IOException {
SocketChannel socketChannel = (SocketChannel) key.channel();
synchronized (this.pendingData) {
List queue = (List) this.pendingData.get(socketChannel);
// Write until there's not more data ...
while (!queue.isEmpty()) {
ByteBuffer buf = (ByteBuffer) queue.get(0);
socketChannel.write(buf);
if (buf.remaining() > 0) {
// ... or the socket's buffer fills up
break;
queue.remove(0);
if (queue.isEmpty()) {
// We wrote away all data, so we're no longer interested
// in writing on this socket. Switch back to waiting for
// data.
key.interestOps(SelectionKey.OP_READ);
private void finishConnection(SelectionKey key) throws IOException {
SocketChannel socketChannel = (SocketChannel) key.channel();
// Finish the connection. If the connection operation failed
// this will raise an IOException.
try {
socketChannel.finishConnect();
} catch (IOException e) {
// Cancel the channel's registration with our selector
System.out.println(e);
key.cancel();
return;
// Register an interest in writing on this channel
key.interestOps(SelectionKey.OP_WRITE);
private SocketChannel initiateConnection() throws IOException {
// Create a non-blocking socket channel
SocketChannel socketChannel = SocketChannel.open();
socketChannel.configureBlocking(false);
// Kick off connection establishment
socketChannel.connect(new InetSocketAddress(this.host, this.port));
// Queue a channel registration since the caller is not the
// selecting thread. As part of the registration we'll register
// an interest in connection events. These are raised when a channel
// is ready to complete connection establishment.
synchronized(this.pendingChanges) {
this.pendingChanges.add(new ChangeRequest(socketChannel, ChangeRequest.REGISTER, SelectionKey.OP_CONNECT));
return socketChannel;
private Selector initSelector() throws IOException {
// Create a new selector
return SelectorProvider.provider().openSelector();
public class RspHandler {
private byte[] rsp = null;
public synchronized boolean handleResponse(byte[] rsp) {
this.rsp = rsp;
this.notify();
return true;
public synchronized void waitForResponse() {
while(this.rsp == null) {
try {
this.wait();
} catch (InterruptedException e) {
System.out.println(new String(this.rsp));
} NioClient NioClient = new NioClient();
Thread t = new Thread(NioClient);
t.setDaemon(true);
t.start();
RspHandler handler = new RspHandler();
NioClient.connect("69.28.156.250", 27040, handler);
NioClient.connect("72.165.61.188", 27040, handler);
NioClient.connect("208.111.133.84", 27011, handler);
NioClient.connect("72.165.61.136", 27012, handler);
Edited by: 915967 on 01.08.2012 7:07 -
I have copied this, one program from a book that would have to read file of gives to me to you mixed but it does not work, you could me why?
import java.io.FileInputStream;
import java.io.IOException;
import java.io.File;
import java.io.FileNotFoundException;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
public class ReadPrimesMixedData {
public static void main(String[] args) {
File aFile = new File("C:/Beg Java Stuff/primes.txt");
FileInputStream inFile = null;
try {
inFile = new FileInputStream(aFile);
} catch(FileNotFoundException e) {
e.printStackTrace(System.err);
System.exit(1);
FileChannel inChannel = inFile.getChannel();
try {
ByteBuffer lengthBuf = ByteBuffer.allocate(8);
int strLength = 0; // Stores the string length
ByteBuffer buf = null; // Stores a reference to the second byte buffer
byte[] strChars = null; // Stores a reference to an array to hold the string
while(true) {
if(inChannel.read(lengthBuf) == -1) // Read the string length, if its EOF
break; // exit the loop
lengthBuf.flip();
strLength = (int)lengthBuf.getDouble(); // Extract the length and convert to int
buf = ByteBuffer.allocate(strLength+8); // Buffer for the string & the prime
if(inChannel.read(buf) == -1) { // Read the string & binary prime value
assert false; // Should not get here!
break; // Exit loop on EOF
buf.flip();
strChars = new byte[strLength]; // Create the array for the string
buf.get(strChars); // Extract string & binary prime value
System.out.println("String length: " + strChars.length+ " String: " +
new String(strChars) + " Binary value: " + buf.getLong());
lengthBuf.clear(); // Clear the buffer for the next read
System.out.println("\nEOF reached.");
inFile.close(); // Close the file and the channel
} catch(IOException e) {
e.printStackTrace(System.err);
System.exit(1);
System.exit(0);
This e' the program that writes the file
import java.io.*;
import java.nio.*;
import java.nio.channels.FileChannel;
public class PrimesToFile2 {
public static void main(String[] args) {
int primesRequired = 100; // Default count
if (args.length > 0) {
try {
primesRequired = Integer.valueOf(args[0]).intValue();
} catch (NumberFormatException e) {
System.out.println("Prime count value invalid. Using default of "
+ primesRequired);
long[] primes = new long[primesRequired]; // Array to store primes
primes[0] = 2; // Seed the first prime
primes[1] = 3; // and the second
// Count of primes found - up to now, which is also the array index
int count = 2;
long number = 5; // Next integer to be tested
outer:
for (; count < primesRequired; number += 2) {
// The maximum divisor we need to try is square root of number
long limit = (long) Math.ceil(Math.sqrt((double) number));
// Divide by all the primes we have up to limit
for (int i = 1; i < count && primes[i] <= limit; i++)
if (number % primes[i] == 0) // Is it an exact divisor?
continue outer; // yes, try the next number
primes[count++] = number; // We got one!
File aFile = new File("C:/Beg Java Stuff/primes.txt");
FileOutputStream outputFile = null;
try {
outputFile = new FileOutputStream(aFile);
} catch (FileNotFoundException e) {
e.printStackTrace(System.err);
System.exit(1);
FileChannel file = outputFile.getChannel();
final int BUFFERSIZE = 100; // Buffer size in bytes
ByteBuffer buf = ByteBuffer.allocate(BUFFERSIZE);
DoubleBuffer doubleBuf = buf.asDoubleBuffer();
buf.position(8);
CharBuffer charBuf = buf.asCharBuffer();
LongBuffer longBuf = null;
String primeStr = null;
for (int i = 0; i < primes.length; i++) {
primeStr = "prime = " + primes; // Create the string
doubleBuf.put(0,(double) primeStr.length());// Store the string length
charBuf.put(primeStr); // Store the string
buf.position(2 * charBuf.position() + 8); // Position for 3rd buffer
longBuf = buf.asLongBuffer(); // Create the buffer
longBuf.put(primes[i]); // Store the binary long value
buf.position(buf.position() + 8); // Set position after last value
buf.flip(); // and flip
try {
file.write(buf); // Write the buffer as before.
} catch (IOException e) {
e.printStackTrace(System.err);
System.exit(1);
buf.clear();
doubleBuf.clear();
charBuf.clear();
try {
System.out.println("File written is " + file.size() + " bytes.");
outputFile.close(); // Close the file and its channel
} catch (IOException e) {
e.printStackTrace(System.err);
System.exit(1);
System.exit(0);
This works correctlyI don't have problems when I compile the program but if I run the program ....I have this
String length: 9 String: prim Binary value: 7277852183226228736
String length: 0 String: Binary value: 162166969980682240
String length: 0 String: Binary value: 7854388801345436928
String length: 0 String: Binary value: 3573983215616
Stjava.lang.IllegalArgumentException
at java.nio.ByteBuffer.allocate(ByteBuffer.java:303)
at ReadPrimesMixedData.main(ReadPrimesMixedData.java:35)
ring length: 0 String: Binary value: 7566167222444367872
String length: 0 String: Binary value: 88089088
String length: 0 String: Binary value: 8214681170873443584
String length: 0 String: Binary value: 1856
String length: 0 String: Binary value: 8070575878335130880
Exception in thread "main" -
Hello,
I just started to learn the java.nio package so I decided to make a simple Echo server. I made a client which reads a line from the keyboard, sends it to the server and the server returns it. It all works except one little detail. Here's little code from the server:
int n = client.read(buffer);
if ( n > 0)
buffer.flip();
client.write(buffer);
Charset charset = Charset.forName("ISO-8859-1");
CharsetDecoder decoder = charset.newDecoder();
charBuffer = decoder.decode(buffer);
System.out.println(charBuffer.toString());
buffer.clear();
}So that works, I send the data and then I receive it back. But only for the client. I also wanted the server to print the line which is the reason for the charset and the decoder. The above code however prints only a blank line. Thus I tried this:
int n = client.read(buffer);
if ( n > 0)
buffer.flip();
Charset charset = Charset.forName("ISO-8859-1");
CharsetDecoder decoder = charset.newDecoder();
charBuffer = decoder.decode(buffer);
System.out.println(charBuffer.toString());
client.write(buffer);
buffer.clear();
}Or in other words I just moved the write() part downwards. So far so good, now the server was actually printing the lines that the client was sending but nothing was sent back to the client.
The question is how to make both, the send back line and the print line on the server side to work as intended. Also a little explanation why the events described above are happening is going to be more than welcome :)
Thanks in advance!Strike notice
A number of the regular posters here are striking in protest at the poor
management of these forums. Although it is our unpaid efforts which make the
forums function, the Sun employees responsible for them seem to regard us as
contemptible. We hope that this strike will enable them to see the value
which we provide to Sun. Apologies to unsuspecting innocents caught up in
the cross-fire. -
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.
-
String.getBytes() & String(byte[]) - java.nio.BufferOverflowException
The application in question uses JNI for legacy integration and I suspect the legacy code is corrupting the stack causing the above error. However, the error does not occur in Java 1.3, only Java 1.4.
Is there some way to suppress 1.4's use of the native IO API when encoding and decoding byte streams? This would at least provide a workaround in the meantime.
Thanks.This is beginning to make a little sense. The problem is that you got a String and you don't want one. A String wraps an array of chars, which your app needs, right? Specifically they're chars because you need 16-bit char sets.
Presumably the getBytes() method call is used to get an array of bytes for some data transfer operation. java.nio was probably added in 1.4 as it has some very efficient ways of handling buffers as simultaneously of two or more types. It's trying to use the underlying char array as a byte array and there's a straight up bug someplace.
Workaround is strange to contemplate, but I'm pretty sure it will work: use String.getChars() to get an array of chars, and then use java.nio yourself to create your byte array! If you've never been there, it's not very hard. I use nio all the time and it's never been a problem. -
Please, need help.
I'm using java.nio to get large files contents (txt) and need to put these data into MSSQL SERVER 2000 database tables. NIO have capabilityies to get data and transfer directly to the tables? If so, how can i do it?
Thanks a lot
AloisioChuckBing, i'm connected with database trough JDBC yet and i can retrieve data meaning my connection is OK.
I'm able to read data from a txt file (250mb large) trough MappedByteBuffer and write into another with the same size and content. It's working fine.
My question is if i can read the txt file and, instead write the data into another txt file, put these data into a table.
Thanks for your reply -
Someone explain what java.nio.channels.Pipe should be uses for, and how to use it?
You can use this class to transfer the content of a channel from one thread to another thread.
The writing thread blocks when the pipe is full.
package com.desoft.pipetest;
import java.io.*;
import java.nio.*;
import java.nio.channels.*;
public class PipeTest {
public static void main (String args[])
try
FileInputStream fis = new FileInputStream(args[0]);
FileChannel fc = fis.getChannel();
Pipe p = Pipe.open();
PipeReader pr = new PipeReader( p );
Thread t = new Thread( pr );
t.start();
fc.transferTo(0, fc.size(), p.sink() );
catch( IOException ioe )
ioe.printStackTrace();
* Read from a Pipe and write Content to System.out
static class PipeReader implements Runnable
Pipe p;
public PipeReader( Pipe p )
this.p = p;
public void run()
try
ByteBuffer buffer = ByteBuffer.allocate( 10 );
int len = 0;
while( (len=p.source().read( buffer )) > 0 )
buffer.rewind();
for( int i = 0; i < len; i++ )
System.out.print( (char)buffer.get());
buffer.rewind();
catch( IOException ioe )
ioe.printStackTrace(); -
Socket disconnection event not being reveived java.nio
Hi All
My question is as below
i am using java.nio package + win 2K + jdk1.4.1_02
I have a Server accepting socket connection and is configured
in Nonblocking mode.
-The server receives (selector) events (accept event)
when a client requests for a connection .
-The server is getting read and write events when
client wants to read and write
-The server gets a read event when the client disconnects
My only problem is that the Server is not getting any events
when the client disconnect due to network break down
for EX when the network connection breaks the client disconnects
but the server selector is not getting any events
I am storing the client Socket objects in a Hash Table and
if i execute the .isConnected() method it returns true
even though the the client is down
The only work around is to try to read and write on the socket
i get an IO exception and am able to make out that the
client is disconnected
But this is not desirable for my client
as client modification to give any kind of echo is not possible and
a read /write event will cause problem.
Can any one tell how to detect client side disconnection
with out Read and Write on the client socket
I get an socket Exception when the socket is in Blocking IO and is blocked on read/ write but I am facing this problem in NonBlockingIO
Regards
Avinashint ct = read.selectNow();
if (ct > 0)
Set readyKeys = read.selectedKeys();
Iterator i = readyKeys.iterator();
while (i.hasNext())
SelectionKey key = (SelectionKey) i.next();
i.remove();
if (key.isReadable())
SelectableChannel nextReady = (SelectableChannel) key.channel();
SocketChannel sc = (SocketChannel) key.channel();
int rd = sc.read(buffer);
// Link is dead
if (rd == -1)
key.cancel();
key.attach(null);
nextReady.close();
continue;
// Process your data
catch (Exception e)
e.printStackTrace(); -
How to set proxy information in JAVA.NIO framework MINA or Netty?
Hi all,
THERE IS NO PROXY SUPPORT VIA JAVA.NIO.
How to use MINA or Netty,other framework support proxy?
Thanks in advance!The forum is focus on questionNo. The forum is provided by Sun and latterly Oracle to talk about core Java programming: in this case the Java networking APIs. Questions about 3rd party products should be directed to the people who supply them. And asking questions in places where the relevant expertise isn't concentrated is not a rational strategy.
I think you really need patience as a professional expert.Expert, yes. Professional? Is somebody paying me to post here?
And don't talk to me about patience. You have already completely exhausted any patience I may ever have had by repeating a question five times after I had already answered it. Judging by the below you are now in the process of repeating that process.
The information is shared by anybody.Correct, including me, and including the information that there are better places to ask than here about 3rd party products.
Besides, I think I submitted right question on right place.Then once again you are proving yourself incompetent, as I have already told you that it isn't the right place. -
Need help with java.nio.socket program.
Can someone please help me here? I am trying to create a class that listens on a socket for an incoming connection, but I am getting the following error on compile:
SocketIn.java:48: incompatible types
found : java.nio.channels.SocketChannel
required: java.net.Socket
Socket requestSocket = requestChannel.accept();
Here is my code:
package NETC;
import java.net.*;
import java.util.*;
import java.io.*;
import java.nio.*;
import java.nio.charset.*;
import java.nio.channels.*;
import java.nio.channels.spi.*;
public class SocketIn{
// Buffer for any incoming data.
private static ByteBuffer inBuffer = ByteBuffer.allocateDirect(1024);
CharBuffer charBuffer = null;
public SocketIn(int intPort)throws Exception{
// Create a non-blocking server socket.
ServerSocketChannel serverChannel = ServerSocketChannel.open();
serverChannel.configureBlocking(false);
// Use the host and port to bind the server socket.
InetAddress inetAddress = InetAddress.getLocalHost();
InetSocketAddress socketAddress = new InetSocketAddress(inetAddress, intPort);
serverChannel.socket().bind(socketAddress);
// The selector for incoming requests.
Selector requestSelector = SelectorProvider.provider().openSelector();
// Put the server socket on the selectors 'ready list'.
serverChannel.register(requestSelector, SelectionKey.OP_ACCEPT);
while(requestSelector.select() > 0){
System.out.println("Connection Accepted...");
// A request has been made and is ready for IO.
Set requestKeys = requestSelector.selectedKeys();
Iterator iterator = requestKeys.iterator();
while(iterator.hasNext()){
SelectionKey requestKey = (SelectionKey)iterator.next();
// Get the socket that's ready for IO.
ServerSocketChannel requestChannel = (ServerSocketChannel)requestKey.channel();
// This shouldn't block.
Socket requestSocket = requestChannel.accept();
inBuffer.clear();
requestSocket.read(inBuffer);
inBuffer.flip();
Charset charset = Charset.forName("ISO-8859-1");
CharsetDecoder decoder = charset.newDecoder();
charBuffer = decoder.decode(inBuffer);
iterator.remove();
}Well its been about a month and a half so I guess you have your answer. In case you don't...
// This shouldn't block.
Socket requestSocket = requestChannel.accept();
The problem is quite simple. The ServerSocketChannel.accept() returns a SocketChannel. (Channel -> Channel).
You can get access to the socket using the SocketChannel.
SocketChannel requestSocketChannel = requestChannel.accept();
Socket requestSocket = requestSocketChannel.socket();
But you don't need the socket to read and write.
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