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,
Nick
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-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
Similar Messages
-
Hey, I've just start reading and programming a client/server using NIO and got to a point where i need to keep a list of connected clients to send them messages as the server processes information it received... How could i handle this selection of clients that i want to send a specific message and how should I store those clients after they connect (I mean, when a client connects, a channel is started, but how can i identify later that a channel is related to THAT client?)
Thanks in advance
Message was edited by:
LemmerichGenerally you will associate some kind of client session object with the channel via the attachment. This will also contain the input buffer and whatever you need in your application to identify the client.
-
General java programming question.
i have trouble knowing when something is referred to in contrast to something being copied.
in this case, the array has changed, but not the character.
public class ReturnArray2
public static int[] getArray()
int a[] = new int[3];
a[0] = 2;
a[1] = 4;
a[2] = 6;
return a;
public static void mystery(int[] b, char r)
r = 'Q';
for(int i = 0; i < b.length; i++)
b[i] = b[i] + 5;
System.out.println("array b contains: ");
for(int i = 0; i < 3; i++)
System.out.println(b[i] + " ");
public static void main(String args[])
int scores[];
char x = 'L';
scores = getArray();
System.out.println("Array in main.");
for (int i = 0; i < 3; i++)
System.out.println(scores[i] + " ");
mystery(scores, x);
System.out.println("After return from mystery.");
System.out.println("character is " + x);
for(int i = 0; i < 3; i++)
System.out.println(scores[i] + " ");
Array in main.
2
4
6
array b contains:
7
9
11
After return from mystery.
character is L
7
9
11
*/and in this case, why didn't the array change?
public class ReturnArray2
public static int[] getArray()
int a[] = new int[3];
a[0] = 2;
a[1] = 4;
a[2] = 6;
System.out.println("array in function");
for(int i = 0; i < 3; i++)
System.out.println(a[i] + " ");
return a;
public static void mystery(int[] b)
for(int i = 0; i < b.length; i++)
b[i] = b[i] * 2 + 5;
int[] c = new int [3];
c[0] = 55;
c[1] = 44;
c[2] = 33;
System.out.println("array c contains: ");
for (int i = 0; i < 3; i++)
System.out.println(c[i] + " ");
b = c;
System.out.println("array b contains: ");
for(int i = 0; i < 3; i++)
System.out.println(b[i] + " ");
public static void main(String args[])
int scores[];
scores = getArray();
System.out.println("Array in main.");
for (int i = 0; i < 3; i++)
System.out.println(scores[i] + " ");
mystery(scores);
System.out.println("After return from mystery.");
for(int i = 0; i < 3; i++)
System.out.println(scores[i] + " ");
array in function
2
4
6
Array in main.
2
4
6
array c contains:
55
44
33
array b contains:
55
44
33
After return from mystery.
9
13
17
*/i have trouble knowing when something is referred to
in contrast to something being copied.Java has only one passing mode: pass-by-value. The value, whether it be of an int or a reference, is always copied.
in this case, the array has changed, but not the
character.A reference has a value, that value is either null or the address of an Object. The value of scores is the address of the array returned by getArray(). When you pass scores to mystery() the value of scores is copied to a new reference called b on the local stack frame. The value of b is the same as the value of scores, but they are two different references. However, since the value is the same they both contain the same address which is the address of the array. When you modify the array you are modifying the array at the address that b has as it's value. Since scores has that same address as it's value, in other words they both point to the same array, you will see it modified in both places. When you passed the char the value (L) was copied to the local stack frame. Your copy r now has the value L. Modifying r modifies the value at r, which is independent of the value at x.
So, with the char you changed the value at the address. With the reference you changed the value at the address the reference contained as it's value.
and in this case, why didn't the array change?You didn't modify the array, you simply printed it's contents concatenated with an empty String. -
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. -
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(); -
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. -
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. -
hi,all
In traditonal thread-pool based programming way,the Server can process multi-clients by thread(time-sharing),all clients's time is equal.
In Java NIO programming way,the [select] will process multi-clients without thread pool.So,the the second client must be processed after the first client be complished.if the first client is cost much time,other cients must be long time waiting?
plz help me - thanks for your time
Tony.
Hangzhou,chinaAs an NIO server in non-blocking mode obviously never blocks (or rather it only blocks in select(), when nothing is happening), it can implement any kind of scheduling it likes between the various SocketChannels it has accepted as connected clients. It isn't obliged in any way to completely finish with one client before starting on the next, and it generally can't do so because data from any particular client doesn't necessarily arrive in a single chunk.
-
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 -
Hello there.
I've been using Java for quite some time, but the few really networked client/server applications I have used, have used java.io and java.net. Now, even I have heard the rumours about Java NIO, and I am curious. I have tried reading up and down the API on java.nio.* , but I must say I am still kind of confused.
Basically, I am looking for some example code, or a thorough explanation of how all the classes and components come together to form efficient asynchronous non-blocking I/O.
What I picture is a server over TCP/IP meant to handle 100+ clients, written with an emphasis on performance. Think MMORPG, I guess (no no, I am not ambitious enough to want to write one, but I can imagine that gives a good analogy of how I would have the communication set up). The server needs to quickly figure out which clients need to be handled at any given time, with as little overhead or reduntant iteration as possible.
Ok, I am asking alot perhaps.. I just wonder if anyone could offer links to example source-code, write something to show me, or basically just try to explain to me how this all works.
I would be very very grateful if anyone stepped up to the plate.
Thanks,
-TerjeTake a look at my thread Taming the NIO Circus. It starts with simple examples of a single thread echo server and a swing client.
-
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(); -
Hi help,
I'm studying new java.io classes. I've compiled and learnt
a basic server like this...
import java.io.*;
import java.net.*;
import java.nio.*;
import java.nio.channels.*;
import java.util.*;
public class Server {
private static int port = 9999;
public static void main(String args[])
throws Exception {
Selector selector = Selector.open();
ServerSocketChannel channel =
ServerSocketChannel.open();
channel.configureBlocking(false);
InetSocketAddress isa = new InetSocketAddress(port);
channel.socket().bind(isa);
// Register interest in when connection
channel.register(selector, SelectionKey.OP_ACCEPT);
// Wait for something of interest to happen
while (selector.select() > 0) {
// Get set of ready objects
Set readyKeys = selector.selectedKeys();
Iterator readyItor = readyKeys.iterator();
// Walk through set
while (readyItor.hasNext()) {
// Get key from set
SelectionKey key =
(SelectionKey)readyItor.next();
// Remove current entry
readyItor.remove();
if (key.isAcceptable()) {
// Get channel
ServerSocketChannel keyChannel =
(ServerSocketChannel)key.channel();
// Get server socket
ServerSocket serverSocket = keyChannel.socket();
// Accept request
Socket socket = serverSocket.accept();
// Return canned message
PrintWriter out = new PrintWriter
(socket.getOutputStream(), true);
out.println("Hello, NIO");
out.close();
} else {
System.err.println("Ooops");
// Never ends
} now I'd like to write a Proxy Server. In other
words the Server must
1. listen for a request
2. forward the request to another server
3. listen its reply
4. forward it back to the original caller.
I've tried to modify the basic class but with no success....
unfortunately I'm not that smart with these new Apis.
anybody can give me some guidelines about how should I
struct it ?
Thanks a lot
FrancescoNot a guru but I'll offer some suggestions. Are these persistent connections to the proxy, or is a connection made per request? You'll probably do things a little bit differently in the two different cases.
In general though, you can have one thread running a request dispatcher which accepts incoming connections and puts read ready channels on a queue. Another thread(or threads) can take requests off the queue and process them. Also, when you accept new connections, I think its better to do it through channels, rather than work directly with the socket. Something like this:
SocketChannel clientChannel = serverChannel.accept();
clientChannel.configureBlocking(false);
SelectionKey newReadKey = clientChannel.register(selector, SelectionKey.OP_READ);
Where are you getting into problems? -
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. -
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
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