Asynchronous socket programming in Java?

I am a C++ programmer, I just wonder how do I do asynchronous programming in Java?
In VC++, you can hook an event handler to the socket and the system will fire an event whenever there is data coming in to the socket. The event handler can then spawn a thread and handle the network message.
In Unix, you can use the select() function. This function will return whenever the indicated socket fires events. If nothing happens within the timeout period, the function simply returns.
What about in Java? I don't see any methods that allows you to hook an event handler to it. Is there anything like select() function in Unix?
Thanks so much.

There is something very much like C's select: selectors. I don't immediately know where to read more about them but google for things like "java selector example", "java nio tutorial", etc (NIO = new I/O, the library where selectors live.)
Another way to do async sockets in Java is by threading. That is the traditional way before New I/O. It's still a perfectly good and easy way, thanks to Java's easy threading. Downside is that it scales to only maybe 100-200 simultaneous connections per server (will depend on your operating system). For thread-based sockets check Sun's Java socket tutorial (first item when you google "java socket tutorial").

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import java.io.EOFException;
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import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
import java.net.UnknownHostException;
public class client
public client()
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Hello Dear Java Forums Team I'am Alfonso Franco who is reporting my socket program
as http://www.javaworld.com without a port number assigned only the Input of www.javaworld.com more the following Code: System.out.printIn( " Enter a Host Name: ", + name) ;
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Alfonso Franco
[email protected]

Remove "if (input.ready())". readLine() will block, consuming zero cpu, until it gets data, EOF or an IOException.
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JPCap

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PS:
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import java.util.*;
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          BufferedReader userIn=null;
          PrintWriter sockOut=null;
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Sorry everyone but I'd been giving a wong IP address thinking it's my own. The problem's solved.
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We run this program in solaris.
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Don't close the selector. There is a selector leak. Just close the socket channel. As this is a client you should then also call selector.selctNow() to have the close take final effect. Otherwise there is also a socket leak.

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[Urgent]3G Socket programming

May I use socket for 3G networks?
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1.     We want to create a socket connection which can
remain open and live for ever till it is closed. Is
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2.     I am just wondering in order to communicate with
the third party over the socket connection, does this
other party requires to run something specific on
their end? I am not able to understand how will my
java code communicate with their server otherwise.It has nothing to do with java. Sockets send and recieve messages. The applications at either end, regardless of the language that they are written in, must handle those messages.
3.     Can we send and receive data over the socket
created and also is their specific format for the
data? Yes.
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http://java.sun.com/docs/books/tutorial/networking/sockets/index.html

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I want to establish socket connection between Java client and C server (on Unix). Can anybody tell how to do it? Will the socket created in client be available in server. I tried out but there was no response from the server.

We too can't connect the daemon server written by "c". The phenomena is below.
<< Execution of this Question1.class >> ---------------------------------------
[kazuyuki@CryptOne tmp]$ java Question1 E 1.2.3.4 MFrame.java 195.211.1.1 15021
<< Output message >> ----------------------------------------------------------
Quetion1 : flg_ = E
Quetion1 : key_ = 1.2.3.4
Quetion1 : fn_ = MFrame.java
Quetion1 : adr_ = CryptOne.localhost/195.211.1.1
Quetion1 : port_ = 15021
java.net.ConnectException: Connection refused
     at java.net.PlainSocketImpl.socketConnect(Native Method)
     at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:350)
     at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:137)
     at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:124)
     at java.net.Socket.<init>(Socket.java:268)
     at java.net.Socket.<init>(Socket.java:122)
     at Question1.UPLOAD(Question1.java:65)
     at Question1.main(Question1.java:155)
<< Question >> ----------------------------------------------------------------
Why the event "java.net.ConnectException: Connection refused" has occured ?
The server to connect from Question1 can accept the connection request from
the client program coded by "c" program. We have written down the daemon server
program by "c" code tcp/ip socket functions (socket, bind, listen, accept).
Security manager admits the access from this Question1.class, we have checked.
Would you like please answer this Connction refuse occurrence ?
                                                                 2002.05.18 11:50:00.0(JST)
                                                                 K.Masuda
<< Java client code>> -------------------------------------------------
     (c)Copyright     All rights reserved.
          K.Masuda     2002.05.18
               << Question1.java >>
import     java.lang.String;
import     java.io.InputStream;
import     java.io.OutputStream;
import     java.io.DataInputStream;
import     java.io.DataOutputStream;
import     java.io.FileInputStream;
import     java.io.FileOutputStream;
import     java.io.IOException;
import     java.io.FileNotFoundException;
import     java.net.Socket;
import     java.net.InetAddress;
import     java.net.UnknownHostException;
import     java.net.ConnectException;
import     java.net.NoRouteToHostException;
class Question1 {
     char               flg_;
     String               key_;
     String               fn_;
     InetAddress          adr_;
     int                    port_;
     Socket               sock_;
     Question1(
          char          flg,
          String          key,
          String          fn,
          String          adr,
          int               port
          flg_     = flg;
          key_     = key;
          fn_          = fn;
          try{
               adr_     = InetAddress.getByName( adr );
          catch( UnknownHostException e ){
               e.printStackTrace();
          port_     = port;
System.out.println( "Quetion1 : flg_ = " + flg_ );
System.out.println( "Quetion1 : key_ = " + key_ );
System.out.println( "Quetion1 : fn_ = " + fn_ );
System.out.println( "Quetion1 : adr_ = " + adr_ );
System.out.println( "Quetion1 : port_ = " + port_ );
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          try{
               sock_     = new Socket( adr_, port_ );
               UpLoad();
               DnLoad();
               sock_.close();
          catch( UnknownHostException e ){
               e.printStackTrace();
          catch( ConnectException e ){
               e.printStackTrace();
          catch( NoRouteToHostException e ){
               e.printStackTrace();
          catch( IOException e ){
               e.printStackTrace();
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          byte[]                         buf          = new byte[ 512 ];
          int                              rlen;
          int                              wlen;
          try {
               OutputStream          sos          = sock_.getOutputStream();
               FileInputStream          fis          = new FileInputStream( fn_ );
               DataInputStream          dis          = new DataInputStream( fis );
               DataOutputStream     dos          = new DataOutputStream( sos );
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                    dos.write( buf, 0, rlen );
               dis.close();
               dos.close();
               fis.close();
               sos.close();
          catch( IOException e ){
               e.printStackTrace();
     public void DnLoad(
          byte[]                         buf          = new byte[ 512 ];
          int                              rlen;
          int                              wlen;
          try {
               InputStream               sis          = sock_.getInputStream();
               FileOutputStream     fos          = new FileOutputStream( fn_ + ".cry" );
               DataInputStream          dis          = new DataInputStream( sis );
               DataOutputStream     dos          = new DataOutputStream( fos );
               while( ( rlen =     dis.read( buf, 0, buf.length ) ) >= 0 ){
                    dos.write( buf, 0, rlen );
               dis.close();
               dos.close();
               fos.close();
               sis.close();
          catch( IOException e ){
               e.printStackTrace();
     public static void main(
          String[] args
          char[]     chrs     = ( new String( args[ 0 ] ) ).toCharArray();
          Question1     clnt     = new Question1(
                                                                 // E or D
                                        chrs[ 0 ],
                                        args[ 1 ],               // key string
                                        args[ 2 ],               // file to be processed
                                        args[ 3 ],               // IP address
                                                                 // port
                                        Integer.parseInt( args[ 4 ] )
          clnt.UPLOAD();
}

Never programmed with Java

Hello
I have never programmed with Java, and dont know, what i can do, I use PHP, but, i am only a novice at it.
I was wondering, is it possable to get data from a page, and put it into an image? if there is no data from the page, it will ask for the data to be added, and this will update every so often?
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I think Google Maps is programmed in JavaScript using AJAX (short for Asynchronous JavaScript and XML) and is what as known as a web application. Google has released an API (still in beta) for working with Google Maps. The webpage for this API is http://www.google.com/apis/maps/. More about the development facilities Google provides can be found at http://code.google.com/.
I've never read the source code to Google Maps before (a lot of which is available by just viewing the source code of the Google Maps webpage, which can be done by clicking, View > Source in Internet Explorer and View > Page Source in Mozilla Firefox), however I don't think it is a terribly complex application (this does not mean, however, that the source code is easy to read). I think the way it works is by requesting individual images as needed from the Google server and piecing them together on the client side (i.e. in the browser). Basically what you would need to do to use their existing code is to replace all requests made to the Google server with requests to a server of your own and have the server return the corresponding images. This might not be particularly easy to do.
In my opinion, a better approach is just to write your own custom application (probably in Java) which simply mimics the behavior of Google maps, except with your own custom images. This way, you don't have to reverse engineer an entire web application before beginning to write one.
Writing your own application for this purpose is not as difficult as it sounds, especially not in Java. Once understanding the basics, you will not be too far off from being able to write your application.
Let's start with the most basic program (this program would be located in a file called Program.java):
public class Program {
public static void main(String[] args) {
}This program simply starts, does nothing, and exits. I will explain this piece of code line by line, but first, I would like to gauge how much you already know to figure out how best to explain this. Have you used classes in PHP before?

RESTFUL Web Services vs Socket Programming Performance

Hi guys,
I will have an application which will have a service serving about to 30 million users/day and a mean of 5 requests/user.
It means that there will be about 150 million requests per day. I will have two servers behind a load balancer and my clients will be both Java and C++.
I think to implement RESTFUL Web Services but afraid of performance issues.
Did you have a knowledge about the performances of web service and socket programming in such a high loaded project?
Tnx.
Ayberk

ayberkcansever wrote:
Hi guys,
I will have an application which will have a service serving about to 30 million users/day and a mean of 5 requests/user.
It means that there will be about 150 million requests per day. I will have two servers behind a load balancer and my clients will be both Java and C++.
I think to implement RESTFUL Web Services but afraid of performance issues.
Did you have a knowledge about the performances of web service and socket programming in such a high loaded project?It depends on the CPUs, RAM, disks, and network configurations of those servers.
It depends on how the requests are distributed throughout the day.
It depends on how big the requests are and how big the responses are.

Asynchronous socket programming in Java?

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