Simple Java Client Server Program

Question

I m writing my first java client server program which just establishes a connection with the server sends it a sentence and the server sends the sentence back all capitalized  This is actually an example straight out of the book  and it works well and fine when I m running the client and server on the same machine and using localhost for the server address  But when I put the client program on a different computer  it times out and never makes a connection with the server  I m not sure why this is and its kind of lame making a your first client server program and not actually be able to use it on two different machines  Here is the client code   import java io    import java net     public class TCPClient       public static void main String argv    throws Exception           String sentence          String modifiedSentence          BufferedReader inFromUser   new BufferedReader new InputStreamReader System in             Socket clientSocket   new Socket  localhost   6789           DataOutputStream outToServer   new DataOutputStream clientSocket getOutputStream             BufferedReader inFromServer   new BufferedReader new InputStreamReader clientSocket getInputStream               sentence   inFromUser readLine            outToServer writeBytes sentence     n            modifiedSentence   inFromServer readLine            System out println modifiedSentence           clientSocket close              Here is the server code   import java io    import java net     public class TCPServer       public static void main String args    throws Exception           String clientSentence          String capitalizedSentence          ServerSocket welcomeSocket   new ServerSocket 6789            while true                Socket connectionSocket   welcomeSocket accept                BufferedReader inFromClient   new BufferedReader new InputStreamReader connectionSocket getInputStream                  DataOutputStream outToClient   new DataOutputStream connectionSocket getOutputStream                 clientSentence   inFromClient readLine                capitalizedSentence   clientSentence toUpperCase       n               outToClient writeBytes capitalizedSentence                       The only thing I change when I run it on two different machines is the client program makes its socket with the IP address of the machine with the server program  which I got from whatismyipaddress com   Thanks a lot for any help   Update  I am indeed on a campus and it seems that its probably not allowing me to use that random port  Any suggestions on finding out what port I can use and or a port that is more than likely allowed

User · Answer

There is a fundamental concept of IP routing  You must have a unique IP address if you want your machine to be reachable via the Internet  This is called a  Public IP Address    www whatismyipaddress com  will give you this  If your server is behind some default gateway  IP packets would reach you via that router  You can not be reached via your private IP address from the outside world  You should note that private IP addresses of client and server may be same as long as their corresponding default gateways have different addresses  that s why IPv4 is still in effect  I guess you re trying to ping from your private address of your client to the public IP address of the server  provided by whatismyipaddress com   This is not feasible  In order to achieve this  a mapping from private to public address is required  a process called Network Address Translation or NAT in short  This is configured in Firewall or Router  You can create your own private network  say via wifi   In this case  since your client and server would be on the same logical network  no private to public address translation would be required and hence you can communicate using your private IP addresses only

User · Answer

Instead of using the IP address from whatismyipaddress com  what if you just get the IP address directly from the machine and plug that in  whatismyipaddress com will give you the address of your router  I m assuming you re on a home network   I don t think port forwarding will work since your request will come from within the network  not outside

User · Answer

If you got your IP address from an external web site  http   whatismyipaddress com    you have your external IP address   If your server is on the same local network  you may need an internal IP address instead   Local IP addresses look like 10 X X X  172 X X X  or 192 168 X X   Try the suggestions on this page to find what your machine thinks its IP address is

User · Answer

Outstream is not closed     close the stream so that response goes back to test client  Hope this helps

User · Answer

My try to do client socket program  server reads file and print it to console and copies it to output file   Server Program   package SocketProgramming copy   import java io BufferedOutputStream  import java io File  import java io FileOutputStream  import java io IOException  import java io InputStream  import java net ServerSocket  import java net Socket   public class ServerRecieveFile       public static void main String   args  throws IOException              TODO Auto-enerated method stub         int filesize   1022386          int bytesRead          int currentTot          ServerSocket s   new ServerSocket 0           int port   s getLocalPort            ServerSocket serverSocket   new ServerSocket 15123           while  true                Socket socket   serverSocket accept                byte   bytearray   new byte filesize               InputStream is   socket getInputStream                File copyFileName   new File  C  Users Username Desktop Output file txt                FileOutputStream fos   new FileOutputStream copyFileName               BufferedOutputStream bos   new BufferedOutputStream fos               bytesRead   is read bytearray  0  bytearray length               currentTot   bytesRead              do                   bytesRead   is read bytearray  currentTot                           bytearray length - currentTot                    if  bytesRead  gt   0                      currentTot    bytesRead                while  bytesRead  gt  -1               bos write bytearray  0  currentTot               bos flush                bos close                socket close                        Client program   package SocketProgramming copy   import java io BufferedInputStream  import java io BufferedReader  import java io File  import java io FileInputStream  import java io FileReader  import java io IOException  import java io OutputStream  import java net InetAddress  import java net ServerSocket  import java net Socket  import java net UnknownHostException   public class ClientSendFile       public static void main String   args  throws UnknownHostException              IOException              final String FILE NAME  C  Users Username Desktop Input file txt           final String FILE NAME    C  Users Username Desktop Input file txt           ServerSocket s   new ServerSocket 0           int port   s getLocalPort            Socket socket   new Socket InetAddress getLocalHost    15123           System out println  Accepted connection       socket           File transferFile   new File FILE NAME           byte   bytearray   new byte  int  transferFile length             FileInputStream fin   new FileInputStream transferFile           BufferedInputStream bin   new BufferedInputStream fin           bin read bytearray  0  bytearray length           OutputStream os   socket getOutputStream            System out println  Sending Files                os write bytearray  0  bytearray length            BufferedReader r   new BufferedReader new FileReader FILE NAME            String as       line   null          while   line   r readLine       null                as    line     n                  as    line                     System out print  Input File contains following data      as           os flush            fin close            bin close            os close            socket close             System out println  File transfer complete

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this is client code  first run the server program then on another cmd run client program  import java io    import java net     public class frmclient     public static void main String args   throws Exception        try                     DataInputStream d new DataInputStream System in             System out print   n1 fact n2 Sum of digit nEnter ur choice                 int ch Integer parseInt d readLine                System out print   nEnter number                int num Integer parseInt d readLine                 Socket s new Socket  localhost  1024               PrintStream ps new PrintStream s getOutputStream                ps println ch                 ps println num                 DataInputStream dis new DataInputStream s getInputStream                String response dis readLine                     System out print  Answer   response                     s close                      catch Exception ex                                this is sever side code  import java io    import java net    public class frmserver      public static void main String args   throws Exception      try            ServerSocket ss new ServerSocket 1024          System out print   nWaiting for client                Socket s ss accept           System out print   nConnected            DataInputStream d new DataInputStream s getInputStream              int ch Integer parseInt d readLine            int num Integer parseInt d readLine              int result 0           PrintStream ps new PrintStream s getOutputStream             switch ch                      case 1 result fact num                    ps println result                     break            case 2 result sum num                    ps println result                     break                       ss close              s close          catch Exception ex              public static int fact int n        int ans 1      for int i n i gt 0 i--              ans ans i            return ans        public static int sum int n         String str n        int ans 0      for int i 0 i lt str length   i                int tmp Integer parseInt str charAt i             ans ans tmp            return ans

User · Answer

you can get ip of that computer runs server program from DHCP list in that router you connected to

User · Answer

It s probably a firewall issue  Make sure you port forward the port you want to connect to on the server side  localhost maps directly to an ip and also moves through your network stack  You re changing some text in your code but the way your program is working is fundamentally the same

User · Answer

import java io    import java net    class serversvi1     public static void main String svi    throws IOException         try             ServerSocket servsock new ServerSocket 5510         DataInputStream dis new DataInputStream System in          System out println  enter the file name           String fil dis readLine          System out println fil    is file transfer           File myfile new File fil         while true                  Socket sock servsock accept            byte   mybytearray new byte  int myfile length              BufferedInputStream bis new BufferedInputStream new FileInputStream myfile             bis read mybytearray 0 mybytearray length            OutputStream os sock getOutputStream            os write mybytearray 0 mybytearray length           os flush             sock close                      catch Exception saranvi              System out print saranvi                 import java io    import java net     class clientsvi1     public static void main String svi   throws IOException         try             Socket sock new Socket  localhost  5510         byte   bytearray new byte 1024          InputStream is sock getInputStream          DataInputStream dis new DataInputStream System in         System out println  enter the file name           String fil dis readLine          FileOutputStream fos new FileOutputStream fil         BufferedOutputStream bos new  BufferedOutputStream fos         int bytesread is read bytearray 0 bytearray length         bos write bytearray 0 bytesread         System out println  out txt file is received          bos close          sock close              catch Exception SVI              System out print SVI

[java] Simple Java Client/Server Program

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