Listen to port via a Java socket

Question

A server software my client communicates with regularly sends transaction messages on port 4000  I need to print those messages to the console line by line   Eventually I will have to write those values to a table  but I   m saving that for later    I tried this code but it doesn   t output anything   package merchanttransaction   import java io IOException  import java io ObjectInputStream  import java io ObjectOutputStream  import java lang ClassNotFoundException  import java net InetAddress  import java net Socket  import java net UnknownHostException   public class MerchantTransaction       public static void main String   args            try               InetAddress host   InetAddress getLocalHost                Socket socket   new Socket  192 168 1 104   4000               ObjectInputStream ois   new ObjectInputStream socket getInputStream                 String message    String  ois readObject                System out println  Message      message                ois close              catch  UnknownHostException e                e printStackTrace              catch  IOException e                e printStackTrace              catch  ClassNotFoundException e                e printStackTrace                        By the way  I need to be able to monitor that port until the program terminates  I   m not sure if the code above will be able to do that because I don   t see any iteration to the code   I   m using Java version 1 6 0 24  SE Runtime Environment  build 1 6 0 24-b07  running on Ubuntu

User · Answer

Try this piece of code  rather than ObjectInputStream   BufferedReader in   new BufferedReader  new InputStreamReader  socket getInputStream       while  true        String cominginText           try               cominginText   in readLine             System out println  cominginText             catch  IOException e                  error   System       Connection to server lost             System exit  1           break

User · Answer

What do you actually want to achieve  What your code does is it tries to connect to a server located at 192 168 1 104 4000  Is this the address of a server that sends the messages  because this looks like a client-side code   If I run fake server locally    nc -l 4000     and change socket address to localhost 4000  it will work and try to read something from nc-created server  What you probably want is to create a ServerSocket and listen on it  ServerSocket serverSocket   new ServerSocket 4000   Socket socket   serverSocket accept     The second line will block until some other piece of software connects to your machine on port 4000  Then you can read from the returned socket  Look at this tutorial  this is actually a very broad topic  threading  protocols

User · Answer

You need to use a ServerSocket  You can find an explanation here

[java] Listen to port via a Java socket

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