java - Need help on a simple server/multiple client chat application -

this scenario .. have 2 clients connected server.. want them able chat eachother. after couple of messages error.

    exception in thread "thread-0" java.lang.classcastexception:     java.io.objectstreamclass cannot cast message.mesaj     @ server.serverthread.readandwrite(serverthread.java:43)     @ server.serverthread.run(serverthread.java:61)     java.io.streamcorruptedexception: invalid type code: 00     @ java.io.objectinputstream.readobject0(unknown source)     @ java.io.objectinputstream.readobject(unknown source)     @ server.serverthread.readandwrite(serverthread.java:43)     @ server.serverthread.run(serverthread.java:61) 

this client:

package client;  import java.io.ioexception; import java.io.objectinputstream; import java.io.objectoutputstream; import java.net.socket; import java.util.scanner; import message.mesaj;  public class client {  public static int port=4321; public static socket socket; public static objectoutputstream oo; public static objectinputstream oi; public static scanner sc;  public client() throws ioexception{     socket = new socket ("localhost",4321);     oi = new objectinputstream(socket.getinputstream());     oo = new objectoutputstream(socket.getoutputstream());  }   public static void listen() throws classnotfoundexception, ioexception{     while(true){         mesaj m = (mesaj) oi.readobject();         if(m!=null){             system.out.println("mesajul este: " + m.getmesaj());         }     } }  public static void write() throws ioexception{     sc= new scanner(system.in);      while(true){         string trimite= sc.nextline();         mesaj m = new mesaj();         m.setmesaj(trimite);          oo.writeobject(m);         oo.flush();      }  }   public static thread t = new thread(){     public void run(){          try {             listen();         } catch (classnotfoundexception | ioexception e) {             // todo auto-generated catch block             e.printstacktrace();         }       } };  public static thread t2 = new thread(){     public void run(){         try {             write();         } catch (ioexception e) {             // todo auto-generated catch block             e.printstacktrace();         }     } };  public static void main(string[] args) throws ioexception{         new client();         t.start();         t2.start();    } 

this server:

package server;  import java.io.ioexception; import java.net.serversocket; import java.net.socket; import java.util.arraylist;  public class server { public int port; public static socket socket; public static serversocket serversocket;   public server() throws ioexception{ this.port=4321; serversocket = new serversocket(port);  }  public static void main (string [] args){  try {     new server(); } catch (ioexception e1) {     // todo auto-generated catch block     e1.printstacktrace(); } system.out.println("server functionabil..asteptam conexiune client"); while(true){     try {            socket= serversocket.accept();         serverthread st= new serverthread(socket);         st.start();         system.out.println("conexiune realizata -client conectat");      } catch (ioexception e) {         // todo auto-generated catch block         e.printstacktrace();     } catch (classnotfoundexception e) {         // todo auto-generated catch block         e.printstacktrace(); }   }    }   } 

..and server thread:

   package server;     import java.io.ioexception;    import java.io.objectinputstream;    import java.io.objectoutputstream;    import java.net.socket;    import java.util.arraylist;     import message.mesaj;     public class serverthread extends thread {     boolean running;    public static objectoutputstream oo;    public static objectinputstream oi;    public static mesaj m;    public static socket socket;     public serverthread(socket socket) throws classnotfoundexception{     try {                running=true;         this.socket=socket;         oo = new objectoutputstream(socket.getoutputstream());       } catch (ioexception e) {         // todo auto-generated catch block         e.printstacktrace();     }  }    public static void readandwrite() throws classnotfoundexception, ioexception{      oi = new objectinputstream(socket.getinputstream());          while(true){             m= (mesaj) oi.readobject();                  if(m!=null){         oo.writeobject(m);         oo.flush();          system.out.println(m.getmesaj());      }         } }      public void run(){     system.out.println("server thread contectat");     try {        readandwrite();               } catch (ioexception | classnotfoundexception e) {         // todo auto-generated catch block         e.printstacktrace();     } } 

}

edit:
message class:

package message;  import java.io.serializable;  public class mesaj implements serializable {  private string mesaj;  public string getmesaj() {     return mesaj; }  public void setmesaj(string mesaj) {     this.mesaj = mesaj; }     } 

you having concurrency issues.

both serverthreads access same static outputstream, meaning there change corruption object streams aren't designed this.

in serverthread, remove static variables , method "readandwrite".

public objectoutputstream oo; public objectinputstream oi; public mesaj m; public socket socket; ... public void readandwrite() throws classnotfoundexception, ioexception{ 

if want access output streams multiple threads, should synchronize on them.