multithreading - Read/write in simple client-server app in Java -

i'm new java , i'm trying learn threads , socket. decide make simple client-server application following official java tutorial. idea simple - server wait connection, if appears, makes new thread new socket, input , output. client side -> make connection; new thread socket, input, output , stdin (to read line , after send server). wrong (don't have idea why) code. connection established, there's no exceptions. explain why doesn't work , how fix it? have suggestions code (probably it's not best practices , things that):

client side:  public class client {     private bufferedreader reader;     private socket sock;     private printwriter writer;  public static void main(string[] args) {     client client = new client();     client.go(); }  public void go() {     setupnetworking();  }  private void setupnetworking() {     try{         sock = new socket("127.0.0.1", 5000);         system.out.println("network established");          serverthread serverthread= new serverthread(sock);         serverthread.start();          system.out.println("type message: ");     } catch (ioexception e) {         system.out.println("problem establishing network: " + e);     } }  class serverthread extends thread {     socket socket;     printwriter out;     bufferedreader in;     bufferedreader stdin;      serverthread(socket socket) {         this.socket = socket;          try{             out = new printwriter(socket.getoutputstream());             in = new bufferedreader(new inputstreamreader(socket.getinputstream()));             stdin = new bufferedreader(new inputstreamreader(system.in));         }catch (ioexception e) {             system.out.println("problem trying read/write server: " + e);         }     }     @override     public void run() {         string fromserver;         string fromclient;         while(true){             try{                  if((fromserver = in.readline()) != null) system.out.println(" " + fromserver);                 else if((fromclient = stdin.readline()) != null) out.println(fromclient);              }catch(exception e) {                 system.out.println("msg exception: " + e);             }          }     } }  } 

server side:

public class server {     //run server until keepgoing = false     private boolean keepgoing = true;        public static void main(string[] args) {         server server = new server();         server.go();     }      public void go() {              try {                 serversocket serversocket = new serversocket(5000);                  while(keepgoing) {                      socket clientsocket = serversocket.accept();                     clientthread t = new clientthread(clientsocket);                     t.start();                 }             } catch (ioexception e) {                 system.out.println("problem socket/network: " + e);             }     }      class clientthread extends thread {         socket clientsocket;         printwriter out;         bufferedreader in;          clientthread(socket clientsocket) {             this.clientsocket = clientsocket;              try{                 out = new printwriter(clientsocket.getoutputstream());                 in = new bufferedreader(new inputstreamreader(clientsocket.getinputstream()));             } catch (ioexception e) {                 system.out.println("problem creating in/out: " + e);             }         }          @override         public void run() {             string message;             while(keepgoing) {                 try{                     message = in.readline();                     out.println(message);                     system.out.println(message);                  } catch (ioexception e){                     system.out.println("exception while try read line: " + e);                 }              }         }     }  } 

ps i've changed bit code - instead of made clientthread class, made new runnable class , pass variable thread class. inspired question: "implements runnable" vs. "extends thread".

i think problem both server , client waiting input. server:

message = in.readline(); 

client:

if((fromserver = in.readline()) != null)    system.out.println(" " + fromserver); else if((fromclient = stdin.readline()) != null)    out.println(fromclient); 

but client code blocks on fromserver = in.readline() part, never gets read standard in, , nothing sent out server.

you move attempt read standard in setupnetworking method, right after system.out.println("type message: ");. build loop there exit if user types "exit" or "quit" or that:

bufferedreader stdin = new bufferedreader(new inputstreamreader(system.in)); string read = ""; {     read = stdin.readline();     system.out.println("read stdin: " + read);     serverthread.send(read);  } while (!read.equals("exit")); 

the serverthread.send() method simple:

void send(string string) {     system.out.println("sending server: " + string);     out.println(string); } 

however, make work, either have flush stream manually after writing out, or use following constructor:

out = new printwriter(socket.getoutputstream(), true); 

see printwriter's javadoc: true means auto-flush on newline.

i tested setup , worked me. able send client server.

however, first step. implement both reading , writing separate threads, both client , server. , there no graceful shutdown of sockets implemenented yet. more complete yet simple example can found on oracle.