Develop Reference

Unable to Create ObjectInputStream Object

This is my code. When I run this, I get up to "Three and a Half" printed. (The prints are added for debugging since I don't know any other way.) After that, the execution hangs. No exceptions, no prompts, nothing. So what is wrong with my object creation? Each and every tutorial I see online has the same code, but mine won't work.
public class Connection {
Socket socket;
ObjectInputStream iStream;
ObjectOutput outputStream;
public Connection(Socket s) {
try {
System.out.println("One");
socket = s;
System.out.println("Two");
outputStream = new ObjectOutputStream(new BufferedOutputStream(socket.getOutputStream()));
System.out.println("Three");
InputStream is = socket.getInputStream();
System.out.println("Three and a Half");
iStream = new ObjectInputStream(is);
System.out.println("Four");
} catch (IOException e) {
e.printStackTrace();
}
}
}
Thanks in advance.

It's in the Javadoc:
A serialization stream header is read from the stream and verified. This constructor will block until the corresponding ObjectOutputStream has written and flushed the header.
So the new ObjectInputStream is hanging because it's waiting on input. You need to create an ObjectOutputStream and send data through the socket.

one single ObjectOutputStream for multiple use with sockets

I'm trying to make a very basic example of a network connection where I use an ObjectOutputStream, ObjectInputStream and sockets. The client sends the string "Hello" to the server. As you see this string is sent 10 times with the very same ObjectOutputStream. Then the server sends the string "Goodbye" to the client. The console should display 10 times the string "hello" and 10 times the string "Goodbye". But they are shown only one time. I read in many threads about the method reset() of the ObjectOutputStream. But it does not seem to work for me. Any ideas what the problem is? I've already tried many different things without success.
Here is the client:
try
{
Socket socket = new Socket("localhost", 5555);
ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream());
ObjectInputStream in = new ObjectInputStream(socket.getInputStream());
int i = 10;
while (i > 0)
{
//send String
out.writeObject("Hello");
out.flush();
out.reset();
//receive String
String result = (String) in.readObject();
System.out.println(result);
i--;
}
} catch (IOException e)
{
e.printStackTrace();
} catch (ClassNotFoundException e)
{
e.printStackTrace();
} finally
{
out.close();
in.close();
socket.close();
}
Here is the server:
try
{
ServerSocket server = new ServerSocket(5555);
while(true)
{
try
{
Socket client = server.accept();
ObjectInputStream in = new ObjectInputStream(client.getInputStream());
ObjectOutputStream out = new ObjectOutputStream(client.getOutputStream());
//receive String
String input = (String) in.readObject();
System.out.println(input);
out.writeObject("Goodbye");
out.flush();
out.reset();
} catch(IOException e1)
{
e1.printStackTrace();
} catch (ClassNotFoundException e)
{
e.printStackTrace();
}
}
} catch(IOException e2)
{
e2.printStackTrace();
}

Your server is only reading and writing once to each accepted socket. So the client can't possibly read an object ten times.
Your server also isn't closing the stream when it's finished.

Java SocketException Broken pipe

I am doing a client to server Log-in communication.
I met a java.net.SocketException: broke Pipe at Server end. And I have narrowed the
problem to one single line at the client end. If I move a position for this line,
the code works. plese see the following code.
Client End:
Socket socket = new Socket(Const.destIp, 12101);
ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream());
out.writeObject(this.message);
out.close();//Line that cause problem
ObjectInputStream in = new ObjectInputStream(socket.getInputStream());
ServerToClientLogin msg = (ServerToClientLogin) in.readObject();
//out.close();//move it to here, problem solved
in.close();
socket.close();
Server end:
while (true) {
socket = _serverSocket.accept();
in = new ObjectInputStream(socket.getInputStream());
msg = (ClientToServerLogin) in.readObject();
ServerToClientLogin msgToSend = null;
out = new ObjectOutputStream(socket.getOutputStream());
msgToSend = handleLoginRequest(msg);
if(msgToSend != null) out.writeObject(msgToSend);
try { in.close(); } catch (IOException e) {e.printStackTrace();}
try { out.close();} catch (IOException e) {e.printStackTrace(); }
try { socket.close();} catch (IOException e) {e.printStackTrace();}
}
Since readObject and writeObject are blocking call, I have no idea why close it earlier would case such problem.

out.close();: Closes this (out) output stream and releases any system resources associated with this stream.
See the API here.

server connections

I'm doing my own server in Java. I need to do one socket connection and receive a lot of object from client. I did it, it works, but I don`t know if this is the best(fastest) solution. Here is example of my code:
try {
serverSocket=new ServerSocket(18234, 1000);
} catch (IOException e) {
System.out.print("Server failed..");
e.printStackTrace();
}
Object x;
ObjectInputStream ois;
System.out.println("Waiting for connection...");
Socket connection= serverSocket.accept();
System.out.println("Connection received from " + connection.getInetAddress().getHostName());
while(true){
ois = new ObjectInputStream(connection.getInputStream());
x=ois.readObject();
System.out.println(x.getString());
if(x.getString().equals("END")) break;
}
Problem is, that when I try receive new object, all time I must do new ObjectInputStream.. Is this solution correct? I must do really fast server and all time doing new ObjectInputStream is too expensive in my opinion.

Use the same ObjectOutputStream and ObjectInputStream for the life of the socket, at both ends. Your statement about being obliged to use a new one each object is incorrect.

Not receiving final data from stream

I am currently not receiving the last object from my object stream until another set of data is sent from the server. The objects sent have either a 1,2 or 3 int to state whether they are the first middle or last packets. I have sent these objects to an array and analysed this in the debugger, it shows that the last packet does not come through until the first one is sent again.
This is the server code:
public void telleveryone(Object message){
Iterator it = clientOutputStream.iterator();
while(it.hasNext()){
try{
ObjectOutputStream everyone = (ObjectOutputStream)it.next();
everyone.writeObject(message);
everyone.flush();
}catch(Exception ex){
ex.printStackTrace();
}
}
}
This is the receiving code on the client:
public void run() {
try{
sock = new Socket("10.42.34.46", 1337);
InputStream is = sock.getInputStream();
ois = new ObjectInputStream(new BufferedInputStream(is));
OutputStream os = sock.getOutputStream();
oops = new ObjectOutputStream(os);
while(true){
serverDraw = (com.DrawTastic.Drawring) ois.readObject();
test.add(serverDraw);
}
}catch(IOException ex){
ex.printStackTrace();
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

You need to flush the header:
callers may wish to flush the stream immediately to ensure that
constructors for receiving ObjectInputStreams will not block when
reading the header
oops = new ObjectOutputStream(os);
oops.flush();

I didn't read over the code thoroughly, but I've run into this problem with Python. I noticed a lot of my commands to the server were not executing until my program pinged the server again. My solution was to ensure there was a newline at the end of each command to the server, or you could flush the buffer.