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Java Socket stuck at new ObjectInputStream() [duplicate]

This question already has answers here:
ObjectInputStream/ObjectOutputStream work not right
(3 answers)
Closed 7 years ago.
I have this server/client model for a game but it keeps getting stuck at the ObjectInputStream initialization.
Here is the code for the client's start method:
public void start(){
try {
Socket s = new Socket("127.0.0.1", 24680);
Thread.sleep(1000);
ois = new ObjectInputStream(s.getInputStream()); // stuck here
oos = new ObjectOutputStream(s.getOutputStream());
startGame();
} catch (Exception e) {
e.printStackTrace();
}
}
}
here is the server code:
try {
InputStream fis = socket.getInputStream();
ObjectInputStream ois = new ObjectInputStream(fis);
while (true) {
ArrayList < Dot > lists = (ArrayList < Dot > ) ois.readObject();
for (Socket s: sockets) {
ObjectOutputStream oos = new ObjectOutputStream(s.getOutputStream());
oos.writeObject(lists);
}
}
} catch (Exception e) {
e.printStackTrace();
}
Thanks in advance!

You need to construct the ObjectOutputStream before the ObjectInputStream at at least one end, preferably both to avoid accidents. Otherwise new ObjectInputStream() blocks trying to read the stream header which hasn't been written yet by the peer's new ObjectOutputStream(), because he also is blocked in new ObjectInputStream().
Other notes:
You must use the same object streams for the life of the socket, at both ends, unlike your current code. The reason is the same: the stream header. If you keep creating new ObjectOutputStreams you will keep writing new stream headers, which the peer won't expect or understand.
Remove the sleep(). There is no need for sleeps in networking code. They are just literally a waste of time. Cargo-cult programming.

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.

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.

Streams via Socket

I am writing server-client application. Client sends some sort of data via different streams to the server. Once I place streams like this in the main method the program does nothing; no exception just empty console:
try {
socket = new Socket("localhost", 4050);
din = new DataInputStream(socket.getInputStream());
oin = new ObjectInputStream(socket.getInputStream());
dout = new DataOutputStream(socket.getOutputStream());
} catch (UnknownHostException e) {
System.out.println("Exception: the host is unknown");
} catch (IOException e) {
System.out.println("I/O exception thrown by socket");
}
Once I remove this stream oin = new ObjectInputStream(socket.getInputStream()); from that part of main method the program throws EOFException or connection reset exception.
What is so special in the above code that the program does nothing and throws no exceptions?
Once you place the mentioned stream in to a separate method
private static MessageObject readObject(){
MessageObject mo = null;
try{
oin = new ObjectInputStream(socket.getInputStream());
mo = (MessageObject)oin.readObject();
}
catch(IOException e){
System.err.println(e.getCause());
}
catch(ClassNotFoundException e){
System.err.println(e.getCause());
}
return mo;
}
It throws this exception:
Exception in thread "main" java.net.SocketException: Connection reset
at java.net.SocketInputStream.read(Unknown Source)
at java.net.SocketInputStream.read(Unknown Source)
at java.io.DataInputStream.readBoolean(Unknown Source)
at Server.main(Server.java:77)
On the server it is on the if branch:
if (din.readBoolean()) {
ObjectInputStream oin = new ObjectInputStream(s.getInputStream());
MessageObject o = (MessageObject)oin.readObject();
// server saves the whole thing
MessageDB.add(o);
}
I can't place here all my code, it is my assignment.
ooops, sorry people, the mistake has been found. Some logical mistake, the server was expecting some input,but the client was refusing to send it.

You are making several mistakes here.
You are using multiple streams over the same socket. Don't do that, they will only confuse each other. As you need object I/O, just use an ObjectInputStream and ObjectOutputStream for everything.
Incorrect construction order. You must construct the ObjectOutputStream before the ObjectInputStream, at both ends.
You are using streams with different lifetimes. You haven't hit the problem yet but eventually this will lead to a StreamCorruptedException. Use the same ObjectInputStream and ObjectOutputStream for the life of the Socket, at both ends.
You probably also need to read the Javadoc for ObjectOutputStream.reset() and .writeUnshared() to understand what they do, and why you might need to call one or the other of them.

ObjectOutputStream not sending data

Client code:
try {
Socket socket = new Socket(ip, port);
OutputStream output = socket.getOutputStream();
ObjectOutputStream out = new ObjectOutputStream(output);
InputStream input = socket.getInputStream();
ObjectInputStream in = new ObjectInputStream(input);
out.writeByte(1);
FileHandler fh = (FileHandler) in.readObject();
//processing stuff
out.flush();
out.close();
output.flush();
output.close();
input.close();
in.close();
socket.close();
} catch (Exception e) {
e.printStackTrace();
}
Server code:
try {
ServerSocket server = new ServerSocket(port);
Socket socket = server.accept();
InputStream input = socket.getInputStream();
ObjectInputStream in = new ObjectInputStream(input);
int type = in.readByte();
//processing stuff (which includes closing the streams and sending FileHandler object)
socket.close();
} catch (Exception e) {
e.printStackTrace();
}
The server never receives the byte. It just waits for the byte from the client, and it never comes. I'm not sure why it isn't sending, or getting received. Any help is much appreciated.

If I had to make a guess it's because in your client you block on in.readObject(); waiting for the server to send you something thus never flush the output stream thus ... nothing ever gets sent.
Move your read to after you flush your output stream.

Try to use the writeObject and readObject methods. Also write an Integer not an int to the stream. Read this really good lecture before proceeding any further.
This is also a good lecture for your problem.
Regards!