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java.io.EOFException when reading from socket

I have a server and a client set up in this way. I can't find the cause of the EOFException, because it happens randomly. It throws the following exception every time a client connects, but I can't figure out the source of it. It always occurs before it reads what the client has sent. The exception always is at this line:
ObjectInputStream objectInputStream = new ObjectInputStream(socket.getInputStream());
Here is the exception:
java.io.EOFException
at java.base/java.io.ObjectInputStream$PeekInputStream.readFully(ObjectInputStream.java:2860)
at java.base/java.io.ObjectInputStream$BlockDataInputStream.readShort(ObjectInputStream.java:3355)
at java.base/java.io.ObjectInputStream.readStreamHeader(ObjectInputStream.java:939)
at java.base/java.io.ObjectInputStream.<init>(ObjectInputStream.java:381)
at com.denesgarda.Socketeer.data.End$3.run(End.java:62)
at com.denesgarda.Socketeer.data.End$3.run(End.java:76)
at com.denesgarda.Socketeer.data.End$3.run(End.java:76)
at com.denesgarda.Socketeer.data.End.listen(End.java:83)
at Server.<init>(Server.java:10)
at SStart.main(SStart.java:5)
Here is my server code:
if(listener == null) this.voidListener();
ServerSocket serverSocket = new ServerSocket(port);
End THIS = this;
TimerTask timerTask = new TimerTask() {
#Override
public void run() {
try {
Socket socket = serverSocket.accept();
socket.setSoTimeout(10000);
Connection connection = new Connection(THIS, new End((((InetSocketAddress) socket.getRemoteSocketAddress()).getAddress()).toString().replace("/","")), port, listener);
try {
ObjectInputStream objectInputStream = new ObjectInputStream(socket.getInputStream());
Object o = objectInputStream.readObject();
if (o.equals("01101100 01101001 01110011 01110100 01100101 01101110 00100000 01110011 01110100 01100001 01110010 01110100")) {
listener.event(new ConnectionEvent(connection));
listener.event(new ConnectionSuccessfulEvent(connection));
}
else {
listener.event(new ReceivedEvent(connection, o));
}
socket.close();
}
catch(EOFException e) {
e.printStackTrace();
}
this.run();
}
catch(Exception e) {
e.printStackTrace();
}
}
};
timerTask.run();
Here is my client code:
if(listener == null) this.voidListener();
Socket socket = new Socket(address, port);
Runtime.getRuntime().addShutdownHook(new Thread() {
#Override
public void run() {
try {
socket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
});
send("Message");
public void send(Object object) throws IOException {
Socket socket = new Socket(THAT.getAddress(), this.port);
OutputStream outputStream = socket.getOutputStream();
ObjectOutputStream objectOutputStream = new ObjectOutputStream(outputStream);
objectOutputStream.writeObject(object);
socket.close();
}
What I've Tried
I've tried to fix this issue many times before. I tried to create object output streams. I've switched the order that I initialize the object input stream and object output stream. This is so that the server doesn't get frozen in a deadlock with the client. I have no idea what could be causing this error.

I think I know what is going on here, but I can't be certain because your code is fragmentary, and the symptoms are not well characterized. (The exceptions are unlikely to really be random, for example.)
First there is one indisputable fact. A one side of a connection sees an EOFException because the other side has closed the network connection. That's what that exception means.
In your case, the server gets the exception in the ObjectInputStream constructor because the constructor attempts to read an object stream header that the client side never sends ... on that connection.
Now, the theory. I think I know why. Here is the relevant part of your code (with some bits snipped out for brevity).
Socket socket = new Socket(address, port);
Runtime.getRuntime().addShutdownHook(new Thread() {
#Override
public void run() {
[...]
socket.close();
[...]
}
});
send("Message");
public void send(Object object) throws IOException {
Socket socket = new Socket(THAT.getAddress(), this.port);
[...]
}
Notice that there are two sockets! The first one is created and passed to the shutdown hook. The second one is created and used within send and then closed.
I think the problem is the first Socket. When that is created, it establishes a connection to the server. The server code will accept it and then attempt to read. The read will block ... since the client side hasn't written anything to that socket. The client will then call send which opens and uses a different Socket.
Eventually, the client application exits.
When it exits, the shutdown hook closes the first socket. That causes the server side to see the end of stream ... and triggers the EOFException.
So how to fix this?
It rather depends on the "big picture". Is the real client sending a single message to the server, or does it need to reuse the socket to send multiple messages?
Assuming the former, the solution is simple:
Get rid of the code that creates a socket and passes it to a shutdown hook. As you have written it, it serves no useful purpose.
Rewrite the send method to use try with resources; e.g.
public void send(Object object) throws IOException {
try (Socket socket = new Socket(THAT.getAddress(), this.port);
OutputStream os = socket.getOutputStream();
ObjectOutputStream oos = new ObjectOutputStream(os)) {
oos.writeObject(object);
}
}
Note that the above will automatically close the 3 resources in the correct order.

Create ObjectInputStream according to a socket

I'm trying to create an ObjectInputStream according to a Socket and add this stream into a List.
The client is connected in the main class of my program, and the socket is sent in an other method in a Thread. Then the socket is used to create the stream.
The problem is that the stream is never create. I don't get why...
Below is my code :
In my Thread :
public void addClient(Socket socket){
try{
streamList.add(new ObjectInputStream(socket.getInputStream()));
}catch(IOException e){
e.printStackTrace();
}
}
And in my main class :
ServerSocket serverSocket = new ServerSocket(PORT);
Socket socket;
ClientThread clientThread = new ClientThread();
//start the thread
try{
socket = serverSocket.accept();
clientThread.addClient(socket);
}
catch(IOException e){
e.printStackTrace();
}
Thanks in advance.

The peer needs to create his ObjectOutputStream immediately on connection. Otherwise new ObjectInputStream will block until he does so.
It would be better if you could defer creation of the ObjectInputStream to the run() method of the thread that handles the accepted socket. You shouldn't do any I/O in the accept loop, just the accept itself. Otherwise you can block subsequent clients.

app get stuck at serverSocket.accept() and gives bind exception address already in use on the second call for the thread

I have two problems with an app that i have built for socket communication, first I'll try to explain what the app does and then I'll go into the details of those two problems.
First I click on a button, which starts a thread, which sends a multicast massage "group address" through a UDP socket. Once any of the devices receive the massage, they will send a response through TCP socket and my device will act as a server to the one that sent the response. So after debugging I found out the first problem which is clientSocket = serverSocket.accept(); sometimes gets stuck and the app will block everything and keep executing it, which might happen because the udp massage might never arrive at the destination which means there is no client for the tcp server that I've created.
First question: Is there any way to make the serverSocket.accept(); non-blocking or set a time out? I've tried serverSocket.setTimeSoOut() method, but that didn't work. Maybe this problem comes from something other than the UDP message?
The second problem is that if I press the button that calls the thread twice it will throw a BindException address already in use: Which will happen because of the re execution of serverSocket.bind(new InetSocketAddress(4125));. Is there any way to fix/avoid that?
Here are the threads that I'm using:
This one is called after I press the button:
private class ChatClientThread extends Thread {
DatagramSocket socket;
String sentence;
String modifiedSentence;
BufferedReader inFromUser;
DataOutputStream outToServer;
BufferedReader inFromServer;
Socket clientSocket;
ServerSocket serverSocket;
#Override
public void run() {
/*Socket socket = null;
DataOutputStream dataOutputStream = null;
DataInputStream dataInputStream=null;*/
clientSocket=null;
try {
String data="NewTask_"+EmpPhoneNumber;
serverSocket=new ServerSocket();
serverSocket.setReuseAddress(true);
serverSocket.bind(new InetSocketAddress(4125));
socket = new DatagramSocket(52276);
socket.setBroadcast(true);
InetAddress group = InetAddress.getByName(
"224.0.1.2");
DatagramPacket packet = new DatagramPacket(data.getBytes(), data.length(),
group, 52276);
socket.send(packet);
while(true){
clientSocket = serverSocket.accept();
ConnectThread ct=new ConnectThread(clientSocket);
ct.start();
}
} catch (UnknownHostException e) {
e.printStackTrace();
final String eString = e.toString();
TicketDetails.this.runOnUiThread(new Runnable() {
#Override
public void run() {
Toast.makeText(TicketDetails.this, eString, Toast.LENGTH_LONG).show();
}
});
} catch (IOException e) {
e.printStackTrace();
final String eString = e.toString();
TicketDetails.this.runOnUiThread(new Runnable() {
#Override
public void run() {
Toast.makeText(TicketDetails.this, eString, Toast.LENGTH_LONG).show();
}
});
} finally {
TicketDetails.this.runOnUiThread(new Runnable() {
#Override
public void run() {
}
});
}
}
}
this one is called from the above thread as you can see:
private class ConnectThread extends Thread {
Socket socket;
String sentence;
String modifiedSentence;
BufferedReader inFromUser;
DataOutputStream outToServer;
BufferedReader inFromServer;
ConnectThread(Socket socket){
this.socket= socket;
}
#Override
public void run() {
DataInputStream dataInputStream = null;
DataOutputStream dataOutputStream = null;
Socket socket2 = null;
DataOutputStream dataOutputStream2= null;
DataInputStream dataInputStream2=null;
try {
while(true){
inFromUser = new BufferedReader( new InputStreamReader(System.in));
outToServer = new DataOutputStream(socket.getOutputStream());
inFromServer = new BufferedReader(new InputStreamReader(socket.getInputStream()));
sentence = inFromUser.readLine();
modifiedSentence = inFromServer.readLine();
socket2 = new Socket(socket.getInetAddress().getHostAddress(), 4125);
dataOutputStream2 = new DataOutputStream(
socket2.getOutputStream());
String[] parts = modifiedSentence.split("_");
String partGive = parts[0].substring(4); // 004
String partEmpId = parts[1];
if(partGive.equals("GiveMeATask")&&Integer.parseInt(partEmpId)==empId){
dataOutputStream2.writeUTF(" "+"SolveProblemOrder_2");
dataOutputStream2.flush();
}
System.out.println("FROM SERVER: " + modifiedSentence);
if(modifiedSentence!=null) break;}
outToServer.close();
inFromServer.close();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (dataInputStream != null) {
try {
dataInputStream.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if (dataOutputStream != null) {
try {
dataOutputStream.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
}

Those are two very commmon problems. I'll answer the two in reverse order.
The button you are talking about is creating a ServerSocket and binding it to a specific port. In your case, the port is 4125. From looking at your code, you don't seem to be closing that serversocket anywhere. When you click the button a second time, a second instance of ServerSocket tries to bind to the same port - but that port is still in use by the first ServerSocket. In that case, you get a bind exception. One port cannot be used by more than one ServerSocket. The solution would be to close the existing ServerSocket before creating a new one using serverSocket.close();
If you read the documentation, it clearly states what ServerSocket.accept() does: "[...] The method blocks until a connection is made." This is the "getting stuck" that you described. The thread that executes that code is put into a waiting position and continues only when a connection is made, then returns that new connection. The classic approach is to start a new thread that waits for incoming connections so that your main thread continues to execute and your whole application does not "freeze". Another approach would be a non-blocking framework that encapsulates all that overhead away from you, one of those is Apache MINA.
I would highly suggest to look into small example projects that deal with basic client/server behaviour as you will most likely deal with threads here.

First problem: It is very likely that your application is not receiving the UDP packages. If serverSocket.accept() doesn't get any clients it'll wait indefinitely for someone to connect. You could avoid this by using yet another thread that just accepts connections to avoid freezing your application. Another way would be to use Java's NIO classes that provide non-blocking IO for pretty much anything. That would require you to use ServerSocketChannel and related classes. (Quick googling also gave me this guide which seems fairly easy to follow).
Second problem: You need to close your ServerSocket once you're done using it. Otherwise the port will never be free again to be used by another ServerSocket.
Alternatively you could just leave the Socket open and remember that you already openend it (e.g. with a boolean field in your class).

Recieving objects through ObjectInputStream (Java)

It's a messenger application in java. I want to send objects and not just text, I think it's much better. I'm using a ServerSocketChannel and a new Thread for every connected client.
-Same package, same constructor, same serialVersionUID.
It just prints out the "before" command, can't read the Client's object.
Part of the server's code:
public static void startServer(){
try{
ServerSocketChannel ssc=ServerSocketChannel.open();
ssc.socket().bind(new InetSocketAddress(hostName,portNumber));
while(isServerRunning()){
removeLoggedOutClients();
try{
SocketChannel sc=ssc.accept();
Socket s=sc.socket();
ObjectInputStream ois=new ObjectInputStream(s.getInputStream());
Client cli=null;
System.out.println("before");
cli=(Client)ois.readObject();
System.out.println("after");
ois.close();
if(checkLogin(cli)){
System.out.println(cli.getUsername()+" signed in.");
cli.setSocket(s);
ClientThread ct=new ClientThread(s,cli.getClientID());
ct.setDaemon(true);
clientThreads.add(ct);
ct.start();
}
}
catch(Exception e){
Error err=new Error("Server","void startServer()",2,e.toString());
}
}
}
catch(Exception e){
Error err=new Error("Server","void startServer()",1,e.toString());
}
}
Part of the client's code:
public static void connectToServer(Client user){
try{
SocketChannel sc=SocketChannel.open();
sc.configureBlocking(true);
sc.connect(new InetSocketAddress(serverHostName,serverPortNumber));
Socket s=sc.socket();
ObjectOutputStream oos=new ObjectOutputStream(s.getOutputStream());
ObjectInputStream ois=new ObjectInputStream(s.getInputStream());
oos.writeObject(user);
oos.flush();
RecieveThread rt=new RecieveThread(s,ois,user);
rt.setDaemon(true);
rt.start();
setOut(oos);
}
catch(Exception e){
Error err=new Error("Client","connectToServer(Client user)",1,e.toString());
}
}
(The purpose of my "Error" class is to insert all possible exceptions to database.)

The main problem is that you're creating an ObjectInputStream in the client: this will block until the ObjectOutputStream in the peer is created, and you're not creating one, at least not in the code you posted. You need to create the ObjectOutputStream and then the ObjectInputStream, immediately, in that order, at both ends.
However you have a further problem. You shouldn't do any I/O whatsoever in the accept loop other than accepting connections. All the object stream creation, login, etc., should be done in the thread created to handle he connection, and NB not in its constructor but in its run() method. Otherwise one rogue or malfunctioning client can block the whole system.

ObjectOutputStream not sending data (server stuck at socket.accept())

I am trying to send an object over a connection using Java. This is my client side code. The server receives the data the first time, but the second time is stuck at socket.accept(). Am i doing something wrong here? Thank you!
public class Client
{
public static void main(String args[])
{
try
{
Socket socket = new Socket("localhost", 40003);
ClientObject c = new ClientObject(socket);
c.init();
}
catch (Exception e)
{
e.printStackTrace();
}
}
}
class ClientObject
{
Socket socket;
public ClientObject(Socket socket)
{
this.socket = socket;
}
public void init()
{
try
{
// computation
SendObject so = new SendObject(toSend1, toSend2, rand, username.length());
// send all of this
OutputStream o = socket.getOutputStream();
ObjectOutputStream oos = new ObjectOutputStream(o);
oos.writeObject(so);
o.flush();
InputStream i = socket.getInputStream();
ObjectInputStream ois = new ObjectInputStream(i);
// works, data received from the server
so = (SendObject)ois.readObject();
// further computation
so = new SendObject(null, digest, rand + 1, -1);
oos.reset();
oos.writeObject(so);
// doesn't work :(
o.flush();
}
}

Two things:
Flush the ObjectOutputStream instead of the underlying OutputStream.
The client it's using the same stream and thus the same connection to write to the server, hence the server should not expect a second accept but rather keep reading the stream of the same connection. You can of course also set up a new connect (Socket) and send the second object over that socket. Then the server should accept another socket.

Looks for me, that the server has successfully accepted the connection, otherwise you would not be able to send and receive. Look at your server code the problem may be that you close() the socket connection after the server has received from the client. Pleas provide your server code to have a look at.