I'm trying to code a TCP client in android java. Most works fine. But i have one issue. If the socket is connected and the remeote host shuts down or the network goes down or something else, the socket.getinputstream keeps blocking.
I don't know if the socket is still connected. I code in objective-c too and in objective-c i get an event that the socket forcefully shuts down and i can try to reconnect. So on objective c the socket tracks the state.
In java the socket and the inputstream is still connected or blocked even the socket is down. How can i check if the socket is still connected?
#Override
protected Void doInBackground(String... params) {
try {
String host = params[0];
int port = Integer.parseInt(params[1]);
SocketAddress sockaddr = new InetSocketAddress(host, port);
Socket socket = new Socket();
socket.connect(sockaddr,5000);
socket.setSoTimeout(7000);
out = new PrintWriter(socket.getOutputStream(), true);
mBufferIn = new BufferedReader(new InputStreamReader(socket.getInputStream()));
while (mRun) {
try {
-----> mServerMessage = mBufferIn.readLine();
}catch (Exception e){
Log.d("my","hier3" + e.getMessage());
}
if (mServerMessage.trim() != null) {
sender.messageReceived(s2);
}else{
}
}
}
} catch (UnknownHostException e
) {
The question of how to detect if the remote peer/socket has closed the connection has been answered here as well as here.
Basically, the answers suggest that you attempt to read from the socket, and then observe what happens (read() returns -1, or readLine() returns null or your read methods raise EOFException.
Related
I'm programming an application which opens socket in service and sends some data to server and also listens for incoming data. Problem of course appears when connection with internet is lost on android device.
Here is code snippet where i get
java.net.SocketException: recvfrom failed: ETIMEDOUT (Connection timed
out)
try{
mSocket = new Socket("xxx.xxx.xxx.xxx", xxxxx);
out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(mSocket.getOutputStream())), true);
BufferedReader in = new BufferedReader(new InputStreamReader(mSocket.getInputStream()));
String s;
while((s = in.readLine())!= null){ //here error of course
...
}
mSocket.close();
}catch(Exception e){
e.printStackTrace();
}
Error is thrown when internet connection is lost and BufferedReader try to
readLine(). How to avoid this and why is it of course?
UPDATE
Error didn't bother me until I tryed to do next scenario:
1) run socket with wifi turned on
2) turn on also mobile data
3) turned off wifi
When wifi is turned off error occourse, but i'm connected to internet through mobile data, so I would like continu to listen on socket without error. Is this possible and how?
What you should do is reconnect a new socket in your catch block. The original connection is now gone, and I don't know a way of "seamlessly" swapping it.
try {
mSocket = new Socket("xxx.xxx.xxx.xxx", xxxxx);
...
} catch(Exception e){
try {
mSocket = new Socket("xxx.xxx.xxx.xxx", xxxxx);
...
} catch (Exception e2) {
// OK you really lost connectivity at this point, tell the user.
}
}
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).
i'm trying create "multi-client -- single server" connection.
My client(s) opens connection and in the server side I've create
Client clt = new Client("127.0.0.1", 9000);
clt.openConn();
...
public Client(String serverAddress, int serverPort) {
this.serverAddress = serverAddress;
this.serverPort = serverPort;
}
try {
this.clientSocket = new Socket(this.serverAddress, this.serverPort);
this.clientSocket.setKeepAlive(true);
this.clientSocket.setSoTimeout(0);
oos = new DataOutputStream(this.clientSocket.getOutputStream());
ois = new DataInputStream(this.clientSocket.getInputStream());...}
...
on the server side i've created ListArray of ServerSocket's each onf them I wrapped on the Thread.
ServerSocket serverSocket = null ;
Socket clientSocket;
boolean listening = true;
ArrayList threadList = new ArrayList();
Iterator itSrvThr;
try {
serverSocket = new ServerSocket(port);
} catch (IOException e) {
System.err.println("Could not listen on port: " + port + ".");
System.exit(-1);
}
while (listening) {
clientSocket = serverSocket.accept();
ServerThread srvThread = new ServerThread(clientSocket);
srvThread.start();
`...`
}
where
ServerThread extends Thread
{...
public void run() {
this.ois = new DataInputStream(socket.getInputStream());
this.oos = new DataOutputStream(socket.getOutputStream());
}
}
my program send and receive objects(i've called them "Datagramm") which are some kind of wrappers for file and strings (let us say it is some language for client-server)
And now about problem which I have. I must to make verification every time when need to test for "alive" socket from server side...
i'm trying to make this verification when appears new element in the ArrayList in that moment but it brings me problem with "Datagramm's" sending
itSrvThr = threadList.iterator();
while (itSrvThr.hasNext()) {
ServerThread st = (ServerThread) itSrvThr.next();
boolean stoppedSocket = st.getStopped();
if (stoppedSocket) {
st.stop();
itSrvThr.remove();
}else {??? resolution???}
stoppedSocket - it's a value which significate programly turned off socket from client site.
Honestly, i'm working with sockets and threads only a couple weeks, that is why every help and critics will be acceptable.
...
Thank for answer but I have problems with codding of heartbeats. First of them where exactly the place of heartbeat must be placed on the server side.
I suggest you send a heartbeat message from the client and/or the server whenever you haven't sent a message for a while (seconds) The other end can timeout when you haven't recieved anything for some multiple of this time.
If you have a protocol like {message length} {message} I use a message-length=0 as a heartbeat.
I am learning currently about client server communication using Java through sockets.
First of all I retrieve my own machine's IP Address using following code.
InetAddress ownIP=InetAddress.getLocalHost();
//the result being 192.168.56.1
Now I write the simple client server application using the above mentioned address as follow
public class SimpleClientServer {
public static void main(String[] args)
{
//sending "Hello World" to the server
Socket clientSocket = null;
PrintWriter out = null;
BufferedReader in = null;
try
{
clientSocket = new Socket("192.168.56.1", 16000);
out = new PrintWriter(clientSocket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(
clientSocket.getInputStream()));
out.println("Hello World");
out.close();
in.close();
clientSocket.close();
}
catch(IOException e)
{
System.err.println("Error occured " + e);
}
}
}
The result hower reads a follow.
Error occured java.net.ConnectException: Connection refused: connect
What is the reason for this. Is it just the wrong host address?
From the code you have given you seem to suggest that there is currently nothing listening on port 16000 for the socket to connect to.
If this is the case you need to implement something like
ServerSocket serverSocket = null;
try {
serverSocket = new ServerSocket(16000);
}
catch (IOException e) {
System.err.println("Could not listen on port: 16000.");
System.exit(1);
}
More information can be found in the Java online documentation and a full example is included.
With sockets, no matter what language you're using, you either initiate a connection with socket_connect or you listen and accept with socket_listen and socket_accept. Your socket_connect call is trying to connect to an ip address that doesn't seem to be listening to anything.
I am fairly new to java and I am currently experimenting with sockets and buffers.
What I wanted to try was just to instantiate a connection from one local java app and another. I am using ServerSocket and Socket.
The server app has a thread that listens for connections:
public void run() {
try{
ServerSocket serverSock = new ServerSocket(62666);
while(doRun){
Socket sock = serverSock.accept();
BufferedReader reader = new BufferedReader(new InputStreamReader(sock.getInputStream()));
InfoReader.gui.writeToTextArea(reader.readLine() + "\n");
reader.close();
}
}catch(IOException e){
e.printStackTrace();
}
}
The "client" simply sends a string to the server (well it should, but I can't make it work):
try{
Socket sock = new Socket("127.0.0.1",62666);
PrintWriter writer = new PrintWriter(sock.getOutputStream());
writer.print("Connection works!");
}catch(IOException e){
e.printStackTrace();
}
I am sure that the port is open and forwarded to the local machine already. I've checked on http://canyouseeme.org/.
I've also tried using my external IP address as the IP of the socket in the client. It did not work either.
Any help appreciated :).
Mike.
Ok, then as an answer so you can close the question ;-)
Add a flush() and a close() to the Writer.
Hope that helps. :-)