I'm trying to create a socket that connects to a server. A user can manually enter the socket's IP address and IP port.
When the address and port are valid nothing goes wrong, but when they don't, it causes my entire app to freeze.
This is the code:
public void connect() {
try {
String txHostIP = settings.getString("txHostIP", "");
int txHostport = Integer.parseInt(settings.getString("txHostPort", ""));
//Where it all goes wrong. The program just hangs here for eternity
socket = new Socket(txHostIP, txHostport);
writer = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
} catch (IOException e) {
showMessage(context, "Something went wrong");
}
}
What I want is for a message to pop up when no connection can be made but the program doesn't throw an exception if an IP port or address is incorrect.
How can I fix this? Any help is greatly appreciated!
EDIT:
I've added some System.out prints to show how the program hangs. I've also added a socket connect timeout of 5 seconds. Still the program won't even reach that block of code.
public void connect() {
try {
String txHostIP = settings.getString("txHostIP", "");
int txHostport = Integer.parseInt(settings.getString("txHostPort", ""));
System.out.println("1");
socket = new Socket(txHostIP, txHostport);
System.out.println("2");
socket.connect(socket.getLocalSocketAddress(), 5000);
System.out.println("3");
writer = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
System.out.println("4");
} catch (IOException e) {
showMessage(context, "Something went wrong");
}
}
It just prints the 1 and then hangs on forever.
If you want to let the socket abort after a certain amount of time you have to do this:
int timeout = 5000;
int port = 1234;
String address = "localhost";
InetSocketAddress inetAddress = new InetSocketAddress(address, port);
Socket socket = new Socket();
socket.connect(inetAddress, timeout);
Otherways the socket will hang before you set the soTimeout. The connect method will throw an SocketTimeoutException if the remote host is not reachable.
Set a connection timeout of say, 5 seconds - run a counter based on the system clock and when the time is up, if it hasn't connected - throw the exception and cancel the connection.
Related
I've just started with both java and networking with servers and clients. Although i understand the basics of whats going on, i was struggling to put it all together and do what i wanted to do in the title.
I was able to make this to send a message to the server, however i was wondering how i'd turn the message into a input string from the user, and also how id send multiple messages between the client and server
thanks
SERVER
import java.io.*;
import java.net.*;
public class Server {
//Main Method:- called when running the class file.
public static void main(String[] args){
//Portnumber:- number of the port we wish to connect on.
int portNumber = 15882;
try{
//Setup the socket for communication and accept incoming communication
ServerSocket serverSoc = new ServerSocket(portNumber);
Socket soc = serverSoc.accept();
//Catch the incoming data in a data stream, read a line and output it to the console
DataInputStream dataIn = new DataInputStream(soc.getInputStream());
System.out.println("--> " + dataIn.readUTF());
//Remember to close the socket once we have finished with it.
soc.close();
}
catch (Exception except){
//Exception thrown (except) when something went wrong, pushing message to the console
System.out.println("Error --> " + except.getMessage());
}
}}
CLIENT
import java.io.*;
import java.net.*;
public class Client {
//Main Method:- called when running the class file.
public static void main(String[] args){
//Portnumber:- number of the port we wish to connect on.
int portNumber = 15882;
//ServerIP:- IP address of the server.
String serverIP = "localhost";
try{
//Create a new socket for communication
Socket soc = new Socket(serverIP,portNumber);
//Create the outputstream to send data through
DataOutputStream dataOut = new DataOutputStream(soc.getOutputStream());
//Write message to output stream and send through socket
dataOut.writeUTF("Hello other world!");
dataOut.flush();
//close the data stream and socket
dataOut.close();
soc.close();
}
catch (Exception except){
//Exception thrown (except) when something went wrong, pushing message to the console
System.out.println("Error --> " + except.getMessage());
}
}}
There are some "problems" with your code.
You should only close the ServerSocket if you are done.
You should handle the newly connected client inside a thread to allow multiple clients to simultaniously "send messages".
1.
you could easily wrap your code inside an while loop.
boolean someCondition = true;
try{
//Setup the socket for communication and accept incoming communication
ServerSocket serverSoc = new ServerSocket(portNumber);
// repeat the whole process over and over again.
while(someCondition) {
Socket soc = serverSoc.accept();
//Catch the incoming data in a data stream, read a line and output it to the console
DataInputStream dataIn = new DataInputStream(soc.getInputStream());
System.out.println("--> " + dataIn.readUTF());
}
//Remember to close the socket once we have finished with it.
soc.close();
}
Now your programm should continue to accept clients. But only one at a time. You can now terminate the Server by stopping the programm or by changing the someCondition to false and accepting the next client.
A bit more advanced would be, to shutdown the ServerSocket to stop the programm and catching the exception inside the while loop.
2.
To allow multiple clients to be handled simultaniously, you should pack the handle part into another Thread.
private ExecutorService threadPool = Executors.newCachedThreadPool();
boolean someCondition = true;
try{
//Setup the socket for communication and accept incoming communication
ServerSocket serverSoc = new ServerSocket(portNumber);
// repeat the whole process over and over again.
while(someCondition) {
Socket soc = serverSoc.accept();
//Catch the incoming data in a data stream, read a line and output it to the console in a new Thread.
threadPool.submit(() -> {
DataInputStream dataIn = new
DataInputStream(soc.getInputStream());
System.out.println("--> " + dataIn.readUTF());
}
}
//Remember to close the socket once we have finished with it.
soc.close();
}
The part inside the threadPool.submit block could be specified as an custom instance of the Runnable interface of as an method, to call it using method reference.
I assumed you are knowing about ThreadPools. They have multiple advantages over Threads
This should get you going for any number of clients.
Note: This is not good designed, but it is for demonstrational porpurses only.
I have written a code in java to interface my computer with a transmitter a transmitter device, with a communication board already implemented and ready to connect via TCP/IP to any server with a specific address IP (say 192.168.2.2) and listening to a specific port number (say 4000).
I followed the exact strep how to create a server side application in Java offering a that listening port, so that I can connect to that transmitter.
I don't understand why when I try to debug the code, it blocks a the line clientSocket = serverSocket.accept(), and throws a timeout exception.
Could someone help me find out where the error might be in my code?
Any help would be greatly appreciated.
Thanks.
Here is the code:
public class Server {
public static void main(String[] args) {
// TODO Auto-generated method stub
//Declares server and client socket, as well as the input and the output stream
ServerSocket serverSocket = null;
Socket clientSocket = null;
PrintWriter out;
//BufferedReader in;
BufferedReader in;
try{
InetAddress addr = InetAddress.getByName("192.168.2.2");
//Opens a server socket on port 4000
serverSocket = new ServerSocket(4000) ;
//Sets the timeout
serverSocket.setSoTimeout(30000);
System.out.println("Server has connected");
//Create a connection to server
System.out.println("Server listening connection from client ....");
//Listens and waits for client's connection to the server
clientSocket = serverSocket.accept();
// Creates input and output streams to socket
out = new PrintWriter(clientSocket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
//Reads response from socket
while((in.readLine())!= null ){
System.out.println ( in.readLine() );
}
System.out.println ( "Closing connection ....");
//Terminates connection
clientSocket.close();
serverSocket.close();
System.out.println("Connecton successfully closed");
}
catch(IOException e){
System.out.println(e);
}
}
}
Could someone help me find out where the error might be in my code?
There is no error in your code that could cause this problem. Clearly you haven't configured the device to connect to this server correctly, or the device isn't running, or it isn't connecting, or there is a firewall in the way. Investigate that.
However:
InetAddress addr = InetAddress.getByName("192.168.2.2");
What is this for? It isn't used.
System.out.println("Server has connected");
This is simply not true. The server hasn't connected. At this point all it has done is create a listening socket.
while((in.readLine())!= null ){
Here you are reading a line and throwing it away.
System.out.println ( in.readLine() );
Here you are printing every second line, having thrown every odd line away. The correct way to write this loop is:
String line;
while ((line = in.readLine()) != null)
{
System.out.println(line);
}
Note also that this server will service exactly one client and then exit. There should be a loop around everything from accept() to clientSocket.close(), and if there are multiple devices it should start a new thread per accepted socket to handle the I/O.
You specified timeout of 30 seconds, didn't you? :
serverSocket.setSoTimeout(30000);
So after 30 seconds, no matter whether stopped in debugger or running, this will timeout and throw exception.
I am writing a program with TCP sockets connection between client and server. When the server starts I want to display the IP and port that clients need to use to connect, and when client connects I want the server to show what IP did the client connect from. I am getting confused which command should i use to each of those:
getInetAdress()
getLocalAdress()
getRemoteSocketAdress()
edit
I earlier used int port = 1234 and String IP = "localhost" to test and it worked, but I only used it on one PC, so I think localhost will not work if i start server and client on different computers.
This is server side:
int port = 1234;
...
public void start() {
keepRunning = true;
// create socket
try {
ServerSocket server = new ServerSocket(port);
while (keepRunning) {
display("Waiting for client connections on "
+ server.getInetAddress().getLocalHost()
.getHostAddress() + ":" + port);
Socket conn = server.accept();
if (!keepRunning)
break;
ClientThread t = new ClientThread(conn);
cList.add(t);
t.start();
And this is client:
int port = 1234;
String IP = "localhost";
//these variables can be changed from Client GUI before making connection
...
public boolean start() {
try {
socket = new Socket(IP, port);
} catch (Exception e) {
display("Error connectiong to server:" + e);
return false;
}
try {
sInput = new ObjectInputStream(socket.getInputStream());
sOutput = new ObjectOutputStream(socket.getOutputStream());
} catch (IOException e) {
display("Exception creating new Input/output Streams: " + e);
return false;
}
When i start the server,
display("Waiting for client connections on " + server.getInetAddress().getLocalHost().getHostAddress() + ":" + port);
return this:
Waiting for client connections on 192.168.1.104:1234
which is kind of what i want, but I still cant get it to show me the port. 1234 is a fixed value i used, but I want to use ServerSocket server = new ServerSocket(0); to asign port dynamically, then when i start the client i just put in the values that i got from server and connect.
I tried to use server.getLocalPort() in the display line in server and it returned 55410 or something like that, but when i put this port in client to make connection, it doesn't work. I get Error connectiong to server:java.net.ConnectException: Connection refused: connect. from client
To get the current port that the ServerSocket is listening to, use getLocalPort();
http://download.java.net/jdk7/archive/b123/docs/api/java/net/ServerSocket.html#getLocalPort%28%29
getLocalPort
public int getLocalPort()
Returns the port number on which this socket is listening.
If the socket was bound prior to being closed, then this method will continue to return the port number after the socket is closed.
Edit: Just saw your edit. Are you trying to connect by explicitly referencing the IP and Port? If so, and it's still failing, your server machine might be running a firewall. I'd check for that first.
In my server located in a android device , if the number number of clients exceeds a specific number then the server close the socket. But in my client(other android device) i get a force close. How can i handle it gracefully?
Here is the connect part on my client:
serverIpAddress = serverIp.getText().toString();
if (!serverIpAddress.equals(""))
{
try
{
InetAddress serverAddr = InetAddress.getByName(serverIpAddress);
SocketAddress sockaddr = new InetSocketAddress(serverAddr, 5000);
nsocket = new Socket();
nsocket.connect(sockaddr);
}catch(Exception e){
Log.i("Connect", "Connection Error");
}
if (nsocket.isConnected()){
score.setText("Your score is " + sc);
serverIp.setVisibility(View.GONE);
connectPhones.setVisibility(View.GONE);
enterIP.setVisibility(View.GONE);
Log.i("Connect", "Socket created, streams assigned");
Log.i("Connect", "Waiting for inital data..." + nsocket.isConnected());
receiveMsg();
}
Keep checking the socket connection is still open or not using isClosed() within an infinite loop, when server closes its connection, the isClosed() gets true, and then display a message or toast giving your desired reason to the user.
Sounds like whatever you are using to read the socket is a blocking read, and throws an exception when the socket closes and it is stuck at that read. Make sure that read is in a try block, and use the catch/finally to gracefully exit whatever you are doing at that moment.
I am writing a port scanner in Java and I want to be able to distinct the following 4 use cases:
port is open
port is open and server banner was read
port is closed
server is not live
I have the following code:
InetAddress address = InetAddress.getByName("google.com");
int[] ports = new int[]{21, 22, 23, 80, 443};
for (int i = 0; i < ports.length; i++) {
int port = ports[i];
Socket socket = null;
try {
socket = new Socket(address, port);
socket.setSoTimeout(500);
System.out.println("port " + port + " open");
BufferedReader reader = new BufferedReader(
new InputStreamReader(socket.getInputStream()));
String line = reader.readLine();
if (line != null) {
System.out.println(line);
}
socket.close();
} catch (SocketTimeoutException ex) {
// port was open but nothing was read from input stream
ex.printStackTrace();
} catch (ConnectException ex) {
// port is closed
ex.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (socket != null && !socket.isClosed()) {
try {
socket.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
The problem is that I get a ConnectionException both when the port is closed and the server cannot be reached but with a different exception message:
java.net.ConnectException: Connection timed out: connect
when the connection was never established and
java.net.ConnectException: Connection refused: connect
when the port was closed
so I cannot make the distinction between the two use cases without digging into the actual exception message.
Same thing happens when I try a different approach for the socket creation. If I use:
socket = new Socket();
socket.setSoTimeout(500);
socket.connect(new InetSocketAddress(address, port), 1000);
I have the same problem but with the SocketTimeoutException instead. I get a
java.net.SocketTimeoutException: Read timed out
if port was open but there was no banner to be read and
java.net.SocketTimeoutException: connect timed out
if server is not live or port is closed.
Any ideas? Thanks in advance!
I don't think you have any options besides parsing the exception message. Is there a reason you'd rather not do this?
ConnectException only has an empty constructor and an errorMesssage constructor. There are no subclasses of ConnectException in the API. So I am afraid, Java does no proper way to access the reason. Parsing the exception message seems to be the only way, despite it being really messy with translations.