I'm using java and received some json string from a server. I received json strings with readUTF but there is some data lost. I didn't received first two character of the every json packet.
Another problem is there is delay to received json strings. For example server sent one json string and client could not received it until approximately 50 json strings sent by server and client shows all the json strings suddenly.
What is the main problems?
public void run() {
System.out.println("hi from thread" + id);
try {
clientSocket = new Socket("192.168.1.22", id);
output = new PrintStream(clientSocket.getOutputStream());
input = new DataInputStream(clientSocket.getInputStream());
inputLine = new DataInputStream(new BufferedInputStream(System.in));
}
catch( IOException e){
System.out.println(e);
}
String responseLine;
try{
while(true){
output.println( id + " ");
System.out.println("sent:" + id + " ");
responseLine = input.readUTF();
System.out.println("received: " + responseLine);
}
}
catch (IOException e) {
System.out.println(e);
}
}
Because of server send data with UTF format, so I cannot receive them with Bufferedreader
I've had this problem before with applications like this, the main cause is DataInputStream which expects input to be in a certain format which I assume is not being conformed to by the server, try using BufferedReader instead as so:
BufferedReader input = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
Then whenever you wish to read data just use
some_string_here = input.readLine();
Note this requires each data value sent to end with a end line character "\n" or "\r".
Related
When i am trying to send an input from a client, if i don't concat "\r\n" at the end of the string, my inputstream waits forever. I have seen various similar posts but couldn't find a proper solution. My code is as follows:
public void run() {
PrintWriter out = null;
BufferedReader in = null;
try {
out = new PrintWriter(clientSocket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
String line;
if (in.ready()) {
if ((line = in.readLine()) != null) {
System.out.println("Received from client: " + line);
out.write("Echoing: " + line);
out.flush();
}
}
} catch (Exception e) {
e.printStackTrace();
} finally {
out.close();
try {
in.close();
clientSocket.close();
System.out.println("Closing connection from " + socketAddress + ", #" + connectionId);
} catch (IOException e) {
e.printStackTrace();
}
}
}
If you only want to read some of the data that was sent, use the read(char[]) method instead of the readLine method. This method returns the number of characters it read as an int. Example:
char[] buffer = new char[2000];
int read;
if ((read = in.read(buffer)) != -1) {
String line = new String(buffer, 0, read);
System.out.println("Received from client: " + line);
out.write("Echoing: " + line);
out.flush();
}
What you'll see happen next is that this code sometimes fails to read the entire message you send from PHP, or that two or more messages are read as one.
If you want to fix that:
This will never work, and it's not because of PHP or Java. You're using TCP, a stream oriented protocol. There is no guarantee that the message you write to the socket from the PHP program will arrive in one piece to the receiver. The message may be broken up and you need multiple socket function calls to read it. Or it may go the other direction, and a single call to read returns more than one message.
The solution is to add some kind of framing for the messages so that the receiver knows when it has a complete message. Always ending a message with a line break serves as framing, if messages themselves are single lines. Another solution is to ditch TCP and use a message oriented protocol (like UDP) instead, but that will come with its own complications.
I am currently working on a Java console application. It is run through the command prompt, connects to a server application coded in python and communicates with that server over TCP. My application sends "ISND" string to server which it accepts and in return server sends three images. The format in which Images are sent in is
Where "<"">" are not actually included. "ISND" is encoded into bytes using ascii. Size is the size of the image converted into bytes from int and it is always composed of 3 bytes regardless of the size of the image. For each individual image, a message in this format is sent.
I have been using BufferedReader to read server responses but at this point, I am at a loss on how to actually handle this message. I searched for ways to separate the incoming message into components since I know the length of the first two parts which are always fixed yet I couldn't find a way to actually accomplish that goal.
It has come to the point it feels like I am smashing my head into a wall. As such, I need advice from anyone that is more familiar with Java and Socket programming on how to handle this issue.
My current code
public class ImageLabeler {
/**
* #param args
*/
public static void main(String[] args) {
String IP = args[0];
System.out.println(IP + "\n");
String port = args[1];
System.out.println(port + "\n");
Socket clientSocket;
DataOutputStream outToServer = null;
BufferedReader inFromServer = null;
String serverResponse;
try {
clientSocket = new Socket(IP, Integer.parseInt(port));
outToServer = new DataOutputStream(clientSocket.getOutputStream());
inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
System.out.println("Connection success\n");
} catch (IOException ex) {
System.out.println("Connection failed\n");
System.exit(0);
}
PrintWriter writer = new PrintWriter(outToServer, true);
try {
//outToServer.writeBytes("USER bilkentstu\\n");
//outToServer.flush();
//System.out.println("check\n");
writer.println("USER bilkentstu");
serverResponse = inFromServer.readLine();
System.out.println(serverResponse + "\n");
writer.println("PASS cs421f2019");
//outToServer.writeBytes("PASS cs421f2019\\r\\n");
//outToServer.flush();
serverResponse = inFromServer.readLine();
System.out.println(serverResponse + "\n");
writer.println("IGET");
//This is where I need to handle the incoming Image messages.
writer.println("EXIT");
} catch (IOException ex) {
Logger.getLogger(ImageLabeler.class.getName()).log(Level.SEVERE, null, ex);
}
System.exit(0);
}
}
Don't use buffered reader. You need to write the code reading a string from the InputStream of the socket one byte at a time.
I am trying to create an application that will count the amount of times a button has been clicked. This client would connect to a server, and when the user clicks the button, it should increment the counter on the server. The server should then send back the current amount of clicks to the client. But that's where I'm having a bit of problems.
This is the relevant client-sided code.
public void actionPerformed(ActionEvent arg0) {
try {
OutputStream os = socket.getOutputStream();
OutputStreamWriter osw = new OutputStreamWriter(os);
BufferedWriter bw = new BufferedWriter(osw);
String target = "";
bw.write("increment" + "\n");
bw.flush();
InputStream is = socket.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String id = br.readLine();
System.out.println("test: " + id);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
});
The client stops at:
String id = br.readLine();
I just want to get the output from the server.
This is the relevant server-sided code.
public void run() {
try {
while (true) {
InputStream is = socket.getInputStream();
InputStreamReader isr = new InputStreamReader(is); //Create the input Streams
BufferedReader br = new BufferedReader(isr);
String input = br.readLine();
System.out.println("got input");
OutputStream os = socket.getOutputStream();
OutputStreamWriter osw = new OutputStreamWriter(os);
BufferedWriter bw = new BufferedWriter(osw);
System.out.println("wrote to out");
if(input.equals("increment" + "\n")) {
totalBets++;
System.out.println("inif");
bw.write(totalBets);
System.out.println("wrote");
bw.flush();
System.out.println("flushed");
System.out.println("Total Bets: " + totalBets);
}
}
} catch (IOException e) {
log("Error handling client# " + clientNumber + ": " + e);
} finally {
try {
socket.close();
} catch (IOException e) {
log("Couldn't close a socket, what's going on?");
}
log("Connection with client# " + clientNumber + " closed");
}
}
I found that it also stops here:
String input = br.readLine();
I'm just trying to get the bw.write("imcrement") from the client, so the server can increment the counter, and send back the total clicks.
Any help?
Thank you.
You are writing the totalBets value using BufferedWriter.write(int).
This interprets the value as a single character. So, for example, if totalBets is 65, it writes the character 'A'!
Moreover, it does not add a newline. So the client reads that 'A' but tries to read more characters as it is trying to read a whole line. Remember that you have to write lines to read lines.
Thus, you should replace the part that writes totalBets with:
bw.write(String.valueOf(totalBets));
bw.newLine();
Also remember, as I pointed in a comment, that you have to write a line with a \n (or preferably BufferedWriter.newLine()), but when you read the line on the other side, the line separator is stripped away, so you should compare the string you expect without a \n.
You need to set TCP_NODELAY on the client's socket. The default is for data to be buffered until it will fill an entire packet. When the buffer is full, a packet is sent. However, for this protocol you want the data to be sent immediately so that the server can respond.
I frequently use wireshark when testing and debugging my networking code. It will show exactly what packets are sent and received. (note, however, that on Windows you can not capture from the loopback interface; this is a limitation of Windows and does not apply to other systems)
I'm testing out sockets on my local machine. I'm trying to run both a socket and server in one program using threads. My server is an echo server so that it sends back whatever message it receives. My problem is that when I start both threads, on both the client and server, they 'freeze' when they reach the part where I read from the input stream. It works fine up to the part where the client sends the message. Afterwards, it simply stops as it appears that the client is waiting for a message and so is the server even if I already sent a message to the server via writing to the outputstream. What's wrong with the code?
Client.java
#Override
public void run() {
try {
Socket socket = new Socket("localhost", 22600);
BufferedReader br = new BufferedReader(new InputStreamReader(
socket.getInputStream()));
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(
socket.getOutputStream()));
BufferedReader input = new BufferedReader(new InputStreamReader(
System.in));
System.out.println("Client 1");
while (true) {
System.out.print("\nEnter text : ");
String inputText = input.readLine();
writer.write(inputText);
System.out.println("Client 2");
System.out.println("Client 3");
String s = br.readLine();
System.out.println("CLIENT RECEIVED : " + s);
}
} catch (Exception e) {
e.printStackTrace();
}
}
Server.java
#Override
public void run() {
try {
ServerSocket server = new ServerSocket(22600);
Socket socket = server.accept();
BufferedReader br = new BufferedReader(new InputStreamReader(
socket.getInputStream()));
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(
socket.getOutputStream()));
System.out.println("Server 1");
while (true) {
System.out.println("Server 2");
String s = br.readLine();
System.out.println("Server 3");
if (s == null) {
System.out.println("NULL SERVER SIDE ERROR");
break;
}
writer.write("ECHO : " + s);
System.out.println("SYSOUT ECHO " + s);
}
server.close();
} catch (Exception e) {
e.printStackTrace();
}
}
You are writing a string that does not have an end-of-line at its end.
String inputText = input.readLine();
writer.write(inputText);
System.out.println("Client 2");
The inputText string does not include the end-of-line you typed. And you write it as-is to the server. However, the server tries to read a line:
String s = br.readLine();
System.out.println("Server 3");
So it will keep waiting until the client sends in a newline. But by now the client is waiting for an answer from the server, and now they are deadlocked.
So, you should add a writer.newLine() to the client, as well as the server's echo, which suffers from the same issue. It's also recommended, after each write, to use writer.flush(), on both server and client. Otherwise, it may wait until the buffer is full before actually writing, and the same deadlock will result.
The readLine method of BufferedReader requires a new line terminator to return a value (unless the end of Stream is reached), and then returns the line without this character. So the Client
Reads a line from the user into the variable inputText
Client writes inputText to the OutputStream
Server receives data, but waits until it receives a new line (which it does not).
If you wish to use new line as a delimiter for communication, append this to the end of the data sent
writer.write(inputText + "\n");
I'm writing a simple server in Java, and I'm able to retrieve incoming data from the client on the server side, but not on the client side due to a 2000ms timeout. Anyone know why this times out?
This is the server's code:
private static void listen() throws IOException {
while(true) {
Socket clientSocket = serverSocket.accept();
StringBuilder bufferedStringInput = new StringBuilder();
CharBuffer cbuf = CharBuffer.allocate(4096);
try {
InputStream is = clientSocket.getInputStream();
BufferedReader br = new BufferedReader(new InputStreamReader(is, "UTF8"));
int noCharsLeft = 0;
while ((noCharsLeft = br.read(cbuf)) != -1) {
char[] arr = new char[noCharsLeft];
cbuf.rewind();
cbuf.get(arr);
bufferedStringInput.append(arr);
cbuf.clear();
}
System.out.println(bufferedStringInput.toString());
} catch (IOException e) {
System.out.println("Error received client data: " + e.getMessage());
}
String message = "Hello client";
try {
PrintWriter out = new PrintWriter(clientSocket.getOutputStream());
out.print(message);
} catch (IOException e) {
System.out.println("Error getting output stream from client: " + e.getMessage());
}
clientSocket.close();
}
}
You're reading the input until end of stream, which only happens when the peer closes the connection, then you're trying to write to it, so of course you get a broken pipe. Doesn't make sense. You should just read the input until you have one entire request, whatever that means in your protocol.
There are other problems lurking here:
If the client code uses readLine(), you're not sending a line terminator: use println(), not print(), and close the PrintWriter, not just the client socket.
cbuf.rewind()/get()/clear() should be cbuf.flip()/get()/compact().
But it would make more sense to read directly into a char[] cbuf = new char[8192]; array, then bufferedStringInput.append(cbuf, 0, noCharsLeft), and forget about the CharBuffer altogether. Too much data copying at present.
noCharsLeft is a poor name for that variable. It is a read count.