I'm trying to build a simple web server in Java as practice but I'm running into a very strange issue. When I attempt to read the InputStream from the Socket, sometimes there is no data to be read.
The process I'm following is this:
I create a ServerSocket, listening on port 80, and call accept() to get a Socket. I then send a request from my browser (Firefox) to localhost, which triggers the accept() to return the Socket.
Sometimes, it will read the HTTP request perfectly. Other times, it fails to read any data (read() returns a -1).
Here is some sample code to illustrate what I'm doing, without any exception handling thrown in:
ServerSocket serv = new ServerSocket(80);
while (true)
{
Socket con = ServerSocket.accept();
InputStream input = con.getInputStream();
bytes[] bytes = new bytes[4000000]; // for simplicity, I figured I'd
// just make the array huge for now
int bytesRead = input.read(bytes);
if (bytesRead > 0)
{
StringBuffer sBuffer = new StringBuffer(bytesRead);
for (int i = 0; i < bytesRead; i++)
{
sBuffer.append((char) bytes[i]);
}
System.out.println(sBuffer.toString());
}
}
EDIT: I've also tried using a BufferedInputStream and BufferedReader to not avail.
One socket can receive more packets. So you should create a new thread for every socket. Something like:
while(true){
Socket socket = serv.accept();
Client client = new Client(socket);
new Thread(client).start();
}
Then you need to create the Client class which implements the runable interface.
Socket socket;
public Client(Socket socket){
this.socket = socket;
}
public void run(){
while(socket.isConnected()){
//here reads the packets from the inputstream
}
}
You should always loop when reading data from an InputStream. there is no guarantee that all the data will be returned from a single read() call (loop until you receive -1).
Related
I am trying to send data to one of my servers and receive an ACK back from it. However, the processing gets hung up when waiting for a response from the server. I know for a fact that there is a connection because I can see the data reaching the server. I also know that the server is outputting data correctly because my C# client is receiving data back from the server. I will note that this client is running on a centOS virtual machine. The server is a remote windows machine. I wouldn't imagine that there would be an issue due to the virtual environment because I am able to use an SNMP java client (SNMP4j package) to make calls to a remote server. I believe my server is outputting raw binary too, but I would expect to see some kind of output either way.
// A Java program for a Client
import java.net.*;
import java.io.*;
public class Client
{
// initialize socket and input output streams
private Socket socket = null;
private DataInputStream input = null;
private DataOutputStream out = null;
private DataInputStream serveroutput= null;
// constructor to put ip address and port
public Client(String address, int port)
{
// establish a connection
try
{
socket = new Socket(address, port);
System.out.println("Connected");
// takes input from terminal
input = new DataInputStream(System.in);
// sends output to the socket
out = new DataOutputStream(socket.getOutputStream());
serveroutput = new DataInputStream(socket.getInputStream());
}
catch(UnknownHostException u)
{
System.out.println(u);
}
catch(IOException i)
{
System.out.println(i);
}
// string to read message from input
String line = "";
// keep reading until "Over" is input
while (!line.equals("Over"))
{
try
{
line = input.readLine();
out.writeUTF(line);
System.out.println(serveroutput.readLine())
}
catch(IOException i)
{
System.out.println(i);
}
}
// close the connection
try
{
input.close();
out.close();
socket.close();
}
catch(IOException i)
{
System.out.println(i);
}
}
Could be great if you would share the otherside codes. (sorry cannot comment yet)
Try use something else over writeUTF(), simply maybe a PrintStream, as mentioned by #marquis-of-lorne (read|write)UTF may be confusing by the peer.
Also this might be a good practice to flush() out the output from both side when there is nothing else to send to make sure data is sent completely.
You may also try BufferedReader over InputDataStream as you are trying to read lines. readLine() from InputDataStream is deprecated.
I'm trying to read from a SSLSocket server, I need the client to be open 24/7, Note I am only making the client, The server is already set up, I'm trying to read data and send data from the server, How ever when I do try to read the data it blocks my current thread and I can't seem to do anything else after that since the loop never ends, and if I make a loop that ends the program returns. I want it to be open always and keep getting incoming request and then send request back according to what I receive, this is what I currently have.
private SSLSocketFactory sslsocketfactory = (SSLSocketFactory) SSLSocketFactory.getDefault();
private SSLSocket sslsocket = (SSLSocket) sslsocketfactory.createSocket(host, port);
private BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(sslsocket.getOutputStream()));
private InputStream is = sslsocket.getInputStream();
these are the global vars I have defined, and this is how I write data to the server
private void write_to_server(String date) throws IOException {
writer.write(date);
writer.flush();
}
and finally this is how I receive response and this is where I am having the problem.
public String getResponse() throws IOException {
byte[] buffer = new byte[16384];
String a = "";
for (int b; ((b = is.read(buffer)) > 0); ) {
a = new String(buffer, 0, b, StandardCharsets.UTF_8);
Log(a);
}
return a;
}
The loop never ends, causing the thread to be stuck, and even if the loop ends the program will just return after that causing the program to end. I need to know how I can have it set up to receive data 24/7 and then send data back after I received response.
I am writing Socket program , Here Client Sends a String through Stream , Server Process it and writes back to Client. My problem is, after Server process the String , it Writes back to Stream but in client It can't able to read the Stream its showing exception as Exception in while: java.net.SocketException: socket closed Here is my code,
Client ,
public void run() {
while (true) {
try {
// Open your connection to a server, at port 1231
s1 = new Socket("localhost", 1231);
OutputStream s1out = s1.getOutputStream();
DataOutputStream dos = new DataOutputStream(s1out);
InputStream in=s1.getInputStream();
DataInputStream dis=new DataInputStream(in);
String s = br.readLine();
dos.writeUTF(s);
dos.flush();
dos.close();
System.out.println(dis.readUTF());//it is the String from Server after processing
dis.close();
} catch (IOException ex) {
// Logger.getLogger(SimpleClient.class.getName()).log(Level.SEVERE, null, ex);
System.out.println("Exception in while: " + ex);
}
}
In Server
public void run()
{
while(true){
try {
System.out.println("Waiting for connect to client");
s1=serverSocket.accept();
s1In = s1.getInputStream();
dis = new DataInputStream(s1In);
out=s1.getOutputStream();
dos=new DataOutputStream(out);
String clientData=dis.readUTF();
//processing task String
dos.writeUTF("Bus Registered Successfully");
dos.flush();
}
}
Here I am not able to read Bus Registered Successfully at client side . How to Solve this.?
Well there are many things not right in your program. But first let me answer your question ... you are closing the socket just after writing the stream ... so server throws exception, just remove dos.close(); just after the dos.flush();. It will run fine.
Now back to the programming practices ...
1) Server should accept the connection in a while(true) loop and then make a new thread. So following statement should not be the part of run method.
System.out.println("Waiting for connect to client");
s1=serverSocket.accept();
s1In = s1.getInputStream();
dis = new DataInputStream(s1In);
out=s1.getOutputStream();
dos=new DataOutputStream(out);
2) There is no need of run method in client. Because Every new client will be a new program that has its own variables and socket.
A quick look shows me that the reason the socket is closed is because you used dos.close().
Closing a DataInputStream (or PrintStream, or any similiar stream) will close the underlying socket.
Just take out dos.close().
You can also move the dos.close() to the very end of the try block. As a general rule, don't close anything related to the socket until you're done with the socket.
I'm a bit of a beginner programmer so it's possible this is quite obvious and I'm overlooking the answer. But on to the question.
I have a two-part program (its a little more complicated than this example, but the situation is the same). The program has multiple messages fired between the client and the server. I have a PrintWriter on the server-side to send messages to the client, and on the client, I have a BufferedReader to read the messages sent.
When this example is run, I'm given two lines as output. The first message is both messages, and the second is NULL. What I am wondering is if there is a way to basically halt the server until I am ready for the second message, so that I can do something on the client-side before the second message is sent.
I am hoping to not use Thread.Sleep, as I would rather the Server wait around until the Client says it is ready.
This is the client:
public class Client{
public void run(){
Socket socket = null;
InputStream in = null;
BufferedReader reader = null;
try{
socket = new socket("LocalHost",1234);
in = socket.getInputStream();
reader = new BufferedReader(new InputStreamReader(in));
}
String messageFromServer = "";
try{
messageFromServer=reader.readLine();
}
System.out.println(messageFromServer);
String messageFromServer = "";
try{
messageFromServer=reader.readLine();
}
System.out.println(messagefromServer);
//close everything
}
}
This is the server:
public class Server{
public void run(){
ServerSocket server = null;
Socket client = null;
try{
server = new ServerSocket(1234);
client = server.accept();
}
PrintWriter writer = null;
OutputStream out = null;
try{
out = client.getOutputStream();
writer = new PrintWriter(out, true);
}
writer.write("Hi I'm a server");
//do some stuff that takes some time, user input, etc. etc.
writer.write("I'm still a server");
//close everything
}
Thanks :)
The problem with the way you currently have you code is the fact that you are using a BufferedReader, but the server is not terminating it's messages with a new line.
When you close the writer, the client is reaching the EOF or EOS and unblocking the read so it appears that both strings are being sent at once...
If you do something like...
writer.write("Hi I'm a server\n");
// This will force the message to be written to the client and picked up ;)
writer.flush();
writer.write("I'm still a server\n");
writer.flush();
Then you will get the messages seperatly...
You can use ObjectInputStream to read Objects instead of Strings.
This way you will read only one Message(String in your case) every call to ObjectInputStream.readObject();
BTW you can read the first message, "do something" and then read the second message. you don't have to read all of the sent messages at once.
If there are no other messages, then your thread will be blocked when trying to read an object from the ObjectInputStream.
Use it like:
ObjectInputStream inputStream = new ObjectInputStream( socket.getInputStream() )
i've a minimal server which wait until a client connect ,then he start a thread which will send a reply back to the client, the problem is the reply.
This is the code of the server:
int port = 1234;
ServerSocket servSock = null;
servSock = new ServerSocket(port);
while (true) {
Socket link = servSock.accept();
serverThread st = new serverThread(link);
st.start();
}
This is the code of the run() method of the thread,the one which send the answer back, sk is the socket "link" passed by parameter in the server code
public void run() {
String dato = "";
InputStream i = null;
try {
i = sk.getInputStream();
} catch (IOException ex) {
Logger.getLogger(serverThread.class.getName()).log(Level.SEVERE, null, ex);
}
Scanner input = new Scanner(i);
//i receive the data sent
while (input.hasNext()) {
dato += input.nextLine();
}
// then i send a reply
DataOutputStream outputStream=new DataOutputStream(sk.getOutputStream());
outputStream.writeInt(1);
outputStream.close();
Client side ( only the code which should receive the answer from the server) :
Socket link;
int valid = 0;
String url="localhost";
int port=1234;
link = new Socket(InetAddress.getByName(url), port);
//i've to send some data to the server
PrintWriter output = new PrintWriter(link.getOutputStream(), true);
String a = new String(Base64.encode(mex));
output.println(createXml(tag, a));
output.flush();
//then i need to receive an answer from the server
DataInputStream answerI = new DataInputStream(link.getInputStream());
while(answerI.available()!=0)// but answerI.available() is always equal 0
valid = answerI.readInt();
answerI.close();
output.close ();
link.close();
With this code the istruction valid = answerI.readInt(); is not reached.
Without the while cycle, the client freeze at line : valid = answerI.readInt();
Can anyone help me?
Thank you in advance
I'm guessing that the server is blocked in a call to input.hasNext(). This will return false when the socket is closed, and its InputStream returns -1 to signal the end of the stream. However, the socket is still open. The client can send another line; the Scanner is blocking to see what the client's next move will be.
There are ways to shutdown "half" of a socket, so that the server can tell that the client has closed its sending channel but can still receive a response.
However, this approach is complicated. I suggest a change to the protocol so that the server can determine when it is allowed to respond.
In this protocol you don't need the reply if it is always '1'. Just close the socket. The client should block in a read() which will return -1 when the server closes the socket.