We Keep Coding

Stuck on readLine() even if the line is null

I wrote this loop in my server, where he just sends some strings to a client:
PrintWriter out = new PrintWriter(incoming.getOutputStream(), true);
for (int j = 0; j < i; j++) {
out.println(tmp[j]); // send the strings to the client
}
The client has another loop to retrieve all these strings but never exit from there. For example, if I send him 4 strings the output will be:
-hi
-how
-are
-you
And then after this last string it hangs and I cannot do anything else than closing the server. When I close it, the client exit from the while. This is the loop that doesn't work:
/* PHASE 2: The client receives the ArrayList with the emails */
BufferedReader in = new BufferedReader(new InputStreamReader(s.getInputStream()));
String line;
String message[] = new String[5];
for (int j=0; ((line = in.readLine()) != null) && (line.length())>0;) {
System.out.println(line); //DEBUG
message[j++] = line;
if (j==5) {
data = format.parse(message[3]);
email.add(new Email((Integer.parseInt(message[0])), message[1], account, message[2], message[4], data));
j=0;
}
}
System.out.println("Out");
Here is the code of the client with the loop incriminated:
public void loadData() throws IOException, ClassNotFoundException, ParseException {
try {
connect();
ArrayList<Email> email = new ArrayList<Email>();
DateFormat format = new SimpleDateFormat("dd/MM/yyyy");
Date data;
/* PHASE 1: The client sends a string to the server */
try {
PrintWriter out = new PrintWriter(s.getOutputStream(), true);
out.println(account+"\n"); // send the account name to server
/* PHASE 2: The client receives the ArrayList with the emails */
BufferedReader in = new BufferedReader(new InputStreamReader(s.getInputStream()));
String line;
String message[] = new String[5];
for (int j=0; ((line = in.readLine()) != null) && (line.length())>0;) {
System.out.println(line); //DEBUG
message[j++] = line;
if (j==5) {
data = format.parse(message[3]);
email.add(new Email((Integer.parseInt(message[0])), message[1], account, message[2], message[4], data));
j=0;
}
}
System.out.println("Out");
Here is the server code:
class ThreadedEchoHandler implements Runnable {
private Socket incoming;
private String nomeAccount = "";
public void run() {
try {
incoming = s.accept();
} catch (IOException ex) {
System.out.println("Unable to accept requests");
}
contenutoTextArea.append("Connected from: " + incoming.getLocalAddress() + "\n");
textarea.setText(contenutoTextArea.toString());
try {
//PHASE 1: The server receives the email
try {
BufferedReader in = new BufferedReader(new InputStreamReader(incoming.getInputStream()));
nomeAccount = in.readLine();
} catch (IOException ex) {
System.out.println("Not works");
}
//PHASE 2: I'm getting all the emails from the files
File dir = new File("src/server/" + nomeAccount);
String[] tmp = new String[100];
int i = 0;
for (File file : dir.listFiles()) {
if (file.isFile() && !(file.getName().equals(".DS_Store"))) {
try (BufferedReader br = new BufferedReader(new FileReader(file))) {
String line;
while ((line = br.readLine()) != null) {
tmp[i++] = line;
}
br.close();
} catch (IOException ex) {
System.out.println("Cannot read from file");
}
}
}
//PHASE 3: The server sends the ArrayList to the client
PrintWriter out = new PrintWriter(incoming.getOutputStream(), true);
for (int j = 0; j < i; j++) {
out.println(tmp[j]); // send the strings to the client
}
} catch (IOException ex) {
System.out.println("Cannot send the strings to the client");
}
//PHASE 4: Here I loop and wait for the client choise
BufferedReader in;
String op;
boolean exit = false;
try {
in = new BufferedReader(new InputStreamReader(incoming.getInputStream()));
while ((op = in.readLine()) != null) {
System.out.println("OP: " + op);
if (op.equals("Elimina")) {
String tmp = in.readLine();
contenutoTextArea.append("Ho eliminato la mail ").append(tmp).append(" \n");
textarea.setText(contenutoTextArea.toString());
File file = new File("src/server/" + nomeAccount + "/" + tmp + ".txt");
file.delete();
}
}
System.out.println("bbbbb");
} catch (IOException ex) {
System.out.println("Unable to read messages");
} finally {
try {
incoming.close();
} catch (IOException ex) {
System.out.println("Cannot close the socket");
}
}
}
}

Based on reading your client code, it looks like it's blocked waiting for another message, and it's not returning null because the end of the stream hasn't been reached. The fact that it continues once you kill the server process validates this.
As noted in the comments, you should make sure you close the PrintWriter on the server side. However, this by itself won't fix it, since the stream is on the socket, and as long as the socket is still open, this won't return null.
You can use specific control strings to communicate state back and forth (things that would never be user input, just to verify that round of communication is finished) then instead of checking for null, you'd check if the line matched the control string. Simply use that technique on both sides to pass control back and forth, and make sure to close the socket when done.

How can I read from java socket?

I'm trying to send and read the reply from the socket with no luck. What I got so far is, connected to the server and read connection reply (header from Ericsson telco exchange) and printed it on System.out. What I need to be able to do is send a command to the exchange and get the reply and that's where I'm stuck. Below is my test code.
Any help is appreciated.
public class ExchangeClientSocket {
public void run() {
try {
int serverPort = 23;
InetAddress host = InetAddress.getByName("my.host.ip.address");
Socket socket = new Socket(host, serverPort);
InputStreamReader isr = new InputStreamReader(socket.getInputStream());
PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
BufferedReader in = new BufferedReader(isr);
int i;
StringBuffer buffer = new StringBuffer();
while (true) {
i = in.read();
if (i == 60) {
break;
} else {
buffer.append((char) i);
}
}
// this returns the head from exchange
System.out.println(buffer.toString());
out.write("allip;"); // command I want to send to exchange
out.flush();
System.out.println(in.ready()); // this returns false
System.out.println(in.read());
System.out.println("damn..");
buffer = new StringBuffer();
// can't get into this loop
// this is where I want to read the allip response
while ((i = in.read()) != -1) {
i = in.read();
if (i == 60) {
break;
} else {
buffer.append((char) i);
}
}
System.out.println(buffer.toString());
out.close();
in.close();
socket.close();
} catch (UnknownHostException ex) {
ex.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}

Here is a suggestion on how to get input from the server after writing to the output stream: simply get another input stream from the socket.
So instead of reading from the same stream you create a new stream from the socket after you sent the command and read it.
I would therefore suggest to change your code to this here:
public void run() {
try {
int serverPort = 23;
InetAddress host = InetAddress.getByName("my.host.ip.address");
Socket socket = new Socket(host, serverPort);
InputStreamReader isr = new InputStreamReader(socket.getInputStream());
PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
BufferedReader in = new BufferedReader(isr);
int i;
StringBuffer buffer = new StringBuffer();
while (true) {
i = in.read();
if (i == 60) {
break;
} else {
buffer.append((char) i);
}
}
// this returns the head from exchange
System.out.println(buffer.toString());
out.write("allip;"); // command I want to send to exchange
out.flush();
// Create a new input stream here !!!
in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
buffer = new StringBuffer();
// can't get into this loop
while ((i = in.read()) != -1) {
i = in.read();
if (i == 60) {
break;
} else {
buffer.append((char) i);
}
}
System.out.println(buffer.toString());
out.close();
in.close();
socket.close();
} catch (UnknownHostException ex) {
ex.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}

exchange both string and binary data using socket without closing it

i'm working on an instant messaging project which it's client side is android and server is java
i need to use socket with streams
here is my protocol (something like HTTP) :
Method : attachment \n
Content-Length : {some-int-value} \n
\r\n
binary data bla bla bla...
lets assume i want to send this message from client to server
by doing so exchanging header section goes pretty well
but reading binary data at the server side never complete and server goes into hang for good
Client side code :
Socket socket = new Socket();
SocketAddress address = new InetSocketAddress(SERVER_ADDRESS, SERVER_PORT);
try {
socket.connect(address);
InputStream in = socket.getInputStream();
OutputStream out = socket.getOutputStream();
BufferedReader reader = new BufferedReader(new InputStreamReader(in, "UTF-8"));
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(out, "UTF-8"));
byte[] data = getSomeBinaryData();
writer.write("Method : attachment" + "\n");
writer.write("Content-Length : " + data.length + "\n");
writer.write("\r\n");
writer.flush();
out.write(data); // write binary data
// do more exchange later
} catch (IOException ex) {
// handle exception
}
Server starter code :
public static void main(String[] args){
ExecutorService pool = Executors.newFixedThreadPool(50);
try (ServerSocket server = new ServerSocket(PORT_NUMBER)) {
while (true) {
try {
Socket connection = server.accept();
Callable<Void> task = new ClientTask(connection);
pool.submit(task);
} catch (IOException ex) {}
}
} catch (IOException ex) {
System.err.println("Couldn't start server");
}
}
Server Task thread for each client :
class ClientTask implements Callable<Void> {
private Socket connection;
private HashMap<String, String> header = new HashMap<>();
private byte[] content;
ClientTask(Socket c) {
this.connection = c;
}
#Override
public Void call() throws Exception {
InputStream in = connection.getInputStream();
BufferedReader reader = new BufferedReader(new InputStreamReader(in, "UTF-8"));
readHeader(reader);
System.out.println("incoming message : " + header.get("Method"));
int contentLength = Integer.parseInt(header.get("Content-Length"));
content = new byte[contentLength];
int bytesRead = in.read(content, 0, contentLength);
System.out.print(bytesRead);
return null;
}
private void readHeader(BufferedReader reader){
try {
char c;
StringBuilder builder = new StringBuilder();
while ((c = (char) reader.read()) != '\r'){
if(c == '\n'){
String line = builder.toString();
line = line.replaceAll(" ", "");
String[] sections = line.split(":");
header.put(sections[0], sections[1]);
builder = new StringBuilder(); // clear builder
}else {
builder.append(c);
}
}
reader.read(); // skip the last \n character after header
} catch (IOException e) {
e.printStackTrace();
}
}

As James said a clue I wanted to share the solution
maybe it help someone with similar issue
in the call method of ClientTask class i should use this code :
#Override
public Void call() throws Exception {
InputStream in = connection.getInputStream();
BufferedReader reader = new BufferedReader(new InputStreamReader(in, "UTF-8"));
readHeader(reader);
System.out.println("incoming message : " + header.get("Method"));
// read binary Content
int bytesRead = 0;
int bytesToRead = Integer.parseInt(header.get("Content-Length"));
content = new byte[bytesToRead];
while (bytesRead < bytesToRead) {
int result = in.read(content, bytesRead, bytesToRead - bytesRead);
if (result == -1)
break; // end of stream
bytesRead += result;
}
return null;
}

One thread stopping too early regardless of CyclicBarrier

I am aware of the fact that the following code may seem vulgar, but I am new to these things and just tried everything in order to get it to work..
Problem: Even though I am using (possible in a wrong way) a CyclicBarrier, one - and seems to always be the same - thread stops too soon and prints out his vector, leaving 1 out of 11 of those "Incoming connection" messages absent. There is probably something terribly wrong with the last iteration of my loop, but I can't seem to find what exactly.. Now the program just loops waiting to process the last connection.
public class VectorClockClient implements Runnable {
/*
* Attributes
*/
/*
* The client number is store to provide fast
* array access when, for example, a thread's own
* clock simply needs to be incremented.
*/
private int clientNumber;
private File configFile, inputFile;
int[] vectorClock;
/*
* Constructor
* #param
* - File config
* - int line
* - File input
* - int clients
*/
public VectorClockClient(File config, int line, File input, int clients) {
/*
* Make sure that File handles aren't null and that
* the line number is valid.
*/
if (config != null && line >= 0 && input != null) {
configFile = config;
inputFile = input;
clientNumber = line;
/*
* Set the array size to the number of lines found in the
* config file and initialize with zero values.
*/
vectorClock = new int[clients];
for (int i = 0; i < vectorClock.length; i++) {
vectorClock[i] = 0;
}
}
}
private int parsePort() {
int returnable = 0;
try {
FileInputStream fstream = new FileInputStream(configFile.getName());
DataInputStream in = new DataInputStream(fstream);
BufferedReader br = new BufferedReader(new InputStreamReader(in));
String strLine = "";
for (int i = 0; i < clientNumber + 1; i++) {
strLine = br.readLine();
}
String[] tokens = strLine.split(" ");
returnable = Integer.parseInt(tokens[1]);
}
catch (Exception e) {
e.printStackTrace();
}
System.out.println("[" + clientNumber + "] returned with " + returnable + ".");
return returnable;
}
private int parsePort(int client) {
int returnable = 0;
try {
FileInputStream fstream = new FileInputStream(configFile.getName());
DataInputStream in = new DataInputStream(fstream);
BufferedReader br = new BufferedReader(new InputStreamReader(in));
String strLine = "";
for (int i = 0; i < client; i++) {
strLine = br.readLine();
}
String[] tokens = strLine.split(" ");
returnable = Integer.parseInt(tokens[1]);
}
catch (Exception e) {
e.printStackTrace();
}
return returnable;
}
private int parseAction(String s) {
int returnable = -1;
try {
FileInputStream fstream = new FileInputStream(configFile.getName());
DataInputStream in = new DataInputStream(fstream);
BufferedReader br = new BufferedReader(new InputStreamReader(in));
String[] tokens = s.split(" ");
if (!(Integer.parseInt(tokens[0]) == this.clientNumber + 1)) {
return -1;
}
else {
if (tokens[1].equals("L")) {
vectorClock[clientNumber] += Integer.parseInt(tokens[2]);
}
else {
returnable = Integer.parseInt(tokens[2]);
}
}
}
catch (Exception e) {
e.printStackTrace();
}
return returnable;
}
/*
* Do the actual work.
*/
public void run() {
try {
InitClients.barrier.await();
}
catch (Exception e) {
System.out.println(e);
}
int port = parsePort();
String hostname = "localhost";
String strLine;
ServerSocketChannel ssc;
SocketChannel sc;
FileInputStream fstream;
DataInputStream in;
BufferedReader br;
boolean eof = false;
try {
ssc = ServerSocketChannel.open();
ssc.socket().bind(new InetSocketAddress(hostname, port));
ssc.configureBlocking(false);
fstream = new FileInputStream("input_vector.txt");
in = new DataInputStream(fstream);
br = new BufferedReader(new InputStreamReader(in));
try {
InitClients.barrier.await();
}
catch (Exception e) {
System.out.println(e);
}
while (true && (eof == false)) {
sc = ssc.accept();
if (sc == null) {
if ((strLine = br.readLine()) != null) {
int result = parseAction(strLine);
if (result >= 0) {
//System.out.println("[" + (clientNumber + 1)
//+ "] Send a message to " + result + ".");
try {
SocketChannel client = SocketChannel.open();
client.configureBlocking(true);
client.connect(
new InetSocketAddress("localhost",
parsePort(result)));
//ByteBuffer buf = ByteBuffer.allocateDirect(32);
//buf.put((byte)0xFF);
//buf.flip();
//vectorClock[clientNumber] += 1;
//int numBytesWritten = client.write(buf);
String obj = Integer.toString(clientNumber+1);
ObjectOutputStream oos = new
ObjectOutputStream(
client.socket().getOutputStream());
oos.writeObject(obj);
oos.close();
}
catch (Exception e) {
e.printStackTrace();
}
}
}
else {
eof = true;
}
}
else {
ObjectInputStream ois = new
ObjectInputStream(sc.socket().getInputStream());
String clientNumberString = (String)ois.readObject();
System.out.println("At {Client[" + (clientNumber + 1)
+ "]}Incoming connection from: "
+ sc.socket().getRemoteSocketAddress()
+ " from {Client[" + clientNumberString + "]}");
sc.close();
}
try {
InitClients.barrier.await();
}
catch (Exception e) {
e.printStackTrace();
}
}
}
catch (Exception e) {
e.printStackTrace();
}
printVector();
}
private void printVector() {
System.out.print("{Client[" + (clientNumber + 1) + "]}{");
for (int i = 0; i < vectorClock.length; i++) {
System.out.print(vectorClock[i] + "\t");
}
System.out.println("}");
}
}
To clarify, here are the formats of the files used. Config contains hostnames and ports used by clients that are threads and input file's rows mean either "this client sends a message to that client" or "this client increments his logical clock by some constant value".
1 M 2 (M means sending a message)
2 M 3
3 M 4
2 L 7 (L means incrementing clock)
2 M 1
...
127.0.0.1 9000
127.0.0.1 9001
127.0.0.1 9002
127.0.0.1 9003
...

I would look at the logic related to when you are expecting an incoming socket connection. From your question it looks like you expect a certain number of incoming socket connections (potentially an incoming connection after every outgoing message?). Since you are using non-blocking I/O on the incoming socket it is always possible that your while statement loops before an incoming socket could be established. As a result, a thread would be able to continue and read the next line from the file without receiving a connection. Since your end state is reached once the end of the file is reached, it is possible that you may miss an incoming socket connection.
I would add some simple print outs that displays when you read from the file, when you send a message and when you receive an incoming connection. That should quickly tell you whether or not a particular thread is missing an expected incoming connection. If it turns out that the problem is due to the non-blocking I/O, then you may need to disable non-blocking I/O when you expect an incoming socket or implement a control that keeps track of how many incoming sockets you expect and continues until that goal is met.
Hope this helps.

Missing bytes in sending files over TCP connection

Some bytes are missing when I'm sending files over TCP connection. Though there are times that file transfer is complete.
Sending side:
class SendFile extends Thread {
Socket s;
String toIP;
String fileName;
PrintWriter pw;
BufferedReader br;
String fromIP;
String nextHopIP;
String transferTime;
int routingIndex;
final int bufferSize = 65536;
int readFile;
byte[] buffer;
FileInputStream fileIn;
OutputStream fileOut;
long fileTransferTime;
SendFile(String toIP, String fileName) {
this.toIP = toIP;
this.fileName = fileName;
}
public void run() {
while (true) {
try {
fromIP = InetAddress.getLocalHost().getHostAddress();
nextHopIP = Tables.checkRoutingTable(toIP);
if (nextHopIP.equals("none")) {
System.out.println("Invalid IP address");
} else {
s = new Socket(nextHopIP, 3434);
fileIn = new FileInputStream(fileName);
fileOut = s.getOutputStream();
buffer = new byte[bufferSize];
pw = new PrintWriter(s.getOutputStream());
br = new BufferedReader(new InputStreamReader(s.getInputStream()));
pw.println(fromIP);
pw.println(toIP);
pw.println(fileName.split("\\\\")[fileName.split("\\\\").length - 1]);
pw.flush();
//Send file
fileTransferTime = System.currentTimeMillis();
int sum = 0;
while ((readFile = fileIn.read(buffer)) != -1) {
fileOut.write(buffer, 0, readFile);
sum += readFile;
}
System.out.println(sum);
fileIn.close();
s.shutdownOutput();
br.readLine();
fileTransferTime = System.currentTimeMillis() - fileTransferTime;
System.out.println("File transfer time: " + fileTransferTime + " ms");
s.close();
break;
}
} catch (IOException ex) {
//Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
System.out.println("Connection timed out. Retrying...");
}
}
}
}
Receiving side:
class FileTransferThread extends Thread {
Socket fromSocket;
Socket toSocket;
String ip;
BufferedReader fromBR;
BufferedReader toBR;
PrintWriter fromPW;
PrintWriter toPW;
String[][] delta;
String token;
String toIP;
String fromIP;
String nextHopIP;
String absoluteFileName;
String fileName;
int deltaCount;
int entryCount;
int socketIndex;
int i;
int j;
int readFile;
final int bufferSize = 65536;
byte[] buffer;
InputStream fileIn;
FileOutputStream fileOut;
OutputStream fileHopOut;
File directory;
long fileTransferTime;
FileTransferThread(Socket s) {
this.fromSocket = s;
}
public void run() {
try {
ip = InetAddress.getLocalHost().getHostAddress();
fromBR = new BufferedReader(new InputStreamReader(fromSocket.getInputStream()));
fromPW = new PrintWriter(fromSocket.getOutputStream());
fromIP = fromBR.readLine();
toIP = fromBR.readLine();
nextHopIP = Tables.checkRoutingTable(toIP);
buffer = new byte[bufferSize];
fileIn = fromSocket.getInputStream();
fileName = fromBR.readLine();
if (!fileName.equals("\\send")) {
directory = new File("c:\\" + fromIP);
directory.mkdirs();
absoluteFileName = "c:\\" + fromIP + "\\" + fileName;
fileOut = new FileOutputStream(absoluteFileName);
while (true) {
try {
//if not yet the destination IP, pass to next hop
if (!toIP.equals(ip)) {
toSocket = new Socket(toIP, 3434);
fileHopOut = toSocket.getOutputStream();
toBR = new BufferedReader(new InputStreamReader(toSocket.getInputStream()));
toPW = new PrintWriter(toSocket.getOutputStream());
toPW.println(fromIP);
toPW.println(toIP);
toPW.println(fileName);
toPW.flush();
//Send file
while ((readFile = fileIn.read(buffer)) != -1) {
fileHopOut.write(buffer, 0, readFile);
}
toSocket.shutdownOutput();
fromPW.println(toBR.readLine());
fromPW.flush();
toSocket.close();
} else {
int sum = 0;
while ((readFile = fileIn.read(buffer)) != -1) {
fileOut.write(buffer, 0, readFile);
sum += readFile;
}
System.out.println(sum);
fileOut.flush();
fileOut.close();
fromPW.println("1");
fromPW.flush();
}
fromSocket.close();
break;
} catch (IOException ex) {
//Logger.getLogger(FileTransferThread.class.getName()).log(Level.SEVERE, null, ex);
System.out.println("Connection timed out. Retrying...");
}
}
} else {
while(true) {
try {
//if not yet the destination IP, pass to next hop
if (!toIP.equals(ip)) {
toSocket = new Socket(toIP, 3434);
fileHopOut = toSocket.getOutputStream();
toBR = new BufferedReader(new InputStreamReader(toSocket.getInputStream()));
toPW = new PrintWriter(toSocket.getOutputStream());
toPW.println(fromIP);
toPW.println(toIP);
toPW.println(fileName);
toPW.flush();
//Send file
while ((readFile = fileIn.read(buffer)) != -1) {
fileHopOut.write(buffer, 0, readFile);
}
toSocket.shutdownOutput();
fromPW.println(toBR.readLine());
fromPW.flush();
toSocket.close();
} else {
while ((readFile = fileIn.read(buffer)) != -1) {
}
fromPW.println("1");
fromPW.flush();
}
fromSocket.close();
break;
}
catch (IOException ex) {
//Logger.getLogger(FileTransferThread.class.getName()).log(Level.SEVERE, null, ex);
System.out.println("Connection timed out. Retrying...");
}
}
}
fromSocket.close();
} catch (IOException ex) {
Logger.getLogger(FileTransferThread.class.getName()).log(Level.SEVERE, null, ex);
}
}
}

You are not closing - and hence not flushing - the SocketOutputStream called fileout. (You really should consider less misleading names ...).
Hm ... it appears shutdownOutput does that; its javadoc writes:
Disables the output stream for this socket.
For a TCP socket, any previously written data will be sent
followed by TCP's normal connection termination sequence.
If you write to a socket output stream after invoking
shutdownOutput() on the socket, the stream will throw
an IOException.
I leave this in case anybody else has the same idea.

Note that socket.getInputStream specifies the sorts of data loss that can happen using that facility. In particular:
The network software may discard bytes
that are buffered by the socket.

Found the error. It seems that BufferedReader is getting a chunk of data which is supposed to be for the file.