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how to serve 1000s of concurrent connection using Java NIO

My sender is sending 10000 requests per second (or even more) but my ServerSocketChannel is only able to read and process (in thread) 8000 requests (~appx).
Dummy code is like this:
public class NioReceiver {
private int port = -1;
private static String message = null;
public void receive() throws IOException {
// Get the selector
Selector selector = Selector.open();
// Selector is open for making connection
// Get the server socket channel and register using selector
ServerSocketChannel SS = ServerSocketChannel.open();
InetSocketAddress hostAddress = new InetSocketAddress(this.port);
SS.bind(hostAddress);
SS.configureBlocking(false);
int ops = SS.validOps();
SelectionKey selectKy = SS.register(selector, ops, null);
for (;;) {
//Waiting for the select operation...
int noOfKeys = selector.select();
// The Number of selected keys are: noOfKeys
Set selectedKeys = selector.selectedKeys();
Iterator itr = selectedKeys.iterator();
while (itr.hasNext()) {
ByteBuffer buffer = ByteBuffer.allocate(1024 * 60);
SelectionKey ky = (SelectionKey) itr.next();
if (ky.isAcceptable()) {
// The new client connection is accepted
SocketChannel client = SS.accept();
client.configureBlocking(false);
// The new connection is added to a selector
client.register(selector, SelectionKey.OP_READ);
// The new connection is accepted from the client: client
} else if (ky.isReadable()) {
// Data is read from the client
SocketChannel client = (SocketChannel) ky.channel();
String output = null;
buffer.clear();
int charRead = -1;
try {
charRead = client.read(buffer);
} catch (IOException e) {
continue;
}
if (charRead <= 0) {
// client closed
client.close();
} else {
output = new String(buffer.array());
message = output;
try {
new Thread(() -> {
processAndStore(message);
}).start();
} catch (Exception e) {
System.err.println("Thread exception:::" + e.getMessage());
}
} // else if of client.isConnected()
} // else if of ky.isReadable()
itr.remove();
} // end of while loop
} // end of for loop
}
public void processAndStore(String output) {
String exchangeName = null;
String dataLine = null;
String Lines[] = output.split("\r\n");
for (int i = 0; i < Lines.length; i++) {
if (Lines[i].contains("Host: ")) {
exchangeName = Lines[i].substring(6);
}
if (Lines[i].isEmpty()) {
dataLine = Lines[i + 1];
}
}
StringBuffer updatedLastLine = null;
if (dataLine != null) {
if (dataLine.contains("POST")) {
updatedLastLine = new StringBuffer(dataLine.substring(0, dataLine.indexOf("POST")));
} else {
updatedLastLine = new StringBuffer(dataLine);
}
if (!dataLine.equals("")) {
try {
if (updatedLastLine.lastIndexOf("}") != -1) {
updatedLastLine.replace(updatedLastLine.lastIndexOf("}"), updatedLastLine.lastIndexOf("}") + 1, ",\"name\":\"" + exchangeName
+ "\"}");
} else {
return;
}
} catch (StringIndexOutOfBoundsException e) {
System.out.println(updatedLastLine + "::" + dataLine);
System.out.println(e);
}
store(updatedLastLine.toString());
}
}
}
public NioReceiver(int port) {
this.port = port;
}
}
When I am removing processing logic it is able to receive more requests but not all.
how can I improve my code to receive all 10000s incoming requests.

Use a thread pool / message queue instead of creating 1000's of threads for calling processAndStore().
Starting a thread is expensive.
Starting 10000 threads per second? Yikes!
As #EJP said in a comment:
The purpose of NIO is to reduce the number of required threads. You don't seem to have got the message.
In addition to that, profile your code to see where the bottleneck is, rather than guessing.
But, here are some guesses anyway:
Don't use StringBuffer, use StringBuilder.
Reason: See Difference between StringBuilder and StringBuffer.
Don't call lastIndexOf("}") three times.
Reason: lastIndexOf() is a sequential search, so relatively slow. The JVM may or may not optimize the multiple calls away, but if performance is critical, don't rely on it. Do it yourself by assigning result to variable. See also Does Java optimize method calls via an interface which has a single implementor marked as final?

MQTT Java publisher and Nodejs subscriber

In my current project, we are trying to enable communication between two software component as follow. Here, the Temperaturesensor (written in JavaSE) component periodically publishing sensor measurement, written in MQTT JavaSE Publisher. And CalculateTemp(written in Nodejs) component has subscribed using MQTT Nodejs and received data. My problem is -- when data is received at CalculateAvgTempcomponent is Junk (Possibly, the problem is TemperatureSensor is sending data in byte[] and on the calculateAvgTemp component side, the data is not converted from byte[].-- How can I convert the byte[] data to JSON format????)
The Publish method at TemperatureSensor as follows. Please note that data are converted to byte, before publishing to MQTT broker.
public void publish(String topicName, Object arg, Device deviceInfo) {
DataWrapper dw = new DataWrapper();
dw.setObject(arg);
dw.setDevice(deviceInfo);
java.io.ByteArrayOutputStream bstream = new java.io.ByteArrayOutputStream();
java.io.ObjectOutputStream st;
try {
st = new java.io.ObjectOutputStream(bstream);
st.writeObject(dw);
st.flush();
} catch (IOException e) {
e.printStackTrace();
}
byte[] bytes = bstream.toByteArray();
try {
pub.publish(topicName, 0, bytes);
} catch (Throwable e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
On data receiving side, the CalculateAvgTemp, the code is as follows:
var mqtt = require('mqtt'); // no count for NodeRED
var client = mqtt.connect('mqtt://test.mosquitto.org:1883');
var NUM_SAMPLE_FOR_AVG = 5;
var numSample = 0;
var tempCelcius = 0;
var currentAvg = 0;
client.subscribe('tempMeasurement');
client.on('message', function(topic, payload) {
if (topic.toString() == "tempMeasurement") {
// Here, we may need to convert the byte[] array.
// But I do not know-- how can I convert byte[] array to JSON.
var sensorMeasurement=JSON.parse(payload);
if (numSample <= NUM_SAMPLE_FOR_AVG) {
numSample = numSample + 1;
if (sensorMeasurement.unitOfMeasurement == 'F') {
tempCelcius = ((sensorMeasurement.tempValue - 32) * (5 / 9));
} else {
tempCelcius = sensorMeasurement.tempValue;
}
currentAvg = parseFloat(currentAvg) + parseFloat(tempCelcius);
if (numSample == NUM_SAMPLE_FOR_AVG) {
currentAvg = currentAvg / NUM_SAMPLE_FOR_AVG;
var avgTemp = {
"tempValue" : parseFloat(currentAvg),
"unitOfMeasurement" : sensorMeasurement.unitOfMeasurement
};
client.publish('roomAvgTempMeasurement', JSON
.stringify(avgTemp));
console.log("Publishing Data roomAvgTempMeasurement ");
numSample = 0;
currentAvg = 0;
}
}
}
});
there is possible duplication of question is MQTT communication between nodejs and java
But, the proposed solution is not working or I am not able to understand it clearly that can solve the problem.

A ObjectOutputStream will convert an object into a Serialized Java Object stream, this is Java's internal object notation and can not be understood by anything else (easily).
You need to use a library like the one from json.org to build a JSON object (or build one by hand as a string as shown in the linked question) that holds the same state as your DataWrapper object, then have the JSON object output as a string which can be send as the byte payload of the MQTT message.

Ways to proxy an InputStream

I am using Android-Universal-Image-Loader to load images from remote server over HTTPS on my Android application. To have access to images the client should provide a valid token and sometimes server can return "expired crsf token" error. In order to handle this behavior a custom ImageDownloader should be defined. Below is the base implementation of method that should be overrrided in my implementation.
protected InputStream getStreamFromNetwork(String imageUri, Object extra) throws IOException {
HttpURLConnection conn = createConnection(imageUri, extra);
int redirectCount = 0;
while (conn.getResponseCode() / 100 == 3 && redirectCount < MAX_REDIRECT_COUNT) {
conn = createConnection(conn.getHeaderField("Location"), extra);
redirectCount++;
}
InputStream imageStream;
try {
imageStream = conn.getInputStream();
} catch (IOException e) {
// Read all data to allow reuse connection (http://bit.ly/1ad35PY)
IoUtils.readAndCloseStream(conn.getErrorStream());
throw e;
}
if (!shouldBeProcessed(conn)) {
IoUtils.closeSilently(imageStream);
throw new IOException("Image request failed with response code " + conn.getResponseCode());
}
return new ContentLengthInputStream(new BufferedInputStream(imageStream, BUFFER_SIZE), conn.getContentLength());
}
I want to rewrite it to handle invalid token errors. For example, if the server returns such error it should be recognized, token should be regenerated and request repeated.
The only solution I come up with is like this (shortened code):
imageStream = conn.getInputStream();
byte[] body = org.apache.commons.io.IOUtils.toByteArray(imageStream);
if (body.length < 300 // high probability to contain err message
&& isInvalidToken(body)) {
// handle error
}
return new ByteArrayInputStream(body);
Is is safe to use such kind of solution, considering I use it only for thumbnails of max 80kb size? Are there any other solutions?

Your solution is safe, although it's nicer if you create your ImageDownloaderInputStream class that implements InputStream and wraps the original InputStream. You can pre-load (buffer) some chunk from the underlying input stream to detect if the content is valid or not.
The only method you should override is read().
If the content is valid, you can serve the buffer content to the caller, when the buffer is empty, directly stream from the underlying InputStream.
If the content is invalid, just simply read another stream, or return a zero-length stream.
public class ImageDownloaderInputStream extends InputStream {
private byte[] buffer = null;
private int bufLen = 0;
private int bufIndex = 0;
private boolean isContentValid;
private InputStream wrapped;
public ImageDownloaderInputStream (InputStream wrapped) {
this.wrapped = wrapped;
}
#Override
public ind read() {
if(buffer == null) {
// check content and fill buffer
this.isContentValid = checkContent();
}
if (this.isContentValid) {
if(bufIndex < bufLen) {
return buffer[bufIndex++] & 0xFF;
} else {
return wrapped.read();
}
} else {
// error handling: zero-length stream
return -1;
}
}
private boolean checkContent() {
// fill the buffer
this.buffer = new byte[1024];
this.bufLen = wrapped.read(this.buffer);
// read more if not enough
// check the content
return true;
// return false;
}
}

You can check for a valid token after you checked that the response was 200 OK like so:
conn.getResponseCode() == HttpStatus.RESPONSE_OK && isValidToken(body)
If these conditions are not met then you handle it accordingly i.e repeat the request x times.
I would consider having a isValidToken(...) method instead of your isInvalidToken(...) so that you don't have to negate the response of the method.

Have you considered something like this?
if(conn.getResponseCode()==HttpStatus.RESPONSE_OK) else{ //repeat request...}

Broken pipe error communicating with Java server & C# client in multi thread env

I hope to find any help on my old annoying problem.
I have a TCP sever program with java and client program with c#
packet protocol between those two is simply consist of 4byte length & body ASCII data.
The Problem is that C# client faces FormatException which is from parsing fail on length byte. If I look into an error from client side, then client is trying to parse somewhere in the body which is not length header.
But apparently, Server does not send broken packet.
meanwhile, at the server, I could find an Broken pipe error whenever this kind of problem happens.
Unfortunately this error does not always happen and was not able to recreate the problem situation. it makes me difficult to find exact cause of this problem
Please see below codes for server side
public class SimplifiedServer {
private Map<InetAddress, DataOutputStream> outMap;
private Map<InetAddress,DataInputStream> inMap;
protected void onAcceptNewClient(Socket client) {
DataOutputStream out = null;
DataInputStream in = null;
try {
out = new DataOutputStream(client.getOutputStream());
in = new DataInputStream(client.getInputStream());
} catch (IOException e) {
e.printStackTrace();
}
outMap.put(client.getInetAddress(), out);
inMap.put(client.getInetAddress(), in);
}
public void writeToAll(String packet) {
outMap.forEach((key, out) -> {
try {
byte[] body = packet.getBytes("UTF-8");
int len = body.length;
if (len > 9999) {
throw new IllegalArgumentException("packet length is longer than 10000, this try will be neglected");
}
String lenStr = String.format("%04d%s", len, packet);
byte[] obuf = lenStr.getBytes();
synchronized (out) {
out.write(obuf);
out.flush();
}
} catch (IOException e) {
e.printStackTrace();
}
});
}
public void listenClient(Socket client) {
try {
DataOutputStream out = outMap.get(client.getInetAddress());
DataInputStream in = inMap.get(client.getInetAddress());
while (true) {
byte[] received = SimplePacketHandler.receiveLpControlerData(in);
byte[] lenBytes = new byte[4];
for( int i = 0 ; i < 4 ; i ++){
lenBytes[i] = in.readByte();
}
String lenString = new String(lenBytes);
int length = Integer.parseInt(lenString);
byte[] data = new byte[length];
for ( int i = 0 ; i < length ; i ++){
data[i] = in.readByte();
}
if ( data == null ){
System.out.println("NetWork error, closing socket :" + client.getInetAddress());
in.close();
out.close();
outMap.remove(client.getInetAddress());
inMap.remove(client.getInetAddress());
return;
}
doSomethingWithData(out, data);
}
} catch (NumberFormatException e) {
e.printStackTrace();
} catch ( Exception e ) {
e.printStackTrace();
} finally {
try {
System.out.println(client.getRemoteSocketAddress().toString() + " closing !!! ");
// remove stream handler from map
outMap.remove(client.getInetAddress());
inMap.remove(client.getInetAddress());
//close socket.
client.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
And here is client side code
public class ClientSide
{
public TcpClient client;
public String ip;
public int port;
public NetworkStream ns;
public BinaryWriter writer;
public BinaryReader reader;
public Boolean isConnected = false;
public System.Timers.Timer t;
public String lastPacketSucceeded = String.Empty;
public ClientSide(String ip, int port)
{
this.ip = ip;
this.port = port;
client = new TcpClient();
}
public bool connect()
{
try
{
client.Connect(ip, port);
}
catch (SocketException e)
{
Console.WriteLine(e.ToString());
return false;
}
Console.WriteLine("Connection Established");
reader = new BinaryReader(client.GetStream());
writer = new BinaryWriter(client.GetStream());
isConnected = true;
return true;
}
public void startListen()
{
Thread t = new Thread(new ThreadStart(listen));
t.Start();
}
public void listen()
{
byte[] buffer = new byte[4];
while (true)
{
try
{
reader.Read(buffer, 0, 4);
String len = Encoding.UTF8.GetString(buffer);
int length = Int32.Parse(len);
byte[] bodyBuf = new byte[length];
reader.Read(bodyBuf, 0, length);
String body = Encoding.UTF8.GetString(bodyBuf);
doSomethingWithBody(body);
}
catch (FormatException e)
{
Console.WriteLine(e.Message);
}
}
}
public void writeToServer(String bodyStr)
{
byte[] body = Encoding.UTF8.GetBytes(bodyStr);
int len = body.Length;
if (len > 10000)
{
Console.WriteLine("Send Abort:" + bodyStr);
}
len = len + 10000;
String lenStr = Convert.ToString(len);
lenStr = lenStr.Substring(1);
byte[] lengthHeader = Encoding.UTF8.GetBytes(lenStr);
String fullPacket = lenStr + bodyStr;
byte[] full = Encoding.UTF8.GetBytes(fullPacket);
try
{
writer.Write(full);
}
catch (Exception)
{
reader.Close();
writer.Close();
client.Close();
reader = null;
writer = null;
client = null;
Console.WriteLine("Send Fail" + fullPacket);
}
Console.WriteLine("Send complete " + fullPacket);
}
}
Considering it is impossible to recreate problem, I would guess this problem is from multithread issue. but I could not find any further clue to fix this problem.
Please let me know if you guys need any more information to solve this out.
Any help will be great appreciated, thanks in advance.

A broken pipe exception is caused by closing the connection on the other side. Most likely the C# client has a bug, causing the format exception which causes it to close the connection and therefore the broken pipe on the server side. See what is the meaning of Broken pipe Exception?.
Check the return value of this read:
byte[] bodyBuf = new byte[length];
reader.Read(bodyBuf, 0, length);
According to Microsoft documentation for BinaryReader.Read https://msdn.microsoft.com/en-us/library/ms143295%28v=vs.110%29.aspx
[The return value is ] The number of bytes read into buffer. This might be less than the number of bytes requested if that many bytes are not available, or it might be zero if the end of the stream is reached.
If it reads less than the length bytes then next time it will be parsing the length using data somewhere in the middle of the last message.

These broke pipe exceptions happen when the client (browser) has closed the connection, but the server (your tag) continues to try to write to the stream.
This usually happens when someone clicks Back, Stop, etc. in the browser and it disconnects from the server before the request is finished. Sometimes, it can happen because, for example, the Content-Length header is incorrect (and the browser takes its value as true).
Usually, this is a non-event, and nothing to worry about. But if you are seeing them in your dev environment when you know you have not interrupted your browser, you might dig a bit more to find out why.
WLS server will try to filter these exceptions from the web container out of the log, since it is due to client (browser) action and we can't do anything about it. But the server doesn't catch all of them.
refer from :: https://community.oracle.com/thread/806884

Sending an int from Java to C using sockets

I was just wondering how to send an int from a Java application to a C application using sockets. I have got different C programs communicating with each other and have got the Java application retrieving data from the C application, but I can't work out sending.
The C application is acting as database, the Java application then sends a user id (a 4 digit number) to the C application, if it exists it returns that record's details.
In Java I have tried using a printWriter and DataOutputStream to send the data, printWriter produces weird symbols and DataOutputStream produces "prof_agent.so".
Any help would be appreciated as I don't have a good grasp of sockets at the moment.

You can use DataOutputStream.writeInt. It writes an int already in network byte order by contract.
On a C side you can call recv, or read to fill in the 4-byte buffer, and then you can use ntohl ( Network-TO-Host-Long ) to convert the value you've just read to your platform int representation.

You can send the textual representation. So the number 123 would be sent as 3 bytes '1' '2' '3'.

It's a bit too late but let this answer be here. Using UDP sockets:
Java code:
public void runJavaSocket() {
System.out.println("Java Sockets Program has started."); int i=0;
try {
DatagramSocket socket = new DatagramSocket();
System.out.println("Sending the udp socket...");
// Send the Message "HI"
socket.send(toDatagram("HI",InetAddress.getByName("127.0.0.1"),3800));
while (true)
{
System.out.println("Sending hi " + i);
Thread.currentThread();
Thread.sleep(1000);
socket.send(toDatagram("HI " + String.valueOf(i),InetAddress.getByName("127.0.0.1"),3800));
i++;
}
}
catch (Exception e)
{
e.printStackTrace();
}
}
public DatagramPacket toDatagram(
String s, InetAddress destIA, int destPort) {
// Deprecated in Java 1.1, but it works:
byte[] buf = new byte[s.length() + 1];
s.getBytes(0, s.length(), buf, 0);
// The correct Java 1.1 approach, but it's
// Broken (it truncates the String):
// byte[] buf = s.getBytes();
return new DatagramPacket(buf, buf.length,
destIA, destPort);
}
C# code:
string returnData;
byte[] receiveBytes;
//ConsoleKeyInfo cki = new ConsoleKeyInfo();
using (UdpClient udpClient = new UdpClient(new IPEndPoint(IPAddress.Parse("127.0.0.1"), 3800)))
{
IPEndPoint remoteIpEndPoint = new IPEndPoint(IPAddress.Parse("127.0.0.1"), 3800);
while (true)
{
receiveBytes = udpClient.Receive(ref remoteIpEndPoint);
returnData = Encoding.ASCII.GetString(receiveBytes);
Console.WriteLine(returnData);
}
}

Try this:
Socket s = ...;
DataOutputStream out = null;
try {
out = new DataOutputStream( s.getOutputStream() );
out.writeInt( 123456 );
} catch ( IOException e ) {
// TODO Handle exception
} finally {
if ( out != null ) {
try {
out.close();
} catch ( IOException e ) {
// TODO Handle exception
}
}
}
It whould help if you could explain a little more what your problem is.