Creating multithreaded web server in Java

      Web server is a application which runs on server machine and listens request from various clients on specific port and gives some specific response for each request. Web servers and client machines uses sockets for transferring data between each other. In general if we construct simple web server using single execution instance then it will be able to serve only one client at time, so if multiple clients wants connect to the server then other clients may need to wait. To resolve this problem we can construct multithreaded server, which will create and execute a single thread  for each individual request (may be from same client machine or different client machines). Coding this in Java is very easy as compared to other languages.

 

Java Code of a multithreaded web server available here is able to accept requests from other computers (clients) by using their browser to point towards the server host and, in return displays a web pages or images. Following are steps to create multithreaded web server:

1. Create a Socket to listen webrequest on Port 80.
int port =80;
ServerSocket WebSocket = new ServerSocket(port);
2. Accept a TCP request
Socket connectionSocket = WebSocket.accept();
3. Construct an object to process HTTP request.
HttpRequest request = new HttpRequest(connectionSocket);
    
4. Create a thread to process requests.
Thread thread = new Thread(request);
thread.start(); //start thread

Note:   If you are testing this code with Eclipse or Netbeans IDEs then make one .html file, say index.html in root folder of your project and browse http://127.0.0.1/index.html (similary for other .htlm files).

/*WebServer.java */package webserver;import java.net.ServerSocket;import java.net.Socket;public final class WebServer {   public static void main(String argv[]) throws Exception {     int port =80;     ServerSocket WebSocket = new ServerSocket(port);     while (true) {      // Listen for a TCP connection request.      Socket connectionSocket = WebSocket.accept();      //Construct object to process HTTP request message      HttpRequest request = new HttpRequest(connectionSocket);      Thread thread = new Thread(request);      thread.start(); //start thread     } }}

 

/*HttpRequest.java */package webserver;import java.io.*;import java.net.*;import java.util.*;public final class HttpRequest implements Runnable { final static String CRLF = "\r\n";//For convenience Socket socket; // Constructor public HttpRequest(Socket socket) throws Exception {  this.socket = socket; } // Implement the run() method of the Runnable interface. public void run() {  try {   processRequest();  } catch (Exception e) {   System.out.println(e);  } } private void processRequest() throws Exception {  InputStream is = socket.getInputStream();  DataOutputStream os = new DataOutputStream(    socket.getOutputStream());  // Set up input stream filters.  BufferedReader br = new BufferedReader(    new InputStreamReader(is));   String requestLine = br.readLine();   System.out.println();  //Echoes request line out to screen   System.out.println(requestLine);   //The following obtains the IP address of the incoming connection.	InetAddress incomingAddress = socket.getInetAddress();	String ipString= incomingAddress.getHostAddress();	System.out.println("The incoming address is:   " + ipString);   //String Tokenizer is used to extract file name from this class.   StringTokenizer tokens = new StringTokenizer(requestLine);    tokens.nextToken();  // skip over the method, which should be “GET”    String fileName = tokens.nextToken();    // Prepend a “.” so that file request is within the current directory.    fileName = "." + fileName;   String headerLine = null;   while ((headerLine = br.readLine()).length() != 0) { //While the header still has text, print it    System.out.println(headerLine);   }   // Open the requested file.   FileInputStream fis = null;   boolean fileExists = true;   try {    fis = new FileInputStream(fileName);   } catch (FileNotFoundException e) {    fileExists = false;   }   //Construct the response message   String statusLine = null; //Set initial values to null   String contentTypeLine = null;   String entityBody = null;   if (fileExists) {	   statusLine = "HTTP/1.1 200 OK: ";	   contentTypeLine = "Content-Type: " +	    contentType(fileName) + CRLF;   } else {	   statusLine = "HTTP/1.1 404 Not Found: ";	   contentTypeLine = "Content-Type: text/html" + CRLF;	    entityBody = "<HTML> <HEAD><TITLE>Not Found</TITLE></HEAD> <BODY>Not Found on Kaitec's Multithreaded WebServer</BODY></HTML>";   }   //End of response message construction   // Send the status line.   os.writeBytes(statusLine);   // Send the content type line.   os.writeBytes(contentTypeLine);   // Send a blank line to indicate the end of the header lines.   os.writeBytes(CRLF);   // Send the entity body.   if (fileExists) {    sendBytes(fis, os);    fis.close();   } else {    os.writeBytes(entityBody);   }   os.close(); //Close streams and socket.   br.close();   socket.close();  }//Need this one for sendBytes function called in processRequestprivate static void sendBytes(FileInputStream fis, OutputStream os)throws Exception{   // Construct a 1K buffer to hold bytes on their way to the socket.   byte[] buffer = new byte[1024];   int bytes = 0;   // Copy requested file into the socket’s output stream.   while((bytes = fis.read(buffer)) != -1 ) {      os.write(buffer, 0, bytes);   }}private static String contentType(String fileName) { if(fileName.endsWith(".htm") || fileName.endsWith(".html"))  return "text/html"; if(fileName.endsWith(".jpg"))  return "text/jpg"; if(fileName.endsWith(".gif"))  return "text/gif"; return "application/octet-stream"; }}