File Based Multithreaded Web Server Question

Question

Hi friends,
I have the code of a simple File Based Multithreaded Web Server. I have been asked to add proper http/1.1 Keep-Alive behavior to it. As far as I understand it means to use the same socket for the request coming from the same client without opening a new socket for every request by it. I am unable to implement it. Any help would be greatly appreciated. The entire code is as below:
package multithreadedwebserver.com;
import java.io.*;
import java.net.*;
import java.util.*;
/** This Class declares the general and HTTP constants
* and defines general static methods:
class Constants {
/** 2XX: generally "OK" */
public static final int HTTP_OK = 200;
public static final int HTTP_CREATED = 201;
public static final int HTTP_ACCEPTED = 202;
public static final int HTTP_NOT_AUTHORITATIVE = 203;
public static final int HTTP_NO_CONTENT = 204;
public static final int HTTP_RESET = 205;
public static final int HTTP_PARTIAL = 206;
/** 3XX: relocation/redirect */
public static final int HTTP_MULT_CHOICE = 300;
public static final int HTTP_MOVED_PERM = 301;
public static final int HTTP_MOVED_TEMP = 302;
public static final int HTTP_SEE_OTHER = 303;
public static final int HTTP_NOT_MODIFIED = 304;
public static final int HTTP_USE_PROXY = 305;
/** 4XX: client error */
public static final int HTTP_BAD_REQUEST = 400;
public static final int HTTP_UNAUTHORIZED = 401;
public static final int HTTP_PAYMENT_REQUIRED = 402;
public static final int HTTP_FORBIDDEN = 403;
public static final int HTTP_NOT_FOUND = 404;
public static final int HTTP_BAD_METHOD = 405;
public static final int HTTP_NOT_ACCEPTABLE = 406;
public static final int HTTP_PROXY_AUTH = 407;
public static final int HTTP_CLIENT_TIMEOUT = 408;
public static final int HTTP_CONFLICT = 409;
public static final int HTTP_GONE = 410;
public static final int HTTP_LENGTH_REQUIRED = 411;
public static final int HTTP_PRECON_FAILED = 412;
public static final int HTTP_ENTITY_TOO_LARGE = 413;
public static final int HTTP_REQ_TOO_LONG = 414;
public static final int HTTP_UNSUPPORTED_TYPE = 415;
/** 5XX: server error */
public static final int HTTP_SERVER_ERROR = 500;
public static final int HTTP_INTERNAL_ERROR = 501;
public static final int HTTP_BAD_GATEWAY = 502;
public static final int HTTP_UNAVAILABLE = 503;
public static final int HTTP_GATEWAY_TIMEOUT = 504;
public static final int HTTP_VERSION = 505;
/* the Web server's virtual root directory */
public static File root;
static PrintStream log = null;
/* Configuration information of the Web server is present
* in this props object
protected static Properties props = new Properties();
/* timeout on client connections */
static int timeout = 0;
/* maximum number of worker threads */
static int workerThreads = 5;
/* General method for printing strings */
static void printString(String s) {
System.out.println(s);
/* print logs to the log file */
static void log(String s) {
synchronized (log) {
log.println(s);
log.flush();
/* print to the log file */
static void printProperties() { 
printString("\n");
printString("#####################################################################");
printString("\n");
printString("Web server's virtual root directory= "+root);
printString("Timeout on client connections in milliseconds= "+timeout);
printString("Number of Worker Threads= "+workerThreads);
printString("\n");
printString("#####################################################################");
printString("\n\n");
printString("********************WEBSERVER STARTED SUCCESSFULLY********************\n");
/* load server.properties from java.home */
static void loadServerConfigurationProperties() throws IOException {
File f = new File(System.getProperty("java.home")+"\\lib\\"+"server.properties");
if (f.exists()) {
InputStream is =new BufferedInputStream(new FileInputStream(f));
props.load(is);
is.close();
String r = props.getProperty("root");
if (r != null) {
root = new File(r);
if (!root.exists()) {
throw new Error(root + " Server Root Directory does not exist");
r = props.getProperty("timeout");
if (r != null) {
timeout = Integer.parseInt(r);
r = props.getProperty("workerThreads");
if (r != null) {
workerThreads = Integer.parseInt(r);
r = props.getProperty("log");
if (r != null) {
log = new PrintStream(new BufferedOutputStream(
new FileOutputStream(r)));
/* Assign default values to root, timeout,
* workerThreads and log if the same have
* not been specified in the server.propwerties file
if (root == null) {   
root = new File(System.getProperty("user.dir"));
if (timeout <= 1000) {
timeout = 5000;
if (workerThreads > 25) {
printString("\n");
printString("#####################################################################");
printString("\n");
printString("Too many Threads!!!Maximum number of Worker Threads can be 15 only");
printString("\n");
printString("#####################################################################");
workerThreads = 15;
if (log == null) {
log = System.out;
public class WebServer extends Constants {
/* Specifying Default port for listening the requests */
static int port = 8080;
/* The Vector class implements a growable array of objects.
* Like an array, it contains components that can be accessed using an integer index.
* The size of a Vector can grow or shrink as needed to accommodate adding and
* removing items after the Vector has been created.
* The workerThreads are added to the Vector object threads where the worker threads stand idle
* Vector is used since it is synchronized
static Vector threads = new Vector();
public static void main(String[] userSpecifiedPort) throws Exception {
if (userSpecifiedPort.length > 0) {
port = Integer.parseInt(userSpecifiedPort[0]);
loadServerConfigurationProperties();
printProperties();
/* Instantiate ThreadPoool class and call
* the createThreadPool() method on threadPool object
ThreadPool threadPool= new ThreadPool();
threadPool.createThreadPool();
/* This class implements java.lang.Runnable.
* It runs in a worker thread to process the request and serve files to the clients.
class Worker extends WebServer implements Runnable {
static final byte[] EOL = {(byte)'\r', (byte)'\n' };
final static int BUFFER_SIZE = 2048;
/* A byte array buffer to read and write files.
* Memory is allocated to it once in the construtor of the class Worker
* and reused thereafter
byte[] buffer;
/* Socket for the client being handled */
private Socket socket;
Worker() {
buffer = new byte[BUFFER_SIZE];
socket = null;
synchronized void setSocket(Socket socket) {
this.socket = socket;
notify();
public synchronized void run() {
do {
if (socket == null) {
/* Wait */
try {
wait();
} catch (InterruptedException e) {
continue;
try {
handleClientRequest();
} catch (Exception e) {
e.printStackTrace();
socket = null;
Vector pool = WebServer.threads;
synchronized (pool) {
/* When the request is complete add the worker thread back
* into the pool
pool.addElement(this);
}while(true);
void handleClientRequest() throws IOException {
InputStream is = new BufferedInputStream(socket.getInputStream());
PrintStream ps = new PrintStream(socket.getOutputStream());
/* we will only block in read for this many milliseconds
* before we fail with java.io.InterruptedIOException,
* at which point we will abandon the connection.
socket.setSoTimeout(WebServer.timeout);
socket.setTcpNoDelay(true);
/* Refresh the buffer from last time */
for (int i = 0; i < BUFFER_SIZE; i++) {
buffer[i] = 0;
try {
/* We will only support HTTP GET/HEAD */
int readBuffer = 0, r = 0;
boolean endOfLine=false;
while (readBuffer < BUFFER_SIZE) {
r = is.read(buffer, readBuffer, BUFFER_SIZE - readBuffer);
if (r == -1) {
/* EOF */
return;
int i = readBuffer;
readBuffer += r;
for (; i < readBuffer; i++) {
if (buffer[i] == (byte)'\n' || buffer[i] == (byte)'\r') {
/* read one line */
endOfLine=true;
break;
if (endOfLine)
break;
/*Checking for a GET or a HEAD */
boolean doingGet;
/* beginning of file name */
int index;
if (buffer[0] == (byte)'G' &&
buffer[1] == (byte)'E' &&
buffer[2] == (byte)'T' &&
buffer[3] == (byte)' ') {
doingGet = true;
index = 4;
} else if (buffer[0] == (byte)'H' &&
buffer[1] == (byte)'E' &&
buffer[2] == (byte)'A' &&
buffer[3] == (byte)'D' &&
buffer[4] == (byte)' ') {
doingGet = false;
index = 5;
} else {
/* This method is not supported */
ps.print("HTTP/1.0 " + HTTP_BAD_METHOD +
" unsupported method type: ");
ps.write(buffer, 0, 5);
ps.write(EOL);
ps.flush();
socket.close();
return;
int i = 0;
/* find the file name, from:
* GET /ATG/DAS6.3.0/J2EE-AppClients/index.html HTTP/1.0
* extract "/ATG/DAS6.3.0/J2EE-AppClients/index.html "
for (i = index; i < readBuffer; i++) {
if (buffer[i] == (byte)' ') {
break;
String filename = (new String(buffer, 0, index,
i-index)).replace('/', File.separatorChar);
if (filename.startsWith(File.separator)) {
filename = filename.substring(1);
File targ = new File(WebServer.root, filename);
if (targ.isDirectory()) {
File ind = new File(targ, "index.html");
if (ind.exists()) {
targ = ind;
boolean fileFound = printHeaders(targ, ps);
if (doingGet) {
if (fileFound) {
sendResponseFile(targ, ps);
} else {
fileNotFound(targ, ps);
} finally {  
// socket.close();
System.out.println("Connection Close nahi kiya");
boolean printHeaders(File targ, PrintStream ps) throws IOException {
boolean ret = false;
int responseStatusCode = 0;
if (!targ.exists()) {
responseStatusCode = HTTP_NOT_FOUND;
ps.print("HTTP/1.0 " + HTTP_NOT_FOUND + " not found");
ps.write(EOL);
ret = false;
} else {
responseStatusCode = HTTP_OK;
ps.print("HTTP/1.0 " + HTTP_OK+" OK");
ps.write(EOL);
ret = true;
log("From " socket.getInetAddress().getHostAddress()": GET " +
targ.getAbsolutePath()+"-->"+responseStatusCode);
ps.print("Server: Simple java");
ps.write(EOL);
ps.print("Date: " + (new Date()));
ps.write(EOL);
if (ret) {
if (!targ.isDirectory()) {
ps.print("Content-length: "+targ.length());
ps.write(EOL);
ps.print("Last Modified: " + (new
Date(targ.lastModified())));
ps.write(EOL);
String name = targ.getName();
int ind = name.lastIndexOf('.');
String ct = null;
if (ind > 0) {
ct = (String) map.get(name.substring(ind));
if (ct == null) {
ct = "unknown/unknown";
ps.print("Content-type: " + ct);
ps.write(EOL);
} else {
ps.print("Content-type: text/html");
ps.write(EOL);
return ret;
void fileNotFound(File targ, PrintStream ps) throws IOException {
ps.write(EOL);
ps.write(EOL);
ps.println("The requested file could not be found.\n");
void sendResponseFile(File targ, PrintStream ps) throws IOException {
InputStream is = null;
ps.write(EOL);
if (targ.isDirectory()) { ;
listDirectory(targ, ps);
return;
} else {
is = new FileInputStream(targ.getAbsolutePath());
try {
int n;
while ((n = is.read(buffer)) > 0) {
ps.write(buffer, 0, n);
} finally {
is.close();
/* mapping file extensions to content-types */
static java.util.Hashtable map = new java.util.Hashtable();
void listDirectory(File dir, PrintStream ps) throws IOException {
ps.println("<TITLE>Multithreaded Webserver</TITLE><P>");
ps.println("<html><body align=center>");
ps.println("<center><h3><font color=#9999CC>Simple File Based MultiThreaded WebServer</font></h3></center>");
ps.println("<table border=1 align=center>");
ps.println("<tr bgcolor=#9999CC><td width=100% height=100% align=center><h3>Directory Listing</h3></td>");
ps.println("<td width=40% height=40% align=center><h3>Type</h3></td>");
String[] list = dir.list();
for (int i = 0; list != null && i < list.length; i++) {
File f = new File(dir, list);
if (f.isDirectory()) {
ps.println("<tr><td>");
ps.println("<font size=\""+"2"+"\"face=\""+"Verdana"+"\"> <A HREF=\""+list[i]+"/\">"+list[i]+"</A></font><a href=\""+list[i]+"/\"></a>\n<BR></td>");
ps.println("<td align=center><a href=\""+list[i]+"/\"><img src=\""+"/images/folder.jpg"+"\"></img></a>");
ps.println("</td");
ps.println("</tr>");
} else {
ps.println("<tr><td>");
ps.println("<font size=\""+"2"+"\" face=\""+"Verdana"+"\"></A> <A HREF=\""+list[i]+"\">"+list[i]+"</A></font><A HREF=\""+list[i]+"\"></A>\n<BR></td>");
ps.println("<td align=center><a href=\""+list[i]+"/\"><img src=\""+"/images/file.gif"+"\"></img></a>");
ps.println("</tr>");
ps.println("</table>");
ps.println("<P><HR><I><font color=blue>"+(new Date())+"</font></I>");
ps.println("<I><font color=blue>Copyright to HCL Technology Ltd</font></I>");
ps.println("<I><font color=blue>Author Vivek Kumar Sinha</font></I>");
ps.println("</body></html>");
The ThreadPool class contains a Vector of WorkerThread objects.
These objects are the individual threads that make up the pool.
The WorkerThread objects will start at the time of their construction.
If there are more HTTP requests than there are WorkerThreads,
the extra requests will backlog until WorkerThreads free up.
class ThreadPool extends WebServer{
void createThreadPool(){
for (int i = 1; i <= workerThreads; ++i) {
Worker w = new Worker();
Thread t=new Thread(w, "Worker Thread No."+i);
t.start();
/* Uncomment to check the number of worker threads running */
// printString("Worker Thread No."+i+" Started");
threads.addElement(w);
try{
ServerSocket serversocket = new ServerSocket(port);
do {
Socket socket = serversocket.accept();
Worker w = null;
synchronized (threads) {
if (threads.isEmpty()) {
/* Do nothing */
} else {
w = (Worker) threads.elementAt(0);
threads.removeElementAt(0);
w.setSocket(socket);
} while (true);
} catch (IOException e) {
e.printStackTrace();

Answer 1

Thank you for Welcoming me!!! I am very new to this forum so din't have this idea.
I am unable to add the keep alive behavior . I don't have problem with any part of the code. The problem is i don't know how to make that enhancement in the existing code.
Regards