import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;
/**
* The BulletinBoard servlet allows the user to view posted
* bulletins as well as add their own bulletins to be viewed by
* others.
*
* @author Dustin R. Callaway
* @version 1.0, 04/29/98
*/
public class BulletinBoard extends HttpServlet
{
//class variables
static String filePath; //stores root path for bulletins files
/**
* init method is called when servlet is first loaded. It
* reads from an initialization parameter the directory where
* the bulletin files are stored.
*/
public void init(ServletConfig config) throws ServletException
{
super.init(config); //pass ServletConfig to parent
//get path to support files
filePath = config.getInitParameter("FilePath");
if (filePath == null)
{
//default directory if no FilePath init parameter exists
filePath = "/";
}
}
/**
* doGet method is called in response to any GET request.
* Returns an HTML form that allows the user to select a
* bulletin board topic and choose to view bulletins or post
* a new one.
*/
public void doGet(HttpServletRequest request,
HttpServletResponse response) throws IOException
{
//MIME type to return is HTML
response.setContentType("text/html");
//get a handle to the output stream
PrintWriter out = response.getWriter();
FileInputStream fileTopics=null;
try
{
//open input stream to topics.properties file
fileTopics = new FileInputStream(filePath +
"topics.properties");
Properties propTopics = new Properties();
propTopics.load(fileTopics); //load properties object
//create enumeration from properties object
Enumeration enumTopics = propTopics.propertyNames();
//create HTML form to allow user to select a topic
out.println("");
out.println("");
out.println("Servlet Bulletin Board");
out.println("");
out.println("");
out.println("Servlet Bulletin Board
");
out.println("
");
out.println("");
}
catch (Exception e)
{
//send stack trace back to client
sendErrorToClient(out, e);
}
finally
{
try
{
//close file input stream
fileTopics.close();
}
catch (Exception e) {}
try
{
//close output stream
out.close();
}
catch (Exception e) {}
}
}
/**
* doPost method is called in response to any POST request.
* This method determines if it was called in response to the
* user selecting to view bulletins, post a bulletin, or
* save a bulletin and responds accordingly.
*/
public void doPost(HttpServletRequest request,
HttpServletResponse response)
{
String currentTopic=""; //user's currently selected topic
PrintWriter out=null;
//get bulletin board topic selected from drop-down list
currentTopic = request.getParameter("TOPICS");
//get the name of file containing bulletins for this topic
String file = filePath + currentTopic + ".txt";
//get path to servlet for use in hyperlinks
String servletPath = request.getServletPath();
response.setContentType("text/html"); //html output
try
{
out = response.getWriter(); //get handle to output stream
out.println("");
out.println("" + currentTopic +
" Bulletin Board");
out.println("");
//View Bulletins
if (request.getParameter("VIEW") != null)
{
showBulletins(out, currentTopic, file);
}
//Post a bulletin
else if (request.getParameter("POST") != null)
{
//allows user to enter bulletin and submit it
postBulletin(out, currentTopic);
}
//Save bulletin
else
{
//saves the bulletin to file
saveBulletin(out, currentTopic, file, request);
}
//create hyperlink to return to main page
out.println("
Return to Main Page");
out.println("");
}
catch (Exception e)
{
//send stack trace back to client
sendErrorToClient(out, e);
}
}
/**
* showBulletins method reads bulletins from disk and sends
* them to the client. If file does not exist, client is
* informed that the selected topic contains no bulletins.
*
* @param out Client output stream
* @param currentTopic User's currently selected topic
* @param file File containing bulletins for selected topic
*/
private void showBulletins(PrintWriter out,
String currentTopic, String file)
{
FileReader fr=null;
BufferedReader br=null;
try
{
File fileTopic = new File(file); //get handle to file
if (fileTopic.exists()) //file exists, display it
{
fr = new FileReader(file);
br = new BufferedReader(fr); //get file input stream
out.println("" + currentTopic +
" Bulletin Board
");
out.println("View Bulletins
");
String line = br.readLine();
//iterate through each line of bulletin board file
while (line != null)
{
//send bulletins to client
out.println(line + "
\n");
line = br.readLine();
}
}
else //file doesn't exist, display no bulletins message
{
out.println("This topic currently contains no " +
"bulletins.");
}
}
catch (Exception e)
{
//send stack trace back to client
sendErrorToClient(out, e);
}
finally
{
try
{
br.close(); //close buffered reader
}
catch (Exception e) {}
try
{
fr.close(); //close file reader
}
catch (Exception e) {}
}
}
/**
* postBulletin method generates the HTML form that allows
* the user to enter a new bulletin.
*
* @param out Client output stream
* @param currentTopic User's currently selected topic
*/
private void postBulletin(PrintWriter out,
String currentTopic)
{
//create HTML form to allow user to enter new bulletin
out.println("" + currentTopic + " Bulletin Board
");
out.println("Post Bulletin
");
out.println("");
}
/**
* saveBulletin method saves the bulletin to disk.
*
* @param out Client output stream
* @param currentTopic User's currently selected topic
* @param file File containing bulletins for selected topic
* @param request HttpServletRequest object
*/
private void saveBulletin(PrintWriter out,
String currentTopic, String file,
HttpServletRequest request)
{
FileWriter fw=null;
PrintWriter pw=null;
try
{
fw = new FileWriter(file, true);
pw = new PrintWriter(fw); //get output stream to file
//print separator
pw.println("-----------------------------------");
//print user's bulletin to file
pw.println(request.getParameter("BULLETIN"));
out.println("Bulletin Saved!
");
}
catch (Exception e)
{
//send stack trace back to client
sendErrorToClient(out, e);
}
finally
{
try
{
pw.flush(); //flush output stream to file
pw.close(); //close print writer
}
catch (Exception e) {}
try
{
fw.close(); //close file writer
}
catch (Exception e) {}
}
}
/**
* Return stack trace to client. Useful for debugging.
*
* @param out Client output stream
* @param e Exception
*/
private void sendErrorToClient(PrintWriter out, Exception e)
{
//send stack trace back to client and to standard out
StringWriter stringError = new StringWriter();
PrintWriter printError = new PrintWriter(stringError);
e.printStackTrace(printError);
String stackTrace = stringError.toString();
//send error message to client
out.println("Error");
out.println("Servlet Error
Error
" + e +
"Stack Trace
" + stackTrace + "");
//print stack trace to standard out
System.out.println("Servlet Error: " + stackTrace);
}
}