failure to activate a Web application with database

[Cathy Valdez]

I tried to activate an example Web application with database but failed.
This example is done by:
1. Developing a servlet context listener to initialize connection pool and place it in a global naming context
2. Configuring the deployment descriptor to declare the servlet context listener and set the servlet context initialization parameters
3. Deploying the Web application
4. Activating the Web application
This is an example of a Web application for playing word games.
The servlet allows the user to play a "word scramble" game.
Next, the user is presented with a list of "word categories" to choose from. The user selects a category and clicks the Choose button, which presents her with the next view.
The next view is the main part of the scramble game. The user is presented with a scrambled word and is asked to enter the word in the text field. The user can also ask for a hint by selecting the checkbox. She then clicks the Guess button to process the request. The hint text appears in blue. The game is keeping track of how many "guesses" (including hints)she has made.

Below are software installed in my PC:
Windows98
Tomcat v. 4.1.27
J2SE/JDK v. 1.3.1
MySQL Server v. 4.0.17
MySQL Connector/J v. 3.0.10

Below is the content of AUTOEXEC.BAT:

rem - By Windows Setup - C:\WINDOWS\COMMAND\MSCDEX /V /D:ATAPI_CD /M:10
set PATH=c:\jdk1.3.1\bin;%PATH%
set CLASSPATH=%CLASSPATH%;.;c:\ServletDevel;c:\Tomcat\common\lib\servlet.jar;c:\mysql-connector-java\mysql-connector-java\mysql-connector-java-3.0.10-stable-bin.jar;c:\ServletDevel\jsp;c:\ServletDevel\database
set JAVA_HOME=c:\jdk1.3.1

From MySQL Server, I've created the database wordgames with tables (word, wordcategory & wordhint) under it.
Below is the deployment descriptor (web.xml)and is located in the deployment path, c:\Tomcat\webapps\database\WEB-INF:

<!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN" "http://java.sun.com/j2ee/dtds/web-app_2_3.dtd">
<web-app>
    <display-name>SL-314 Database Exercise #1 Solution</display-name>
    <description>
This Web Application is a solution for Database Exercise #1.
This WebApp demonstrates a typical servlet design using Connection
Pooling and Data Access Objects to interface with a database.
    </description>
    <!--
      Step: Enter the parameters for constructing the Connection Pool.
      -->
    <context-param>
       <param-name>jdbcDriver</param-name>
       <param-value>com.mysql.jdbc.Driver</param-value>
    </context-param>
    <context-param>
       <param-name>jdbcURL</param-name>
       <param-value>jdbc:mysql://host:3306/wordgames</param-value>
    </context-param>
    <context-param>
       <param-name>jdbcUserName</param-name>
       <param-value>cathy</param-value> 
    </context-param>
    <context-param>
       <param-name>jdbcPassword</param-name>
       <param-value>aprfeb</param-value> 
    </context-param>
    <context-param>
       <param-name>minimumConnections</param-name>
       <param-value>1</param-value>
    </context-param>
    <context-param>
       <param-name>maximumConnections</param-name>
       <param-value>5</param-value>
    </context-param>
    <!--
      Step: Enter the servlet context listener class name
      -->
    <listener>
       <listener-class>sl314.web.InitializeConnectionPool</listener-class>
    </listener>
    <servlet>
        <servlet-name>WordScrambleServlet</servlet-name>
        <servlet-class>sl314.web.ScrambleGameServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>WordScrambleServlet</servlet-name>
        <url-pattern>/wordScramble</url-pattern>
    </servlet-mapping>
    <error-page>
        <exception-type>sl314.util.sql.ConnNotAvailException</exception-type>
        <location>/error/server_busy.html</location>
    </error-page>
    <error-page>
        <exception-type>sl314.util.sql.ShuttingDownException</exception-type>
        <location>/error/server_shutdown.html</location>
    </error-page>
</web-app>

Java files below are located at the development path, c:\ServletDevel\database\sl314\domain:
ScrambleGameService.java
Word.java
WordCategory.java
WordCategoryDAO.java
WordCategoryService.java
WordDAO.java
Files above were compiled successful and class files of each is copied in the deployment path, c:\Tomcat\webapps\database\WEB-INF\classes\sl314\domain
Below is the code for ScrambleGameService.java:

package sl314.domain;
import java.util.Random;
public class ScrambleGameService implements java.io.Serializable {
  private Word theWord;
  private char[] theScrambledWord;
  private int howManyGuesses;
  private int howManyHints;
  public ScrambleGameService(Word theWord) {
    this.theWord = theWord;
    initScrambledWord();
    this.howManyGuesses = 0;
    this.howManyHints = 0;
  }
  public Word getWord() {
    return theWord;
  }
  public char[] getScrambledWord() {
    return theScrambledWord;
  }
  public int getHowManyGuessesLeft() {
    return 4 - howManyGuesses;
  }
  public int getHowManyHints() {
    return howManyHints;
  }
  public boolean isCorrectGuess(String guess) {
    howManyGuesses++;
    return theWord.isCorrectGuess(guess);
  }
  public void incHowManyHints() {
    howManyHints++;
    // A hint counts as a guess
    howManyGuesses++;
  }
  private void initScrambledWord() {
    String wordStr = theWord.getWord();
    int wordLen = wordStr.length();
    int i;
    // Create the scrambled character array
    theScrambledWord = new char[wordLen];
    // Populate i twith the word characters (in upper case)
    for ( i = 0; i < wordLen; i++ )
      theScrambledWord[i] = Character.toUpperCase(wordStr.charAt(i));
    // Shuffle the character array
    for ( i = wordLen; i > 1; i-- ) {
      char temp = theScrambledWord[i-1];
      int j = rnd.nextInt(i);
      theScrambledWord[i-1] = theScrambledWord[j];
      theScrambledWord[j] = temp;
    }
  }
  private static Random rnd = new Random();
}

Below is the code for Word.java:

package sl314.domain;
public class Word implements java.io.Serializable {
  private WordCategory category;
  private String word;
  private String description;
  private int    numberOfHints;
  Word(WordCategory category, String word,
       String description, int numberOfHints) {
    this.category = category;
    this.word = word;
    this.description = description;
    this.numberOfHints = numberOfHints;
  }
  //
  // Property accessors
  //
  public WordCategory getCategory() {
    return category;
  }
  public String getWord() {
    return word;
  }
  public String getDescription() {
    return description;
  }
  public int getNumberOfHints() {
    return numberOfHints;
  }
  //
  // Business logic methods
  //
  public boolean isCorrectGuess(String guess) {
    return word.equalsIgnoreCase(guess);
  }
}

Below is the code for WordCategory.java:

package sl314.domain;
public class WordCategory implements java.io.Serializable {
  private String category;
  private String description;
  private int    numberOfWords;
  WordCategory(String category, String description, int numberOfWords) {
    this.category = category;
    this.description = description;
    this.numberOfWords = numberOfWords;
  }
  //
  // Property accessors
  //
  public String getName() {
    return category;
  }
  public String getDescription() {
    return description;
  }
  public int getNumberOfWords() {
    return numberOfWords;
  }
  public String toString() {
    return "#<WordCat name='" + category + "'>";
  }
}

Below is the code for WordCategoryDAO.java:

package sl314.domain;
import sl314.util.NamingService;
import sl314.util.sql.ConnectionPool;
import sl314.util.sql.ObjectNotFoundException;
import sl314.util.sql.ConnNotAvailException;
import sl314.util.sql.ShuttingDownException;
import sl314.util.sql.WrongPoolException;
import java.sql.Connection;
import java.sql.Statement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.List;
import java.util.LinkedList;
import java.util.ArrayList;
class WordCategoryDAO {
  WordCategoryDAO() {
  }
  public List selectAllCategories() {
    // Retrieve the connection pool from the global Naming Service
    NamingService nameSvc = NamingService.getInstance();
    ConnectionPool connectionPool
      = (ConnectionPool) nameSvc.getAttribute("connectionPool");
    Connection connection = null;
    // Database variables
    Statement statement = null;
    ResultSet results = null;
    WordDAO wordDataAccess = new WordDAO();
    // Declare domain variables
    List categories = new LinkedList();
    try {
      // Get a database connection
      connection = connectionPool.getConnectionNoWait();
      // Set auto-commi toff so we can have multiple SELECTs open a tonce
      connection.setAutoCommit(false);
      // Create SQL SELECT statement
      statement = connection.createStatement();
      // Perform the outer query
      results = statement.executeQuery(SELECT_CATEGORIES_STMT);
      while ( results.next() ) {
String category = results.getString("category");
String description = results.getString("description");
int numberOfWords = wordDataAccess.countWords(category);
// Create the category object
WordCategory categoryObject
  = new WordCategory(category, description, numberOfWords);
// Store the category object
categories.add(categoryObject);
      }
      // Rese tauto-commit
      connection.commit();
    // Handle any SQL errors
    } catch (SQLException se) {
      throw new RuntimeException("A database error occured. " + se.getMessage());
    // Handle no available connection
    } catch (ConnNotAvailException cnae) {
      throw new RuntimeException("The server is busy, please try again later.");
    // Handle server shutting down
    } catch (ShuttingDownException sde) {
      throw new RuntimeException("The server is being shutdown.");
    // Clean up JDBC resources
    } finally {
      if ( results != null ) {
        try { results.close(); }
        catch (SQLException se) { se.printStackTrace(System.err); }
      }
      if ( statement != null ) {
        try { statement.close(); }
        catch (SQLException se) { se.printStackTrace(System.err); }
      }
      if ( connection != null ) {
        try { connectionPool.releaseConnection(connection); }
        catch (Exception e) { e.printStackTrace(System.err); }
      }
    }
    return categories;
  }
  private static final String SELECT_CATEGORIES_STMT
    = "SELECT * FROM WordCategory";
}

Below is the code for WordCategoryService.java:

package sl314.domain;
import java.util.List;
public class WordCategoryService {
  public WordCategoryService() {
  }
  //
  // Business methods
  //
  public List getCategories() {
    WordCategoryDAO wordCatDataAccess = new WordCategoryDAO();
    return wordCatDataAccess.selectAllCategories();
  }
  public Word selectWord(WordCategory category) {
    WordDAO wordDataAccess = new WordDAO();
    int     word_idx = 1 + (int) (Math.random() * category.getNumberOfWords());
    return wordDataAccess.selectWord(category, word_idx);
  }
  public String retrieveHint(Word word, int hint_idx) {
    WordDAO wordDataAccess = new WordDAO();
    return wordDataAccess.selectHint(word, hint_idx);
  }
}

Below is the code for WordDAO.java:

package sl314.domain;
import sl314.util.NamingService;
import sl314.util.sql.ConnectionPool;
import sl314.util.sql.ObjectNotFoundException;
import sl314.util.sql.ConnNotAvailException;
import sl314.util.sql.ShuttingDownException;
import sl314.util.sql.WrongPoolException;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
class WordDAO {
  WordDAO() {
  }
  public int countWords(String category) {
    // Retrieve the connection pool from the global Naming Service
    NamingService nameSvc = NamingService.getInstance();
    ConnectionPool connectionPool
      = (ConnectionPool) nameSvc.getAttribute("connectionPool");
    // Database variables
    Connection connection = null;
    PreparedStatement statement = null;
    ResultSet results = null;
    int num_of_rows = 0;
    try {
      // Get a database connection
      connection = connectionPool.getConnectionNoWait();
      // Create SQL SELECT statement
      statement = connection.prepareStatement(COUNT_WORDS_STMT);
      // Specify the CATEGORY in the SELECT COUNT statement
      statement.setString(1, category);
      results = statement.executeQuery();
      results.next();
      return results.getInt(1);
    // Handle any SQL errors
    } catch (SQLException se) {
      throw new RuntimeException("A database error occured. " + se.getMessage());
    // Handle no available connection
    } catch (ConnNotAvailException cnae) {
      throw new RuntimeException("The server is busy, please try again later.");
    // Handle server shutting down
    } catch (ShuttingDownException sde) {
      throw new RuntimeException("The server is being shutdown.");
    // Clean up JDBC resources
    } finally {
      if ( results != null ) {
        try { results.close(); }
        catch (SQLException se) { se.printStackTrace(System.err); }
      }
      if ( statement != null ) {
        try { statement.close(); }
        catch (SQLException se) { se.printStackTrace(System.err); }
      }
      if ( connection != null ) {
        try { connectionPool.releaseConnection(connection); }
        catch (Exception e) { e.printStackTrace(System.err); }
      }
    }
  }
  private static final String COUNT_WORDS_STMT
    = "SELECT count(*) FROM Word WHERE category=?";
  public Word selectWord(WordCategory category, int word_idx) {
    // Retrieve the connection pool from the global Naming Service
    NamingService nameSvc = NamingService.getInstance();
    ConnectionPool connectionPool
      = (ConnectionPool) nameSvc.getAttribute("connectionPool");
    // Database variables
    Connection connection = null;
    PreparedStatement statement = null;
    ResultSet results = null;
    int num_of_rows = 0;
    // Domain variables
    Word wordObject = null;
    try {
      // Get a database connection
      connection = connectionPool.getConnectionNoWait();
      // Create SQL SELECT statement
      statement = connection.prepareStatement(SELECT_WORD_STMT);
      // Specify the CATEGORY and WORD_INDEX in the SELECT statement
      statement.setString(1, category.getName());
      statement.setInt(2, word_idx);
      results = statement.executeQuery();
      while ( results.next() ) {
String word = results.getString("word");
String description = results.getString("description");
int numberOfHints = countHints(word);
// Construct the word object
wordObject = new Word(category, word, description, numberOfHints);
      }
    // Handle any SQL errors
    } catch (SQLException se) {
      throw new RuntimeException("A database error occured. " + se.getMessage());
    // Handle no available connection
    } catch (ConnNotAvailException cnae) {
      throw new RuntimeException("The server is busy, please try again later.");
    // Handle server shutting down
    } catch (ShuttingDownException sde) {
      throw new RuntimeException("The server is being shutdown.");
    // Clean up JDBC resources
    } finally {
      if ( results != null ) {
        try { results.close(); }
        catch (SQLException se) { se.printStackTrace(System.err); }
      }
      if ( statement != null ) {
        try { statement.close(); }
        catch (SQLException se) { se.printStackTrace(System.err); }
      }
      if ( connection != null ) {
        try { connectionPool.releaseConnection(connection); }
        catch (Exception e) { e.printStackTrace(System.err); }
      }
    }
    return wordObject;
  }
  private static final String SELECT_WORD_STMT
    = "SELECT * FROM Word WHERE category=? AND word_index=?";
  public int countHints(String word) {
    // Retrieve the connection pool from the global Naming Service
    NamingService nameSvc = NamingService.getInstance();
    ConnectionPool connectionPool
      = (ConnectionPool) nameSvc.getAttribute("connectionPool");
    // Database variables
    Connection connection = null;
    PreparedStatement statement = null;
    ResultSet results = null;
    int num_of_rows = 0;
    // Domain variables
    int count = 0;
    try {
      // Get a database connection
      connection = connectionPool.getConnectionNoWait();
      // Create SQL SELECT statement
      statement = connection.prepareStatement(COUNT_HINTS_STMT);
      // Specify the WORD in the SELECT COUNT statement
      statement.setString(1, word);
      results = statement.executeQuery();
      results.next();
      count = results.getInt(1);
    // Handle any SQL errors
    } catch (SQLException se) {
      throw new RuntimeException("A database error occured. " + se.getMessage());
    // Handle no available connection
    } catch (ConnNotAvailException cnae) {
      throw new RuntimeException("The server is busy, please try again later.");
    // Handle server shutting down
    } catch (ShuttingDownException sde) {
      throw new RuntimeException("The server is being shutdown.");
    // Clean up JDBC resources
    } finally {
      if ( results != null ) {
        try { results.close(); }
        catch (SQLException se) { se.printStackTrace(System.err); }
      }
      if ( statement != null ) {
        try { statement.close(); }
        catch (SQLException se) { se.printStackTrace(System.err); }
      }
      if ( connection != null ) {
        try { connectionPool.releaseConnection(connection); }
        catch (Exception e) { e.printStackTrace(System.err); }
      }
    }
    return count;
  }
  private static final String COUNT_HINTS_STMT
    = "SELECT count(*) FROM WordHint WHERE word=?";
  public String selectHint(Word word, int hint_idx) {
    // Retrieve the connection pool from the global Naming Service
    NamingService nameSvc = NamingService.getInstance();
    ConnectionPool connectionPool
      = (ConnectionPool) nameSvc.getAttribute("connectionPool");
    // Database variables
    Connection connection = null;
    PreparedStatement statement = null;
    ResultSet results = null;
    // Domain variables
    String hint = null;
    try {
      // Get a database connection
      connection = connectionPool.getConnectionNoWait();
      // Create SQL SELECT statement
      statement = connection.prepareStatement(SELECT_HINT_STMT);
      // Specify the HINT in the SELECT * statement
      statement.setString(1, word.getWord());
      statement.setInt(2, hint_idx);
      results = statement.executeQuery();
      results.next();
      hint = results.getString("hint");
    // Handle any SQL errors
    } catch (SQLException se) {
      throw new RuntimeException("A database error occured. " + se.getMessage());
    // Handle no available connection
    } catch (ConnNotAvailException cnae) {
      throw new RuntimeException("The server is busy, please try again later.");
    // Handle server shutting down
    } catch (ShuttingDownException sde) {
      throw new RuntimeException("The server is being shutdown.");
    // Clean up JDBC resources
    } finally {
      if ( results != null ) {
        try { results.close(); }
        catch (SQLException se) { se.printStackTrace(System.err); }
      }
      if ( statement != null ) {
        try { statement.close(); }
        catch (SQLException se) { se.printStackTrace(System.err); }
      }
      if ( connection != null ) {
        try { connectionPool.releaseConnection(connection); }
        catch (Exception e) { e.printStackTrace(System.err); }
      }
    }
    return hint;
  }
  private static final String SELECT_HINT_STMT
    = "SELECT * FROM WordHint WHERE word=? AND hint_index=?";
}

NamingService.java is located at the development path, c:\ServletDevel\database\sl314\util:
NamingService.java is compiled successful and its class file is copied in the deployment path, c:\Tomcat\webapps\database\WEB-INF\classes\sl314\util
Below is the code for NamingService.java:

package sl314.util;
import java.util.Map;
import java.util.HashMap;
/**
 * This class implements a simple "global naming service".
 * It implements the Singleton interface to guarantee that only
 * one such naming service exists within the JVM and is accessible
 * to all parts of the application.
 *
 * This class could easily have been a Utility class with static
 * methods only.
 */
public final class NamingService {
  //
  // Public interface
  //
  public static NamingService getInstance() {
    return theObject;
  }
  /**
   * This method stores an object by a specific name.
   * @param name  The unique name tha tholds some object.
   * @return Object  The object for that name, or null if name not found
   */
  public Object getAttribute(String name) {
    return nameValuePairs.get(name);
  }
  /**
   * This method stores an object by a specific name.
   * @param name  The unique name that holds some object.
   * @param object  The object to be stored.
   * @thrown  IllegalArgumentException  If the name is already in use
   */
  public void setAttribute(String name, Object object) {
    if ( nameValuePairs.get(name) == null ) {
      nameValuePairs.put(name, object);
    } else {
      throw new IllegalArgumentException("");
    }
  }
  /**
   * This method removes a listing by the specific name.
   * @param name  The unique name that holds some object.
   */
  public void removeAttribute(String name) {
    nameValuePairs.remove(name);
  }
  //
  // Private implementation
  //
  private static NamingService theObject = new NamingService();
  private Map nameValuePairs;
  private NamingService() {
    nameValuePairs = new HashMap();
  }
}

Java files below are located at the development path, c:\ServletDevel\database\sl314\web:
InitializeConnectionPool.java
ScrambleGameServlet.java
Files above were compiled successful and class files of each is copied in the deployment path, c:\Tomcat\webapps\database\WEB-INF\classes\sl314\web
Below is the code for InitializeConnectionPool.java:

package sl314.web;
// Servlet imports
import javax.servlet.ServletContextListener;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContext;
// SQL Utility Imports
import sl314.util.NamingService;
import sl314.util.sql.ConnectionPool;
import java.sql.SQLException;
/**
 * This listenter is used to initialize the JDBC Connection Pool for a
 * given Web Application.
 */
public class InitializeConnectionPool implements ServletContextListener {
   /**
    * This method creates the connection pool.
    */
   public void contextInitialized(ServletContextEvent sce) {
      ServletContext context = sce.getServletContext();
      String jdbcDriver = context.getInitParameter("jdbcDriver");
      String jdbcURL = context.getInitParameter("jdbcURL");
      String jdbcUserName = context.getInitParameter("jdbcUserName");
      String jdbcPassword = context.getInitParameter("jdbcPassword");
      int minimumConnections
= Integer.parseInt(context.getInitParameter("minimumConnections"));
      int maximumConnections
= Integer.parseInt(context.getInitParameter("maximumConnections"));
      ConnectionPool connectionPool;
      // Intialize the connection pool object
      try {
//*** Step: Get a reference to the NamingService singleton
        NamingService nameSvc = NamingService.getInstance();
//*** Step: Create ConnectionPool object
        connectionPool = new ConnectionPool(jdbcDriver, jdbcURL,
                                            jdbcUserName, jdbcPassword,
                                            minimumConnections,
                                            maximumConnections);
//*** Step: Store the connection pool in the "application" scope.
        nameSvc.setAttribute("connectionPool", connectionPool);
context.log("Connection pool created for URL=" + jdbcURL);
      } catch (ClassNotFoundException cnfe) {
         context.log("The JDBC Driver class " + jdbcDriver
                     + " was no tfound.", cnfe);
      } catch (InstantiationException ie) {
         context.log("The JDBC Driver class " + jdbcDriver + " could "
                     + "no tmake an object.", ie);
      } catch (IllegalAccessException iae) {
         context.log("The JDBC Driver (" + jdbcDriver + ") class "
                     + "or initializer is no taccessible.", iae);
      } catch (SQLException sex) {
         context.log("There was an error in creating the "
                     + "connection pool for " + jdbcURL, sex);
      }
   }
   public void contextDestroyed(ServletContextEvent sce) {
      ServletContext context = sce.getServletContext();
      //*** Step: Get a reference to the NamingService singleton.
      NamingService nameSvc = NamingService.getInstance();
      //*** Step: Retrieve the connection pool from the naming service.
      ConnectionPool connectionPool
        = (ConnectionPool) nameSvc.getAttribute("connectionPool");
      //*** Step: Shutdown the connection pool.
      connectionPool.shutdown();
      context.log("Connection pool shutdown.");
   }
}

Below is the code for ScrambleGameServlet.java:

package sl314.web;
// Domain import
import sl314.domain.ScrambleGameService;
import sl314.domain.WordCategoryService;
import sl314.domain.WordCategory;
import sl314.domain.Word;
// Servlet imports
import javax.servlet.ServletContext;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
// Support classes
import javax.servlet.ServletException;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;
import java.util.Iterator;
public class ScrambleGameServlet extends HttpServlet {
  public void doGet(HttpServletRequest request,
    HttpServletResponse response)
 throws IOException, ServletException {
    // Send the user to the "Show Categories" page
    showCategories(request, response);
  }
  public void showCategories(HttpServletRequest request,
     HttpServletResponse response)
 throws IOException, ServletException {
    // Acquire the session object
    HttpSession session = request.getSession();
    try {
      // Create business services
      WordCategoryService wordCatSvc = new WordCategoryService();
      // Select category list
      List categoryList = wordCatSvc.getCategories();
      // Store the category lis tin the session object
      session.setAttribute("categoryList", categoryList);
      // Generate the next View (the "Show Categories" page)
      generateShowCategories(request, response);
    // Catch all exceptions and rethrow to let the Web container
    // handle the display of errors
    } catch (Exception e) {
      throw new ServletException(e);
    }
  }
  public static final String ACTION_SELECT_CATEGORY = "SelectCategory";
  public static final String ACTION_GUESS_WORD = "GuessTheWord";
  public void doPost(HttpServletRequest request,
     HttpServletResponse response)
 throws IOException, ServletException {
    String action = request.getParameter("action");
    if ( action.equals(ACTION_SELECT_CATEGORY) ) {
      processSelectCategory(request, response);
    } else if ( action.equals(ACTION_GUESS_WORD) ) {
      processGuessWord(request, response);
    } else {
      log("Unrecognizable Scramble Game action: " + action);
      // Send the user to the "Show Categories" page
      showCategories(request, response);
    }
  }
  public void processSelectCategory(HttpServletRequest request,
    HttpServletResponse response)
 throws IOException, ServletException {
    // Acquire the session object
    HttpSession session = request.getSession();
    // Verify FORM parameters
    String categoryName = request.getParameter("categoryName");
    // Select the word category from the saved lis tof categories
    WordCategory category = null;
    List list = (List) session.getAttribute("categoryList");
    Iterator cats = list.iterator();
    while ( cats.hasNext() && (category == null) ) {
      WordCategory wordCat = (WordCategory) cats.next();
      if ( wordCat.getName().equals(categoryName) ) {
category = wordCat;
      }
    }
    try {
      // Create business services
      WordCategoryService wordCatSvc = new WordCategoryService();
      // Select a word from the category
      Word word = wordCatSvc.selectWord(category);
      // Create scramble game service
      ScrambleGameService gameSvc = new ScrambleGameService(word);
      // Store the game service in the session object
      session.setAttribute("gameSvc", gameSvc);
      // Generate the next View (the "Show Word" page)
      generateShowWord(request, response);
    // Catch all exceptions and rethrow to let the Web container
    // handle the display of errors
    } catch (Exception e) {
      throw new ServletException(e);
    }
  }
  public void processGuessWord(HttpServletRequest request,
       HttpServletResponse response)
 throws IOException, ServletException {
    // Acquire the session object
    HttpSession session = request.getSession();
    // Retrieve the scramble game service
    ScrambleGameService gameSvc
      = (ScrambleGameService) session.getAttribute("gameSvc");
    // Verify FORM parameters
    String guess = request.getParameter("guess");
    String giveHint = request.getParameter("giveHint");
    try {
      // Create business services
      WordCategoryService wordCatSvc = new WordCategoryService();
      // Check the user's guess
      boolean youWin = false;
      if ( (guess != null) && (guess.length() > 0) ) {
youWin = gameSvc.isCorrectGuess(guess);
      }
      if ( youWin ) {
session.removeAttribute("gameSvc");
// Generate the next View (the "You Win!" page)
generateYouWinResponse(request, response);
return;
      }
      // If the user has guessed too many times
      if ( gameSvc.getHowManyGuessesLeft() <= 0 ) {
session.removeAttribute("gameSvc");
// Generate the next View (the "You Lose!" page)
generateTooManyGuessesResponse(request, response);
return;
      }
      // Check if the user asked for a hint
      if ( (giveHint != null) && giveHint.equals("yes") ) {
gameSvc.incHowManyHints();
String hint = wordCatSvc.retrieveHint(gameSvc.getWord(),
      gameSvc.getHowManyHints());
// Store the hin tin the request object to be used by
// the generateShowWord method
request.setAttribute("hint", hint);
      }
      // Generate the next View (the "Show Word" page)
      generateShowWord(request, response);
    // Catch all exceptions and rethrow to let the Web container
    // handle the display of errors
    } catch (Exception e) {
      throw new ServletException(e);
    }
  }
  public void generateShowCategories(HttpServletRequest request,
     HttpServletResponse response)
 throws IOException {
    // Acquire the session object
    HttpSession session = request.getSession();
    // Select category list
    List categoryList = (List) session.getAttribute("categoryList");
    Iterator cats = categoryList.iterator();
    // Specify the content type is HTML
    response.setContentType("text/html");
    PrintWriter out = response.getWriter();
    // Generate the HTML response
    out.println("<HTML>");
    out.println("<HEAD>");
    out.println("<TITLE>Scramble Game Categories</TITLE>");
    out.println("</HEAD>");
    out.println("<BODY BGCOLOR='white'>");
    out.println("<CENTER><B>Scramble Game Categories</B></CENTER>");
    out.println("Select a word category:");
    out.println("<FORM ACTION='wordScramble' METHOD='POST'>");
    out.println("<INPUT TYPE='hidden' NAME='action' VALUE='"
+ ACTION_SELECT_CATEGORY + "'>");
    while ( cats.hasNext() ) {
      WordCategory category = (WordCategory) cats.next();
      out.println("<INPUT TYPE='radio' NAME='categoryName' ");
      out.println("  VALUE='" + category.getName() + "'>" + category.getName());
      out.println("<BR>");
    }
    out.println("<BR>");
    out.println("<INPUT TYPE='submit' VALUE='Choose'>");
    out.println("</FORM>");
    out.println("</BODY>");
    out.println("</HTML>");
    out.close();
  }
  public void generateShowWord(HttpServletRequest request,
       HttpServletResponse response)
 throws IOException {
    // Acquire the session object
    HttpSession session = request.getSession();
    // Select category list
    ScrambleGameService gameSvc
      = (ScrambleGameService) session.getAttribute("gameSvc");
    char[] letters = gameSvc.getScrambledWord();
    // Specify the content type is HTML
    response.setContentType("text/html");
    PrintWriter out = response.getWriter();
    // Generate the HTML response
    out.println("<HTML>");
    out.println("<HEAD>");
    out.println("<TITLE>Scramble Game: Guess the Word</TITLE>");
    out.println("</HEAD>");
    out.println("<BODY BGCOLOR='white'>");
    out.println("<CENTER><B>Scramble Game: Guess the Word</B></CENTER>");
    out.println("<P>");
    out.println("Here is the scrambled word: ");
    out.print("<B><FONT SIZE='5'>");
    for ( int i=0; i < letters.length; i++ ) {
      out.print("| " + letters[i] + " ");
    }
    out.print("|");
    out.println("</FONT></B>");
    out.println("</P>");
    String hint = (String) request.getAttribute("hint");
    if ( hint != null ) {
      out.println("<P>");
      out.println("Here is the hint you requested:<BR>");
      out.println("<FONT COLOR='blue'>");
      out.println(hint);
      out.println("</FONT>");
      out.println("</P>");
    }
    out.println("<P>");
    out.println("You have " + gameSvc.getHowManyGuessesLeft() + " guesses left.");
    out.println("</P>");
    out.println("<FORM ACTION='wordScramble' METHOD='POST'>");
    out.println("<INPUT TYPE='hidden' NAME='action' VALUE='"
+ ACTION_GUESS_WORD + "'>");
    out.println("Enter your guess: ");
    out.println("<INPUT TYPE='text' NAME='guess'>");
    out.println("<BR>");
    out.println("<INPUT TYPE='checkbox' NAME='giveHint' VALUE='yes'>Do you need a hint?");
    out.println("<BR>");
    out.println("<INPUT TYPE='submit' VALUE='Guess'>");
    out.println("</FORM>");
    out.println("</BODY>");
    out.println("</HTML>");
    out.close();
  }
  public void generateYouWinResponse(HttpServletRequest request,
     HttpServletResponse response)
 throws IOException {
    // Specify the content type is HTML
    response.setContentType("text/html");
    PrintWriter out = response.getWriter();
    // Generate the HTML response
    out.println("<HTML>");
    out.println("<HEAD>");
    out.println("<TITLE>Word Scramble Game</TITLE>");
    out.println("</HEAD>");
    out.println("<BODY BGCOLOR='white'>");
    out.println("<CENTER><B>Word Scramble Game</B></CENTER>");
    out.println("<P>");
    out.println("Your guess was correct. <BR>");
    out.println("<A HREF='wordScramble'>Click here</A> if you want to play again.");
    out.println("</P>");
    out.println("</BODY>");
    out.println("</HTML>");
    out.close();
  }
  public void generateTooManyGuessesResponse(HttpServletRequest request,
     HttpServletResponse response)
 throws IOException {
    // Specify the content type is HTML
    response.setContentType("text/html");
    PrintWriter out = response.getWriter();
    // Generate the HTML response
    out.println("<HTML>");
    out.println("<HEAD>");
    out.println("<TITLE>Word Scramble Game</TITLE>");
    out.println("</HEAD>");
    out.println("<BODY BGCOLOR='white'>");
    out.println("<CENTER><B>Word Scramble Game</B></CENTER>");
    out.println("<P>");
    out.println("Sorry, you have used too many guesses. <BR>");
    out.println("<A HREF='wordScramble'>Click here</A> to star tover.");
    out.println("</P>");
    out.println("</BODY>");
    out.println("</HTML>");
    out.close();
  }
}

When I entered the URL,
http://localhost:8080/database/
for the message form in the Address field, the page for the URL,
http://localhost:8080/database/index.html
is displayed, looks like below:
Duke's Arcade
Select from one of the following games:

Word Scramble
Word Guess

Then I selected the Word Scramble link, but errors below is displayed:

HTTP Status 500 - 
--------------------------------------------------------------------------------
type Exception report
message 
description The server encountered an internal error () that prevented it from fulfilling this request.
exception 
javax.servlet.ServletException
at sl314.web.ScrambleGameServlet.showCategories(ScrambleGameServlet.java:54)
at sl314.web.ScrambleGameServlet.doGet(ScrambleGameServlet.java:29)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:740)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:247)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:256)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.catalina.core.StandardContext.invoke(StandardContext.java:2416)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:180)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.valves.ErrorDispatcherValve.invoke(ErrorDispatcherValve.java:171)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:172)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:174)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.coyote.tomcat4.CoyoteAdapter.service(CoyoteAdapter.java:223)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:601)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:392)
at org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java:565)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:619)
at java.lang.Thread.run(Thread.java:484)
root cause 
java.lang.NullPointerException
at sl314.domain.WordCategoryDAO.selectAllCategories(WordCategoryDAO.java:38)
at sl314.domain.WordCategoryService.getCategories(WordCategoryService.java:16)
at sl314.web.ScrambleGameServlet.showCategories(ScrambleGameServlet.java:43)
at sl314.web.ScrambleGameServlet.doGet(ScrambleGameServlet.java:29)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:740)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:247)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:256)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.catalina.core.StandardContext.invoke(StandardContext.java:2416)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:180)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.valves.ErrorDispatcherValve.invoke(ErrorDispatcherValve.java:171)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:172)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:174)
at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
at org.apache.coyote.tomcat4.CoyoteAdapter.service(CoyoteAdapter.java:223)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:601)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:392)
at org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java:565)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:619)
at java.lang.Thread.run(Thread.java:484)
--------------------------------------------------------------------------------
Apache Tomcat/4.1.27  

Can anybody there help? What do errors above mean? How will I correct those errors? Any suggestions would be greatly appreciated. Thanks in advance.
Cathy
[ February 22, 2004: Message edited by: Cathy Valdez ]

[David O'Meara]

Sometimes providing more information is just... confusing.
root cause java.lang.NullPointerExceptionat sl314.domain.WordCategoryDAO.selectAllCategories(WordCategoryDAO.java:38)
This is where you error is. Despite the reams of sample code you've provided, I'm not able to work out wicj is line 38 of WordCategoryDAO.java. (The code tag removes empty lines)
It's probably just a config error.