JDBC Connection Hangs

Question

I'm using the connection pooling system from Jakarta commons. My database access works fine most of the time, but for some reason sometimes the database hangs. I will try to access the web-app and the login screen will come up fine, but when I try to log in the app will just sit there trying to access the database forever, and from that point on no database access will work. Here is the code I use to get the connections and access the database. Is there anything I am doing wrong that could be causing this?
import java.sql.DriverManager;
import java.sql.Connection;
import javax.sql.DataSource;
import java.io.PrintWriter;
import org.apache.commons.pool.ObjectPool;
import org.apache.commons.pool.impl.GenericObjectPool;
import org.apache.commons.dbcp.ConnectionFactory;
import org.apache.commons.dbcp.PoolingDataSource;
import org.apache.commons.dbcp.PoolableConnectionFactory;
import org.apache.commons.dbcp.DriverManagerConnectionFactory;
public class ConnectionManager {
     private static final ConnectionManager INSTANCE = new ConnectionManager();
     //Name of SQL Driver to load
     private static final String DRIVERNAME = "com.mysql.jdbc.Driver";
     private static final String CONNECTSTRING = "jdbc:mysql:///mysite:admin:mypasswd?autoReconnect=true";
     //The actual pool of Database Connections
     private static DataSource dataSource;
     private static ObjectPool connectionPool;
     // Private constructor supresses
     // default public constructor
     private ConnectionManager( ) {
          // Load the Database SQL Driver
          try{
               Class.forName(DRIVERNAME);
          } catch (java.lang.ClassNotFoundException e) {System.out.println ("Database SQL Driver not found!");}
          try {
               // First, we'll need a ObjectPool that serves as the
               // actual pool of connections.
               // We'll use a GenericObjectPool instance, although
               // any ObjectPool implementation will suffice.
               connectionPool = new GenericObjectPool(null);
               // Next, we'll create a ConnectionFactory that the
               // pool will use to create Connections.
               // We'll use the DriverManagerConnectionFactory,
               // using the connect string passed in the command line
               // arguments.
               ConnectionFactory connectionFactory = new DriverManagerConnectionFactory(CONNECTSTRING,null);
               // Now we'll create the PoolableConnectionFactory, which wraps
               // the "real" Connections created by the ConnectionFactory with
               // the classes that implement the pooling functionality.
               PoolableConnectionFactory poolableConnectionFactory = new PoolableConnectionFactory(connectionFactory,connectionPool,null,null,false,true);
               // Finally, we create the PoolingDriver itself,
               // passing in the object pool we created.
               // We then save the datasource object to the class for later use in getting connections
               dataSource = new PoolingDataSource(connectionPool);
               //System.out.println("Idle: " + connectionPool.getNumIdle() + " - Active: " + connectionPool.getNumActive());
               } catch (Exception e){}
     //Returns and Instance of the ConnectionManager object (not really necessary)
     public static ConnectionManager getInstance( ) {
          return INSTANCE;
     //Returns a database connection object
     public static Connection getConnection(){
          Connection conn = null;
          try{
               conn = dataSource.getConnection();
               } catch(java.sql.SQLException e){
                   System.err.print (e.getStackTrace());
          //System.out.println("Idle: " + connectionPool.getNumIdle() + " - Active: " + connectionPool.getNumActive());
          return conn;
And here is my database code:
import java.sql.*;
import com.mysite.ConnectionManager;
import java.util.HashMap;
import java.util.Iterator;
Manages a database after getting a database connection from a {@url ConnectionManager} object.
Can do queries and database updates, as well open and close connections.
public class DatabaseManager {
     private Connection con = null;
     private Statement st;
     private ResultSet rs;
     //The Structure of the Table, used for query operations
     private String[] tableStruct;
     Constructor
     public DatabaseManager(){
     Retrieves a database connection from a {@url ConnectionManager} object.
     @param
     @return
     @see
     public void connect(){
          con = ConnectionManager.getConnection();
     Identifies whether this database connection is still open
     @param
     @return
     @see
     public boolean isClosed() throws java.sql.SQLException{
          return con.isClosed();
     Execute a query on a database connection and get the resultset for that query
     @param queryString A String representing the database query
     @return The results of the query to the database
     @see Statement, ResultSet
     public ResultSet query(String queryString) throws java.sql.SQLException{
          if (con != null){
               st = con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_UPDATABLE);
               st.executeQuery (queryString);
               rs = st.getResultSet();
               return rs;
          else {
               throw new java.sql.SQLException ("Error has occurred in Datamanager, no Database Connection has been Established.");
     Returns the Number of Rows the last query has executed.
     @return Number of Rows
     public int getRows() throws java.sql.SQLException{
          int count = 0;
          if (rs != null){
               //get the current row number in case were in the middle of a read and want the size
               int rowNumber = rs.getRow();
               rs.beforeFirst();
               while (rs.next()){
                    count = count + 1;
               if (rowNumber == 0){
                    rs.beforeFirst();     
               else {
                    rs.absolute(rowNumber);     
               return count;
          else {
               return 0;
     Does a record in a particular table exist.
     @param tableName name of Table to look in
     @param idName Name if Table ID
     @param id value of ID
     @return True if record exists
     @see
     public boolean doesExist(String tableName, String idName, String id) throws java.sql.SQLException{
          query ("SELECT " + idName + " FROM " + tableName + " WHERE " + idName + "='" + id + "';");
          if (getRows() == 1){
               return true;
          else {
               return false;
     Update a line (or multiple lines) in the database.
     @param updateString The Update Query String to use to update the database
     @return
     public int update(String updateString) throws SQLException{
          int j = 0;
          try {
               st = con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_UPDATABLE);
               j = st.executeUpdate (updateString);     
          catch (SQLException e) {
               throw new SQLException (updateString);
          st.close();
          return j;
     Update a line in the database.
     @param  tableName Name of table to update the line
     @param  items The data to be updated in the table
     @return
     public int update(String tableName, HashMap items, String idname) throws SQLException{
          // UPDATE <tablename> SET name1="value1", name2="value2" WHERE id="idvalue"
          String updateString;
          Iterator keys = items.keySet().iterator();
          Iterator values = items.values().iterator();
          String optionsString = "";
          //Combine the keys into Strings with ,'s separating.
          while (keys.hasNext()){
               optionsString = optionsString + (String)keys.next() + "=\"" + (String)values.next() + "\",";
          //Chop off the last , in the Strings
          optionsString = optionsString.substring (0, optionsString.length()-1);
          updateString = "UPDATE " + tableName + " SET " + optionsString + " WHERE " + idname + "=" + items.get(idname) + ";";
          return insert (updateString);
     Delete a Record or Records from the database
     @param table Name of the Table to delete data from
     @param whereClause what to delete from the table
     @see
     public void delete(String table, String whereClause) throws SQLException{
          String deleteString;
          deleteString = "DELETE FROM " + table;
          if (whereClause != null) {
               if (!whereClause.equals("")){
                    deleteString += (" WHERE " + whereClause);
          deleteString += ";";
          st = con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_UPDATABLE);
          st.execute (deleteString);
          st.close();
     Inserts a line of data into a database connection under a given table
     @param insertString String Containing the query to send with the Insert Data
     @return Number of Rows Affected
     public int insert(String insertString) throws SQLException{
          int j = 0;
          try {
               st = con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_UPDATABLE);
               j = st.executeUpdate (insertString);     
          catch (SQLException e){
               throw new SQLException (insertString);
          st.close();
          return j;
     Inserts a line of data into a database connection under a given table
     @param  tableName Name of table to update the line
     @param  items The data to be updated in the table
     @return Number of Rows Affected
     public int insert(String tableName, HashMap items) throws SQLException{
          // REPLACE INTO <tablename> (itemname1, itemname2) VALUES ("value1", "value2");
          String insertString;
          Iterator keys = items.keySet().iterator();
          Iterator values = items.values().iterator();
          String keysString = "";
          String valuesString = "";
          //Combine the keys into Strings with ,'s separating.
          while (keys.hasNext()){
               keysString = keysString + (String)keys.next() + ",";
               valuesString = valuesString + "\"" + (String)values.next() + "\",";
          //Chop off the last , in the Strings
          keysString = keysString.substring (0, keysString.length()-1);
          valuesString = valuesString.substring (0, valuesString.length()-1);
          insertString = "REPLACE INTO " + tableName + " (" + keysString + ") VALUES (" + valuesString + ");";
          return insert (insertString);
     Sets the table structure for subsequent operations.
     @param An array of names that represent a table in a database.
     @return
     @see
     public void setStructure(String[] struc){
          tableStruct = struc;
     Flushes the Statement and ResultSet object
     in case any resources are being used when they
     shouldn't be.
     public void flushSources() throws java.sql.SQLException{
          if (rs != null){
               rs.close();
               rs = null;
          if (st != null){
               st.close();
               st = null;
     Kills the database connection in this object
     public void close() throws java.sql.SQLException{
          flushSources();
          if (con != null){
               con.close();     
          con = null;     
     }

Answer 1

How do I do that, it doesn't even report an error. I could try sticking log traces all over the place, but it may not tell me anything about why the problem is happening.