Out of heap caused by database access

Hi guys. I have a serious problem in my last project. I use a database to get/insert information that I need. Every now and then there is A LOT of db I/O going on (1-2mb of data being loaded/accessed).
I am using a singeton pattern (one instance) for the db connection to ensure that there is only one connection between the software and the db. The problem here is that I eventually run out of heap size. Is there any way to overcome this situation? Something like flushing db buffer (or whatever).
If I use many connections (open one, perform query/insert, close) I eventually run out of sockets because Java states that closing the db connection doesnt free the resources straigh away.
So I am stuck. If anyone can help I would really appreciate it. thx

You're doing something that doesn't release memory. So stop doing that.
But you don't know what to stop doing, right? Then you'll have to find out what's filling up your memory. The tool for that is called a "profiler". Get one and use it.

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    Regards
    Nikhil

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    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:245)
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    root cause
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    sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
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    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:325)
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    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:245)
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    package Try;
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    import java.sql.DriverManager;
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    import javax.servlet.jsp.JspWriter;
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    <jsp-version>1.2</jsp-version>
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    <display-name>Database Tags</display-name>
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    <tag-class>Try.Connect</tag-class>
    <body-content>empty</body-content>
    <description>
    </description>
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    <name>driver</name>
    <required>false</required>
    <rtexprvalue>true</rtexprvalue>
    <description>
    </description>
    </attribute>
    <attribute>
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    <rtexprvalue>true</rtexprvalue>
    <description>
    </description>
    </attribute>
    <attribute>
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    <description>
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    <attribute>
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    <description>
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    </attribute>
    <attribute>
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    <rtexprvalue>true</rtexprvalue>
    <description>
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    </attribute>
    <attribute>
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    <required>false</required>
    <rtexprvalue>true</rtexprvalue>
    <description>
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    The name of the database that will be used for
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    <attribute>
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    <description>
    </description>
    </attribute>
    <attribute>
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    Answered in your other post:
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  • Database access specific bug

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    Hello,
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    Regards,
    Fanny Liu
    Fanny Liu
    TechNet Community Support

  • Performance Tuning in case of Database Access

    Hi,
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    *MTAB-OBJECT_ID = ITAB-OBJECT_ID.
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    endselect.
    ENDSELECT.
    *ENDLOOP.
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    CONCATENATE mtab-bp_FIRST mtab-bp_LAST INTO mTAB-bp_full
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    modify mtab.
    endloop.
    loop at mtab.
    if mtab-bp_full = ' '.
      select name_org1 into (mtab-bp_full)
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      endselect.
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    clear mtab.
    endloop.
    SELECT OBJECT_ID GUID INTO (NTAB-object_id, Ntab-guid)
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    endselect.
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    from bbp_pdview_bup where guid_hi = Ntab-guid .
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      if sy-subrc = 0.
      SELECT SINGLE DESCRIPTION FROM CDBC_PARTNER_FT INTO NTAB-DESC
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      SELECT  PAFKT ABTNR PAAUTH
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            if sy-subrc = 0.
        SELECT  single BEZ20 FROM TB911
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    *clear ntab.
    *ENDSELECT.
    ENDSELECT.
    *clear ntab.
    ENDSELECT.
    ENDSELECT.
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      if ntab-others = ' '.
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        endselect.
        CONCATENATE ntab-FIRST_NAME1 ntab-LAST_NAME1 INTO nTAB-others
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      modify ntab.
      clear ntab.
    endloop.
    SORT NTAB BY GUID.
    SELECT OBJECT_ID GUID INTO (KTAB-object_id, Ktab-guid)
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    where process_type = '1001' and object_id in o_id.
    Select  partner_no into (Ktab-partner_no1)
    From crmd_order_index where header = Ktab-guid and pft_8 = 'X' and object_type = 'BUS2000126'.
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    Select name_first name_last into (Ktab-first_name, Ktab-last_name)
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    *endselect.
    APPEND KTAB.
    ENDSELECT.
    ENDSELECT.
    ENDSELECT.
    loop at Ktab.
    CONCATENATE Ktab-FIRST_NAME Ktab-LAST_NAME INTO KTAB-RESP_EMPLOYEE
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    MODIFY KTAB.
    clear Ktab.
    endloop.
    loop at Ktab.
      if Ktab-RESP_EMPLOYEE = ' '.
        select name_ORG1 into (Ktab-RESP_EMPLOYEE)
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        endselect.
        endif.
      modify Ktab.
      clear Ktab.
    endloop.
    SELECT OBJECT_ID GUID INTO (itab-object_id, itab-guid)
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    where process_type = '1001' and object_id in o_id.
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              ITAB-DESC = NTAB-DESC.
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    Hi
    i will give you some tips to reduce the daya base load please apply that
    <b>Tips and Tricks</b>
    Optimizing the load of the database
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    Any WHERE clause that contains a sub query or IS NULL expression
    JOIN s
    A SELECT... FOR UPDATE
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    3.   Avoid the SELECT DISTINCT Statement
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    Use of CONTEXT can highly optimize the code.
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         Context advantages:  - no double fetch by DEMAND: 1. fetch, 2. get from buffer  - more performance (best SELECT-statement)  - better survey of code
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                pStmt.setString(5, email);
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            byte[] buf = null;
            while(rs.next())
                   System.out.println("Logon ID         = "
                                     + rs.getString("userID"));
                 System.out.println("Last name        = "
                                   + rs.getString("FirstName"));
                 System.out.println("First name       = "+rs.getString("LastName"));
                 System.out.println("E-mail           = "+rs.getString("email"));
                 System.out.println("Administrative   = "+rs.getBoolean("admin"));
                 System.out.println("Initial password = "+initialPswd);
            // Do NOT use with JDK 1.2.2 using JDBC-ODBC bridge as
            // SQL NULL data value is not handled correctly.
                buf = rs.getBytes("pswd");
                if (buf != null)
                      System.out.println("Password Object  = "
                                      + (pswdFromDB=(Password)deserializeObj(buf)));
                      System.out.println("  AutoExpires    = "+ pswdFromDB.getAutoExpires());
                      System.out.println("  Expiring now   = "+ pswdFromDB.isExpiring());
                      System.out.println("  Remaining uses = "
                                        + pswdFromDB.getRemainingUses()+"\n");
                  else
                      System.out.println("Password Object  = NULL!");
            rs = stmt.executeQuery("SELECT * FROM Student");
            if(!rs.next())
                 System.out.println("Student table contains no records.");
              else
                 System.out.println("Student table still contains records!");
            rs = stmt.executeQuery("SELECT * FROM StudentUserBridge");
            if(!rs.next())
                 System.out.println("StudentUserBridge table contains no records.");
              else
                 System.out.println("StudentUserBridge table still contains records!");
             stmt.close(); // closing Statement also closes ResultSet
        } // end of main()
         // Method to write object to byte array and then insert into prepared statement
        public static byte[] serializeObj(Object obj)
                                  throws IOException
              ByteArrayOutputStream baOStream = new ByteArrayOutputStream();
            ObjectOutputStream objOStream = new ObjectOutputStream(baOStream);
            objOStream.writeObject(obj); // object must be Serializable
            objOStream.flush();
            objOStream.close();
            return baOStream.toByteArray(); // returns stream as byte array
         // Method to read bytes from result set into a byte array and then
         // create an input stream and read the data into an object
        public static Object deserializeObj(byte[] buf)
                                      throws IOException, ClassNotFoundException
             Object obj = null;
            if (buf != null)
              ObjectInputStream objIStream =
                new ObjectInputStream(new ByteArrayInputStream(buf));
              obj = objIStream.readObject(); // throws IOException, ClassNotFoundException
            return obj;
      } // end of class
    //STLogon.java
    import javax.swing.*;
    import javax.swing.border.TitledBorder;
    import java.awt.*;
    import java.awt.event.*;
    import java.util.*;
    import java.io.*;
    import java.sql.*;
    public class STLogon extends JFrame implements ActionListener, Activator
        StudentDB db;
        User user = null;
        String userID;
        String password;
        JTextField userIDField;
        JPasswordField passwordField;
        JButton jbtLogon;
        public STLogon()
            super("Stock Tracker"); // call super (JFrame) constructor
              int width = 300;
              int height = 100;
            try{
                 db = new StudentDB();
            catch(ClassNotFoundException ex){
                        JOptionPane.showMessageDialog(this,
                    ex.getMessage(),
                    "Class not found exception creating database object",
                    JOptionPane.ERROR_MESSAGE);
                           System.exit(0);
            catch(SQLException ex){
                        JOptionPane.showMessageDialog(this,
                    ex.getMessage(),
                    "SQL exception creating database object",
                    JOptionPane.ERROR_MESSAGE);
                           System.exit(0);
              // define GUI components
            JLabel label1 = new JLabel("User ID: ");
            userIDField = new JTextField(20);
            JLabel label2 = new JLabel("Password:   ");
            passwordField = new JPasswordField(20);
            passwordField.setEchoChar('*');
            jbtLogon = new JButton("Log on");
              // set up GUI
            JPanel userPanel= new JPanel(new BorderLayout());
            userPanel.add(label1,BorderLayout.CENTER);
            userPanel.add(userIDField,BorderLayout.EAST);
            JPanel pswdPanel= new JPanel(new BorderLayout());
            pswdPanel.add(label2,BorderLayout.CENTER);
            pswdPanel.add(passwordField,BorderLayout.EAST);
            JPanel buttonPanel= new JPanel(new FlowLayout());
            buttonPanel.add(jbtLogon);
            JPanel contentPanel= new JPanel(new BorderLayout());
            contentPanel.add(userPanel, BorderLayout.NORTH);
            contentPanel.add(pswdPanel, BorderLayout.CENTER);
            contentPanel.add(buttonPanel, BorderLayout.SOUTH);
             contentPanel.setBorder(new TitledBorder("Log on"));
            setContentPane(contentPanel);
            // add listeners
            jbtLogon.addActionListener(this);
            addWindowListener(new WindowAdapter() {
                public void windowClosing(WindowEvent e)
                                       try {db.close();
                                    catch(Exception ex)
                                    System.exit(0);
              // Enable Enter key for each JButton
              InputMap map;
              map = jbtLogon.getInputMap();
              if (map != null){
                   map.put(KeyStroke.getKeyStroke(KeyEvent.VK_ENTER,0,false), "pressed");
                   map.put(KeyStroke.getKeyStroke(KeyEvent.VK_ENTER,0,true), "released");
            pack();
              if( width < getWidth())                    // prevent setting width too small
                 width = getWidth();
              if(height < getHeight())               // prevent setting height too small
                   height = getHeight();
              centerOnScreen(width, height);
           public void centerOnScreen(int width, int height)
             int top, left, x, y;
             // Get the screen dimension
             Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
             // Determine the location for the top left corner of the frame
             x = (screenSize.width - width)/2;
             y = (screenSize.height - height)/2;
             left = (x < 0) ? 0 : x;
             top = (y < 0) ? 0 : y;
             // Set the frame to the specified location & size
           this.setBounds(left, top, width, height);
         private boolean validUser(String userID,String password)
                        throws PasswordException,SQLException,IOException,ClassNotFoundException
              boolean userOK = false;
              user = db.getUser(userID); // get user object from DB for this ID
              if(user != null)
                   user.validate(password); // throws PasswordException
                   userOK = true;
                   if(user.pswdAutoExpires())     // if tracking uses
                        db.updUser(user);          // update DB for this use
             return userOK;
        private void doStockActivity()throws PasswordException,SQLException,
                                                      IOException,ClassNotFoundException
            StockTracker f = new StockTracker(user,this,db);
            f.pack();
            this.setVisible(false);
            f.setVisible(true);
        public void activate()
            this.setVisible(true);
            userIDField.setText("");
            userIDField.requestFocus();
            user = null;
        public void actionPerformed(ActionEvent e)
              try
                   userID = userIDField.getText();
                if(userID.equals(""))
                           JOptionPane.showMessageDialog(this,
                            "Please enter a valid user ID.",
                           "Missing User ID.",
                           JOptionPane.ERROR_MESSAGE);
                       userIDField.requestFocus();
                   else
                        password = new String(passwordField.getPassword());
                     if(password.equals(""))
                                JOptionPane.showMessageDialog(this,
                                 "Please enter a valid password.",
                                "Missing Password.",
                                JOptionPane.ERROR_MESSAGE);
                            passwordField.requestFocus();
                        else
                             try
                                  // See if userID exists and validate password
                                  if(validUser(userID,password))
                                   if(user.pswdIsExpiring())
                                              JOptionPane.showMessageDialog(this,
                                                             user.getUserID()+" logon successful; "
                                                +user.getPswdUses()+" use(s) remaining.");
                                    if(e.getSource() == jbtLogon)
                                               doStockActivity();
                               else
                                    JOptionPane.showMessageDialog(this, "Invalid user.");
                             catch (PasswordExpiredException ex)
                                  JPasswordField pf1 = new JPasswordField();
                                  JPasswordField pf2 = new JPasswordField();
                                  Object[] message1 = new Object[]
                                            {"Password has expired. Please enter a new password.", pf1};
                                  Object[] options = new String[] {"OK", "Cancel"};
                                  JOptionPane op1 = new JOptionPane(message1,
                                                                     JOptionPane.WARNING_MESSAGE,
                                                              JOptionPane.OK_CANCEL_OPTION, null, options);
                                  JDialog dialog1 = op1.createDialog(null, "Change Password");
                                  dialog1.show();
                                  if(op1.getValue() != null && options[0].equals(op1.getValue()))
                                       String pswd1 = new String(pf1.getPassword());
                                       if(pswd1 != null)
                                           Object[] message2 = new Object[]
                                                               {"Please verify new password.", pf2};
                                            JOptionPane op2 = new JOptionPane(message2,
                                                                               JOptionPane.WARNING_MESSAGE,
                                                                       JOptionPane.OK_CANCEL_OPTION,
                                                                       null, options);
                                            JDialog dialog2 = op2.createDialog(null, "Verify Password");
                                            dialog2.show();
                                            if(op2.getValue() != null && options[0].equals(op2.getValue()))
                                                 String pswd2 = new String(pf2.getPassword());
                                                 if(pswd2 != null)
                                                      if(pswd1.equals(pswd2))
                                                        user.changePassword(password, pswd1);
                                                           db.updUser(user);
                                                           doStockActivity();
                                                      else
                                                           JOptionPane.showMessageDialog(this,
                                                          "Both passwords are not identical.",
                                                         "Password not changed",
                                                         JOptionPane.ERROR_MESSAGE);
                 userIDField.setText("");
                passwordField.setText("");
                userIDField.requestFocus();
            }// end of try
            catch (PasswordUsedException ex)
                JOptionPane.showMessageDialog(this,
                    ex.getMessage(),
                    "Password Previously Used. Try again.",
                    JOptionPane.ERROR_MESSAGE);
            catch (PasswordSizeException ex)
                JOptionPane.showMessageDialog(this,
                    ex.getMessage(),
                    "Invalid password size. Try again.",
                    JOptionPane.ERROR_MESSAGE);
            catch (PasswordInvalidFormatException ex)
                if(ex.getCount() > 2) // allows only 3 tries, then exits program
                     System.exit(0);
                else
                     JOptionPane.showMessageDialog(this,ex.getMessage()+", count:"+ex.getCount(),
                                                        "Invalid password format. Try again.",
                                                              JOptionPane.ERROR_MESSAGE);
            catch (PasswordInvalidException ex)
                if(ex.getCount() > 2) // allows only 3 tries, then exits program
                     System.exit(0);
                else
                     JOptionPane.showMessageDialog(this,ex.getMessage()+", count:"+ex.getCount(),
                                                        "Invalid password. Try again.",
                                                              JOptionPane.ERROR_MESSAGE);
            catch (PasswordException ex)
                JOptionPane.showMessageDialog(this,
                    ex.getMessage(),
                    "PasswordException.",
                    JOptionPane.ERROR_MESSAGE);
            catch (IOException ex)
                JOptionPane.showMessageDialog(this,
                    ex.getMessage(),
                    "IOException.",
                    JOptionPane.ERROR_MESSAGE);
            catch (SQLException ex)
                JOptionPane.showMessageDialog(this,
                    ex.getMessage(),
                    "SQLException.",
                    JOptionPane.ERROR_MESSAGE);
            catch (ClassNotFoundException ex)
                JOptionPane.showMessageDialog(this,
                    ex.getMessage(),
                    "ClassNotFoundException.",
                    JOptionPane.ERROR_MESSAGE);
        public static void main(String[] argv)
              final STLogon f = new STLogon();
              f.setVisible(true);
    //StudentDB.java
    import java.io.*;
    import java.sql.*;
    import java.util.*;
    public class StudentDB
         private Connection con = null;
         // Constructor; makes database connection
        public StudentDB() throws ClassNotFoundException,SQLException
              if(con == null)
                   String url = "jdbc:odbc:saad";
                 try
                      Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
                   catch(ClassNotFoundException ex)
                        throw new ClassNotFoundException(ex.getMessage() +
                                  "\nCannot locate sun.jdbc.odbc.JdbcOdbcDriver");
                 try
                        con = DriverManager.getConnection(url);
                   catch(SQLException ex)
                        throw new SQLException(ex.getMessage()+
                                  "\nCannot open database connection for "+url);
         // Close makes database connection; null reference to connection
         public void close() throws SQLException,IOException,ClassNotFoundException
              con.close();
               con = null;
         // Method to serialize object to byte array
        private byte[] serializeObj(Object obj) throws IOException
              ByteArrayOutputStream baOStream = new ByteArrayOutputStream();
            ObjectOutputStream objOStream = new ObjectOutputStream(baOStream);
            objOStream.writeObject(obj); // object must be Serializable
            objOStream.flush();
            objOStream.close();
            return baOStream.toByteArray(); // returns stream as byte array
         // Method to deserialize bytes from a byte array into an object
        private Object deserializeObj(byte[] buf)
                             throws IOException, ClassNotFoundException
             Object obj = null;
            if (buf != null)
                   ObjectInputStream objIStream =
                      new ObjectInputStream(new ByteArrayInputStream(buf));
                obj = objIStream.readObject(); //IOException, ClassNotFoundException
            return obj;
         // Methods for adding a record to a table
        // add to the Student Table
         public void addStudent(String IDNumber, String FirstName, String LastName)
                     throws SQLException, IOException, ClassNotFoundException
              Statement stmt = con.createStatement();
               stmt.executeUpdate("INSERT INTO Student VALUES ('"
                                 +IDNumber+"'"+",'"+FirstName+"'"+",'"+LastName+"')");
               stmt.close();
         // add to the Users table
         public boolean addUser(User user) throws SQLException,IOException,
                                                  ClassNotFoundException
           boolean result = false;
          String dbUserID;
          String dbLastName;
          String dbFirstName;
          Password dbPswd;
          String dbemail;
          boolean isAdmin;
          dbUserID = user.getUserID();
          if(getUser(dbUserID) == null)
                dbLastName = user.getFirstName();
                dbFirstName = user.getLastName();
              Password pswd = user.getPassword();
    //          dbemail = user.getEmail();
                isAdmin = user.isAdmin();
              PreparedStatement pStmt = con.prepareStatement(
                  "INSERT INTO Users VALUES (?,?,?,?,?,?)");
              pStmt.setString(1, dbUserID);
              pStmt.setString(2, dbFirstName);
              pStmt.setString(3, dbLastName);
              pStmt.setBytes(4, serializeObj(pswd));
    //          pStmt.setString(5, dbemail);
              pStmt.setBoolean(5, isAdmin);
              pStmt.executeUpdate();
              pStmt.close();
              result = true;
           else
                throw new IOException("User exists - cannot add.");
           return result;
         // add to the UserStocks table
         public void addStudentUserBridge(String userID, String IDNumber)
                     throws SQLException,IOException,ClassNotFoundException
              Statement stmt = con.createStatement();
               stmt.executeUpdate("INSERT INTO StudentUserBridge VALUES ('"
                                 +userID+"'"
                                 +",'"+IDNumber+"')");
               stmt.close();
         // Methods for updating a record in a table
        // updating the Users Table
         public boolean updUser(User user) throws SQLException,IOException,
                                                  ClassNotFoundException
           boolean result = false;
             String dbUserID;
          String dbLastName;
          String dbFirstName;
          Password dbPswd;
          String dbemail;
          boolean isAdmin;
          dbUserID = user.getUserID();
          if(getUser(dbUserID) != null)
                dbLastName = user.getFirstName();
                dbFirstName = user.getLastName();
              Password pswd = user.getPassword();
    //          dbemail = user.getEmail();
                isAdmin = user.isAdmin();
              PreparedStatement pStmt = con.prepareStatement("UPDATE Users SET FirstName = ?,"
                                           +" LastName = ?, pswd = ?, email = ?, admin = ? WHERE userID = ?");
              pStmt.setString(1, dbFirstName);
              pStmt.setString(2, dbLastName);
              pStmt.setBytes(3, serializeObj(pswd));
    //          pStmt.setString(4, dbemail);
              pStmt.setBoolean(4, isAdmin);
              pStmt.setString(5, dbUserID);
              pStmt.executeUpdate();
              pStmt.close();
              result = true;
           else
                throw new IOException("User does not exist - cannot update.");
           return result;
         // Methods for deleting a record from a table
        // delete a record from the Student Table
         private void delStudent(String IDNumber)
                      throws SQLException,IOException,ClassNotFoundException
              Statement stmt = con.createStatement();
               stmt.executeUpdate("DELETE FROM Student WHERE "
                                 +"IDNumber = '"+IDNumber+"'");
            stmt.close();
        // delete a record from the Users Table
         public void delUser(User user) throws SQLException,IOException,
                                                  ClassNotFoundException
               String dbUserID;
            String stockSymbol;
              Statement stmt = con.createStatement();
              try {
                   con.setAutoCommit(false);
                   dbUserID = user.getUserID();
                   if(getUser(dbUserID) != null)  // verify user exists in database
                         ResultSet rs1 = stmt.executeQuery("SELECT userID, IDNumber "
                                           +"FROM StudentUserBridge WHERE userID = '"+dbUserID+"'");
                         while(rs1.next())
                         try
                             stockSymbol = rs1.getString("IDNumber");
                                  delUserStocks(dbUserID, stockSymbol);
                            catch(SQLException ex)
                                  throw new SQLException("Deletion of user student failed: "
                                                        +ex.getMessage());
                          } // end of loop thru UserStocks
                    try
                    {  // holdings deleted, now delete user
                             stmt.executeUpdate("DELETE FROM Users WHERE "
                                           +"userID = '"+dbUserID+"'");
                       catch(SQLException ex)
                             throw new SQLException("User deletion failed: "+ex.getMessage());
                     else
                          throw new IOException("User not found in database - cannot delete.");
                   try
                      con.commit();
                    catch(SQLException ex)
                        throw new SQLException("Transaction commit failed: "+ex.getMessage());
              catch (SQLException ex)
                   try
                        con.rollback();
                   catch (SQLException sqx)
                        throw new SQLException("Transaction failed then rollback failed: "
                                              +sqx.getMessage());
                   // Transaction failed, was rolled back
                   throw new SQLException("Transaction failed; was rolled back: "
                                         +ex.getMessage());
            stmt.close();
        // delete a record from the StudentUserBridge Table
         public void delUserStocks(String userID, String stockSymbol)
                     throws SQLException,IOException,ClassNotFoundException
              Statement stmt = con.createStatement();
             ResultSet rs;
               stmt.executeUpdate("DELETE FROM StudentUserBridge WHERE "
                                 +"userID = '"+userID+"'"
                                 +"AND IDNumber = '"+stockSymbol+"'");
               rs = stmt.executeQuery("SELECT IDNumber FROM StudentUserBridge "
                                     +"WHERE IDNumber = '"+stockSymbol+"'");
                 if(!rs.next()) // no users have this stock
    //               delStock(stockSymbol);
               stmt.close();
         // Methods for listing record data from a table
         // Ordered by:
         //           methods that obtain individual field(s),
         //           methods that obtain a complete record, and
         //           methods that obtain multiple records
         // Methods to access one or more individual fields
        // get a stock description from the Stocks Table
         public String getStockDesc(String stockSymbol)
                       throws SQLException, IOException, ClassNotFoundException
              Statement stmt = con.createStatement();
                String stockDesc = null;
               ResultSet rs = stmt.executeQuery("SELECT IDNumber, name FROM Student "
                                               +"WHERE IDNumber = '"+stockSymbol+"'");
               if(rs.next())
                   stockDesc = rs.getString("IDNumber");
               rs.close();
               stmt.close();
                return stockDesc;
         // Methods to access a complete record
        // get User data from the Users Table
         public User getUser(String UserID) throws SQLException, IOException,
                                                   ClassNotFoundException
           Statement stmt = con.createStatement();
             String dbUserID;
          String dbLastName;
          String dbFirstName;
          Password dbPswd;
          String dbemail;
          boolean isAdmin;
          byte[] buf = null;
          User user = null;
          ResultSet rs = stmt.executeQuery("SELECT * FROM Users WHERE userID = '"
                                          +UserID+"'");
          if(rs.next())
                dbUserID = rs.getString("userID");
                 dbFirstName = rs.getString("FirstName");
                 dbLastName = rs.getString("LastName");
                 dbemail = rs.getString("email");
            // Do NOT use with JDK 1.2.2 using JDBC-ODBC bridge as
            // SQL NULL data value is not handled correctly.
              buf = rs.getBytes("pswd");
                 dbPswd = (Password)deserializeObj(buf);
                 isAdmin = rs.getBoolean("admin");
                user = new User(dbUserID,dbFirstName,dbLastName,dbPswd,isAdmin);
          rs.close();
          stmt.close();
           return user; // User object created for userID
         // Methods to access a list of records
        // get list of selected fields for all records from the Users Table
         public ArrayList listUsers() throws SQLException,IOException,
                                             ClassNotFoundException
          ArrayList aList = new ArrayList();
           Statement stmt = con.createStatement();
          ResultSet rs = stmt.executeQuery("SELECT userID, FirstName, LastName, admin "
                                          +"FROM Users ORDER BY userID");
          while(rs.next())
                aList.add(rs.getString("userID"));
                  aList.add(rs.getString("FirstName"));
                  aList.add(rs.getString("LastName"));
                  aList.add(new Boolean(rs.getBoolean("admin")));
          rs.close();
          stmt.close();
          return aList;
        // get all fields in all records for a given user from the Userstocks Table
         public ArrayList listUserStocks(String userID) throws SQLException,IOException,
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             

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