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Programming in Java 6 with Swing and Servlets Part 1
Exercises: Database Access Using JDBC
In this exercise, we will implement a graphical front end to provide user access to a database.
We will use the capability of the ResultSet class to scroll through records in both forward and
backward directions. The ResultSet class is a table of data representing a database result set,
which is usually generated by executing a statement that queries the database, and maintains a
cursor pointing to its current row of data. Initially the cursor is positioned before the first row.
The next() method moves the cursor to the next row, and because it returns false when
there are no more rows in the ResultSet object, it can be used in a while loop to iterate
through the result set. A default ResultSet object is not updatable and has a cursor that
moves forward only.
It is possible to produce ResultSet objects that are scrollable and/or updatable in the
JDBC2.0 API provided with the Java SDK Standard Edition 1.2, although not all databases
support these ResultSet operations. We will produce a ResultSet that can utilize both the
next() and previous() methods to move the cursor in both directions, but is not updatable.
Standard SQL statements to insert and delete records will be used to update the database.
A new ResultSet will be generated after each of these operations to maintain concurrency.
The program is a simple data browsing application that will display a Contact's name and email,
which is stored in a Cloudscape database file. The Cloudscape database comes with WebSphere
Studio Application Developer. When the application starts, a connection to the database is
established and the first row in the ResultSet is displayed. The user can progress forwards or
backwards through the results using the buttons in the window. Buttons will also be provided to
allow the user to insert or delete data from the database.
The user of the program controls database access by using four buttons on the window. These
buttons are as follows.




Insert Data
Delete Data
Next Row
Previous Row
A short description of the function of each of these buttons is given below.
Insert Data – Retrieves data from the Name and Email data fields, inserts the data into the
underlying database and rebuilds the ResultSet.
Delete Data – Deletes the current row from the underlying database and rebuilds the
ResultSet.
Next Row – Retrieves data from the next row and displays it in the data fields.
Previous Row – Retrieves data from the previous row and displays it in the data fields.
Copyright ©2008, Custom Training Institute. All rights reserved.
Java Database Connectivity- Exercise: Page 2
Part One: Create and Populate a MySql Database
A simple database must be created in order to do the exercises in this module. This module uses
the MySql database but any database with a JDBC driver available for it will work. The script
below will create the database, tables and populate it. MySql includes a command-line tool
called mysql. To run the script simple type
mysql < ModuleEleven.sql
If your database installation requires a username and password, use this command line:
mysql
-u username –p
< ModuleEleven.sql
MySql will prompt for the password. After running this command your database is ready for the
exercises below. For your information, the ModuleEleven.sql script is shown in the figure
below:
DROP DATABASE ModuleEleven;
CREATE DATABASE ModuleEleven;
USE ModuleEleven;
DROP TABLE IF EXISTS Contact;
CREATE TABLE Contact
(
NAME VARCHAR(64),
EMAIL
VARCHAR(64)
);
INSERT INTO Contact ( NAME, EMAIL )
values ( 'Kevin Rodgers', 'Quest Diagnotics');
INSERT INTO Contact ( NAME, EMAIL )
values ( 'Nancy Myers', '[email protected]');
INSERT INTO Contact ( NAME, EMAIL )
values ( 'Morgan Wiggens', '[email protected]');
INSERT INTO Contact ( NAME, EMAIL )
values ( 'John Smith', '[email protected]');
INSERT INTO Contact ( NAME, EMAIL )
values ( 'Jane Evans', '[email protected]');
Copyright ©2008, Custom Training Institute. All rights reserved.
Java Database Connectivity- Exercise: Page 3
Part Two: GUI Design and ContactDB Project
1. Create a new project directory for ModuleEleven. On windows create the
C:\labs\ModuleEleven directory.
2. Create a new java application in your ModuleEleven directory called ContactDB.java.
The ContactDB class is a Swing application that extends JFrame.
3. The user interface is simply four buttons and two text fields to hold the data. This is
conveniently rendered using a 4 by 2 GridLayout. The figure below represents the look
of the ContactDB application.
4. Add an event handler to close the window. This handler must also close the connection to
the database. First, modify the import statements to import all classes from the
javax.swing package and import the event and sql packages :
import
import
import
import
javax.swing.*;
java.awt.event.*;
java.awt.*;
java.sql.*;
5. Add the following instance variables for the database connection, jdbc driver, query,
statement and result set to the other instance variables:
private
private
private
private
private
private
private
private
Connection conn;
ResultSet rs;
Statement stmt;
String connStr = "jdbc:mysql:///ModuleEleven";
String jdbcDrv = "org.gjt.mm.mysql.Driver";
String query = "select * from Contact.Contact";
JTextField nameField = new JTextField();
JTextField emailField = new JTextField();
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Java Database Connectivity- Exercise: Page 4
6. Add a Window closing event handler that will check the Connection, Statement and
ResultSet objects. If they are not null, they will be closed and then the application will
exit. Place this code in the initialize() method as shown below:
private void initialize()
{
this.addWindowListener(new WindowAdapter()
{
public void windowClosing(WindowEvent e)
{
try
{
if(rs != null)
rs.close();
if(stmt != null)
stmt.close();
if(conn != null)
conn.close();
} catch (Exception ex) {}
finally
{
System.exit(0);
}
}
});
this.setContentPane( getMainPanel() );
initDB();
pack();
}
7. Place the database initialization code in the following method:
public void initDB()
{
try
{
// Check existence of driver class, establish connection
Class.forName(jdbcDrv);
} catch( ClassNotFoundException e )
{
JOptionPane.showMessageDialog(this,
"JDBC driver class : " + jdbcDrv + "\n",
"Driver Not Found",
JOptionPane.ERROR_MESSAGE);
return;
}
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Java Database Connectivity- Exercise: Page 5
try
{
conn = DriverManager.getConnection(connStr);
// Create Statement where ResultSets will be scrollable
// backwards and forwards, are not sensitive to
// changes made by others and are not updateable
stmt = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_READ_ONLY);
// Attempt to create ResultSet from query and set data
// from first row into text fields
rs = stmt.executeQuery(query);
// Make sure there is at least one row in ResultSet
if(rs.next())
{
nameField.setText(rs.getString(1));
emailField.setText(rs.getString(2));
} else
JOptionPane.showMessageDialog(this,
"No rows found using query: \n" + query,
"ResultSet Information",
JOptionPane.PLAIN_MESSAGE);
// catch SQLExceptions and loop through all
} catch (SQLException se)
{
String eMsg = "";
while(se != null)
{
eMsg += "SQLException: " + se.getMessage() + "\n"
+ "\n" + "ANSI-92 SQL State: " + se.getSQLState()
+ "\n" + "Vendor Error Code: "+se.getErrorCode();
se = se.getNextException( );
}
System.err.println(eMsg);
}
}
8. Build the primary GUI panel for the application in the getMainPanel() method. For the
moment in response to a button click action, simple print an indication that the button action
has indeed fired.
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Java Database Connectivity- Exercise: Page 6
public JPanel getMainPanel()
{
JPanel panel = new JPanel( new GridLayout( 4, 2, 10,10 ) );
panel.add( new JLabel( "Name: ", SwingConstants.RIGHT ) );
panel.add( nameField );
panel.add( new JLabel( "Email: ", SwingConstants.RIGHT ) );
panel.add( emailField );
JButton button = new JButton( "Delete Data" );
button.addActionListener( new ActionListener()
{
public void actionPerformed( ActionEvent e )
{
System.out.println("Delete");
}
});
panel.add( button );
button = new JButton( "Insert Data" );
button.addActionListener( new ActionListener()
{
public void actionPerformed( ActionEvent e )
{
System.out.println("Insert");
}
});
panel.add( button );
button = new JButton( "Next" );
button.addActionListener( new ActionListener()
{
public void actionPerformed( ActionEvent e )
{
System.out.println("Next");
}
});
panel.add( button );
button = new JButton( "Previous" );
button.addActionListener( new ActionListener()
{
public void actionPerformed( ActionEvent e )
{
System.out.println("Previous");
}
});
panel.add( button );
return panel;
}
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Java Database Connectivity- Exercise: Page 7
9. Add a constructor for ContactDB.
public ContactDB()
{
super("Database Browser");
initialize();
}
10. Modify the main() method to instantiate a ContactDB object and start it running as
shown below:
public static void main(String[] args)
{
ContactDB contact = new ContactDB();
Contact.setVisible(true);
}
11. Save your file, compile. Resolve any compiler errors and run ContactDB. It will not
access the database yet, but it should display the window and respond to your buttons and to
the button to exit the application. Verify that all your action listeners are working and then
exit the application.
Part Three: Connecting to the Database and Moving
through the ResultSet
Now it's time to navigate the database, create a ResultSet and program the event handlers
for the Next Row and Previous Row buttons that will move through the ResultSet. When
the program is started, the connection to the database should be initialized in the constructor for
ContactDB, the ResultSet should be created and populated and the first row displayed in
the text fields. When the user presses the Next Row button, the ResultSet is queried to
determine if it is on the last row. If it is, the user is informed of this and the cursor is not moved.
If it is not on the last row, the next() method is called to retrieve the next row and the results
displayed in the text fields. When the user presses the Previous Row button, the
ResultSet is queried to determine if it is on the first row. If it is, the user is informed of this
and the cursor is not moved. If it is not on the first row, the previous() method is called to
retrieve the previous row and the results displayed in the text fields.
To use the JDBC driver for the MySql database we will have to use an external java library
with the ContactDB program. The name of this library is mm.mysql.jar. Your instructor will
show you where to get this file. Using an external jar file requires us to add elements the the
classpath of the javac and java commands. The figure below shows ContactDB being compiled
and executed using the mm.mysql.jar library.
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Java Database Connectivity- Exercise: Page 8
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Java Database Connectivity- Exercise: Page 9
 javac –classpath . ContactDB.java
 java –classpath .;mm.mysql.jar ContactDB
Note: The period in the classpaths above indicates the current directory.
We’re included the current directory and the jar file. The semi-colon is the
path separator on Windows systems. On Unix systems the separator is the
colon.
1. Change the actionPerformed method for the Next button method by adding the
following database code to move to the next record in the RecordSet.
public void actionPerformed( ActionEvent e )
{
try
{
// is cursor already on last record?
if(rs.isLast())
JOptionPane.showMessageDialog(ContactDB.this,
"Cannot move beyond last record",
"Warning",
JOptionPane.WARNING_MESSAGE);
else
{
// cursor is not on last record, get next
rs.next();
nameField.setText(rs.getString(1));
emailField.setText(rs.getString(2));
}
} catch (SQLException se)
{
String eMsg = "";
while(se != null)
{
eMsg += "SQLException: "
+ se.getMessage() + "\n"
+ "\n" + "ANSI-92 SQL State: "
+ se.getSQLState() + "\n"
+ "Vendor Error Code: "
+ se.getErrorCode();
}
System.err.println(eMsg);
}
}
2. Change the actionPerformed method for the Previous button method by adding the
following database code to move to the previous record in the RecordSet.
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Java Database Connectivity- Exercise: Page 10
public void actionPerformed( ActionEvent e )
{
try
{
// is cursor already on first record?
if(rs.isFirst())
JOptionPane.showMessageDialog(ContactDB.this,
"Cannot move before first record",
"Warning",
JOptionPane.WARNING_MESSAGE);
else
{
// cursor is not on first record, get prev
rs.previous();
nameField.setText(rs.getString(1));
emailField.setText(rs.getString(2));
}
} catch (SQLException se)
{
String eMsg = "";
while(se != null)
{
eMsg += "SQLException: "
+ se.getMessage() + "\n"
+ "\n" + "ANSI-92 SQL State: "
+ se.getSQLState() + "\n"
+ "Vendor Error Code: "
+ se.getErrorCode();
}
System.err.println(eMsg);
}
}
3. Save your work, rebuild and run the application. You should be able to navigate through the
rows in both forward and backward directions.
Part Four: Inserting and Deleting Records
When the user presses the Delete Data button, the current row from the ResultSet is
deleted, the data is removed from the underlying database using a SQL delete statement and
the ResultSet is rebuilt. When the user presses the Insert Data button, the data is
retrieved from the text fields and inserted into the underlying database using a SQL insert
statement and the ResultSet is rebuilt.
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Java Database Connectivity- Exercise: Page 11
1. Change the actionPerformed method for the Delete Data button method by adding the
following database code to remove the current record in the RecordSet.
public void actionPerformed( ActionEvent e )
{
try
{
String SQLstr = "delete from Contact where ";
SQLstr += "NAME = '" + nameField.getText()
+ "' and ";
SQLstr += "EMAIL = '" + emailField.getText()
+ "'";
// Delete the record
stmt.execute(SQLstr);
JOptionPane.showMessageDialog(ContactDB.this,
"Deleted " + stmt.getUpdateCount()
+ " record(s).",
"Delete Information",
JOptionPane.PLAIN_MESSAGE);
// get new result set, position at first record
rs = stmt.executeQuery(query);
if(rs.next())
{
nameField.setText(rs.getString(1));
emailField.setText(rs.getString(2));
} else
JOptionPane.showMessageDialog(ContactDB.this,
"No data found", "No Data",
JOptionPane.PLAIN_MESSAGE);
} catch (SQLException se)
{
String eMsg = "";
while(se != null)
{
eMsg += "SQLException: "
+ se.getMessage() + "\n"
+ "\n" + "ANSI-92 SQL State: "
+ se.getSQLState()
+ "\n" + "Vendor Error Code: "
+ se.getErrorCode();
}
System.err.println(eMsg);
}
}
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Java Database Connectivity- Exercise: Page 12
2. Change the actionPerformed method for the Insert Data button method by adding the
following database code to insert the current field values into the database.
public void actionPerformed( ActionEvent e )
{
try
{
// Execute the insert statement
String SQLstr = "insert into Contact values ('";
SQLstr += nameField.getText() + "','";
SQLstr += emailField.getText() + "')";
stmt.execute(SQLstr);
JOptionPane.showMessageDialog(ContactDB.this,
"Inserted " + stmt.getUpdateCount()
+ " record(s).",
"Insert Information",
JOptionPane.PLAIN_MESSAGE);
// get new result set, position at first record
rs = stmt.executeQuery(query);
if(rs.next())
{
nameField.setText(rs.getString(1));
emailField.setText(rs.getString(2));
} else
JOptionPane.showMessageDialog(ContactDB.this,
"No data found", "No Data",
JOptionPane.PLAIN_MESSAGE);
} catch (SQLException se){
String eMsg = "";
while(se != null)
{
eMsg += "SQLException: " + se.getMessage()
+ "\n"
+ "\n" + "ANSI-92 SQL State: "
+ se.getSQLState()
+ "\n" + "Vendor Error Code: "
+ se.getErrorCode();
}
System.err.println(eMsg);
}
}
3. Save your work and rebuild the project.
Part Five: Test the Application
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Java Database Connectivity- Exercise: Page 13
1. Run the ContactDB application and test all the functions. Initially, the application should
successfully connect to the database and display the first record.
2. Use the Previous Row button to test the ability of the application to handle a user attempt
to go beyond the first row. You should see a message window appear informing the user that
they cannot move beyond the first row and the cursor will not move from the current
position.
3. Use the Next Row button to move through the records in the database and attempt to move
beyond the last record. A similar message should alert you that you cannot move beyond the
end of the records.
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Java Database Connectivity- Exercise: Page 14
4. Insert a record into the database by entering text into the Name and Email fields and then
clicking Insert Data button. You should see a message that the row was successfully
inserted, a new ResultSet will be retrieved with the first row displayed. Navigate through
the ResultSet to ascertain that the data was entered into the database.
5. Finally, navigate to a record and click the Delete Data button. You should see a message
that the row was successfully deleted, a new ResultSet will be retrieved with the first row
displayed. Navigate through the ResultSet to ascertain that the data was deleted from the
database.
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Java Database Connectivity- Exercise: Page 15
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Java Database Connectivity- Exercise: Page 16
Part Six: The ContactDB code
This application was one of the more complex you were asked to code. The code is reproduced
here for your reference complete with some JavaDoc contents.
Note: By including javadoc comments in you application (i.e. comments
at the beginning of methods that start with /** and end with */ ) you
can make your code self-documenting. Issue the command
javadoc –d docs ContactDB.java
to produce HTML documentation of your code in the directory “docs.”
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
import java.sql.*;
/**
* ContactDB is an implementation of a personal
* Addressbook Database application.
*/
public class ContactDB extends JFrame
{
/** The database connection */
private Connection conn = null;
/** The results of a database operation */
private ResultSet rs = null;
/** A representation of an SQL statement */
private Statement stmt = null;
/** The connection string to a database */
private String connStr = "jdbc:mysql:///ModuleEleven";
/** The JDBC driver class */
private String jdbcDrv = "org.gjt.mm.mysql.Driver";
/** Select all records from the database */
private String query = "select * from Contact";
/** a person's name */
JTextField nameField = new JTextField();
/** a person's email address */
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Java Database Connectivity- Exercise: Page 17
JTextField emailField = new JTextField();
/**
* zero argument constructor
*/
public ContactDB()
{
super("Database Browser");
initialize();
}
/**
* Build the GUI and start the database and
* prepare the application for use.
*/
private void initialize()
{
this.setContentPane( getMainPanel() );
this.addWindowListener(new WindowAdapter()
{
public void windowClosing(WindowEvent e)
{
try
{
if(rs != null)
rs.close();
if(stmt != null)
stmt.close();
if(conn != null)
conn.close();
} catch (Exception ex) {}
finally
{ System.exit(0); }
}
});
initDB();
pack();
}
/**
* Initialize the database.
*/
public void initDB()
{
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Java Database Connectivity- Exercise: Page 18
try
{
// Check existence of driver class, establish connection
Class.forName(jdbcDrv);
} catch( ClassNotFoundException e )
{
JOptionPane.showMessageDialog(this,
"JDBC driver class : " + jdbcDrv + "\n",
"Driver Not Found",
JOptionPane.ERROR_MESSAGE);
return;
}
try
{
conn = DriverManager.getConnection(connStr);
// Create Statement where ResultSets will be scrollable
// backwards and forwards, are not sensitive to
// changes made by others and are not updateable
stmt = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_READ_ONLY);
// Attempt to create ResultSet from query and set data
// from first row into text fields
rs = stmt.executeQuery(query);
// Make sure there is at least one row in ResultSet
if(rs.next())
{
nameField.setText(rs.getString(1));
emailField.setText(rs.getString(2));
} else
JOptionPane.showMessageDialog(this,
"No rows found using query: \n" + query,
"ResultSet Information",
JOptionPane.PLAIN_MESSAGE);
// catch SQLExceptions and loop through all
} catch (SQLException se)
{
String eMsg = "";
while(se != null)
{
eMsg += "SQLException: " + se.getMessage() + "\n"
+ "\n" + "ANSI-92 SQL State: " + se.getSQLState()
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Java Database Connectivity- Exercise: Page 19
+ "\n" + "Vendor Error Code: "+se.getErrorCode();
se = se.getNextException( );
}
System.err.println(eMsg);
}
}
/**
* Build the user interface.
*/
public JPanel getMainPanel()
{
JPanel panel = new JPanel( new GridLayout( 4, 2, 10,10 ) );
panel.add( new JLabel( "Name: ", SwingConstants.RIGHT ) );
panel.add( nameField );
panel.add( new JLabel( "Email: ", SwingConstants.RIGHT ) );
panel.add( emailField );
JButton button = new JButton( "Delete Data" );
button.addActionListener( new ActionListener()
{
public void actionPerformed( ActionEvent e )
{
try
{
String SQLstr = "delete from Contact where ";
SQLstr += "NAME = '" + nameField.getText()
+ "' and ";
SQLstr += "EMAIL = '" + emailField.getText()
+ "'";
// Delete the record
stmt.execute(SQLstr);
JOptionPane.showMessageDialog(ContactDB.this,
"Deleted " + stmt.getUpdateCount()
+ " record(s).",
"Delete Information",
JOptionPane.PLAIN_MESSAGE);
// get new result set, position at first record
rs = stmt.executeQuery(query);
if(rs.next())
{
nameField.setText(rs.getString(1));
emailField.setText(rs.getString(2));
} else
JOptionPane.showMessageDialog(ContactDB.this,
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Java Database Connectivity- Exercise: Page 20
"No data found", "No Data",
JOptionPane.PLAIN_MESSAGE);
} catch (SQLException se){
String eMsg = "";
while(se != null)
{
eMsg += "SQLException: "
+ se.getMessage() + "\n"
+ "\n" + "ANSI-92 SQL State: "
+ se.getSQLState()
+ "\n" + "Vendor Error Code: "
+ se.getErrorCode();
}
System.err.println(eMsg);
}
}
});
panel.add( button );
button = new JButton( "Insert Data" );
button.addActionListener( new ActionListener()
{
public void actionPerformed( ActionEvent e )
{
try
{
// Execute the insert statement
String SQLstr = "insert into Contact values ('";
SQLstr += nameField.getText() + "','";
SQLstr += emailField.getText() + "')";
stmt.execute(SQLstr);
JOptionPane.showMessageDialog(ContactDB.this,
"Inserted " + stmt.getUpdateCount() + " record(s).",
"Insert Information",
JOptionPane.PLAIN_MESSAGE);
// get new result set, position at first record
rs = stmt.executeQuery(query);
if(rs.next())
{
nameField.setText(rs.getString(1));
emailField.setText(rs.getString(2));
} else
JOptionPane.showMessageDialog(ContactDB.this,
"No data found", "No Data",
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Java Database Connectivity- Exercise: Page 21
JOptionPane.PLAIN_MESSAGE);
} catch (SQLException se){
String eMsg = "";
while(se != null)
{
eMsg += "SQLException: " + se.getMessage() + "\n"
+ "\n" + "ANSI-92 SQL State: "
+ se.getSQLState()
+ "\n" + "Vendor Error Code: "
+ se.getErrorCode();
}
System.err.println(eMsg);
}
}
});
panel.add( button );
button = new JButton( "Next" );
button.addActionListener( new ActionListener()
{
public void actionPerformed( ActionEvent e )
{
try
{
// is cursor already on last record?
if(rs.isLast())
JOptionPane.showMessageDialog(ContactDB.this,
"Cannot move beyond last record",
"Warning",
JOptionPane.WARNING_MESSAGE);
else
{
// cursor is not on last record, get next
rs.next();
nameField.setText(rs.getString(1));
emailField.setText(rs.getString(2));
}
} catch (SQLException se)
{
String eMsg = "";
while(se != null)
{
eMsg += "SQLException: "
+ se.getMessage() + "\n"
+ "\n" + "ANSI-92 SQL State: "
+ se.getSQLState() + "\n"
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Java Database Connectivity- Exercise: Page 22
+ "Vendor Error Code: " + se.getErrorCode();
}
System.err.println(eMsg);
}
}
});
panel.add( button );
button = new JButton( "Previous" );
button.addActionListener( new ActionListener()
{
public void actionPerformed( ActionEvent e )
{
try
{
// is cursor already on first record?
if(rs.isFirst())
JOptionPane.showMessageDialog(ContactDB.this,
"Cannot move before first record",
"Warning",
JOptionPane.WARNING_MESSAGE);
else
{
// cursor is not on first record, get prev
rs.previous();
nameField.setText(rs.getString(1));
emailField.setText(rs.getString(2));
}
} catch (SQLException se)
{
String eMsg = "";
while(se != null)
{
eMsg += "SQLException: "
+ se.getMessage() + "\n"
+ "\n" + "ANSI-92 SQL State: "
+ se.getSQLState() + "\n"
+ "Vendor Error Code: "
+ se.getErrorCode();
}
System.err.println(eMsg);
}
}
});
panel.add( button );
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Java Database Connectivity- Exercise: Page 23
return panel;
}
/**
* Run the ContactDB application.
* @param args
ignored
*/
public static void main(String[ ] args)
{
ContactDB contact = new ContactDB();
contact.setVisible(true);
}
}
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