jGuru: Retrieving and Displaying an Image from a Blob

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Exercise Note: This program requires a DBMS that supports Blob columns. The exercise has been tested against UDB2/NT and DB2/400. You will need to set the driver and connection information for your database in the ConnectJ.properties file.

Now that the images are loaded into the database, it's time to write a program to display them. Duane and Chrissie use the basic code from Selecting Data and Presenting Information to present a Swing interface. As before, the Swing work is done for you.

After user information is keyed and the "Connect" button is pressed, the program will connect to the database, retrieve all distinct colors and load them into a combo box. From that point, the user can select a color and press the "Show It!" button. The program will retrieve the corresponding image from the Blob column in the database and display it. The Connection will be maintained until the program ends.

Prerequisites

• Selecting Data and Presenting Information

Skeleton Code

• ConnectJ.properties
• TeeColorsJ.java

Tasks

1. Two query strings are required: one to select all distinct colors in the table and the other for Blob selection in a prepared statement. Here are the SQL statements needed:

   for sQueryD

   SELECT DISTINCT TColor 
     FROM TeeColor
   

   for sQueryP

   
   SELECT TCBlob 
     FROM TeeColor 
     WHERE TColor = ?
   

   Your job is to set up Strings with the appropriate SQL statements.

2. In doConnect(), after connecting and creating a Statement, execute the DISTINCT query, retrieve the rows and load the color names into a combo box.

3. Now that the program is connected, after closing the Statement and doing some screen setup, it is time to execute prepareStatement. This is still in doConnect().

4. In doRetrieve(), set the String and excute the PreparedStatement query; Get the Blob and its length; Materialize the Blob data using Blob.getBytes() and use the resulting aray of bytes to create an ImageIcon with ImageIcon( byte[] ). ( Note that in Blob.getBytes(), the binary data starts at 1. ) Use JLabel.setIcon() to load the image to the JLabel.

5. In EndApp(), insert code to close the connection.

Where help exists, the task numbers above are linked to the step-by-step help page.

Solution Source

• ConnectJ.properties
• TeeColorsJ.java

Demonstration

When this program has been compiled and run, the resulting display should look like this:

Exercises

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