• Introduction
  • Baseline
  • Resources
• Design
  • About the Problem
  • Design Notes
• Source
• Demo

• NPAC's Servlet examples page
• Write JDBC on carver using Oracle 8 driver
• NPAC's JDBC resources page
  • The 2-tier example
  • SQL tutorials
  • The Sun JDBC tutorial
• NPAC's Java resource page for the JDBC API, which is under JDK1.1 API in the package java.sql.

Image Database is a sample Java Servlet application that demonstrates how JDBC 3-Tier model works.
The program consists of three distinct modules:

• One is the Client interface module -- client.html, which offers an form for customers to query (search/insert) images in the database;
  
  
• The second module is the Servlet middle-tier -- ImageDBServlet.java, which accepts request from client side and sends response(result HTML file) back;
  
  
• The third module is the Database Access backend -- myDatabase.java, which forms queries from the data delivered by servlet, performs database access through JDBC.
  
  

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Design Notes

Client.html is an interface at client side, which offers a form for querying the Image Database. The form consists of a table with four fields: Image Name, Color, Type and Url. User can fill in values in those fields or leave unknown value as a blank. The request to Servlet server is done by Form "input" Event Handlers and handles "get" Forms.

ImageDBServlet is a middle-tier module at server side, which accepts request from client and responses. In the Image Database application, ImageDBServlet collects query (form values) from client and forms query command for accessing the Image Database by method of myDatabase through JDBC. The important method for implementing communication with client side is doGet(HttpServletRequest req, HttpServletResponse res), which matches the form method "get" in client.html file. This module also responsible for sending back query results from Database to client in the form of HTML file. One of the advantages of doing this is that the HTML file can be displayed in any browser. User will see images showing up in the browser, rather than URL, as I built link to image source in the HTML file.

myDatabase implements methods to access the Oracle database via JDBC. The API includes open and close database, executeSQL for executing query commands and getRecord for returning multiple records that matches the query. Vector object is used to hold multiple Hashtables as elements, where each record is held by a hashtable. As each query is packaged into a string object that deliverd to execution method. so all of the database access methods take executeSQL and getRecord as the underline methods. And it is very flexible to expand the functions of query based on this scheme. I use oracle.jdbc.driver.OracleDriver to connect to the Oracle database on Carver. The database access part of the program is done on server side using the above JDBC driver. The myDatabase class implements two important methods executeSQL and getRecord.

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Source

• Source Code :
  client.html
  ImageDBServlet.java
  myDatabase.java
  table.sql
  
• Demo :
  Image Database Servlet