Accessing Databases from Web Applications

Accessing Databases from Web Applications

Data that is shared between Web components and persistent between invocations of a Web application is usually maintained by a database. Web applications use the JDBC 2.0 API to access relational databases. For information on this API, see:

http://java.sun.com/docs/books/tutorial/jdbc

1 The Examples

The examples discussed in the chapters Java Servlet Technology (page 367), JavaServer Pages Technology (page 401), Custom Tags in JSP Pages (page 431), and JavaServer Pages Standard Tag Library (page 465) require a database. For this release we have tested the examples with the Pointbase database and we provide an ant build file to create the database tables and populate the database. The remainder of this section describes how to install and start the Pointbase database server, set up the example tables, configure the Web application to use the database, and configure Tomcat to recognize the database.

2 Downloading and Starting the Database Server

You can download a copy of the Pointbase database from:

http://www.pointbase.com

After you have downloaded and installed the Pointbase database, you will need to do the following:

1. Set the PB_HOME environment variable to point to your Pointbase install directory.

2. Copy <PB_HOME> /client/lib/pbclient41ev.jar to <JWSDP_HOME> /common/lib to make the Pointbase client library available to the example applications.

3. In a terminal window, go to <PB_HOME> /server.

4. Start the Pointbase server by typing Server.

3 Populating the Database

1. In a terminal window, set the environment variable PB_HOME to point to your Pointbase installation to make the Pointbase libraries available to the ant task that populates the database.

2. Go to <JWSDP_HOME> /docs/tutorial/examples/web.

3. Execute ant. At the end of the processing, you should see the following output:

   
   [java] ID 
   [java] ----------
   [java] 201 
   [java] 202 
   [java] 203 
   [java] 204 
   [java] 205 
   [java] 206 
   [java] 207 
   [java] 
   [java] 7 Rows Selected. 
   [java] 
   [java] SQL> 
   [java] 
   [java] COMMIT; 
   [java] OK

4 Configuring the Web Application to Use the Database

In order to access a database from a Web application you must declare resource reference in the application's Web application deployment descriptor (see References to Environment Entries, Resource Environment Entries, or Resources (page 358)). The resource reference declares the name and type of resource and the type of authentication used when the resource is accessed.

5 Configuring the Server to Recognize the Database

Since the resource reference declared in the Web application deployment descriptor uses a JNDI name to refer to the database, you must connect the name to an actual database by providing a resource factory in the Tomcat's configuration.

Here is the resource factory used by the application discussed in all the Web technology chapters:

<Resource name="jdbc/BookDB" reloadable="true" 
    auth="Container" type="javax.sql.DataSource"/> 
<ResourceParams name="jdbc/BookDB"> 
    <parameter> 
        <name>user</name> 
        <value>public</value> 
    </parameter> 
    <parameter> 
        <name>password</name> 
        <value>public</value> 
    </parameter> 
    <parameter> 
        <name>driverClassName</name> 
        <value>com.pointbase.jdbc.jdbcUniversalDriver</value> 
    </parameter> 
    <parameter> 
        <name>driverName</name> 
        <value>jdbc:pointbase: 
            server://localhost/sample</value> 
    </parameter> 
</ResourceParams>

Since the resource factory is a subentry of the Context entry described in Running Web Applications (page 360), you add this entry to Tomcat's configuration in the same ways that you can add the Context entry.