Create your own type 3 JDBC driver, Part 2
Tutorial Details:
Create your own type 3 JDBC driver, Part 2
Create your own type 3 JDBC driver, Part 2
By: By Nitin Nanda and Sunil Kumar
Compile, deploy, and access data using your custom-built JDBC driver
n Part 1 of this three-part series, we showed how to construct a type 3 JDBC driver, named JWDriver, that employed RMI (Remote Method Invocation) to let the client talk to the middle tier. Continuing with JWDriver's development, in this article we explain how to compile the driver, then deploy it in a Web server environment. Further, we explain the Java files' directory structure for both the client and server tiers, then we run the driver's server tier, giving any client program access. We also include a sample Java applet (deployed on the Web server) to demonstrate how the driver can access data.
Read the whole "Create Your Own Type 3 JDBC Driver" series:
Part 1: Connect your Java applications to databases?the easy way
Part 2: Compile, deploy, and access data using your custom-built JDBC driver
Part 3: Enhance the custom JWDriver with advanced logging, connection pooling, and Predefined Data Sets
This article comprises three sections: compiling, deployment, and how to create a sample Web application that employs the driver.
Compile the driver
To compile the driver, first download DriverCode.zip . Extract the files, then place them into a directory. You must compile the driver on a machine with a complete Sun Microsystems JDK (Java Developer Kit) 1.3. The DriverCode.zip file additionally contains the compile.bat file, which you should execute from the command line. The compile.bat file first sets the classpath to the local directory containing the Java files as:
set classpath=.;%classpath%
The compile.bat file then compiles the driver's Java files for the server and client tiers using javac as:
javac com\jw\server\*.java
javac com\jw\client\*.java
RMI requires Stub and Skel class files for all remote interfaces exposed by the server. Prepare those files by executing the rmic command on the driver's four remote interface implementations:
rmic -d . com.jw.server.RemoteDriverImpl
rmic -d . com.jw.server.RemoteConnectionImpl
rmic -d . com.jw.server.RemoteStatementImpl
rmic -d . com.jw.server.RemoteResultSetImpl
Deploy the driver server tier in the form of a JWServerDriver.jar file containing the server class files. To prepare the JWServerDriver.jar file, run the cvf command as indicated in compile.bat file.
Deploy the driver
You deploy JWDriver on the Web server. As such, the driver's server tier runs as an RMI server on the Web server machine, as does the driver's client tier, the sample Java applet, and the Webpage that invokes the applet. The driver's client tier and the sample Java applet reside in the same Web directory in the Web server machine. The JDBC driver client tier automatically downloads from the server to the client machine.
We made the driver Internet ready by keeping its configuration settings on the server tier, eliminating the need for any settings at the client tier. Figure 1 depicts the driver's deployment in a typical three-tier setup, with each tier on a different machine.
Figure 1. The type 3 JDBC driver's deployment. Click on thumbnail to view full-size image.
In Figure 1, the Web application deploys on the Web server machine running Microsoft Internet Information Server (IIS). The driver's server tier, configured through a properties file, communicates with the Microsoft SQL Server database.
To deploy the driver on your system, you must:
Set the environment
Configure the driver in the Web server
Set up the database
Run the driver middle tier as an RMI server
Let's look at each step in more detail.
Set the environment
The driver requires each deployment machine to run specific applications:
Client-tier machine: Should run Microsoft Internet Explorer 5.5 or 6.0 and either Microsoft Windows NT or Microsoft Windows 2000.
Server-tier machine: Should run either Microsoft Windows NT or Microsoft Windows 2000, Microsoft Internet Information Server 4.0 or 5.0, and the Sun JDK 1.3 runtime environment.
Database-tier machine: You can deploy any database with JDBC-ODBC (Open Database Connectivity) bridge capabilities. In this article, the sample program employs Microsoft SQL Server 2000.
Configure the driver in the Web server
You deploy the driver on the Web server along with the TestApp Web application. Create a TestApp directory on the Web sever under C:\Inetpub\wwwroot. Then copy the JWServerDriver.jar into the C:\Inetpub\wwwroot\TestApp directory. Also copy the driver client-tier class files, along with the remote interface and stub class files generated during compilation, into the C:\Inetpub\wwwroot\TestApp directory (maintaining their directory structures).
The Deployment.zip file contains the JDK RMI classes you'll copy into the C:\Inetpub\wwwroot\TestApp (again, maintaining their directory structures). Figure 2 shows the resulting directory structure.
Figure 2. Web application directory structure
Set up the database
Next, create in the Web server machine (using Data Sources (ODBC) from the Control Panel) an ODBC data source for the target database. Then create a data source named Pubs , configuring it to hit pubs as the default database in Microsoft SQL Server. (The pubs sample database comes with Microsoft SQL Server.) The sample Java applet accesses the authors table in the pubs database through the driver.
After configuring the ODBC data source, set the driver's settings in the DriverSettings.properties file (available in the DriverCode.zip file). DriverSettings.properties, which you should copy to C:\Inetpub\wwwroot\TestApp, contains the data source attributes DSN , User , and Password , with which the driver connects to the database. User and Password are the Microsoft SQL Server login and password:
DSN=Pubs
User=sa
Password=
Run the driver middle tier as an RMI server
The driver's server tier runs as an RMI server on the Web server machine. Before running the driver middle tier as an RMI server, set the classpath to:
set classpath=.; C:\Inetpub\wwwroot\TestApp\ JWServerDriver.jar;%claasspath%
Then start the Web server machine's RMI registry naming service by executing the following command on the command line, which launches the RMI registry window:
start rmiregistry
The driver's RMI server starts by running the following command on the command line in the C:\Inetpub\wwwroot\TestApp directory:
java -Djava.security.policy=./java.policy com.jw.server.RemoteDriverImpl
Executing the above command displays the command-line window showing the running RMI server. Entering "Y" stops the RMI server. You've now successfully configured the driver, which is now ready for use in the client programs.
Sample Java applet
The sample Java applet, SampleApplet , retrieves the data from the database by executing a SQL statement. The applet executes in the client browsers through an HTML page. In this section, we explain how to develop and run the sample Java applet.
The SampleApplet uses JWDriver for all database communications. The SampleApplet 's code adheres to the standard JDBC interface methods.
Load the driver class
The driver's JWDriver class loads in the applet's init() method:
public void init()
{
btnGetData_ = new Button("Get Data");
add(btnGetData_);
btnGetData_.addActionListener(this);
try
{
// Load the com.jw.client.JWDriver class in the client browser JVM
Class.forName("com.jw.client.JWDriver");
}
catch(Exception ex)
{
msg_ = ex.getMessage();
}
}
The init() method creates a Get Data button. When a user clicks on that button, the data is fetched from the database. The JWDriver class loads in the browser JVM by invoking Class.forName("com.jw.client.JWDriver") . The driver registers with the browser's JDBC driver manager when the JWDriver class loads.
Get the connection
SampleApplet 's getData() method invokes whenever the user clicks on the Get Data button. The method first gets the connection from the JWDriver as:
public void getData()
{
Properties props = new Properties();
String server = getCodeBase().getHost();
// Prepare the JWDriver URL
String DriverProtocol = JWDriver.getURLPrefix() + server;
Connection conn = DriverManager.getConnection(DriverProtocol,props);
---
}
The getData() method first retrieves the host machine name (the Web server running the driver RMI server) from which the applet originated. The getData() method then prepares the driver's requisite URL by appending the name of the Web server machine in the jdbc:JWDriver: . That URL passes to the DriverManager , which returns the connection. Figure 3 illustrates the internal process required to retrieve the connection.
Figure 3. JWDriver's connection sequence diagram. Click on thumbnail to view full-size image.
In Figure 3's sequence diagram, SampleApplet first calls the DriverManager.getConnection() method. The DriverManager asks each registered driver whether it subscribes to the driver URL starting with jdbc:JWDriver: . After the driver returns true, the DriverManager calls the JWDriver.connect() method, which extracts the Web server's name from the given URL string, then DriverManager gets the reference to the remote driver interface IRemoteDriver by checking the RMI naming service for the RemoteDriver object running on the Web server. Because you obtain the remote driver reference only once, all subsequent connection-retrieval calls need not get the remote driver reference. Obtain a remote connection from the remote driver and embed it into a local JWConnection object. The actual JDBC-ODBC bridge connection is held in the remote connection. Eventually, the JWConnection object instance returns to the SampleApplet .
Create the statement
The SampleApplet 's getData() method, using the connection object, then creates the statement:
// Create the statement
Statement stmt = conn.createStatement();
The JWStatement object internally holds the refe
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