|By Boris Minkin||
|November 22, 2005 01:00 PM EST||
In this article I'll show you how to develop and deploy a JSP Web application with WTP in less than an hour. I'll also cover the creation and deployment of a basic servlet and editing JSP with WTP. Let's develop the WTP application together but, first, we need to install the following software:
- J2SE 5.0 JRE: http://java.sun.com/j2se
- Eclipse 3.1: www.eclipse.org
- WTP 0.7.1: www.eclipse.org/webtools
- Tomcat 5.0: http://jakarta.apache.org/tomcat/
- MySQL 4.0.25: www.mysql.com
- MySQL Connector/J Driver 3.1: www.mysql.com/products/connector/j/
Our application will be a basic Web application implementing the following use cases:
- Customers need to register on the site to place orders.
- Customers can place orders.
- Customers can view their orders.
- Admin can list all registered customers.
The system will be implemented using a servlet programming model and MySQL database.
Configuring MySQL Database and the Data Source
By default, when MySQL gets installed, a TEST database is available. Be sure to launch C:\Mysql\winmysqladmin.exe to specify the user name and password (the first time you launch it, it lets you do it and also starts the database server). It's necessary to copy MySQL Connector/J JDBC Driver: mysql-connector-java-3.1.10-bin.jar to the Tomcat/common/lib directory, so the Tomcat server can recognize it.
To configure MySQL database access in Tomcat, we have to add a separate file called Listing 1: DBTest.xml; the file follows a convention of "application_name.xml" under $TOMCAT\conf\catalina\localhost directory. The only problem with this file is that it may get deleted when the application is undeployed, so if you undeploy and redeploy the application, you have to place this file into the same folder again (so it's a good idea to save it somewhere else). Looking inside the DBTest.xml file, please note that in our case we are using "ODBC" for the username and don't provide any password.
Building Our Web Application Using Web Tools and a Database
Before we can start working on the Web project, we must configure Tomcat 5.0 in Eclipse to be our default server. When Web Tools are installed in Eclipse, new perspectives and options are added, such as a J2EE perspective where you can create J2EE projects, Web projects, and Web services. New options are available under the Window-Preferences menu for configuring Tomcat servers with Eclipse. Go to Window - Preferences menu, under Server select - Installed Runtimes, click Add, and then specify Tomcat 5.0 server with the installed JRE and a path to the Tomcat installation directory (see Figure 1). Now create a Dynamic Web Project using the Web Tools wizard by selecting File-New-Other, then expanding Web-Dynamic Web Project.
We'll name the project DBTest, which will also become its context root. The Web module will be targeted to our default server: Tomcat. Click Finish and the DBTest Web project gets created. This project will contain all of our Web resources, such as HTML and JSP files, and servlets, and you'll be able to export it into a standard WAR file later, if needed.
Creating Supporting Domain Classes and Tables
Before creating servlets, let's create supporting classes to represent a customer and an order. The class diagram in Figure 2 depicts the Customer and Order relationship.
Note that when creating Customer and Order classes, we define corresponding fields as their public instance variables and then can automatically generate getters and setters from those fields. This can be easily done by going to Outline view (appears after you double-click on an existing class name or create a new class), selecting a class, and selecting "Source - Generate Getters and Setters..." from the right-button menu (see Figure 3).
Along with the classes, we'd have to create corresponding database tables in a MySQL database:
CREATE TABLE CUSTOMER (
ID INT PRIMARY KEY,
CREATE TABLE ORDERS (
ID INT PRIMARY KEY,
CUST_ID INT REFERENCES CUSTOMER,
Creating Database Command Classes
We'll create a special package with classes that implement a Command design pattern to perform necessary database updates. The Command pattern allows the classes to implement the common interface executing some particular command. Examples of the Command pattern in Java would be classes that implement the ActionListener interface with the actionPerformed() method. Our Command pattern interface for database integration is presented in Listing 2.
Classes implementing this command will be performing the actual database operations for reading and inserting rows into customer and order tables. The following use cases will be addressed:
- Customers want to register on the site in order to place orders (a new row is created in the customer table)
- Customers can place the order (the order gets created in the database for a particular customer)
- Customers can view the orders they have placed
- Admin can list all the customers
Based on these use cases, the following classes have implemented the DatabaseCommand interface (see Listings 3-6):
public class CreateCustomer implements DatabaseCommand
public class CreateOrder implements DatabaseCommand
public class ListCustomers implements DatabaseCommand
public class ListCustomerOrders implements DatabaseCommand
Finally, in order to execute our command classes, we will need to create a class that would access the database datasource, obtain a SQL connection, and then execute a particular database command. This class will implement a Singleton design pattern, which we'll call CommandExecutor:
Object o = CommandExecutor.getInstance().executeDatabaseCommand
(<<instance of the particular database command class goes here>>).
The CommandExecutor class will perform the datasource lookup as follows:
InitialContext ctx = new InitialContext();
Context envCtx = (Context) ctx.lookup("java:comp/env");
ds = (DataSource) envCtx.lookup("jdbc/TestDB");
This finds the reference to the data-source we have defined in DBTest.xml by resolving its reference in a Web deployment descriptor (web.xml), which we'll define in a section below. Listing 7 has the complete code of the Command Executor class.
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