Getting Started with Enterprise Beans

This chapter shows how to develop, deploy, and run a simple Jakarta EE application named converter that uses an enterprise bean for its business logic. The purpose of converter is to calculate currency conversions among Japanese yen, euros, and US dollars. The converter application consists of an enterprise bean, which performs the calculations, and a web client.

Starting With Enterprise Beans

Here’s an overview of the steps you’ll follow:

Create the enterprise bean: ConverterBean.
Create the web client.
Deploy converter onto the server.
Using a browser, run the web client.

Before proceeding, make sure that you’ve done the following:

Read Overview
Become familiar with enterprise beans (see Enterprise Beans)
Started the server (see Starting and Stopping GlassFish Server)

Creating the Enterprise Bean

The enterprise bean in our example is a stateless session bean called ConverterBean. The source code for ConverterBean is in the jakartaee-examples/tutorial/ejb/converter/src/main/java/ directory.

Creating ConverterBean requires these steps:

Coding the bean’s implementation class (the source code is provided)
Compiling the source code

Coding the Enterprise Bean Class

The enterprise bean class for this example is called ConverterBean. This class implements two business methods: dollarToYen and yenToEuro. Because the enterprise bean class doesn’t implement a business interface, the enterprise bean exposes a local, no-interface view. The public methods in the enterprise bean class are available to clients that obtain a reference to ConverterBean. The source code for the ConverterBean class is as follows:

package ee.jakarta.tutorial.converter.ejb;

import java.math.BigDecimal;
import jakarta.ejb.*;

@Stateless
public class ConverterBean {
    private BigDecimal yenRate = new BigDecimal("83.0602");
    private BigDecimal euroRate = new BigDecimal("0.0093016");

    public BigDecimal dollarToYen(BigDecimal dollars) {
        BigDecimal result = dollars.multiply(yenRate);
        return result.setScale(2, BigDecimal.ROUND_UP);
    }

    public BigDecimal yenToEuro(BigDecimal yen) {
        BigDecimal result = yen.multiply(euroRate);
        return result.setScale(2, BigDecimal.ROUND_UP);
    }
}

Note the @Stateless annotation decorating the enterprise bean class. This annotation lets the container know that ConverterBean is a stateless session bean.

Creating the converter Web Client

The web client is contained in the following servlet class under the jakartaee-examples/tutorial/ejb/converter/src/main/java/ directory:

converter/web/ConverterServlet.java

A Jakarta servlet is a web component that responds to HTTP requests.

The ConverterServlet class uses dependency injection to obtain a reference to ConverterBean. The jakarta.ejb.EJB annotation is added to the declaration of the private member variable converter, which is of type ConverterBean. ConverterBean exposes a local, no-interface view, so the enterprise bean implementation class is the variable type:

@WebServlet(urlPatterns="/")
public class ConverterServlet extends HttpServlet {
  @EJB
  ConverterBean converter;
  ...
}

When the user enters an amount to be converted to yen and euro, the amount is retrieved from the request parameters; then the ConverterBean.dollarToYen and the ConverterBean.yenToEuro methods are called:

...
try {
  String amount = request.getParameter("amount");
  if (amount != null && amount.length() > 0) {
    // convert the amount to a BigDecimal from the request parameter
    BigDecimal d = new BigDecimal(amount);
    // call the ConverterBean.dollarToYen() method to get the amount
    // in Yen
    BigDecimal yenAmount = converter.dollarToYen(d);

    // call the ConverterBean.yenToEuro() method to get the amount
    // in Euros
    BigDecimal euroAmount = converter.yenToEuro(yenAmount);
    ...
  }
  ...
}

The results are displayed to the user.

Running the converter Example

Now you are ready to compile the enterprise bean class (ConverterBean.java) and the servlet class (ConverterServlet.java) and to package the compiled classes into a WAR file. You can use either NetBeans IDE or Maven to build, package, deploy, and run the converter example.

To Run the converter Example Using NetBeans IDE

Make sure that GlassFish Server has been started (see Starting and Stopping GlassFish Server).
From the File menu, choose Open Project.
In the Open Project dialog box, navigate to:
```
jakartaee-examples/tutorial/ejb
```
Select the converter folder.
Click Open Project.
In the Projects tab, right-click the converter project and select Build.
Open a web browser to the following URL:
```
http://localhost:8080/converter
```
On the Servlet ConverterServlet page, enter 100 in the field and click Submit.

A second page opens, showing the converted values.

To Run the converter Example Using Maven

Make sure that GlassFish Server has been started (see Starting and Stopping GlassFish Server).

In a terminal window, go to:

jakartaee-examples/tutorial/ejb/converter/

Enter the following command:
```
mvn install
```
This command compiles the source files for the enterprise bean and the servlet, packages the project into a WAR module (converter.war), and deploys the WAR to the server. For more information about Maven, see Building the Examples.
Open a web browser to the following URL:
```
http://localhost:8080/converter
```
On the Servlet ConverterServlet page, enter 100 in the field and click Submit.

A second page opens, showing the converted values.

Modifying the Jakarta EE Application

GlassFish Server supports iterative development. Whenever you make a change to a Jakarta EE application, you must redeploy the application.

To Modify a Class File

To modify a class file in an enterprise bean, you change the source code, recompile it, and redeploy the application. For example, to update the exchange rate in the dollarToYen business method of the ConverterBean class, you would follow these steps.

To modify ConverterServlet, the procedure is the same.

Edit ConverterBean.java and save the file.
Recompile the source file.
1. To recompile ConverterBean.java in NetBeans IDE, right-click the converter project and select Run.
  
  This recompiles the ConverterBean.java file, replaces the old class file in the build directory, and redeploys the application to GlassFish Server.
2. Recompile ConverterBean.java using Maven.
  1. In a terminal window, go to the jakartaee-examples/tutorial/ejb/converter/ directory.
  2. Enter the following command:
    
    mvn install
    
    This command repackages and deploys the application.