33.1.1 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 javaeetutorial.converter.ejb;

import java.math.BigDecimal;
import javax.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.

33.1.2 Creating the converter Web Client

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

converter/web/ConverterServlet.java

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

The ConverterServlet class uses dependency injection to obtain a reference to ConverterBean. The javax.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.

33.1.3 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.