JAVA

Session Beans in EJB 3.0

Enterprise applications revolve mostly around three aspects of data: transfer of data, retrieval of data and transformation of data by applying the business rules of a particular organization. Since these three aspects are specific to an organization, Enterprise Java Beans (EJB) are known as Business Specific Components. Even among the three aspects, the former two are more generic in nature whereas the latter is closer to the policies of a given organization.

Author Info:

By: A.P.Rajshekhar

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March 28, 2007

TABLE OF CONTENTS:

   public ArrayList <Integer> starts = new ArrayList <Integer> ();
   public ArrayList <Integer> ends = new ArrayList <Integer> ();
   public ArrayList <Double> growthrates = new ArrayList <Double> ();
   public ArrayList <Double> savings = new ArrayList <Double> ();
   public ArrayList <Double> results = new ArrayList <Double> ();

   public double calculate (int start, int end, double growthrate, double saving) {
     double tmp = Math.pow(1. + growthrate / 12., 12. * (end - start) + 1);
     double result = saving * 12. * (tmp - 1) / growthrate;

     starts.add(Integer.valueOf(start));
     ends.add(Integer.valueOf(end));
     growthrates.add(Double.valueOf(growthrate));
     savings.add(Double.valueOf(saving));
     results.add(Double.valueOf(result));

return result;
}

   public ArrayList <Integer> getStarts () {
     return starts;
   }

   public ArrayList <Integer> getEnds () {
     return ends;
   }

   public ArrayList <Double> getGrowthrates () {
     return growthrates;
   }

   public ArrayList <Double> getSavings () {
     return savings;
   }

   public ArrayList <Double> getResults () {
     return results;
   }

}

This implementation contains an instance variable that is part of Conversational State. Next is the Client in the form of JSP:

<%@ page import=" examples.session.stateful.*,
                  javax.naming.*,
                  java.text.*,
                  java.util.ArrayList"%>

<%!
private NumberFormat nf = null;

   public void jspInit () {
     nf = NumberFormat.getInstance();
     nf.setMaximumFractionDigits(2);
   }
%>

<%
   Calculator cal =
      (Calculator) session.getAttribute("sfsb_cal");
   if (cal == null) {
     try {
       InitialContext ctx = new InitialContext();
       cal = (Calculator) ctx.lookup(
               "EJB3Trail/StatefulCalculator/local");
       session.setAttribute ("sfsb_cal", cal);
     } catch (Exception e) {
       e.printStackTrace ();
     }
   }

String result;

   int start = 25;
   int end = 65;
   double growthrate = 0.08;
   double saving = 300.0;

   try {
     start = Integer.parseInt(request.getParameter ("start"));
     end = Integer.parseInt(request.getParameter ("end"));
     growthrate = Double.parseDouble(request.getParameter ("growthrate"));
     saving = Double.parseDouble(request.getParameter ("saving"));

double res = cal.calculate(start, end, growthrate, saving);
result = nf.format(res);

   } catch (Exception e) {
     // e.printStackTrace ();
     result = "Not valid";
   }
%>

<html><body>

<p>Investment calculator with session history<br/>
<form action="calculator.jsp" method="POST">
   Start age = <input type="text" name="start" value="<%=start%>"><br/>
   End age = <input type="text" name="end" value="<%=end%>"><br/>
   Annual Growth Rate = <input type="text" name="growthrate" value="<%=growthrate%>"><br/>
   Montly Saving = <input type="text" name="saving" value="<%=saving%>"><br/>
   <input type="submit" value="Calculate">
   <INPUT type="button" value="Close Window" onClick="window.close()">
</form>
</p>

<p>The result from the last calculation: The total investment at end age is
<b><%=result%></b></p>

<p><i>Past results</i><br/>
<%
int entries = cal.getStarts().size();
%>
<table>
<tr>
    <td>Start Age</td>
    <td>Edn Age</td>
    <td>Annual Growth rate</td>
    <td>Monthly savings</td>
    <td><b>Total investment</b></td>
</tr>

<%
for (int i = 0; i < entries; i++) {
%>

<tr>
    <td><%=cal.getStarts().get(i)%></td>
    <td><%=cal.getEnds().get(i)%></td>
    <td><%=nf.format(cal.getGrowthrates().get(i))%></td>
    <td><%=nf.format(cal.getSavings().get(i))%></td>
    <td><%=nf.format(cal.getResults().get(i))%></td>
</tr>

<%
}
%>
</table></p>

</body></html>

The JSP file takes the input and calculates the result. Apart from that, it shows all the previous results calculated. Thus it takes the advantage of statefulness of the Bean. That brings us to the end of this discussion. The next time I take up this topic I will discuss the basics of the Entity Bean and the process of deploying Beans in JBoss. Till then...

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