Filtering Java Server Pages (JSPs)

We can also put filter chains in front of JSPs.

Create a calculator JSP:

Here's the JSP:

<%!
    private double calcAmount(int age, double income, int years)           throws ServletException {
       if (age < 0 || income < 0 || years < 0) {
           throw new ServletException("inputs must be > 0");
       }
        double result = 1500.0;
        if (age < 65) {
            result = 0;
        } else if (age < 75) {
            result *= (age- 65)/10.0;
        }

        if (50000 < income) {
            result = 0;
        } else if (20000 < income) {
            result *= (50000 - income)/30000;
        }

        if (years < 10) {
            result = 0;
        } else if (years < 20) {
            result *= (years - 10)/10.0;
        }

        return result;
    }
%>
<html>
<head>
    <title>calculator</title>
</head>
<body>

      <%
        int age = new Integer(request.getParameter("age"));
        double income = new Double(request.getParameter("income"));
        int years = new Integer(request.getParameter("years"));
        double stipend = calcAmount(age, income, years);
       %>
      You could qualify for $<%=stipend%>/month!!!
</body>
</html>

We must make some changes. We must change the action of the form:

action = "servlet.jsp"

We must also add the following mappings to web.xml:

   <filter-mapping>
        <filter-name>AgeFilter</filter-name>
        <url-pattern>calculator.jsp</url-pattern>
    </filter-mapping>
    <filter-mapping>
        <filter-name>IncomeFilter</filter-name>
        <url-pattern>calculator.jsp</url-pattern>
    </filter-mapping>