Filtering the Rich

We repeat the above steps to create an income filter.

In step three of the filter wizard we specify the maximum income:

Here's the implementation of doFilter:

    public void doFilter(
      ServletRequest request,
      ServletResponse response,
      FilterChain chain) throws IOException, ServletException {

        double income = new Double(request.getParameter("income"));
        double maxIncome =
            new Double(_filterConfig.getInitParameter("maxIncome"));

        if (maxIncome < income) {
            PrintWriter out = response.getWriter();
            out.println("<html>");
            out.println("<head><title>Calculator</title></head>");
            out.println("<body>");
            out.println(
               "sorry, your income must be <= $50,000/year.");
            out.println("</body></html>");
            out.close();
            return;
        }
        chain.doFilter(request, response);
    }

Note that this time instead of hard wiring the maximum income into the servlet, it is stored in the filter configuration, which is initialized in the filter's init method:

    public void init(FilterConfig filterConfig)
      throws ServletException {
        _filterConfig = filterConfig;
    }

Let's take a look at the beginning of the web.xml file. This is used by the servlet container to initialize the web application:

<web-app ...>
    <description>
      Empty web.xml file for Web Application
   </description>
    <filter>
        <filter-name>AgeFilter</filter-name>
        <filter-class>stipcalc.AgeFilter</filter-class>
    </filter>
    <filter>
        <filter-name>IncomeFilter</filter-name>
        <filter-class>stipcalc.IncomeFilter</filter-class>
        <init-param>
            <param-name>maxIncome</param-name>
            <param-value>50000</param-value>
        </init-param>
    </filter>
    <filter-mapping>
        <filter-name>AgeFilter</filter-name>
        <url-pattern>/calculator</url-pattern>
    </filter-mapping>
    <filter-mapping>
        <filter-name>IncomeFilter</filter-name>
        <url-pattern>/calculator</url-pattern>
    </filter-mapping>
    <servlet>
        <servlet-name>Calculator</servlet-name>
        <servlet-class>stipcalc.Calculator</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>Calculator</servlet-name>
        <url-pattern>/calculator</url-pattern>
    </servlet-mapping>
   ...
</web-app>

Note the filter element for IncomeFilter is where the initial value of maxIncome is stored.

Note also that requests for the /caclulator URL are mapped to the age filter first, then the income filter.

Here's a sample request:

And here's the short circuit response: