The Problem with Servlets

In many Java servlet-based applications, processing the request and generating the response are both handled by a single servlet class. Example 3-1 shows how a servlet class often looks.

Example 3-1. A typical servlet class
public class OrderServlet extends HttpServlet {
    public void doGet((HttpServletRequest request, 
        HttpServletResponse response)
        throws ServletException, IOException  {
  
        response.setContentType("text/html");
        PrintWriter out = response.getWriter(  );
        
        if (isOrderInfoValid(request)) {
            saveOrderInfo(request);
            out.println("<html>");
            out.println("  <head>");
            out.println("    <title>Order Confirmation</title>");
            out.println("  </head>");
            out.println("  <body>");
            out.println("    <h1>Order Confirmation</h1>");
            renderOrderInfo(request);
            out.println("  </body>");
            out.println("</html>");
       }
 ...

If you’re not a programmer, don’t worry about all the details in this code. The point is that the servlet contains request processing and business logic (implemented by methods such as isOrderInfoValid() and saveOrderInfo( )), and also generates the response HTML code, embedded directly in the servlet code using println( ) calls. A more structured servlet application isolates different pieces of the processing in various reusable utility classes and may also use a separate class library for generating the actual HTML elements in the response. Even so, the pure servlet-based approach still has a few problems:

  • Thorough Java programming knowledge is needed to develop and maintain ...

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