Creating the Servlet

The servlet is the final Java class that you need to create for this tutorial. The servlet interprets the incoming POST and GET requests, and dispatches them to the correct interface method. The servlet also binds the output BookBean into the request, and forwards that request to the JSP for response.

Create a new Java class as before. Put it in the com.microfocus.book package, and give it the name BookServlet.
Overwrite the skeleton contents of the file with the BookServlet.java file that you downloaded previously (the file is stored in C:\myfiles\COBOL_JSP_DEMO_2_2_SRC\JSPBookDemo\src\com\microfocus\book).
Click File > Save.

Comments

As before, the sample code contains some important concepts, which are explained here. There are four significant parts to the servlet class.

The interpretation of the POST parameters

The doProcessing method includes the following code

    String subValue = req.getParameter(SUBMIT_PARAMETER);

    ...
      
    if(subValue.equals(READ_PARAMETER))
    {
      performRead(req, res);
    }
    else if(subValue.equals(ADD_PARAMETER))
    {
      performAdd(req, res);
    }
    else if(subValue.equals(DELETE_PARAMETER))
    {
      performDelete(req, res);
    }

This code interprets the value of the submit parameter from the request object, and invokes the appropriate method in the application for each known request. An example of one of the methods is performRead, and is explained next.

The resulting calls into BookInterface

The performRead method contains the following code:

    BookInterface bookInterface = getBookInterface(req.getSession());
    String bookId = getStockNo(req, res);
    
    try
    {
      BookBean book = bookInterface.readBook(bookId);
      
      outputBook(req, res, book);
    }
    catch(JavaBookException e)
    {
      outputBookException(req, res, e);
    }
    catch (Exception e)
    {
      outputException(req, res, e);
    }

This code defines a BookInterface class by passing the session object from the request object to the constructor of BookInterface.java. Then it gets the stock number from the request parameters, and makes a call to readBook on the interface. Finally, it registers the BookBean object with the JSP by calling outputBook.

Binding an output BookBean into the request attributes

The outputBook method includes the following code:

private void outputBook(HttpServletRequest req, HttpServletResponse res,
      BookBean book)
    if(book != null)
    {
          req.setAttribute("book", book);
    }
    else
    {
          req.setAttribute("book", BookBean.msgBook("ERROR! book is null in output book"));
    }

This method binds the book as a request attribute to our JSP view, namely BookJsp.jsp. The JSP unpacks this book object and outputs its values.

Forwarding the request onto the JSP so it can create the response

The doProcessing method also contains the following code:

    RequestDispatcher dispatcher = getServletContext().getRequestDispatcher(VIEW_URL);
    try
    {
      dispatcher.forward(req, res);
    }
    catch(Exception e)
    {
      throw new RuntimeException(e);
    }

This method gets a dispatch object for the JSP view, and then forwards the request to it. With all the necessary attributes set up, the JSP view can output the book record correctly.