Splitting a servlet file into multiple files

Question

I am currently building a Budget Estimator web application using JSP, Servlets and Apache POI.

I have a servlet file which accepts form inputs from a user and writes budget estimate values into an Excel File based on these inputs after performing some computations. There are 4 different budget categories. I'll be referring to them as A,B,C,D for convenience. The application generates an Excel File which comprises of: 1) Budget summary sheet 2) Separate sheet for each of the 4 categories

Currently, the budget computation code for all these categories is in a single servlet file. I want to split the computation part for these 4 categories into separate servlet files. I want to allow the user to track how much budget is allocated for each category. I am planning to implement this as follows: A button will be placed at the end of each category. When the user clicks that button, a servlet should be called which will perform the budget computations and return the budget estimate for that category which should be displayed on the same webpage (maybe within a text field). Same for categories B,C and D. Eventually, if the user is satisfied with the allocations, he can generate an excel report by clicking on a "Generate report" button. Clicking this button will call the main servlet file will in turn will call 5 different servlets that generate the 5 sheets of the Excel file. The final excel would be generated by binding these 5 sheets together and returned to the user through the main servlet file.

I need advice on how to go about this and efficient ways to accomplish this. Any help is appreciated! Thanks in advance!

Answer 1

You still can do it in 1 servlet, pass a parameter say calculate with the request to determine which process you want to do, then call the appropriate method in the servlet, all calculations method should be in a separate class BudgetCalculation , that you instantiate and use in the servlet

find below a suggestion:

public class BudgetCalculation {

    public String calculateA(...some params...){

        return result;
    }

    public String calculateB(...some params...){

        return result;
    }

    public String calculateC(...some params...){

        return result;
    }

    public String calculateD(...some params...){

        return result;
    }
}

assume you have a library that generates Excel sheets, ExcelUtil

public class MyServlet extends HttpServlet {

    public void doGet(...request,....){ // this can also be doPost(), use the one your current solution works with
        BudgetCalculation budgetCalculation = new BudgetCalculation();

        if(request.getParameter("calculate").equals("a")){
            return budgetCalculation.calculateA(...params...);
        }else if(request.getParameter("calculate").equals("b")){
            return budgetCalculation.calculateB(...params...);
        }else if(request.getParameter("calculate").equals("c")){
            return budgetCalculation.calculateC(...params...);
        }else if(request.getParameter("calculate").equals("d")){
            return budgetCalculation.calculateD(...params...);
        }else if(request.getParameter("calculate").equals("all")){
            ExcelUtil excelUtil = new ExcelUtil();
            excelUtil.createExcelFile(..params...);
            return ExcelFileUrl;
        }
    }
}

now send a, b, c, d or all with each button click as a value for parameter calculate

Answer 2

As others have already pointed out, you should use a class to perform this operation but if you are really looking to call multiple servlts in a sequence, you can use a RequestDispatcher which works by mapping urls to servlet requests (as suggested by BalusC here):

public class Test_ALL extends HttpServlet {
  public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
     response.setContentType("text/plain");
     request.getRequestDispatcher("/Servlet1").include(request, response);
     request.getRequestDispatcher("/Servlet2").include(request, response);
     .....

  }
}