How do I Unit Test a servlet?

Question

I have a servlet called Calculator. It reads the parameters left, right and op and returns by setting an attribute result in the response.

What is the easiest way to unit test this: basically I want to create an HttpServletRequest, set the parameters, and then checking the response - but how do I do that?

Here's the servlet code (it's small and silly on purpose):

public class Calculator extends javax.servlet.http.HttpServlet implements javax.servlet.Servlet {
public Calculator() {
    super();
}       
protected void doGet(HttpServletRequest request, HttpServletResponse response) 
    throws ServletException, IOException {
}   
protected void doPost(HttpServletRequest request, HttpServletResponse response) 
    throws ServletException, IOException {
    Integer left = Integer.valueOf(request.getParameter("left"));
    Integer right = Integer.valueOf(request.getParameter("right"));
    Integer result = 0;
    String op = request.getParameter("operator");
    if ("add".equals(op)) result = this.opAdd(left, right);
    if ("subtract".equals(op)) result = this.opSub(left, right);
    if ("multiply".equals(op)) result = this.opMul(left, right);
    if ("power".equals(op)) result = this.opPow(left, right);
    if ("divide".equals(op)) result = this.opDiv(left, right);
    if ("modulo".equals(op)) result = this.opMod(left, right);

    request.setAttribute("result", result); // It'll be available as ${sum}.
    request.getRequestDispatcher("index.jsp").forward(request, response);
    }
}
...

}

Answer 1

Often, the important logic of a program is factored out into other classes, that are usable in a variety of contexts, instead of being tightly coupled to a Servlet Engine. This leaves the servlet itself as a simple adapter between the web and your application.

This makes the program easier to test, and easier to reuse in other contexts like a desktop or mobile app.