This tutorial is an example of using Servlets.
It is about registering cars to a Car-park and let the
servlet response to the client with a list of all registered cars
each time a new car is registered.
We are not using any persistent storage in this example so
all registered cars
will be stored in a Vector which is stored in the user session object.
Therefore, when the session is ended all data is gone. A similar Servlet
application with use of persistent storage can be found in the
Servlet Examples.
It is recommended that you study all the subjects that are under
Java Servlets menu.
If you just want to look through the solution of this tutorial you can download it
here
When the user Submit this form our CarparkServlet, which we will create in the back-end part, come in action and
handle this POST request which will contain the parameters: regNo, cartype, model and dayPrice.
For each new registered car, we want to have a car object that we add to a dynamic Vector on the session object, which exist in the servlet.
Creating the Back-end.
Create data transporter and controller.
To collect data for each registration we need a java class
which we can use to create new objects for each car registration.
This is all the member variables of a Car object, but we need get/set accessors for all the member variables.
Place the cursor after the last member variable and inside the class
and right click to get the menu for inserting get/set accessors
for all the member variables.
Select Insert code... from the menu and then Getter and Setter ... from the
new menu.
Select all fields and click the Generate button. You should now have
get/set accessors for all the member variables in the class.
We like to have an object that contain all the registered cars
, with some kind of functionality and can be stored as an object
on the Http Session object.
private Vector<Car> cars;
public CarPark() {
cars= new Vector<Car>();
}
public Vector<Car> getCars() {
return cars;
}
public void addCar(Car car) {
cars.add(car);
}
Right click inside the class and select Fix Imports
The car's Vector variable member is meant to hold all registered cars.
The addCar() method is to add new car to the Vector, cars, and the getCars()
method will return the Vector of all cars.
We have now the tools to hold the data and then we need the Servlet
to control flow of data and in this case handling the
presentation of registered cars.
With help from Netbeans we have now created a Servlet that have a doGet() method
and a doPost() method, which both call the processRequest() method.
In this way, we have a common handling for both GET and POST type requests.
It is now for us to put some code inside the try braces in the processRequest() method.
You must now replace the existing code in the method, processRequest(), using the code below.:
// get the session object// if not exists - create one
HttpSession session = request.getSession();
// get the carPark object from the session object
CarPark carPark = (CarPark) session.getAttribute("carPark");
// if no carPark object exists on the session object - create oneif (carPark == null) {
carPark = new CarPark();
session.setAttribute("carPark", carPark);
}
// Test for any request parameters
Enumeration enumr = request.getParameterNames();
if (enumr.hasMoreElements()) {
// Register a new car only if the regNo have a valueif (!request.getParameter("regNo").equals("")) {
Car car = new Car();
car.setRegNo(request.getParameter("regNo"));
car.setCartype(request.getParameter("cartype"));
car.setModel(Integer.parseInt(request.getParameter("model")));
car.setDayPrice(Double.parseDouble(request.getParameter("dayPrice")));
carPark.addCar(car); // add a car to the carPark object
}
}
// get all the cars that are regitered
Vector<Car> cars = carPark.getCars();
// print out to the response a table header for all cars
out.println("<html><body>");
out.println(" <h2>Registered Cars</h2>");
out.println(" <table border=\"1px\" >");
out.println(" <tr>");
out.println(" <td align=\"left\" style=\"width:120px\" >RegNo:</td>");
out.println(" <td align=\"left\" style=\"width:120px\">Cartype:</td>");
out.println(" <td align=\"left\" style=\"width:120px\">Model:</td>");
out.println(" <td align=\"left\" style=\"width:120px\">DayPrice:</td>");
out.println(" </tr>");
// If any car regitered - get each car and print out to the response// a table row for each carif (!cars.isEmpty()) {
for (int i = 0; i < cars.size(); i++) {
Car car = (Car) cars.get(i);
out.println(" <tr>");
out.println(" <td align=\"left\">" + car.getRegNo() + "</td>");
out.println(" <td align=\"left\">" + car.getCartype() + "</td>");
out.println(" <td align=\"left\">" +
String.valueOf(car.getModel()) + "</td>");
out.println(" <td align=\"left\">" +
String.valueOf(car.getDayPrice()) + "</td>");
out.println(" </tr>");
}
}
out.println(" </table>");
out.println(" <p><a href=\"/Servlet01/RegCars.html\">Return" +
"</a> car registration</p>");
out.println("</body></html>");
Right click inside the class, CarParkServlet, and select Fix Imports.
For more understanding please read the comments in this code.
Configuration.
The last thing to do is to change the welcome file name so
open the web.xml file in the Configuration folder of the project, select Pages, and then change the Welcome File(s) to be RegCars.html.
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