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Servlet

A Java Servlet is a class that extends javax.servlet.http.HttpServlet.

public class HelloWorldServlet extends HttpServlet {
  @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    String name = req.getParameter("nm");
    String outputText = "Hello " + name;
    PrintWriter pw = resp.getWriter();
    // HTML text added to response
    pw.println("<html>");
    pw.println("<head><title>Hello World</title></head>");
    pw.println(" <body>" + outputText + "</body>");
    pw.println("</html>");
    pw.close();
  }

  @Override
  protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    // Handle POST same as GET
    doGet(req, resp);
  }
}

Drill

JavaWebIntro

Run this project on Eclipse's Tomcat server by right-clicking the project and selecting Run As->Run on Server.

The HelloWorldServlet class has two methods for handling requests.

  • doGet(HttpServletRequest req, HttpServletResponse resp) to handle GET requests
  • doPost(HttpServletRequest req, HttpServletResponse resp) to handle POST requests

The Web Container maps a request to either method depending on the type of request.

GET mapped to doGet

HttpServletRequest and HttpServletResponse

Whether the request is a GET or POST, the Web Container creates objects that represent the request and response.

  • HttpServletRequest represents the request and contains any data passed from the user.

  • HttpServletResponse is created for returning content to the user.

HttpServletRequest and Response

This object creation happens on every request from browser to server. * If we make a new request with data, new objects are created, and the HttpServletRequest contains the data.

HttpServletRequest and Response with data

Practice Exercise

The contract between classes like HttpServlet and the Web Container is defined by the Java Servlet Specification.

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