JSP and Servlets

Based on udemy course


Basic concept

JSP: similar to html page, with some Java code. It’s processed on the server, results of Java code included in HTML returned to browser

  • jsp expression<%= new java.util.Date() %>
    • Obj, <%= new String(“hello”).toUpperCase() %>
    • number, <%= 25*4 %>
    • boolean, <%= 5>6 %>
  • jsp scriptlet <% some Java %> out.println() to print. Minimisze the use here.
  • jsp declaration <%! variable or method declaration%>
    <% String lower(String data){
      return data.toLowerCase();
  • call Java class from JSP
<%@ page import="com.hello" %>

  • include files
<jsp:include page="header.html"/>
  • form/radio/checkbox action:response.jsp, this is where we response the input form. Use ${param.firstName} in response page to output/match the input name in form.

Session object

created once for user’s browser session, unique for this user. Keep track of user’s actions.

  • add data to session object
List<String> items = new ArrayList<>();
session.SetAttribute("myTodoList", items);
List<String> myStuff = (List<String>) session.getAttribute("myTodoList);

  • commonly used: isNew, getID, invalidate, setMaxInactiveInterval(long mills)

  • cookies

    1. form, submit name favoriteLanguage
    2. response.jsp, String favL = request.getParameter("favoriteLanguage")
    3. Cookie theCookie = new Cookie("myapp.ck", favL) theCookie.setMaxAge
    4. response.addCookie(theCookie) Notice this step, send cookie to browser, with response.
    5. homepage, Cookie[] cookies = resquest.getCookies();
    6. for loop, tempCk.getName().equals("myapp.ck"), get tempCk.getValue()

JSTL, jsp standard tag library

  • Choose
<c:choose>, <c:when test=>,<c:otherwise>
  • if
<c:if test="${not tempStudent.goldCustomer}">
  • forEach/forTokens
<c:forEach var="tempStu" items="${myStudnets}">
${ tempStu.firstName }
  • function
<c:set var="data" value="haha" />
Length of ${data}: ${fn: length(data)}
  • I18N/Formatting



  • Java class that processed on the server
  • Java class generates HTML that is returned to browser
  • can read HTML form data, use cookies and sessions etc.
  • At a high level, simialr to JSPs
public class HelloWorldServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
     * @see HttpServlet#HttpServlet()
    public HelloWorldServlet() {
        // TODO Auto-generated constructor stub

	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

		// Step 1: set the content type
		// Step 2: get the printwriter
		PrintWriter out = response.getWriter();
		// Step 3: generate HTML content
		out.println("<h2>Hello World</h2>");
		out.println("Time on the server is: " + new java.util.Date());
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);


  • form action=“StudentServlet”, method=“GET”. doGet method then use request.getParameter(“firstName”) to get the form data.
  • in doGet, response.setContentType("text/html")
  • PrintWriter out = response.getWriter.getWriter()
  • out.println("<html><body>")

Get/Post difference

  • GET: url?field=1?… good for debug, bookmark/email. limitation on data length.
  • Post: won’t see in url. No limitations on data length. can send binary data.

Servlet with JSP

Servlet can call JSP using a request dispatcher

  • RequestDispatcher dispatcher = request.getRequestDispatcher("/view_student.jsp");
  • Forward to JSP
  • dispatcher.forward(request, response);

Sending data to JSP


tomcat config

  • Define connection pool in context.xml
  • in java world, see Datasource, think of connection pool.
  • maxIdle=“5”, no user in our system, at least 5 connections available
  • maxWait=“10000”, waiting 10 seconds.


  • resource injection with Servlets