Java Servlets
What Are Servlets?
What Do They Do?
Who Uses Servlets?
History
Servlets vs. CGI
Servlets vs. CGI
What Servlets Need
Java Server Web Development Kit
Servlet capable server
Apache
Other servers are available
Java Server Pages
<head>
</head>
<body>
<%
// jsp sample code
out.println(" JSP, ASP, CF, PHP - you name it, we support it!");
%>
</body>
</html>
Servlet Code
package servlet_tutorials.PhoneBook;�import javax.servlet.*;�import javax.servlet.http.*;�import java.io.*;�import java.util.*; �import java.sql.*; �import java.net.*;��public class SearchPhoneBookServlet extends HttpServlet { ��public void doGet(HttpServletRequest req, HttpServletResponse res) �throws ServletException, IOException { ��String query = null; �String where = null; �String firstname = null; �String lastname = null; �ResultSet rs = null;��res.setContentType("text/html"); �PrintWriter out = res.getWriter();��// check which if any fields in the submitted form are empty �if (req.getParameter("FirstName").length() > 0) �firstname = req.getParameter("FirstName"); �else firstname = null;�} �
Life Cycle
Servlet Class Loading
Servlet instance creation
Init method invoking
Service method invoking
Service - Request
Destroy
Client Interaction
Client
Server
Servlets
Saving State
Servlet Communication
Calling Servlets
Request Attributes and Resources
Multithreading
import java.io.*; �import javax.servlet.*; �import javax.servlet.http.*;
Simple Counter Example
MultiThread Problems
count++; // by thread1
count++; // by thread2
out.println.. // by thread1
out.println.. // by thread2
Two Requests will
get the same
value of counter
Better Approach
PrintWriter out = res.getWriter(); �synchronized(this) �{� count++; � out.println("This servlet has been accessed " + � count + "times since loading");�}�This reduces the amount of time the servlet spends in its synchronized block, and still maintains a consistent count.
Example: On-line Phone Book
Example: On-line Phone Book
Search Form
<html>�<head> �<title>Search Phonebook</title> �</head> �<body bgcolor="#FFFFFF"> <p><b>�Search Company Phone Book</b></p> �<form name="form1" method="get" action="servlet/servlet_tutorials.PhoneBook.SearchPhoneBookServlet"> �<table border="0" cellspacing="0" cellpadding="6"> <tr> <td >Search by</td> <td>�</td> </tr> <tr> <td><b>�First Name �</b></td> <td> �<input type="text" name="FirstName"> AND/OR</td> </tr> <tr> <td ><b>�Last Name�</b></td> <td >�<input type="text" name="LastName"></td> </tr> <tr> <td ></td> <td >�<input type="submit" name="Submit" value="Submit">�</td> </tr> </table>�</form>�</body>�</html>
Java server Page
Search_phone_book.jsp
Example: On-line Phone Book
Display Results
<html>�<%@page import ="java.sql.*" %>�<jsp:useBean id="phone" class="servlet_tutorials.PhoneBook.PhoneBookBean"/> �<%@ page buffer=35 %>�<%@ page errorPage="error.jsp" %>�<html>�<head>�<title>Phone Book Search Results</title>�<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> </head>�<body bgcolor="#FFFFFF"> <b>Search Results</b> <p> �<% String q = request.getParameter("query"); �ResultSet rs = phone.getResultSet(q); �%>�<% if (rs.wasNull()) { �%> �"NO RESULTS FOUND" �<% �} else �%>�<table> <tr> <td> <div align="center">First Name</b></div> </td> <td> <div align="center">Last Name</font></b></div> </td> <td> <div align="center">Phone Number</font></b></div> </td> <td> <div align="center">Email</font></b></div> </td> </tr>��<% while(rs.next()) { %> <tr> <td>�<%= rs.getString("first_name") %></td> <td><%= rs.getString("last_name") %></td> <td><%= rs.getString("phone_number") %>�</td> <td>�<%= rs.getString("e_mail") %>�</td> </tr> �<% } %> �</table>
Java Server Page
Display_search_results.jsp
Servlet
Java Bean & Database linked
Java Server Page -JSP
JSP technology is used to create web application just like Servlet technology. It can be thought of as an extension to Servlet because it provides more functionality than servlet such as expression language, JSTL-(Java Standard Tag Library), etc.
A JSP page consists of HTML tags and JSP tags. The JSP pages are easier to maintain than Servlet because we can separate designing and development. It provides some additional features such as Expression Language, Custom Tags, etc.
Advantages of JSP over Servlet
1) Extension to Servlet
JSP technology is the extension to Servlet technology. We can use all the features of the Servlet in JSP. In addition to, we can use implicit objects, predefined tags, expression language and Custom tags in JSP, that makes JSP development easy.
2) Easy to maintain
JSP can be easily managed because we can easily separate our business logic with presentation logic. In Servlet technology, we mix our business logic with the presentation logic.
3) Fast Development: No need to recompile and redeploy
If JSP page is modified, we don't need to recompile and redeploy the project. The Servlet code needs to be updated and recompiled if we have to change the look and feel of the application.
4) Less code than Servlet
In JSP, we can use many tags such as action tags, JSTL, custom tags, etc. that reduces the code. Moreover, we can use EL, implicit objects, etc.
The Lifecycle of a JSP Page
The JSP pages follow these phases:
Note: jspInit(), _jspService() and jspDestroy() are the life cycle methods of JSP.
JSP page is translated into Servlet by the help of JSP translator. The JSP translator is a part of the web server which is responsible for translating the JSP page into Servlet. After that, Servlet page is compiled by the compiler and gets converted into the class file. Moreover, all the processes that happen in Servlet are performed on JSP later like initialization, committing response to the browser and destroy.
Creating a simple JSP Page
To create the first JSP page, write some HTML code as given below, and save it by .jsp extension. We have saved this file as index.jsp. Put it in a folder and paste the folder in the web-apps directory in apache tomcat to run the JSP page.
index.jsp
Let's see the simple example of JSP where we are using the scriptlet tag to put Java code in the JSP page. We will learn scriptlet tag later.
It will print 10 on the browser.
How to run a simple JSP Page?
Follow the following steps to execute this JSP page:
Do I need to follow the directory structure to run a simple JSP?
No, there is no need of directory structure if you don't have class files or TLD files. For example, put JSP files in a folder directly and deploy that folder. It will be running fine. However, if you are using Bean class, Servlet or TLD file, the directory structure is required.
The Directory structure of JSP
The directory structure of JSP page is same as Servlet. We contain the JSP page outside the WEB-INF folder or in any directory.