What is JSP. How to create one JSP application in Eclipse

JSP - Java Server Pages Technology

Java Server Pages (JSP) technology allows you to easily create web content that has both static and dynamic components. JSP technology makes available all the dynamic capabilities of Java Servlet technology but provides a more natural approach to creating static content.

The main features of JSP technology are as follows:

· A language for developing JSP pages, which are text-based documents that describe how to process a request and construct a response

· An expression language for accessing server-side objects

· Mechanisms for defining extensions to the JSP language

JSP technology also contains an API that is used by developers of web containers. Using this technology developer can design UI for client (browser) as well as business logic for communicating server. A JSP file contains HTML, JavaScript, CSS & Java codes.

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, 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

There are many advantages of JSP over the Servlet. They are as follows:

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, which 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.

5) The Lifecycle of a JSP Page

The JSP pages follow these phases:

Translation of JSP Page
Compilation of JSP Page
Class loading (the classloader loads class file)
Instantiation (Object of the Generated Servlet is created).
Initialization (the container invokes jspInit() method).
Request processing (the container invokes _jspService() method).
Destroy (the container invokes jspDestroy() method).

Here jspInit(),_jspService(), and jspDestroy are the 3 life cycle methods of JSP.

Unlike other java files, user no need to compile a JSP files. Once it deployed in web server, JSP container compiles the JSP files and create equivalent _java files and its class files.

Every JSP container having one JSP translator. 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.

6) A Simple JSP Page Example

Localized Date Form

The JSP page, index.jsp, appears below; it is a typical mixture of static HTML markup and JSP elements. If you have developed web pages, you are probably familiar with the HTML document structure statements (<head>, <body>, and so on) and the HTML statements that create a form (<form>) and a menu (<select>).

The lines in bold in the example code contain the following types of JSP constructs:

· A page directive (<%@page ... %>) sets the content type returned by the page.

· Tag library directives (<%@taglib ... %>) import custom tag libraries.

· jsp:useBean is a standard element that creates an object containing a collection of locales and initializes an identifier that points to that object.

· JSP expression language expressions (${ }) retrieve the value of object properties. The values are used to set custom tag attribute values and create dynamic content.

· Custom tags set a variable (c:set), iterate over a collection of locale names (c:forEach), and conditionally insert HTML text into the response (c:if, c:choose, c:when, c:otherwise).

· jsp:setProperty is another standard element that sets the value of an object property.

· A function (f:equals) tests the equality of an attribute and the current item of a collection. (A built-in == operator is usually used to test equality.)

Here is the example of JSP page:

<%@ page contentType="text/html; charset=UTF-8" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ taglib uri="/functions" prefix="f" %>

<jsp:useBean id="locales" scope="application" class="mypkg.MyLocales"/>

<html>
<head>
               <title>Localized Dates</title>
</head>
<body bgcolor="white">

               <form name="localeForm" action="index.jsp" method="post">
               <c:set var="selectedLocaleString" value="${param.locale}" />
               <c:set var="selectedFlag" value="${!empty selectedLocaleString}" />
               <b>Locale:</b>
               <select name=locale>
               <c:forEach var="localeString" items="${locales.localeNames}" >
               <c:choose>
               <c:when test="${selectedFlag}">
                               <c:choose>
        <c:when
                 test="${f:equals(selectedLocaleString, localeString)}" >
                <option selected>${localeString}</option>
            </c:when>
            <c:otherwise>
                <option>${localeString}</option>
            </c:otherwise>
        </c:choose>
    </c:when>
    <c:otherwise>
        <option>${localeString}</option>
    </c:otherwise>
</c:choose>
</c:forEach>
</select>
<input type="submit" name="Submit" value="Get Date">
</form>
<c:if test="${selectedFlag}" >
    <jsp:setProperty name="locales"
        property="selectedLocaleString"
        value="${selectedLocaleString}" />
    <jsp:useBean id="date" class="mypkg.MyDate"/>
    <jsp:setProperty name="date" property="locale"
        value="${locales.selectedLocale}"/>
    <b>Date: </b>${date.date}</c:if>
</body>
</html>

Process To deploy the MyFirstWeb application with Eclipse IDE :-

1) Open Eclipse à File menu à New à Dynamic Web Project

à Type the project name as “MyFirstWeb”

à Click on Next

à Click on Next à tick on web.xml and click on Finish.

2) Now open your project (double click on your project name)

à Right click on WebApp

àtype the file name as index.jsp and click on Finish

à Now your index.jsp file is open à type the souce code in file editor area and save

<%@ page language="java" contentType="text/html; charset=ISO-8859-1" pageEncoding="ISO-8859-1"%>

<html>
<head>
<title>My First Web Page</title>
</head>
<body bgcolor="white">

       <form name="page1" action="display.jsp" method="post">
       <table>
              <tr>
                     <td>Enter Your First Name :</td>
                     <td><input type="text" name="txtFirstName" value=""></td>
              </tr>
              <tr>
                     <td>Enter Your Second Name :</td>
                     <td><input type="text" name="txtSecondName" value=""></td>
              </tr>
       </table>

       <input type="submit" name="btnSubmit" value="Nex Page">
       </form>

</body>

</html>

à Using above process create another jsp file “display.jsp”.

àtype the file name as display.jsp and click on Finish

à open display.jsp, write the below code and save it.

<%@ page language="java" contentType="text/html; charset=ISO-8859-1" pageEncoding="ISO-8859-1"%>

<%
String sFirstName = "";
String sSecondName = "";

try{
       if(request.getParameter("txtFirstName")!=null){
              sFirstName = request.getParameter("txtFirstName");
       }
       if(request.getParameter("txtSecondName")!=null){
              sSecondName = request.getParameter("txtSecondName");
       }
}catch(Exception e){
       e.printStackTrace();
}

%>
<html>
<head>
<title>My Second Web Page</title>
</head>
<body bgcolor="white">

       <form name="page2" action="index.jsp" method="post">
              <table>
                     <tr>
                           <td>Your First Name :</td>
                           <td><%=sFirstName%></td>
                     </tr>
                     <tr>
                           <td>Your Second Name :</td>
                           <td><%=sSecondName%></td>
                     </tr>
              </table>

              <input type="submit" name="btnSubmit" value="Back Page">
       </form>

</body>
</html>