JSP technology is used to create web application just like Servlet technology. It can be thought of as an extension to the servlet because it provides more functionality than servlet.
A JSP page contains HTML code 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 Tag etc.
Advantage of JSP over Servlet
There are many advantages of JSP over servlet. These are as follows:
- JSP is the extension to the servlet technology. We can use all the features of 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.
- JSP can be easily managed because we can easily separate our business logic with presentation logic. In servet, we mix our business logic with the presentation logic.
- If JSP page is modified, we don’t need to redeploy the project. The servlet code needs to be updated and recompiled if we have to change the look and feel of the application.
Life cycle of a JSP Page
The JSP pages follows these phases:
- Translation of JSP Page
- Compilation of JSP Page
- Classloading (class file is loaded by the classloader)
- Instantiation (Object of the Generated Servlet is created).
- Initialization ( jspInit() method is invoked by the container).
- Reqeust processing ( _jspService() method is invoked by the container).
- Destroy ( jspDestroy() method is invoked by the container).
Note: jspInit(), _jspService() and jspDestroy() are the life cycle methods of JSP.
As depicted in the above diagram, JSP page is translated into servlet by the help of JSP translator. The JSP translator is a part of webserver that is responsible to translate the JSP page into servlet. Afterthat Servlet page is compiled by the compiler and gets converted into the class file. Moreover, all the processes that happens in servlet is performed on JSP later like initialization, commiting 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 extention. We have save 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.
<html> <body> <% out.print(2*5); %> </body> </html>
It will print 10 on the browser.
How to run a simple JSP Page ?
Follow the following steps to execute this JSP page:
- Start the server
- put the jsp file in a folder and deploy on the server
- visit the browser by the url http://localhost:portno/contextRoot/jspfile e.g. http://localhost:8888/myapplication/index.jsp
Do I need to follow 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.But if you are using bean class, Servlet or tld file then directory structure is required.
Directory structure of JSP
The directory structure of JSP page is same as servlet. We contains the jsp page outside the WEB-INF folder or in any directory.