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 Tag etc.
Advantage of JSP over Servlet
There are many advantages of JSP over servlet. They are as follows:
1) Extension to Servlet
JSP technology is the extension to 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.
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 a lot of tags such as action tags, jstl, custom tags etc. that reduces the code. Moreover, we can use EL, implicit objects etc.
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, 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 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.
Let's see the simple example of JSP, here 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:
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.
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.