Jsp-Intro.Pdf

Java Server Pages (JSP)

What is JSP

JSP simply puts Java inside HTML pages. You can take any existing HTML page and change its extension to ".jsp" instead of ".html". Scripting elements are used to provide dynamic pages

JSP and Servlets

Each JSP page is turned into a Java servlet, compiled and loaded. This compilation happens on the first request. After the first request, the file doesn't take long to load anymore. Every time you change the JSP file, it will be re-compiled again.

Java Server Page translator Java servlet source code compiler Java Servlet class file

Generated servlets

You can examine the source code produced by the JSP translation process. There is a directory called generated in Sun Java J2EE Application Server where you can find the source code. Note that the _jspService method corresponds to the servlet service method (which is called by doGet or doPost)

JSP elements (overview)

Directives of the form Scripting elements

Expressions of the form Scriptlets of the form Declarations of the form JSP Comments

Standard actions

Example: ...

Implicit variables like request, response, out

JSP Directives

They have the form

page include taglib

Specify page properties Include a file at translation time Specify custom tags

JSP Directive Examples

Import java packages

Multiple import statements

Including file at translation time

For include the path is relative to the JSP file

JSP Scripting Elements: Expressions

For an expression scripting element like , expr is evaluated and the result is converted to a string and placed into the JSP's servlet output stream. In a Java servlet this would be equivalent to

PrintWriter out = response.getWriter(); ... out.print(expr);

JSP Expression Examples

Displaying request parameters (request is an implicit object available in a JSP)

Your name is and your age is

Doing calculations

The value of pi is and the square root of two is and today's date...