List of JSP elements and their
default values
JSP tag type
Description
Tag syntax
Directive
Specifies
translation time instructions to the JSP engine
<%@
Directive %>
Declaration
Declares
and defines methods and variables
<%!
Declaration %>
Scriptlet
Allows
the developer to write Java code in a JSP page
<%
Java code %>
Expression
Used to
print values in the output HTML of the JSP page
<%=
Expression %>
Action
Specifies
request time instructions to the JSP engine
<jsp:actionName
/>
Comments
General
comments used in documentation and debugging
<%--
Comment --%>
List of attributes of the page
directive, and their default values.
The
syntax of the page directive is as follows:
<%@
page {attribute-list} %>
where
attribute-list is the list of attribute-value pairs as defined in the table
below.
multiple attributes are defined within the same page directive, then they must
not be comma-separated.
e.g.
<%@ page buffer=”8kb”, session=”true” %>
The page
directive defined above is Invalid, as the two attributes, buffer and session
are separated by a comma.
import attribute has multiple packages, then all packages must be within the
same string, and must be comma separated.
e.g.
<%@ page import=”java.util.”,”java.text.” %>
This is
Invalid. The correct syntax is as follows,
<%@
page import=”java.util., java.text.” %>
Attribute Name
Description
Default Value
import
Comma
separated list of Java classes and
Packages
that will be used in the JSP page
java.lang.
javax.servlet.
javax.servlet.http.
javax.servlet.jsp.
session
Boolean
literal, specifies whether the JSP page will take part in an HTTP session
True
errorPage
Specifies
the URL to another JSP, which is capable of handling exceptions
Null
isErrorPage
Boolean
literal, specifies if the current page is capable of handling exceptions
False
language
Scripting
language used by the JSP engine
Java
extends
Any
valid Java class that extends javax.servlet.jsp.JspPage
Implementation
dependent
buffer
Specifies
the size of the output buffer. Value defined is in Kb, and the suffix kb is
mandatory. If no buffer is required, specify the String “none”
Implementation
dependent
autoFlush
Boolean
literal, specifies if the buffer should be flushed when full
true
isThreadSafe
Boolean
literal, specifies if the JSP page is thread safe
true
info
Information
about the JSP page
Implementation
dependent
contentType
Mime
type and character encoding for the output
text/html;charset=ISO-8859-1
pageEncoding
Character
encoding of the JSP page
ISO-8859-1
JSP
Life-Cycle stages
Lifecycle stage
Description
Page
Translation
The JSP
page is parsed and a Java file containing the corresponding servlet is
created.
Page
Compilation
The JSP
engine compiles the generated servlet file into a class file. The compiler
used is the javac compiler or any vendor specified compiler.
Load
the class
The
compiled class is loaded.
Create
an instance
An
instance of the servlet class is created.
Call
jspInit method
This
method is called before any other method, to allow initialization.
Call
_jspService method
This
method is called for each request. Do not override this method. The JSP
engine does it during the page translation phase.
Call
jspDestroy method
This
method is called when the servlet container takes the servlet out of service.
Translation Process:
The JSP
engine parses the JSP page and applies the following rules for generating the
servlet.
This is
the first stage in the Lifecycle of a JSP. During this stage, the JSP engine
reads the JSP page, parses and validates it. The JSP engine checks the syntax
of all the tags used. In addition, it also checks if the same Java bean is not
defined more than once in the translation unit. Variables are not defined more
than once, and if any custom tags are used, then they must be properly
formatted, and the tag library must be valid.
Compilation:
The
servlet generated during the translation phase gets compiled into a class file,
using the javac compiler (or any other vendor specific compiler). The scripting
language (Java) errors are caught during the compilation phase. All the Java
code written between scriptlets, expression and declarations is compiled during
this phase.
Loading and Instantiation:
After
compilation, the servlet container loads the servlet class into memory and
instantiates it.
Implicit variables and implicit
objects available in a JSP page.
Identifier name
Class or Interface
Description
application
javax.servlet.ServletContext
Refers
to the web application’s environment
session
javax.servlet.http.HttpSession
Refers
to the user’s session
request
javax.servlet.http.HttpServletRequest
Refers
to the current request to the page
response
javax.servlet.http.HttpServletResponse
Used
for sending response back to the client.
out
javax.servlet.jsp.JSPWriter
page
java.lang.Object
pageContext
javax.servlet.jsp.PageContext
config
javax.servlet.ServletConfig
exception
java.lang.Throwable
