JSP - Syntax
This tutorial will give basic
idea on simple syntax (ie. elements) involved with JSP development:
The Scriptlet:
A scriptlet
can contain any number of JAVA language statements, variable or method
declarations, or expressions that are valid in the page scripting language.
Following is the syntax of Scriptlet:
<% code fragment %>
You can write XML equivalent of the above
syntax as follows:
<jsp:scriptlet>
code
fragment
</jsp:scriptlet>
Any text,
HTML tags, or JSP elements you write must be outside the scriptlet. Following
is the simple and first example for JSP:
<html>
<head>
<title>Hello
World</title></head>
<body>
Hello
World!<br/>
<% out.println("Your IP address is
" + request.getRemoteAddr()); %>
</body> </html>
</body> </html>
NOTE: Assuming that Apache Tomcat is installed in C:\apache-tomcat-7.0.2 and your environment is setup as per environment setup tutorial. Let us keep above code in JSP file hello.jsp and put this file in C:\apache-tomcat-7.0.2\webapps\ROOT directory and try to browse it by giving URL http://localhost:8080/hello.jsp. This would generate following result:
JSP Declarations:
A declaration declares one or more
variables or methods that you can use in Java code later in the JSP file. You
must declare the variable or method before you use it in the JSP file.
Following is the syntax of JSP Declarations:
<%!
declaration; [ declaration; ]+ ... %>
You can write XML equivalent of the
above syntax as follows:
<jsp:declaration>
code
fragment
</jsp:declaration>
Following is the simple example for JSP Comments:
<%! int i = 0; %>
<%! int
a, b, c; %>
<%! Circle a = new Circle(2.0); %>
JSP Expression:
A JSP expression element contains a
scripting language expression that is evaluated, converted to a String, and
inserted where the expression appears in the JSP file. Because the value of an
expression is converted to a String, you can use an expression within a line of
text, whether or not it is tagged with HTML, in a JSP file. The expression
element can contain any expression that is valid according to the Java Language
Specification but you cannot use a semicolon to end an expression.
Following is the syntax of JSP
Expression:
<%=
expression %>
You can write XML equivalent of
the above syntax as follows:
<jsp:expression>
expression
</jsp:expression>
Following is the simple example
for JSP Expression:
<html>
<head><title>A Comment
Test</title></head>
<body>
<p> Today's date: <%= (new
java.util.Date()).toLocaleString()%> </p> </body>
</html>
This would generate following
result:
Today's date:
11-Sep-2014 21:12:23
JSP Comments:
JSP comment marks text or
statements that the JSP container should ignore. A JSP comment is useful when
you want to hide or "comment out" part of your JSP page. Following
is the syntax of JSP comments:
<%--
This is JSP comment --%>
Following is the simple
example for JSP Comments:
<html>
<head><title>A
Comment Test</title></head>
<body>
<h2>A
Test of Comments</h2> <%-- This comment will not be visible in the
page source --%>
</body>
</html>
This
would generate following result:
|
There are a small number of special constructs you can use in various cases to insert comments or characters that would otherwise be treated specially. Here's a summary:
Syntax Purpose
<%-- comment --%> A JSP comment. Ignored by the JSP engine.
<\% Represents static <% literal.
%\> Represents static %> literal.
\' A single quote in an attribute that uses single quotes.
\" A double quote in an attribute that uses double quotes.
JSP Directives:
A JSP directive affects the overall
structure of the servlet class. It usually has the following form: <%@
directive attribute="value" %> There are
three types of directive tag:
<%@ page ... %>
|
Defines page-dependent attributes,
such as scripting language, error page, and buffering requirements.
|
<%@ include ... %>
|
Includes a file during the
translation phase.
|
<%@ taglib ... %>
|
Declares a tag library, containing
custom actions, used in the page
|
JSP Actions:
JSP actions use constructs in XML syntax to control the behavior of the servlet engine. You can dynamically insert a file, reuse JavaBeans components, forward the user to another page, or generate HTML for the Java plugin. There is only one syntax for the Action element, as it conforms to the XML standard:
<jsp:action_name attribute="value"
/>
Action
elements are basically predefined functions and there are following JSP actions
available:
Syntax |
Purpose
|
jsp:include
|
Includes
a file at the time the page is requested
|
jsp:include
|
Includes
a file at the time the page is requested
|
jsp:useBean
|
Finds
or instantiates a JavaBean
|
jsp:setProperty
|
Sets
the property of a JavaBean
|
jsp:getProperty
|
Inserts
the property of a JavaBean into the output
|
jsp:forward
|
Forwards
the requester to a new page
|
jsp:plugin
|
Generates
browser-specific code that makes an OBJECT or EMBED tag for the Java plugin
|
jsp:element
|
Defines
XML elements dynamically.
|
jsp:attribute
|
Defines
dynamically defined XML element's attribute.
|
jsp:body
|
Defines
dynamically defined XML element's body.
|
jsp:text
|
Use
to write template text in JSP pages and documents.
|
JSP Implicit Objects:
JSP supports nine
automatically defined variables, which are also called implicit objects. These
variables are:
Objects |
Description
|
request
|
This is the HttpServletRequest object
associated with the request.
|
response
|
This is the HttpServletResponse object
associated with the response to the client.
|
out
|
This is the PrintWriter object
used to send output to the client.
|
session
|
This is the HttpSession object
associated with the request.
|
application
|
This is the ServletContext object
associated with application context.
|
config
|
This is the ServletConfig object
associated with the page.
|
pageContext
|
This encapsulates use of
server-specific features like higher performance JspWriters.
|
page
|
This is simply a synonym for this,
and is used to call the methods defined by the translated servlet class.
|
Exception
|
The Exception object allows
the exception data to be accessed by designated JSP.
|
Control-Flow Statements:
JSP provides full power of Java to be
embeded in your web application. You can use all the APIs and building blocks
of Java in your JSP programming including decision making statements, loops
etc.
Decision-Making Statements:
The if...else block starts out
like an ordinary Scriptlet, but the Scriptlet is closed at each line with HTML
text included between Scriptlet tags.
<%! int
day = 3; %>
<html>
<head><title>IF...ELSE
Example</title></head>
<body>
<% if (day == 1 | day == 7)
{ %> <p> Today is weekend</p>
<% }
else { %>
<p> Today is not weekend</p>
<% }
%> </body>
</html>
This would
produce following result:
Today
is not weekend
|
Now look at
the following switch...case block which has been written a bit
differentlty using out.println() and inside Scriptletas:
<%! int
day = 3; %>
<html>
<head><title>SWITCH...CASE
Example</title></head>
<body>
<% switch(day)
{
case 0:
out.println("It\'s Sunday.");
break;
case 1: out.println("It\'s
Monday.");
break;
case 2: out.println("It\'s
Tuesday.");
break;
case 3:
out.println("It\'s Wednesday.");
break;
case 4: out.println("It\'s
Thursday.");
break;
case 5:
out.println("It\'s Friday.");
break;
default: out.println("It's
Saturday.");
}
%>
</body>
</html>
This would produce following
result:
It's
Wednesday
|
Loop Statements:
You can also use
three basic types of looping blocks in Java: for, while,and do…while blocks
in your JSP programming. Let us look at the following for loop example:
<%! int fontSize; %>
<html>
<head><title>FOR LOOP Example</title></head>
<body>
<%for ( fontSize = 1; fontSize <= 3;
fontSize++){ %>
<font color="green"
size="<%= fontSize %>"> JSP Tutorial </font>
<br /> <%}%>
</body>
</html>
This would produce
following result:
JSP Tutorial JSP Tutorial
|
JSP Operators:
JSP supports all the
logical and arithmatic operators supported by Java. Following table give a list
of all the operators with the highest precedence appear at the top of the
table, those with the lowest appear at the bottom. Within an expression, higher
precedenace operators will be evaluated first.
name Symbols priority
Postfix
|
() [] . (dot operator)
|
Left to right
|
Unary
|
++ - - ! ~
|
Right to left
|
Multiplicative
|
* / %
|
Left to right
|
Additive
|
+ -
|
Left to right
|
Shift
|
>> >>> <<
|
Left to right
|
Relational
|
> >= < <=
|
Left to right
|
Equality
|
== !=
|
Left to right
|
Bitwise AND
|
&
|
Left to right
|
Bitwise XOR
|
^
|
Left to right
|
Bitwise OR
|
|
|
Left to right
|
Logical AND
|
&&
|
Left to right
|
Logical OR
|
||
|
Left to right
|
Conditional
|
?:
|
Right to left
|
Assignment
|
= += -= *= /= %= >>=
<<= &= ^= |=
|
Right to left
|
Comma
|
,
|
Left to right
|
JSP Literals:
The JSP expression
language defines the following literals:
Boolean:
true and false
Integer:
as in Java
Floating
point: as in Java
String:
with single and double quotes; " is escaped as \", ' is
escaped as \', and \ is escaped as \\.
Null:
null
next tutorial conti........................................
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