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>
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 Declarations:
<%! 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-2010 21:24:25
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:
A Test of Comments
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. |
| <!– comment –> |
An HTML comment. Ignored by the browser. |
| <\% |
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:
| Directive |
Description |
| <%@ 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 |
We would explain JSP directive in separate chapter JSP – Directives
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: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. |
We would explain JSP actions in separate chapter JSP – Actions
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. |
We would explain JSP Implicit Objects in separate chapter JSP – Implicit Objects.
Control-Flow Statements:
JSP provides full power of Java to be embedded 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 Tutorial
Above example can be written using while loop as follows:
<%! int fontSize; %>
<html>
<head><title>WHILE LOOP Example</title></head>
<body>
<%while ( fontSize <= 3){ %>
<font color="green" size="<%= fontSize %>">
JSP Tutorial
</font><br />
<%fontSize++;%>
<%}%>
</body>
</html>
This would also produce following result:
JSP Tutorial
JSP Tutorial
JSP Tutorial
JSP Operators:
JSP supports all the logical and arithmetic 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 precedence operators will be evaluated first.
| Category |
Operator |
Associativity |
| 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
JSP directives provide directions and instructions to the container, telling it how to handle certain aspects of JSP processing.
A JSP directive affects the overall structure of the servlet class. It usually has the following form:
<%@ directive attribute="value" %>
Directives can have a number of attributes which you can list down as key-value pairs and separated by commas.
The blanks between the @ symbol and the directive name, and between the last attribute and the closing %>, are optional.
There are three types of directive tag:
| Directive |
Description |
| <%@ 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 |
The page Directive:
The page directive is used to provide instructions to the container that pertain to the current JSP page. You may code page directives anywhere in your JSP page. By convention, page directives are coded at the top of the JSP page.
Following is the basic syntax of page directive:
<%@ page attribute="value" %>
You can write XML equivalent of the above syntax as follows:
<jsp:directive.page attribute="value" />
Attributes:
Following is the list of attributes associated with page directive:
| Attribute |
Purpose |
| buffer |
Specifies a buffering model for the output stream. |
| autoFlush |
Controls the behavior of the servlet output buffer. |
| contentType |
Defines the character encoding scheme. |
| errorPage |
Defines the URL of another JSP that reports on Java unchecked runtime exceptions. |
| isErrorPage |
Indicates if this JSP page is a URL specified by another JSP page’s errorPage attribute. |
| extends |
Specifies a superclass that the generated servlet must extend |
| import |
Specifies a list of packages or classes for use in the JSP as the Java import statement does for Java classes. |
| info |
Defines a string that can be accessed with the servlet’s getServletInfo() method. |
| isThreadSafe |
Defines the threading model for the generated servlet. |
| language |
Defines the programming language used in the JSP page. |
| session |
Specifies whether or not the JSP page participates in HTTP sessions |
| isELIgnored |
Specifies whether or not EL expression within the JSP page will be ignored. |
| isScriptingEnabled |
Determines if scripting elements are allowed for use. |
Check more detail related to all the above attributes at Page Directive.
The include Directive:
The include directive is used to includes a file during the translation phase. This directive tells the container to merge the content of other external files with the current JSP during the translation phase. You may code include directives anywhere in your JSP page.
The general usage form of this directive is as follows:
<%@ include file="relative url" >
The filename in the include directive is actually a relative URL. If you just specify a filename with no associated path, the JSP compiler assumes that the file is in the same directory as your JSP.
You can write XML equivalent of the above syntax as follows:
<jsp:directive.include file="relative url" />
Check more detail related to include directive at Include Directive.
The taglib Directive:
The JavaServer Pages API allows you to define custom JSP tags that look like HTML or XML tags and a tag library is a set of user-defined tags that implement custom behavior.
The taglib directive declares that your JSP page uses a set of custom tags, identifies the location of the library, and provides a means for identifying the custom tags in your JSP page.
The taglib directive follows the following syntax:
<%@ taglib uri="uri" prefix="prefixOfTag" >
Where the uri attribute value resolves to a location the container understands and the prefix attribute informs a container what bits of markup are custom actions.
You can write XML equivalent of the above syntax as follows:
<jsp:directive.taglib uri="uri" prefix="prefixOfTag" />
Further information about configuring and running Tomcat can be found in the documentation included here, as well as on the Tomcat web site: 
Typically, the JSP engine checks to see whether a servlet for a JSP file already exists and whether the modification date on the JSP is older than the servlet. If the JSP is older than its generated servlet, the JSP container assumes that the JSP hasn’t changed and that the generated servlet still matches the JSP’s contents. This makes the process more efficient than with other scripting languages (such as PHP) and therefore faster.
shivam singla 