JSP - Syntax

In this chapter, we will discuss Syntax in JSP. We will understand the basic use of simple syntax (i.e, elements) involved with JSP development.
The elements of JSP have been described below −
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 the 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 the above code in JSP file hello.jsp and put this file in C:\apache-tomcat7.0.2\webapps\ROOT directory. Browse through the same using URL http://localhost:8080/hello.jsp. The above code will generate the following result −
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 for JSP Declarations −
<%! declaration; [ declaration; ]+ ... %>

You can write the XML equivalent of the above syntax as follows −
<jsp:declaration>
   code fragment
</jsp:declaration>

Following is an example for JSP Declarations −
<%! int i = 0; %> 
<%! int a, b, c; %> 
<%! Circle a = new Circle(2.0); %> 

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 the XML equivalent of the above syntax as follows −
<jsp:expression>
   expression
</jsp:expression>
Following example shows a JSP Expression −
<html> 
   <head><title>A Comment Test</title></head> 
   
   <body>
      <p>Today's date: <%= (new java.util.Date()).toLocaleString()%></p>
   </body> 
</html> 
The above code will generate the following result −
Today's date: 11-Sep-2010 21:24:25

Today's date: 11-Sep-2010 21:24:25
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", a part of your JSP page.
Following is the syntax of the JSP comments −
<%-- This is JSP comment --%>

Following example shows the 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> 
The above code will generate the 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 −
<%-- 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.
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
We would explain the JSP directive in a separate chapter JSP - Directives
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. Following table lists out the available JSP Actions −
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
Used to write template text in JSP pages and documents.
We would explain JSP actions in a separate chapter JSP - Actions
JSP supports nine automatically defined variables, which are also called implicit objects. These variables are −
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 the 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 a separate chapter JSP - Implicit Objects.
You can use all the APIs and building blocks of Java in your JSP programming including decision-making statements, loops, etc.
The if...else block starts out like an ordinary Scriptlet, but the Scriptlet is closed at each line with HTML text included between the 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> 
The above code will generate the 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> 
The above code will generate the following result −
It's Wednesday.

It's Wednesday.
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> 
The above code will generate the following result −

   JSP Tutorial



   JSP Tutorial



   JSP Tutorial


Above example can be written using the 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> 
The above code will generate the following result −

   JSP Tutorial



   JSP Tutorial



   JSP Tutorial


JSP supports all the logical and arithmetic operators supported by Java. Following table lists out 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.
The JSP expression language defines the following literals −
Boolean − true and false
Boolean − true and false
Integer − as in Java
Integer − as in Java
Floating point − as in Java
Floating point − as in Java
String − with single and double quotes; " is escaped as \", ' is escaped as \', and \ is escaped as \\.
String − with single and double quotes; " is escaped as \", ' is escaped as \', and \ is escaped as \\.
Null − null
Null − null

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