JSP Syntax

This section will briefly introduce the basic syntax in JSP development.

Script Program

The script program can contain any amount of Java statements, variables, methods, or expressions, as long as they are valid in the script language.

The syntax format of the script program is:

<% Code snippet %>

Or, you can also write an equivalent XML statement, as shown below:

<jsp:scriptlet>
　　　Code snippet
</jsp:scriptlet>

Any text, HTML tags, or JSP elements must be written outside of the script program.

Below is an example, which is also the first JSP example in this tutorial:

<html>
<head><title>Hello World</title></head>
<body>
Hello World!<br/>
<%
out.println("Your IP address is ")　+　request.getRemoteAddr());
%>
</body>
</html>

Note:Please ensure that Apache Tomcat is installed at C:\apache-tomcat-7.0.2directory, and make sure the runtime environment is correctly set.

Save the above code in hello.jsp, then place it in C:\apache-tomcat-7.0.2\webapps\ROOT directory, open the browser and enter http: in the address bar://localhost:8080/Running hello.jsp gives the following result:

Chinese Encoding Issue

To display Chinese characters normally on the page, we need to add the following code to the header of the JSP file:

<%@ page language="java" contentType="text/html; charset=UTF-8"
　　　　pageEncoding="UTF-8">

Next, we will modify the above program as follows:

<%@ page language="java" contentType="text/html; charset=UTF-8"
　　　　pageEncoding="UTF-8">
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Basic Tutorial Website(oldtoolbag.com)</title>
</head>
<body>
Hello World!<br/>
<%
out.println("Your IP address ")　+　request.getRemoteAddr());
%>
</body>
</html>

This way, Chinese characters can be displayed normally.

　　 JSP Declaration

A declaration statement can declare one or more variables or methods for use in subsequent Java code. In a JSP file, you must declare these variables and methods before you can use them.

JSP declaration syntax format:

<%!　declaration;　[　declaration;　]+　...　%>

Or, you can also write an equivalent XML statement, as shown below:

<jsp:declaration>
　　　Code snippet
</jsp:declaration>

Program example:

<%!　int　i　=　0;　%>　
<%!　int　a,　b,　c;　%>　
<%!　Circle　a　=　new　Circle(2.0);　%>

　　 JSP expression

A script language expression contained in a JSP expression is first converted to a String and then inserted at the location where the expression appears.

Since the value of the expression will be converted to a String, you can use an expression in a text line without worrying whether it is an HTML tag or not.

Any expression that conforms to the Java language specification can be included in the expression element, but semicolons cannot be used to end the expression.

JSP expression syntax format:

<%= 表达式 %>

Similarly, you can also write an equivalent XML statement:

<jsp:expression>
　　　Expression
</jsp:expression>

Program example:

<%@ page language="java" contentType="text/html; charset=UTF-8"
　　　　pageEncoding="UTF-8">
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Basic Tutorial Website(oldtoolbag.com)</title>
</head>
<body>
<p>
　　　Today's date is:　<%=　(new　java.util.Date()).toLocaleString()%>
</p>
</body>　
</html>

After running, the following results are obtained:

Today's date is:　2016-6-25　13:40:07

　　 JSP comment

JSP comments mainly have two functions: to annotate code and to comment out a section of code.

JSP comment syntax format:

<%@ page language="java" contentType="text/html; charset=UTF-8"
　　　　pageEncoding="UTF-8">
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Basic Tutorial Website(oldtoolbag.com)</title>
</head>
<body>
<%--　This part of the comment will not be displayed in the web page--%>　
<p>
　　　Today's date is:　<%=　(new　java.util.Date()).toLocaleString()%>
</p>
</body>　
</html>

After running, the following results are obtained:

Today's date is:　2016-6-25　13:41:26

Syntax rules for comments used in different situations:

Syntax	Description
<%-- Comments --%>	JSP comments, the content of which will not be sent to the browser and will not be compiled
<!-- Comments -->	HTML comments, the content of which can be seen when viewing the web page source code through the browser
<\%	Represents the static <% constant
%\>	Represents the static %> constant
\'	Single quotes used in attributes
\"	Double quotes used in attributes

　　 JSP directive

JSP directives are used to set properties related to the entire JSP page.

JSP directive syntax format:

<%@ directive attribute="value" %>

There are three types of directive tags here:

Directives	Description
<%@ page ... %>	Define the dependency properties of the page, such as scripting language, error page, caching requirements, etc.
<%@ include ... %>	Include other files
<%@ taglib ... %>	Introduce the definition of tag libraries, which can be custom tags

　　 JSP behavior

JSP behavior tags use XML syntax structure to control the servlet engine. It can dynamically insert a file, reuse JavaBean components, redirect users to another page, generate relevant HTML for Java plugins, etc.

Behavior tags have only one syntax format, which strictly adheres to the XML standard:

<jsp:action_name attribute="value">　/>

Behavior tags are basically some predefined functions. The following table lists some available JSP behavior tags:

Syntax	Description
jsp:include	Used to include static or dynamic resources in the current page
jsp:useBean	Search and initialize a JavaBean component
jsp:setProperty	Set the value of a JavaBean component
jsp:getProperty	Insert the value of a JavaBean component into the output
jsp:forward	Pass a request object containing a user request from one JSP file to another file
jsp:plugin	Used to include Applet and JavaBean objects in the generated HTML page
jsp:element	Dynamically create an XML element
jsp:attribute	Define the attributes of dynamically created XML elements
jsp:body	Define the body of dynamically created XML elements
jsp:text	Used to encapsulate template data

　　 JSP implicit objects

JSP supports nine automatically defined variables, known as implicit objects in the江湖. The brief introduction of these nine implicit objects is shown in the following table:

Object	Description
request	HttpServletRequestAn example of the class
response	HttpServletResponseAn example of the class
out	PrintWriterAn example of the class, used to output results to the web page
session	HttpSessionAn example of the class
application	ServletContextAn example of the class, related to the application context
config	ServletConfigAn example of the class
pageContext	PageContextAn example of the class, providing access to all objects of the JSP page and the namespace
page	Similar to the 'this' keyword in Java classes
exception	exception An object of the class, representing the corresponding exception object of the JSP page where an error occurs

　　 Control flow statements

JSP provides comprehensive support for the Java language. You can use Java API in JSP programs and even establish Java code blocks, including conditional statements and loop statements, etc.

　　 Conditional Statements

If…else block, please see the following example:

<%@ page language="java" contentType="text/html; charset=UTF-8"
　　　　pageEncoding="UTF-8">
<% int day =　3; %>　
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Basic Tutorial(oldtoolbag.com)</title>
</head>
<body>
<h2>IF...ELSE Example</h2>
<% if (day ==　1　| day ==　7) { %>
　　　　　　<p>It's the weekend today</p>
<% } else { %>
　　　　　　<p>It's not the weekend today</p>
<% } %>
</body>　
</html>

After running, the following results are obtained:

IF...ELSE Example
It's not the weekend today

Now let's take a look at the switch…case block, which is quite different from the if…else block. It uses out.println() and is all enclosed within the script program tags, as shown below:

<%@ page language="java" contentType="text/html; charset=UTF-8"
　　　　pageEncoding="UTF-8">
<% int day =　3; %>　
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Basic Tutorial(oldtoolbag.com)</title>
</head>
<body>
<h2>SWITCH...CASE Example</h2>
<%　
switch(day) {
case 0:
　　　out.println("Sunday");
　　　break;
case　1:
　　　out.println("Monday");
　　　break;
case　2:
　　　out.println("Tuesday");
　　　break;
case　3:
　　　out.println("Wednesday");
　　　break;
case　4:
　　　out.println("Thursday");
　　　break;
case　5:
　　　out.println("Friday");
　　　break;
default:
　　　out.println("Saturday");
}
%>
</body>　
</html>

After visiting the browser and running, the following results are obtained:

SWITCH...CASE Example
Wednesday

Loop Statements

In a JSP program, you can use three basic Java loop types: for, while, and do…while.

Let's take a look at the for loop example, which outputs "Basic Tutorial Website" with different font sizes as shown below:

<%@ page language="java" contentType="text/html; charset=UTF-8"
　　　　pageEncoding="UTF-8">
<% int fontSize; %>　
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Basic Tutorial Website(oldtoolbag.com)</title>
</head>
<body>
<h2>For Loop Example</h2>
<% for ( fontSize =　1; fontSize <=　3; fontSize++{　%>
　　　<font color="green" size="<%= fontSize %>">
　　　　Basic Tutorial
　　　</font><br　/>
<%}%>
</body>　
</html>

After running, the following results are obtained:

Rewrite the following example using a while loop:

<%@ page language="java" contentType="text/html; charset=UTF-8"
　　　　pageEncoding="UTF-8">
<% int fontSize = 0; %>　
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Basic Tutorial(oldtoolbag.com)</title>
</head>
<body>
<h2>While loop example</h2>
<%while ( fontSize <=　3{　%>
　　　<font color="green" size="<%= fontSize %>">
　　　　Basic Tutorial
　　　</font><br　/>
<%fontSize++;%>
<%}%>
</body>　
</html>

Browser access, the output result is (fontSize is initialized to 0, so an extra line is output):

　　 JSP Operators

JSP supports all Java logical and arithmetic operators.

The following table lists common JSP operators, sorted by priority from high to low:

Category	Operator	Associativity
Postfix	( ) [ ] . (dot operator)	Left to right
Unary	++ - - ! ~	Right to left
Multiplicativity	* / %	Left to right
Additivity	+ -	Left to right
Shift	>> >>> <<	Left to right
Relation	> >= < <=	Left to right
Equal/Not equal	== !=	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

JSP defines the following literals:

　　　　　　 Boolean (boolean): true and false;
　　　　　　 Integer (int): Same as in Java;
　　　　　　 Float (float): Same as in Java;
　　　　　　 String (string): Starts and ends with a single or double quote;
　　　　　　 Null: null.

JSP Directives JSP Lifecycle

Basic JSP Tutorial

Advanced JSP Tutorial

JSP Syntax

Script Program

Chinese Encoding Issue

JSP Declaration

JSP expression

JSP comment

JSP directive

JSP behavior

JSP implicit objects

Control flow statements

Conditional Statements

Loop Statements

JSP Literals