JSP syntax

May 12, 2021 JSP

1. JSP syntax

2. The script

3. JSP declaration

8. JSP implied object

9. Control flow statements

10.. Judgment statement

11.. JSP operator

12.. JSP constant

JSP syntax

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

The script

Scripts can contain any number of Java statements, variables, methods, or expressions, as long as they are valid in the scripting language.

The syntax format of the script:

<% 代码片段 %>

Alternatively, you can write an XML statement equivalent to it, as follows:

<jsp:scriptlet>   




  代码片段
</jsp:scriptlet>

Any text, HTML tags, and JSP elements must be written outside the script.

Here's an example, and the first JSP example of this tutorial:

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

Note: Make sure that Apache Tomcat is installed in the C: .apache-tomcat-7.0.2 directory and that the operating environment is set up correctly.

Save the above code in the hello .jsp, and then place it in the directory of C: .apache-tomcat-7.0.2. webapps.ROOT, open the browser and enter the information in the http://localhost:8080/hello.jsp. When you run, you get the following results:

JSP syntax

JSP declaration

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

The syntax format of the JSP declaration:

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

Alternatively, you can write an XML statement equivalent to it, as follows:

<jsp:declaration>   
  代码片段
</jsp:declaration>

Examples of programs:

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

JSP expression

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

Because the value of an expression is converted to String, you can use the expression in a line of text without having to worry about whether it is an HTML tag.

Expression elements can contain any expression that conforms to the Java language specification, but you cannot end the expression with a sign.

The syntax format of the JSP expression:

<%= 表达式 %>

Similarly, you can write an XML statement equivalent to it:

<jsp:expression>   
  表达式
</jsp:expression>

Examples of programs:

<html> 
<head>
<title>A Comment Test</title>
</head> 
<body>
<p>   
  Today's date: <%= (new java.util.Date()).toLocaleString()%>
</p>
</body> 
</html>

When you run, you get the following results:

Today's date: 11-Sep-2013 21:24:25

JSP comments

JSP comments have two main functions: commenting on code and commenting out a piece of code.

Syntax format for JSP comments:

<%-- 这里可以填写 JSP 注释 --%>

Examples of programs:

<html> 
<head>
<title>A Comment Test</title>
</head> 
<body> 
<h2>A Test of Comments</h2> 
<%-- 该部分注释在网页中不会被显示--%> 
</body> 
</html>

When you run, you get the following results:

A Test of Comments

Grammar rules that use comments in different situations:

Grammar	Describe
slt;%--Note --%;gt;	JSP comments, comment content will not be sent to the browser or even compiled
Note !-- --	HTML comments, which you can see when you view the source code of a web page through your browser
<\%	Represents a static and lt;% constant
%\>	Represents a static %?gt; constant
\'	Single quotes used in properties
\"	Double quotes used in properties

JSP instructions

The JSP directive is used to set properties related to the entire JSP page.

JSP instruction syntax format:

<%@ directive attribute="value" %>

There are three instruction labels:

Instructions	Describe
<%@ page ... %>	Define the dependent properties of a page, such as scripting language, error page, cache requirements, and so on
<%@ include ... %>	Contains other files
<%@ taglib ... %>	The definition that introduces a label library can be a custom label

JSP behavior

JSP behavior tags use the XML syntax structure to control the servlet engine. It dynamically inserts a file, reuses JavaBean components, directs users to another page, generates related HTML for Java plug-ins, and so on.

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

<jsp:action_name attribute="value" />

Behavior tags are basically pre-defined functions, and the following table lists some of the available JSP behavior tags: :

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

JSP implied object

The JSP supports nine automatically defined variables, which the Lakers call hidden objects. An introduction to these nine implied objects can be found in the table below:

Object	Describe
request	An instance of the HttpServletRequest class
response	An instance of the HttpServletResponse class
out	An instance of the PrintWriter class that outputs the results to a Web page
session	An instance of the HttpSession class
application	An instance of the ServletContext class, related to the application context
config	An instance of the ServletConfig class
pageContext	An instance of the PageContext class that provides access to all objects and namespaces of JSP pages
page	Similar to the this keyword in a Java class
Exception	The object of the Exception class, which represents the corresponding exception object on the JSP page where the error occurred

Control flow statements

JSP provides full support for the Java language. You can use the Java API in your JSP program and even build Java blocks of code, including judgment statements and loop statements, and so on.

Judgment statement

If... Else block, see the following example:

<%! 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>

When you run, you get the following results:

Today is not weekend

Now let's take a look at switch... c ase block, with if... The else block is very different, it uses out.println(), and the whole thing is in the script's label, as follows:

<%! 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>

After running, you get the following results:

It's Wednesday.

Loop statement

Three basic loop types of Java can be used in JSP programs: for, while, and do... while。

Let's take a look at an example of a for loop:

<%! 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>

When you run, you get the following results:

JSP Tutorial
JSP Tutorial
JSP Tutorial

Replace the example above with a while loop to write:

<%! 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>

Run with the same results:

JSP Tutorial
JSP Tutorial
JSP Tutorial

JSP operator

JSP supports all Java logic and arithmetic operators.

The following table lists the common JSP operators, with high priority:

Category	Operator	Binding
Suffix	() [] . (point operator)	Left to right
One dollar	++ - - ! ~	Right to left
Multiplicity	* / %	Left to right
Addability	+ -	Left to right
Shift	>> >>> <<	Left to right
Relationship	> >= < <=	Left to right
Equal/unequal	== !=	Left to right
bit with	&	Left to right
Bit difference or	^	Left to right
bit or	\|	Left to right
Logic and	&&	Left to right
Logic or	\|\|	Left to right
Conditional judgment	?:	Right to left
Assignment	= += -= *= /= %= >>= <<= &= ^= \|=	Right to left
Comma	,	Left to right

JSP constant

The JSP language defines the following constants:

Boolean: true and false;
Integer (int): the same as in Java;
float: the same as in Java;
String: Starts and ends with single or double quotes;
Null：null。

JSP syntax

Table of contents

JSP syntax

The script

JSP declaration

JSP expression

JSP comments

JSP instructions

JSP behavior

JSP implied object

Control flow statements

Judgment statement

JSP operator

JSP constant

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