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JSP syntax

This section will briefly introduce JSP Development of basic grammar.


Script

Java script statement can contain any amount of variables, methods, or expression, so long as they are valid in the scripting language.

Script syntax:

<% 代码片段 %>

Alternatively, you can also write its equivalent XML statement, like this below:

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

Any text, HTML tags, JSP elements must be written out of the script.

Here's an example, but also the first example of a JSP 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 already installed in the C: \ apache-tomcat-7.0.2 directory and the operating environment has been set correctly.

The above code is stored in hello.jsp, and then place it in the C: \ apache-tomcat-7.0.2 \ webapps \ ROOT directory under, open a browser and type in the address bar http: // localhost: 8080 / hello .jsp. After running the following results:

Chinese coding problem

If we are to properly display the page in Chinese, we need to head in a JSP file, add the following code: <>

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

We resolve to modify the above program:

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>本教程(w3big.com)</title>
</head>
<body>
Hello World!<br/>
<%
out.println("你的 IP 地址 " + request.getRemoteAddr());
%>
</body>
</html>

So Chinese will be displayed correctly.


JSP declaration

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

JSP declaration syntax:

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

Alternatively, you can also write its equivalent XML statement, like this below:

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

Program example:

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

JSP expressions

A JSP scripting language expressions contained in the expression, is first converted to String, and then inserted into the local expressions arise.

Since the value of the expression is converted into a String, so you can use expressions in a line of text without having of whether it is HTML tags.

Expression element can contain any expression that conforms to the Java language specification, but you can not use a semicolon to the end of the expression.

JSP expression syntax:

<%= 表达式 %>

Similarly, you can also write its equivalent XML statement:

<jsp:expression>
   表达式
</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>本教程(w3big.com)</title>
</head>
<body>
<p>
   今天的日期是: <%= (new java.util.Date()).toLocaleString()%>
</p>
</body> 
</html> 

After running the following results:

今天的日期是: 2016-6-25 13:40:07

JSP comments

JSP comments have two main functions: to annotate the code and the piece of code commented out.

JSP comment syntax:

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>本教程(w3big.com)</title>
</head>
<body>
<%-- 该部分注释在网页中不会被显示--%> 
<p>
   今天的日期是: <%= (new java.util.Date()).toLocaleString()%>
</p>
</body> 
</html> 

After running the following results:

今天的日期是: 2016-6-25 13:41:26

Under different circumstances the use of annotation syntax rules:

grammar description
<% - Comment -%> JSP comments, the comment will not be sent to the browser will not even be compiled
<! - Comment -> You can see the comments in HTML comments, view the page source code through the browser
<\% Representative static <% constant
% \> Representative static%> constants
\ ' Use single quotes in the property
\ " Use double quotes in the property

JSP directives

JSP directive to set the attributes associated with the entire JSP page.

JSP command syntax:

<%@ directive attribute="value" %>

There are three instruction tags:

instruction description
<% @ Page ...%> Dependency property definition page, such as a scripting language, error pages, cache requirements, etc.
<% @ Include ...%> It contains additional files
<% @ Taglib ...%> Introducing tag library definitions can be custom label

JSP behavior

JSP tags using XML syntax structure acts to control the servlet engine. It can dynamically insert a file, reuse JavaBean components, lead the user to another page, the associated HTML generated for the Java plug-in and so on.

Behavior is only one label syntax that strict adherence to XML standards:

<jsp:action_name attribute="value" />

Behavior tab is basically on some pre-defined functions, the following table lists some of the JSP behavior Luo available label ::

grammar description
jsp: include For containing static or dynamic resource in the current page
jsp: useBean Find and initialize a JavaBean components
jsp: setProperty Setting JavaBean components
jsp: getProperty The value of the JavaBean components into the output of
jsp: forward Transfer request object that contains the user's request from a JSP file to another file
jsp: plugin Applet used to contain and JavaBean objects in the generated HTML pages
jsp: element Dynamically create an XML element
jsp: attribute Attribute XML element defines the dynamic created
jsp: body Body XML element defines a dynamically created
jsp: text Template used to encapsulate data

JSP implicit objects

JSP support variables nine automatically defined, rivers and lakes known hidden objects. The nine implicit objects Introduction follows:

Objects description
request Examples of HttpServletRequest class
response Examples HttpServletResponse class
out Examples PrintWriter class is used to output the result on the page
session Examples HttpSession class
application ServletContext instance of the class, and context-sensitive application
config Examples ServletConfig class
pageContext Examples PageContext class JSP page provides access to all the objects and namespaces
page Similar to the Java class in this keyword
Exception Exception class object that represents the error occurred JSP page corresponding exception object

Control flow statements

JSP provides comprehensive support for the Java language. You can use the program in JSP Java API even create blocks of Java code, including the judge statements and loops, and so on.

Judge sentences

If ... else block, consider 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>本教程(w3big.com)</title>
</head>
<body>
<h3>IF...ELSE 实例</h3>
<% if (day == 1 | day == 7) { %>
      <p>今天是周末</p>
<% } else { %>
      <p>今天不是周末</p>
<% } %>
</body> 
</html> 

After running the following results:

IF...ELSE 实例
今天不是周末

Now look at the switch ... case block, and if ... else blocks are very different, it uses out.println (), and the entire script tags are installed in the program, like this:

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%! int day = 3; %> 
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>本教程(w3big.com)</title>
</head>
<body>
<h3>SWITCH...CASE 实例</h3>
<% 
switch(day) {
case 0:
   out.println("星期天");
   break;
case 1:
   out.println("星期一");
   break;
case 2:
   out.println("星期二");
   break;
case 3:
   out.println("星期三");
   break;
case 4:
   out.println("星期四");
   break;
case 5:
   out.println("星期五");
   break;
default:
   out.println("星期六");
}
%>
</body> 
</html> 

Browser access, run the following results:

SWITCH...CASE 实例

星期三

Loops

Three basic types of circulation in the JSP program, you can use the Java: for, while, and do ... while.

Let's look at an example of a for loop, the following output of different font sizes of the "Guide":

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%! int fontSize; %> 
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>本教程(w3big.com)</title>
</head>
<body>
<h3>For 循环实例</h3>
<%for ( fontSize = 1; fontSize <= 3; fontSize++){ %>
   <font color="green" size="<%= fontSize %>">
    本教程
   </font><br />
<%}%>
</body> 
</html> 

After running the following results:

The above example use a while loop to write:

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%! int fontSize; %> 
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>本教程(w3big.com)</title>
</head>
<body>
<h3>While 循环实例</h3>
<%while ( fontSize <= 3){ %>
   <font color="green" size="<%= fontSize %>">
    本教程
   </font><br />
<%fontSize++;%>
<%}%>
</body> 
</html> 
Browser access, output is (fontSize initialized to 0, so the output of a multi-line):

JSP operator

JSP supports all Java logical and arithmetic operators.

The following table lists the JSP Luo common operator precedence from high in the end:

category Operators Binding
suffix () []. (Dot operator) Left to Right
One yuan + + - -! ~ Right to Left
Multiplicativity * /% Left to Right
Additivity + - Left to Right
Displacement >> << >>> Left to Right
relationship >> = <<= Left to right
Equal / unequal ==! = Left to Right
Bits and & Left to Right
Bit XOR ^ Left to Right
Bit or | Left to Right
Logic and && Left to Right
Logical or || Left to Right
Conditional ?: Right to Left
Assignment = + = - = * = / =% = >> = << = & = ^ = | = Right to Left
comma , Left to Right

JSP literal

JSP language defines the following words face amount:

  • Boolean values ​​(boolean): true and false;
  • Integer (int): the same as those in Java;
  • Float (float): the same as those in Java;
  • String (string): single or double quotes to start and end;
  • Null: null.