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This article mainly explains "JSP grammar, instructions, expressions and objects of knowledge collation", the content of the explanation is simple and clear, easy to learn and understand, the following please follow the editor's ideas slowly in depth, together to study and learn "JSP grammar, instructions, expressions and objects of knowledge collation" bar!

JSP syntax

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Script program

A script 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: alternatively, you can write its equivalent XML statement, like this:

Code snippet

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

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

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

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JSP statement

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

The syntax format of the JSP declaration: alternatively, you can write its equivalent XML statement, like this:

Code snippet

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JSP expression

A scripting language expression contained in an JSP expression is first converted to String and then inserted where the expression appears.

Because the value of the expression is converted to String, you can use the expression in a line of text regardless of whether it is a HTML tag or not.

An expression element can contain any expression that conforms to the Java language specification, but you cannot end the expression with a semicolon.

Syntax format for JSP expressions: similarly, you can write equivalent XML statements:

Expression.

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JSP comment http://www.iis7.com/a/lm/zzxzgj/

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

Syntax format of JSP comments:

Syntax rules for using annotations in different situations:

Grammatical description

JSP comments, the comment content will not be sent to the browser or even compiled

HTML comments, which can be seen when viewing the source code of a web page through a browser

Constant

\ 'single quotation marks used in attributes

\ "double quotation marks used in attributes

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JSP instruction

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

JSP instruction syntax format:

There are three kinds of instruction tags:

Instruction description

Define the dependency properties of the page, such as scripting languages, error pages, caching requirements, and so on

Include other files

Introduce the definition of tag library, which can be a custom tag

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JSP behavior

The JSP behavior tag uses the servlet syntax structure to control the XML engine. It can dynamically insert a file, reuse JavaBean components, guide users to another page, generate relevant HTML for Java plug-ins, and so on.

There is only one syntax format for the behavior tag, which strictly adheres to the XML standard:

Behavior tags are basically pre-defined functions. Here are some available JSP behavior tags:

Grammatical description

Jsp:include is used to include static or dynamic resources in the current page

Jsp:useBean finds and initializes a JavaBean component

Jsp:setProperty sets the value of the JavaBean component

Jsp:getProperty inserts the value of the JavaBean component into output

Jsp:forward passes a request object containing user requests from one JSP file to another

Jsp:plugin is used to include Applet and JavaBean objects in the generated HTML page

Jsp:element dynamically creates a XML element

Jsp:attribute defines the attributes of dynamically created XML elements

Jsp:body defines the body of a dynamically created XML element

Jsp:text is used to encapsulate template data

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JSP implied object

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

Object description

Instance of the request HttpServletRequest class

Instance of the response HttpServletResponse class

An instance of the out PrintWriter class, which is used to output the results to a web page

Instance of the session HttpSession class

An instance of the application ServletContext class, depending on the application context

Instance of the config ServletConfig class

An instance of the pageContext PageContext class that provides access to all objects and namespaces on the JSP page

Page is similar to the this keyword in the Java class

The object of the Exception Exception class, which represents the corresponding exception object in the JSP page where the error occurred

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Control flow statement

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

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Judgment sentence

If... Else block

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Loop statement

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

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JSP operator

JSP supports all Java logical and arithmetic operators.

The following is a list of common JSP operators, from high to low:

Category operator associativity

Suffix () []. (dot operator) left to right

Unary + + -! ~ right to left

Multiplicability * /% left to right

Additivity +-left to right

Shift > =

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