HTML comment
Display a comment on the client.
JSP syntax
<! -- Comment [<% = expression %>] -->
Example 1
<! -- This file displays the user login screen -->
Generate the same data as the above in the HTML source code of the client:
<! -- This file displays the user login screen -->
Example 2
<! -- This page was loaded on <% = (new java. util. Date (). toLocaleString () %> -->
In the HTML source code of the client, it is displayed:
<! -- This page was loaded on January 1, 2000 -->
Description
This annotation is similar to HTML, that is, it can be seen in "View Source Code.
The only difference is that you can use an expression in this comment (example 2 ). this expression is indefinite. Different pages allow you to use various expressions as long as they are valid. For more expressions, see
Hide Comments
Written in the JSP program, but not sent to the customer.
JSP syntax
<% -- Comment -- %>
Example:
<% @ Page language = "java" %>
<Html>
<Head> <title> A Comment Test </title> <Body>
<H2> A Test of Comments <% -- This comment will not be visible in the page source -- %>
</Body>
</Html>
Description
Characters marked with hidden comments are ignored during JSP compilation. This annotation is useful when you want to hide or annotate your JSP program. The JSP compiler does not compile the statements between <% -- and -- %>. It is not displayed in the client's browser or in the source code.
Statement
Declare valid variables and methods in JSP programs
JSP syntax
<%! Declaration; [declaration;] +... %>
Example
<%! Int I = 0; %>
<%! Int a, B, c; %>
<%! Circle a = new Circle (2.0); %>
Description
Declare the variables and methods you will use in the JSP program. You must do the same. Otherwise, an error will occur.
You can declare multiple variables and methods at a time, as long as they end with ";". Of course, these declarations are valid in Java.
When declaring methods or variables, pay attention to the following rules:
The declaration must end with ";" (Scriptlet has the same rule, but the expression is different ).
You can directly use declared variables and methods included in <% @ page %> without declaring them again.
A statement is valid only on one page. If you want to use some declarations for each page, you 'd better write them into a separate file and include them with the <% @ include %> or <jsp: include> element.
Expression
Contains an expression that complies with the JSP syntax.
JSP syntax
<% = Expression %>
Example
<Font color = "blue"> <% = map. size () %> </font>
<B> <% = numguess. getHint () %> </B>.
Description
The expression element represents an expression defined in the script language. It is automatically converted to a string after running, and then inserted into the expression for display at the location of the JSP file. Because the value of this expression has been converted into a string, you can insert this expression in a line of text (in the same form as ASP ).
When using expressions in JSP, remember the following:
You cannot use a semicolon (";") as the expression Terminator. But the same expression must end with a semicolon when used in scriptlet! View Scriptlet
This expression element can include any</
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