JSP directives provide instructions to the JSP engine on how to handle JSP.
A JSP directive affects the structure of the servlet class. It usually has the following form:
<%@ directive attribute="value" %>
Directives can have a list of attributes defined in key-value pairs and separated by commas.
There are three types of directive tag:
| Directive | Description |
|---|---|
| <%@ page ... %> | Defines page-dependent attributes, such as scripting language, error page, and buffering requirements. |
| <%@ include ... %> | Includes another file. |
| <%@ taglib ... %> | Declares a tag library containing custom actions which can be used in the page. |
The page directive instructs JSP engine on how to process the current JSP page.
We can add page directives anywhere in the JSP page.
By convention, page directives are listed at the top of the JSP page.
The following example shows the basic syntax of page directive:
<%@ page attribute="value" %>
You can write XML equivalent of the above syntax as follows:
<jsp:directive.page attribute="value" />
The following lists of attributes associated with page directive.
| Attribute | Description |
|---|---|
| buffer | Set a buffering model for the output stream. |
| autoFlush | Set behavior of the servlet output buffer. |
| contentType | Set the character encoding scheme. |
| errorPage | Set the URL of another JSP for Java unchecked runtime exceptions. |
| isErrorPage | Set if this JSP page is used by another JSP page as errorPage. |
| extends | Set a superclass that the generated servlet must extend |
| import | A list of packages as Java import statement in the JSP. |
| info | Provides a string that will be returned from the servlet's getServletInfo() method. |
| isThreadSafe | Set the threading model for the generated servlet. |
| language | Defines the programming language used in the JSP page. |
| session | Specifies whether or not the JSP page is in HTTP sessions |
| isELIgnored | Whether to igore EL expression within the JSP page. |
| isScriptingEnabled | Determines if scripting elements are allowed. |
The include directive includes a file into the current JSP page.
This directive merges the content from external files with the current JSP during the translation phase.
You may code include directives anywhere in your JSP page.
The include directive has the following syntax:
<%@ include file="relative url" >
The XML equivalent of the above syntax is as follows:
<jsp:directive.include file="relative url" />
We can define custom JSP tags in JavaServer Pages that look like HTML tags.
A tag library is a set of user-defined tags that implement custom behavior.
The taglib directive declares a set of custom tags, identifies the location of the library, and defines a prefix for the custom tags.
The taglib directive follows the following syntax:
<%@ taglib uri="uri" prefix="prefixOfTag" >
The XML equivalent of the above syntax is as follows:
<jsp:directive.taglib uri="uri" prefix="prefixOfTag" />
The import attribute is used to import class,interface or all the members of a package. It is similar to import keyword in java class or interface.
<html> <body> <%@ page import="java.util.Date" %> Today is: <%= new Date() %> </body> </html>
The contentType attribute defines the MIME(Multipurpose Internet Mail Extension) type of the HTTP response.The default value is "text/html;charset=ISO-8859-1".
<html>
<body>
<%@ page contentType=application/msword %>
Today is: <%= new java.util.Date() %>
</body>
</html>
info attribute sets the information of the JSP page
which is retrieved later by using getServletInfo() method of Servlet interface.
<html> <body> <%@ page info="composed by java2s.com" %> Today is: <%= new java.util.Date() %> </body> </html>
The buffer attribute sets the buffer size in kilobytes to handle output generated by the JSP page. The default size of the buffer is 8Kb.
<html> <body> <%@ page buffer="16kb" %> Today is: <%= new java.util.Date() %> </body> </html>
The errorPage attribute is used to define the error page, if exception occurs in the current page, it will be redirected to the error page.
//index.jsp
<html>
<body>
<%@ page errorPage="myerrorpage.jsp" %>
<%= 100/0 %>
</body>
</html>
The isErrorPage attribute is used to declare that the current page is the error page.
The exception object can only be used in the error page.
//myerrorpage.jsp
<html>
<body>
<%@ page isErrorPage="true" %>
Sorry an exception occured!<br/>
The exception is: <%= exception %>
</body>
</html>