JSP Directives

The JSP page Directive

The page directive lets us define one or more of the following case-sensitive attributes:

. import="package.class"

or

import="package.class1,...,package.classN".

This lets us specify what packages should be imported.

For example:

<%@ page import="java.util.*" %>

The import attribute is the only one that is allowed to appear multiple times.

. contentType="MIME-Type"

or

contentType="MIME-Type; charset=Character-Set"

This specifies the MIME type of the output. The default is text/html.

For example, the directive

<%@ page contentType="text/plain" %>

has the same effect as the scriptlet

<% response.setContentType("text/plain"); %>

. isThreadSafe="true|false".

A value of true (the default) indicates normal servlet processing, where multiple requests can be processed simultaneously with a single servlet instance, under the assumption that the author synchronized access to instance variables.

A value of false indicates that the servlet should implement SingleThreadModel, with requests either delivered serially or with simultaneous requests being given separate servlet instances.

. session="true|false".

A value of true (the default) indicates that the predefined variable session (of type HttpSession) should be bound to the existing session if one exists, otherwise a new session should be created and bound to it.

A value of false indicates that no sessions will be used, and attempts to access the variable session will result in errors at the time the JSP page is translated into a servlet.

. buffer="sizekb|none".

This specifies the buffer size for the JspWriter out. The default is server-specific, but must be at least 8kb.

. autoflush="true|false".

A value of true, the default, indicates that the buffer should be flushed when it is full. A value of false, rarely used, indicates that an exception should be thrown when the buffer overflows. A value of false is illegal when also using buffer="none".

. extends="package.class".

This indicates the superclass of servlet that will be generated. Use this with extreme caution, since the server may be using a custom superclass already.

. info="message".

This defines a string that can be retrieved via the getServletInfo method.

. errorPage="url".

This specifies a JSP page that should process any Throwables thrown but not caught in the current page.

. isErrorPage="true|false".

This indicates whether or not the current page can act as the error page for another JSP page. The default is false.

. language="java".

At some point, this is intended to specify the underlying language being used. For now, don't bother with this since java is both the default and the only legal choice.

The XML syntax for defining directives is

<jsp:directive.directiveType attribute=value />

For example, the XML equivalent of :

<%@ page import="java.util.*" %>

is

<jsp:directive.page import="java.util.*" />