Jakarta Taglibs
Name that Tag
Let's look at the Jakarta tag libraries that are available and what
each provides.
At the time of this writing there were twenty supported libraries
and one unsupported library. There seem to be new libraries added
constantly. If you are interested in using a specific library, it is
best to check the Jakarta
site for specific installation instructions and requirements for
that taglib.
The application taglib contains tags that can be used to access
information contained in the ServletContext. Tags that
are defined in application scope as well as application init
parameters can be accessed. Tags are included for setting, getting,
removing, and testing of attributes. Looping and value testing are
provided for init parameters. A sample tag from this library looks
like
<app:equalsattribute name="sue"
match="oreilly">
The application attribute with name sue matches the string
"oreilly".
</app:equalsattribute>
The Bean Scripting Framework (BSF) is used for incorporating
various scripting into Java applications and applets. Supported
scripts in BSF include Javascript, VBScript, Perl, Tcl, Python,
NetRexx, and Rexx. If you are interested in more details pertaining to
BSF you can check out IBM's Bean Scripting Framework
page. The BSF taglib allows any of these languages to be used in
JSPs. There are scriptlet tags that are the equivalent of
<% in a JSP, and expression tags that are equivalent
to <%=. You specify which language you are using to
the tag.
The DateTime taglib makes dealing with dates and times
easier. It contains tags that handle formatting, generating dates,
using time zones, dealing with localization, and parsing. It doesn't
get much easier than
<%-- Display the current time formatted --%>
The current time is: <dt:format pattern="MM/dd/yyyy
hh:mm"><dt:currenttime/></dt:format>
DBTags, formerly called JDBC, contain tags that can be used to read
and write to an SQL database. It includes connection management,
creating and executing statements, prepared statements, testing and
formatting of result sets. To say that this taglib could save you
hours of coding is probably an understatement; having some
understanding of JDBC helps.
The I18N taglib is useful for creating
internationalized web applications. The bundle tag is used for loading
the resource bundle based on locale, while the message tag is used for
looking up keys in the bundle.
The Input taglib allows the user to present HTML
<form> elements that are tied to the
ServletRequest. Tags in this lib allow for default values
to be placed on forms when necessary. This lib is optimized for a
special case -- tying data to the ServletRequest object
and providing the standard form elements.
The IO library allows URLs and HTTP requests to be performed. So
JSP can be used to perform HTTP GET or PUT
operations and to make XML-RPC and SOAP requests. Currently the IO
library supports any protocol supported by the Java URL class. This
includes file system, FTP, HTTP, HTTPS, XML-RPC, and SOAP. The
<jsp:include> is only capable of including a
servlet that is in your current web application. The
<io:request> included in this taglib can be used to
make "server side include" style calls to any web server anywhere for
any resource. There is also a Unix-like pipe tag that can be used to
pipe between tags that can't pipe themselves.
The JNDI Library creates an instance of a
javax.naming.Context from attributes providing some of
the standard values. Attributes can include URL, initialFactory, id,
and scope. You can also do lookups, searches, and listings of
contexts.
The JSP Spec taglib is the resource to use if you are looking for
examples of how to do the things described in version 1.1 of the JSP
specification. This library focuses on techniques more than on
production scenarios. It can be useful to those just coming up to
speed on writing custom tag libraries.