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Jakarta Taglibs
Pages: 1, 2, 3

If you need to send mail from a JSP, the Mailer taglib can help you out. Mail can be sent in three ways; using the name of the SMTP host, using the name of a JNDI Resource for a JavaMail Session, or using the name of a JNDI Resource for a JavaMail MimePartDataSource. Tags for including all necessary message parts, including body, header, to, cc, subject, and send, are included. Using Mailer might look like

<!-- Create a message by using the SMTP host, specified
in the --> 
 <!—- server attribute --> 
<!-- The body of the e-mail is supplied in the -->
<!-- message tag. The send tag is necessary to send the message. -->
<<a href="mailto:mt:mail%20server=%22switchbacksoftware.com%22%20to= %22developers@switchbacksoftware.com%22%20from= %22sspielman@switchbacksoftware.com%22%20subject= %22Mark%20Twain%20Quote"> mt:mail server="switchbacksoftware.com" to="developers@switchbacksoftware.com" from="sspielman@switchbacksoftware.com" subject="Mark Twain Quote</a>"> <mt:message>Always do right. This will gratify some people and astonish the rest. </mt:message> <mt:send/> </mt:mail>

There are four separate taglibs that are focused on tags related to Page, Request, Response, and Session. If you need to access the PageContext, or attributes within a page-scope, the Page taglib will provide tags for getting, setting, and testing of attributes. The Request lib currently has 28 tags that provide a variety of actions. They can be grouped into the following categories: session, attributes, cookie, header, and queryStrings. Basically anything that you want or need to do with a request can be handled with this tag library. The Response lib can be used to set cookies, encode, redirect, set header information, or send status in a response. Tags in the Session lib are useful for getting, setting, and, testing attributes in the session as well as for invalidating and setting timeout limits.

The regexp custom tag library contains tags that can be used to perform Perl-like regular expressions. These tags implement the three most common Perl 5 operations involving regular expressions:

  • [m]/pattern/[i][m][s][x]
  • s/pattern/replacement/[g][i][m][o][s][x]
  • and split()

As with Perl, any non-alphanumeric character can be used in lieu of the slashes. In order to use this taglib you not only need a servlet container, but you also need the Jakarta ORO Perl Regular Expression package.

Scraping or extracting content from web documents is common these days. After your JSP scrapes a document for the first time, the results can be cached for subsequent JSP requests using the Scrape taglib. These results are returned unless the JSP determines that the document must be rescraped using predefined logic. By specifying the URL and text anchors to mark the beginning and ending of content to be scraped, you can easily provide information from other sites, such as stock quotes, in your pages.

The Utility taglib has samples of some basic tags. Some of which, like the hello tag, are strictly for demonstration purposes, while others can actually be used like the copy, paste, and showsource tags. There are also conditional and looping tags.

XSL (eXtensible Stylesheet Language) uses XSLT to perform transformations of XML documents. The XSL taglib provides tags to apply a specified URI that points an XSL file to an XML document (which is itself specified by a URI). The InsertWithXSL will insert the transformed result into the writer of the JSP. This taglib requires the binary distributions of the Apache Xerces XML parser as well as the Apache Xalan XSL processor. Both can be found on the Apache XML site.

Last but not least is the Xtags taglib. This is a brand new taglib that was just added to the Jakarta project by Citria Ltd. XTags implement an XSLT-like JSP tag library to allow navigating, processing, and styling of XML documents directly in JSP. XTags makes heavy use of the XPath expression language and is built on top of dom4j. Using this taglib requires dom4j and log4j. To be able to use the <xtags:style> tag, JAXP is required along with an XSLT implementation such as xalan.jar and crimson.jar, both available from http://xml.apache.org.

There is also an SQL sample taglib, but it's no longer supported. So if you want the SQL functionality, try using the DBTags mentioned above.

Summary

So there you have it. Hours of coding (not to mention debugging) saved by using one of the many available taglibs from the Jakarta project. Chances are some of them have tags that you could use in your current JSP application. Why reinvent the wheel?

The value of open source is that you can use (and contribute) code that has been run, reviewed, and tested by many. Let's rephrase that: if you are using custom tag libraries in your JSP, and you are not using at least one of the Jakarta taglibs in the project, you may be spending money on development cycles that are both unnecessary and wasteful. Simple enough.

Sue Spielman is an associate editor for ONJava.com, covering JSP and Servlets technologies. She is also President and Senior Consulting Engineer for Switchback Software LLC.


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