Extending ColdFusion with Servlets

Introduction

Allaire Corporation's Cold Fusion Markup Language (CFML) is perhaps the easiest way to generate dynamic web content from a database. Its tag-based scripting commands are simple for HTML authors to learn, yet powerful enough for building full-featured web applications. Since 1995, thousands of websites have been developed with Allaire's popular ColdFusion Application Server. Custom CF tags can be developed either in CFML or with the CFX plugin API in C++. The market for third-party custom tags is growing extremely quickly.

In the meantime, Java servlets are becoming the most effective way to build server-side web plugins. Servlets can run just about anywhere and connect to nearly anything. They are faster than CGI scripts and easier to write than native plugins such as ISAPI, NSAPI, and CFX. You can write entire applications with servlets or use them as "web glue" to webify anything from a printer to a mainframe. And Live Software's JRun is the leading platform for developing and deploying servlets.

With a few simple examples, this article will demonstrate how to invoke servlets within your CFML pages using JRun, combining these two technologies into one great solution. CF_SERVLET

Anyone familiar with the <SERVLET> tag will immediately understand <CF_SERVLET>. It invokes the named servlet, running on JRun, and the results are included in the output of the page. Common HTTP headers, as well as tag attributes, are available to the servlet using ServletRequest.getParameter(), just as in NSCA-style Server Side Includes (SSI).

For example, let's say that we want to invoke Live Software's EmailLiteServlet (included in Servlet Pack One) to send an email after a form submission. In SSI, the invocation would look as follows:

<SERVLET CODE=EmailLiteServlet>
       <PARAM NAME="host" VALUE="pop.somehost.com">
       <PARAM NAME="dest" VALUE="http://www.myhost.com/successpage.shtml">
       <PARAM NAME="from" VALUE="me@myhost.com">
       <PARAM NAME="to" VALUE="you@somehost.com">
       <PARAM NAME="subject" VALUE="Servlets are cool">
       <PARAM NAME="body" VALUE="Because they can run from ColdFusion">
</SERVLET>

The same servlet can be invoked much more simply from ColdFusion as follows:

<CF_SERVLET CODE=EmailLiteServlet
       host="pop.somehost.com"
       dest="http://www.myhost.com/successpage.cfm"
       from="me@myhost.com"
       to="you@somehost.com"
       subject="Servlets are cool"
       body="Because they can run from ColdFusion">

By default, CF_SERVLET connects to JRun running on the same machine as ColdFusion. Since JRun's proxy protocol is TCP/IP based, however, you can invoke servlets anywhere that you have a JRun, even through a firewall:

<CF_SERVLET CODE=MyCoolServlet
       JRUNPROXY=192.168.1.2:8081
       Cool="you bet">

And because you are still running inside a ColdFusion page, you can even dynamically choose where to connect to JRun. For example, the user could enter it in a form field:

<CF_SERVLET CODE=RenderNewDo
       JRUNPROXY=#Form.JRUNPROXY#
       Cool=#Form.HAIRSTYLE#>

The advantages of CF_SERVLET stem from CFML being an easy to use, tag-based scripting language and servlets being easy to write, powerful plugins.

How it Works: CFX_JRUN

CF_SERVLET is a CFML wrapper around CFX_JRUN, a C++ based JRun connector. JRun's out-of-process, connector-based architecture renders it simple to plug into any server environment (web server or application server). CFX_JRUN hooks JRun into ColdFusion, translating between the CFX API and JRun's proxy protocol. Like JRun's other native connectors, CFX_JRUN has a very small footprint. Once CFX_JRUN is configured into ColdFusion, CF_SERVLET can be dropped into any CFML page, wherever it is needed.

What about <CF_Anywhere>?

Live Software's <CF_Anywhere> is a servlet-based CFML engine. It translates CFML pages into Java servlets on the fly, in a manner similar to Java Server Pages (JSP). Although <CF_Anywhere> also uses the CF_SERVLET tag to invoke servlets, the implementation is completely different than in ColdFusion. Your custom servlets can thus be invoked equally well from a CFML page, whether that page is executing on ColdFusion or <CF_Anywhere>. The same thing cannot be said for other custom CFX plugins.

Conclusion

ColdFusion, CF_SERVLET, and JRun together make a great combination: the power of CFML scripting plus the power of Java servlets.

If you are a CFML developer considering writing a ColdFusion custom tag, you now have a choice other than CFML and C++. With CF_SERVLET, you can write a Java servlet that can be used by CFML developers or with any web or application server.

If you are a third-party Java servlet developer writing web plugins for your application, a single servlet could replace your custom ISAPI, NSAPI, and CFX plugins and broaden your customer base dramatically.

If you are a Java servlet developer who wants to tap into the huge market for CF custom tags, CF_SERVLET and JRun are your solution.

Live Software once again provides an innovative solution by combining JRun, CF_SERVLET, and ColdFusion.

Edwin Smith is a Principal Software Engineer at Allaire Corporation and works closely with all aspects of JRun engineering, particularly Java/native integration, system architecture, and performance optimization. Ed is also an avid motorcycle enthusiast and road racer, winning the amateur lightweight superbike national title at Daytona in 1996.