The ColdFusion Markup Language is 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. Custom ColdFusion tags can be developed in either CFML or C++ using the CFX plug-in API.

Java servlets are becoming the most effective way to build server-side Web plug-ins. Because servlets are written in Java, they can run just about anywhere and connect to nearly anything. They're faster than CGI scripts and easier to write than native platform plug-ins such as Microsoft's Internet Server API (ISAPI), Netscape's Server API (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.

JRun is the award-winning, industry-leading servlet engine for developing and deploying Java servlets. It's an easy-to-use Web server plug-in that allows you to deploy Java servlets and JavaServer Pages (JSP). JRun was developed by Live Software, which was recently acquired by Allaire Corporation. For more information on JRun and to download a free copy visit www.livesoftware.com.

With a few simple examples this article will demonstrate how easy it is to invoke Java servlets within your CFML pages using JRun.

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 and tag attributes are available to the servlet using the ServletRequest.getParameter() method.

For example, let's say we want to invoke JRun's EmailLiteServlet (included in the JRun Servlet Pack One) to send an e-mail after a form submission. Using NCSA-style Server Side Includes (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 a JRun running on the same machine as ColdFusion. Since JRun's proxy protocol is TCP/IP based, however, you can invoke servlets anywhere you have a JRun, even through a firewall. The following code shows using the JRUNPROXY attribute to access a JRun running on the MyServer.com host:

<CF_SERVLET CODE=MyCoolServlet JRUNPROXY=MyServer.com:8081 Cool="you bet">

Because you're 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 plug-ins.

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 makes 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.

What About <CF_Anywhere>?
<CF_Anywhere> is a servlet-based CFML engine included in JRun. It translates a CFML subset into Java servlets on the fly, in a manner similar to JSP. Although <CF_Anywhere> also uses the CF_SERVLET tag to invoke servlets, the implementation is completely different from that of 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 can't be said for other custom CFX plug-ins.

Pricing Information
JRun Pro (Win, Unix, Novell, Mac versions): $595 per processor
JRun Pro Unlimited (Win, Unix, Novell, Mac versions): $1,995 per machine

Conclusion
ColdFusion, CF_SERVLET and JRun together make a great combination: the power of CFML scripting plus the power of Java servlets. If you're a CFML developer considering writing a ColdFusion custom tag, you now have a choice other than CFML, C++ or CFX_J (Java-based version of the C++ CFX API). With CF_SERVLET you can write a Java servlet that can be used by CFML developers or with any Web server or application server. If you're a third-party Java servlet developer writing Web plug-ins for your application, a single servlet could replace your custom ISAPI, NSAPI and CFX plug-ins and broaden your customer base dramatically. If you're a Java servlet developer who wants to tap into the huge market for CF custom tags, CF_SERVLET and JRun are your solution.