- The Basics
- Web Pages
- Understanding ColdFusion
- What Is ColdFusion?
- ColdFusion Explained
- Powered by ColdFusion
This chapter is from the book
This chapter is from the book
This chapter is from the book
ColdFusion Explained
You're now ready to take a look at ColdFusion so you can understand what it is and how it works its magic.
And if you're wondering why you went through all this discussion about the Internet and Web servers, here's where it will all fit together.
The ColdFusion Application Server
ColdFusion is an application server—a piece of software that (usually) resides on the same computer as your Web server, enabling the Web server to do things it would not normally know how to do. ColdFusion is actually made up of several pieces of software (applications on Windows; and daemons on Linux, Solaris, and HP-UX). The ColdFusion Application Server is the program that actually parses (reads and compiles) and processes any supplied instructions.
Instructions are passed to ColdFusion using templates. A template looks much like any HTML file, with one big difference. Unlike HTML files, ColdFusion templates can contain special tags that instruct ColdFusion to perform specific operations. This is a sample ColdFusion template; it is one that you'll use later in this book.
<!--- Get movies sorted by release date ---> <CFQUERY DATASOURCE="ows" NAME="movies"> SELECT MovieTitle, DateInTheaters FROM Films ORDER BY DateInTheaters </CFQUERY> <!--- Create HTML page ---> <HTML> <HEAD> <TITLE>Movies by Release Date</TITLE> </HEAD> <BODY> <H1>Movies by Release Date</H1> <!--- Display movies in list format ---> <UL> <CFOUTPUT QUERY="movies"> <LI><B>#Trim(MovieTitle)#</B> - #DateFormat(DateInTheaters)#</LI> </CFOUTPUT> </UL> </BODY> </HTML>
Earlier in this chapter, it was stated that Web servers typically return the contents of a Web page without paying any attention to the file contents.
That's exactly what ColdFusion does not do. When ColdFusion receives a request, it parses through the template looking for special ColdFusion tags (they all begin with CF) or ColdFusion variables and functions (always surrounded by pound signs). Any HTML or plain text is left alone and is output to the Web server untouched. Any ColdFusion instructions are processed, and any existing results are sent to the Web server (just like in Figure 1.6 above). The Web server can then send the entire output back to the requester's browser. As explained earlier, the request file type tells the Web server that a request is to be handled by an application server. All ColdFusion files have an extension of .cfm or .cfml, like this:
){kind=link}
http://www.forta.com/books/index.cfm
When ColdFusion is installed, it configures your Web server so it knows that any file with an extension of .cfm (or .cfml) is a ColdFusion file. Then, whenever a ColdFusion file is requested, the Web server knows to pass the file to ColdFusion for processing rather than return it.
TIP
As ColdFusion is bound to a Web server, ColdFusion can be used to process any and all requests sent to a Web server, regardless of which host or virtual host it is sent to. But, ColdFusion is only ever bound to a single Web server, and so if you have multiple Web servers installed only one of them will be usable with ColdFusion (unless you plan to do lots of tweaking, a process not recommended at all). So, if you need to support multiple hosts, use a single Web server with IP or DNS based virtual hosts rather than multiple Web servers.
It is worth noting that ColdFusion MX actually does not need a Web server because it has one built in. So as not to conflict with any other installed Web servers (like Apache and Microsoft IIS) the internal Web server runs on port 8500 (instead of the default port 80). During ColdFusion MX installation you'll be asked whether you want to run ColdFusion in standalone mode (bound to the integrated Web server) or using an existing Web server. If you opt to use the internal Web server you'll need to specify the port number in all URLs.
NOTE
The examples in this book use the internal Web server, and thus include the port number. If you are using an external Web server just drop the port number from the URL's.
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Macromedia does not recommend that the internal Web server (standalone mode) be used on production boxes. ColdFusion MX's integrated HTTP server is intended for use on development boxes only.
The ColdFusion Markup Language
Earlier it was stated that ColdFusion is an application server, which is true, but that is not all Cold-Fusion is. In fact, ColdFusion is two distinct technologies:
The ColdFusion Application Server
The CFML language
And although the ColdFusion Application Server itself is important, ColdFusion's power comes from its capable and flexible language. ColdFusion Markup Language (CFML) is modeled after HTML, which makes it very easy to learn.
CFML extends HTML by adding tags with the following capabilities:
Read data from, and update data to, databases and tables
Create dynamic data-driven pages
Perform conditional processing
Populate forms with live data
Process form submissions
Generate and retrieve email messages
Interact with local files
Perform HTTP and FTP operations
Perform credit-card verification and authorization
Read and write client-side cookies
And that's not even the complete list.
The majority of this book discusses ColdFusion pages (often called templates) and the use of CFML.
Linking to External Applications
One of ColdFusion's most powerful features is its capability to connect to data created and maintained in other applications. You can use ColdFusion to retrieve or update data in many applications, including the following:
Corporate databases
Client/server database systems (such as Microsoft SQL Server and Oracle)
Spreadsheets
XML data
Contact-management software
ASCII-delimited files
Java beans, JSP tag libraries, and EJBs
Web Services
ColdFusion accesses these applications via database drivers (JDBC and ODBC).
Database drivers are explained in detail in Chapter 5, "Introducing SQL."
Extending ColdFusion
As installed, ColdFusion will probably do most of what you need, interacting with most of the applications and technologies you'll be using. But in the event that you need something more, ColdFusion provides all the hooks and support necessary to communicate with just about any application or service in existence. Integration is made possible via:
- C and C++
- Java
- COM
- CORBA
- Web Services
These technologies and their uses are beyond the scope of this book and are covered in detail in the sequel Advanced ColdFusion MX Application Development (Macromedia Press, ISBN: 0321127102).
Beyond the Web
As was explained earlier, the Web and the Internet are not one and the same. The Web is an application that runs on top of the Internet, one of many applications. Others do exist, and you can use and take advantage of many of them.
One of the most exciting new technologies is Wireless Application Protocol (WAP), which can be used to power applications accessed via wireless devices (such as phones and PDAs).
As explained earlier, Web servers (and thus application servers) send content back to requesters without paying attention to what that content is. The requester (known as the client or user agent) is typically a Web browser, but it need not be. In fact, WAP browsers (the Internet browsers built into WAP devices) can also make requests to Web servers.
WAP and generating WAP content using ColdFusion are discussed in Chapter 32, "Generating Non-HTML Content."
In other words, although ColdFusion is primarily used to generate Web content, it is not limited to doing so in any way, shape, or form. As seen in Figure 1.7, the same server can generate content for the Web, WAP, email, and more.
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Figure 1.7 ColdFusion is client independent and can generate content for
many types of clients, not just Web browsers.
Inside ColdFusion MX
ColdFusion MX is the most remarkable ColdFusion to date, and is the first completely redesigned and rebuilt ColdFusion since the product was first created back in 1995. While understanding the inner workings of ColdFusion MX are not a prerequisite to using the product, understanding what ColdFusion is doing under the hood will help you to better leverage this remarkable product.
As already explained, ColdFusion is a page preprocessor—it processes pages and returns the results as opposed to the page itself. To do this ColdFusion has to read each file, check and validate the contents, and then perform the desired operations. But there is actually much more to it than that—in fact, within ColdFusion is a complete J2EE (Java 2 Enterprise Edition) server that provides the processing power ColdFusion needs.
NOTE
Don't worry, you need know no Java at all to use ColdFusion.
First, a clarification. When people talk about Java they generally mean two very different things:
The Java language is just that, a programming language. It is powerful and not at all easy to learn or use.
The Java platform, a complete set of building blocks and technologies to build rich and powerful applications.
Of the two, the former is of no interest (well, maybe little interest) to ColdFusion developers. After all, why write complex code in Java to do what CFML can do in a single tag? But Java the platform, now that is compelling. The Java platform provides the wherewithal to:
Access all sorts of databases
Interact with legacy systems
Support mobile devices
Use directory services
Create multilingual and internationalized applications
Leverage transactions, queuing, and messaging
Create robust and highly scalable applications
In the past you'd have had to write Java code in order to leverage the Java platform, but not anymore. ColdFusion MX runs on top of the Java platform, providing the power of underlying Java made accessible via the simplicity of CFML.
NOTE
By default, the Java engine running ColdFusion MX is Macromedia's own award-winning J2EE server, JRun. ColdFusion MX can also be run on top of third party J2EE servers like IBM's WebSphere and BEA's WebLogic. See Appendix A, "Installing ColdFusion MX and Dreamweaver MX" for more information.
But don't let the CFML (and CFM files) fool you—when you create a ColdFusion application you are actually creating a Java application. In fact, when ColdFusion MX processes your CFM pages it actually creates Java source code and compiles it into Java bytecode for you, all in the background. This behavior is new to ColdFusion MX, and is part of why this is the most important new Cold-Fusion to date. Using ColdFusion MX you can truly have the best of both worlds—the power of Java, and the simplicity of ColdFusion, and all without having to make any sacrifices at all.
Appendix F, "ColdFusion MX Directory Structure", explains many of the Java files used in ColdFusion MX.