Click here to close now.

Welcome!

You will be redirected in 30 seconds or close now.

ColdFusion Authors: Yakov Fain, Maureen O'Gara, Nancy Y. Nee, Tad Anderson, Daniel Kaar

Related Topics: ColdFusion

ColdFusion: Article

Tagging the Servlet: Part 1

Tagging the Servlet: Part 1

Online stores are the new, next-generation, "revolutionize the world as we see it today" way of doing business. In the context of business transactions, online stores use the global Internet to facilitate the purchase and sale of goods and services. The ability to support online sales is an essential component of the new e-business paradigm for Internet-based businesses today. Putting together an enterprise-level application for an Internet store involves design and integration of various technologies that play specific roles in a distributed computing environment. A distributed topology is a prerequisite for building such Internet applications since the Internet is inherently distributed in nature.

Due to the plethora of technology alternatives available in the computing arena today, designing architectures for an enterprise application involves choosing between technologies based on feasibility, applicability, cost, availability and several other factors. No solution is "the right one." The hard part is to figure out which technology to use to provide a particular functionality. The challenge is to take competing and complementary technologies and make them play nicely together.

This is the first in a series of articles on some of the prominent technologies available to build a simple Internet-based Ticket Store application. This application offers online purchase of airline tickets as well as goods sold in airports. Our discussion focuses on two prominent technologies: ColdFusion and some components of the Java platform, namely Java applets and servlets, RMI and JDBC. The modules implemented using CF will be presented here and in two subsequent issues of ColdFusion Developer's Journal. The modules implemented using Java will be discussed in Volume 4, issues 6, 7, and 9, of Java Developer's Journal.

One of the main objectives of this design is to illustrate how Java servlets can be used as access mechanisms in server modules that serve up data to application modules implemented in ColdFusion. Currently, a majority of services across the Internet are accessed through the use of CGI scripts. Servlets offer an attractive alternative to CGI, especially if you're using Java to provide the server-side functionality. This article will concentrate on why ColdFusion and Java servlets make a great combination for developing Web-based applications and how Java servlets can be accessed from ColdFusion templates. We'll walk through the design of a Custom Tag called CF_Servlet that will allow invocation of Java servlets from ColdFusion templates.

As I'd like to keep this discussion focused on servlet access from ColdFusion, I'll refrain from going into detail on servlets themselves. There are several good books and articles on servlets and I've provided references to a couple of them at the end of the article. While you don't need to be an expert on servlets to benefit from the discussion here, a basic familiarity with CGI, Java, URLs and ColdFusion Custom Tags is assumed.

Why Servlets?
So why would the developers of a full-fledged application server like ColdFusion be interested in using Java servlets? There is certainly an overlap in functionality. Some of the common reasons for opting to use Java servlets and ColdFusion templates are:

  • To access relational databases from the next tier of the distributed system. ColdFusion achieves this through a rich library of SQL-based tags and ODBC. Servlets achieve this via the use of JDBC.
  • To extend the capabilities of the Web server that serves up the data.
  • To add dynamism to the Web applications by enabling client-to-server interactivity.

    ColdFusion's most powerful feature is its capability to connect to data sources that are maintained in other applications. It allows the building of dynamic queries on the fly to retrieve data from such applications. This makes it the ideal tool for creating dynamic Web application components such as shopping carts, account management modules, purchasing modules and customer profiles.

    Servlets on the other hand excel at making server-side services available to the client in a dynamic and interactive fashion. They can be used to efficiently access a variety of services offered across different tiers of a distributed architecture. Basically, servlets serve HTML to the client. They also bring access control and enhanced security into the equation. They are closely tied to the Web server they run on and thus help extend the server's capabilities to the client. One thing servlets are not designed for is building sophisticated GUIs. They are primarily HTML servers.

    The focus in Java technologies is shifting toward server-side Java, and that makes servlets a prominent player in developing Web applications. Typically, ColdFusion-based applications would use servlets:
    1. To access server-side services offered by Java applications
    2. To gain access to RMI/CORBA services
    3. To perform sophisticated computation-intensive tasks on the server as opposed to burdening the client with this responsibility

    Accessing Servlets
    Clients can access servlets in the following ways:

  • Via a URL: This is the same as connecting to any site via a browser. The query string parameters at the end of the URL are picked up by servlets in the same manner as CGI programs.

  • Via Server-Side Includes (SSI): These are used to embed servlets within HTML pages. This is achieved through the use of tags in .html files. Files containing the ... tags are named with an .shtml extension. They can be accessed via any Web browser via a URL, similar to regular .html files.

    The remainder of this article focuses primarily on creating the CF_Servlet Custom Tag. This tag allows the ColdFusion templates to access servlets using either of the mechanisms listed above. It also allows the information needed to invoke the desired servlet to be specified from an Access database. Figure 1 shows the database with the names of three example servlets that can be invoked via the CF_Servlet tag.

    Before getting into the details of the tag, let's go over the pieces required to invoke the servlet on a Web server:

    For a URL invocation we'll need:

  • The name of the servlet class
  • The URL for the Web server that houses the servlet
  • Any query parameters that the servlet expects in the query string

    For an SSI invocation we'll need:

  • The name of the .shtml file
  • The URL for the Web server that houses the servlet

    I've written the following two sample servlets that can be used to test the CF_Servlet tag. You can download these (and the corresponding SSI [.shtml] files) from www.sys-con.com/coldfusion/sourcec.cfm:

    - HelloColdFusionServlet, HelloColdFusionServlet.shtml
    - TicketServlet, TicketServlet.shtml

    These servlets are clearly simplistic and exist only to demonstrate the use of the CF_Servlet tag.

    The servletURL.cfm template
    Before developing the CF_Servlet tag, we'll walk through the development of a template for invoking the servlets from a URL string. This is available in the file servletURL.cfm and is shown in Listing 1. The first part of the code is the usual HTML tags and the specification of the title for the browser. After this, the first statement in the of the document initializes the variable url. It is initialized to "http://" since all URLs will begin with the HTTP protocol (at least for our purposes). Basically, the purpose of this template is to build up this variable based on the input from the browser.

    The first thing we check is whether a trace parameter has been passed in. If it has, it will print out the final URL for invoking the servlet. If it hasn't, only the output from the servlet will be printed. The trace parameter can be used for debugging.

    Next, the variable database is initialized to "cfservlets." This is the name of the table illustrated in Figure 1. The idea is that if the servlet has an entry there, the data for invoking it doesn't need to be supplied with each invocation. If the servletdatabase parameter is supplied, the template will pick up the data from the database name supplied as the value for that parameter. The variable database is initialized with this value.

    The servletclass is a required parameter. Hence it is specified in the tag. None of the tags have any default values in this template because this template is meant for the generic invocation of servlets. In the absence of a parameter, it's better for it to fail than to invoke a default servlet.

    The next section is the CFQUERY tag that retrieves the fields for invoking the servlet. The key used is the servletclass, which is also the primary key in the database. Once the records are obtained from the table, the next step is to build the URL. The URL is built as follows:



    The URL is built up of four segments - the string "http://", the URL for the server, the directory for the servlet plug-ins on the server and the name of the servlet. The standard directory for servlets is the directory "servlet" under the Web server's root directory. A typical URL at this point would be:

    http://myURL.com/servlet/MyServlet

    If we were picking up all the data from the database, at this stage our URL would be complete. The program would skip the section and go on to check whether any queryString parameter was supplied in the URL that was used to invoke the servletURL template. If so, it's appended to the end of the URL (demarcated with a "?" character).

    Next, the trace variable is checked to see whether the URL needs to be printed out. This is followed by a check for the method parameter, which is used to specify "GET" or "POST" for the servlet. The servletURL template doesn't support "POST" yet. If the method parameter isn't supplied, the default service() method of the servlet is called.

    The actual invocation is made in the CFHTTP tag. If the "GET" method was specified, it is passed to the servlet and the doGet() method of the servlet is called. If not, no method is explicitly specified. This causes the servlet's service() method to be invoked (which in turn calls doGet(); hence the end result is the same).

    The last part of the template is the only significant piece as far as the browser user is concerned. The file content is output using the CFHTTP.FileContent variable.

    This template can be used to invoke servlets from the URL. Figure 2 illustrates two such invocations. The first one causes the servlet to be invoked using data from the database. The second supplies the data in the URL and also turns on the Trace flag to print out the URL being invoked. The URLs used in the screens are:

    http://localhost/Test/servletURL.cfm?serv-letdatabase=
    cfservlets&servletclass=HelloColdFusionServlet

    and

    http://localhost/Test/servletURL.cfm?serv-erurl=
    localhost&servletclass=HelloColdFusionServlet&Trace=ON

    The CF_Servlet Custom Tag
    Listing 2 shows the CF_Servlet tag, which is available in the file servlet.cfm. The changes from the template to the Custom Tag are trivial. Basically, instead of reading the parameters from the URL, they are obtained from the ATTRIBUTES supplied by the calling template. The values of the corresponding ATTRIBUTE fields are copied into appropriate variables in the tag.

    Listing 3 illustrates how the CF_Servlet tag is used. The file invokeHelloColdFusionServlet.cfm contains the code to invoke the HelloColdFusionServlet in three different ways to demonstrate the CF_Servlet tag's flexibility. The first one uses the "database invocation." It also supplies three NAME=VALUE style parameters (although they're not used by the servlet). The second invocation supplies the server URL and other data in the parameters passed to the tag. The third invocation uses the SSI file to invoke the servlet. The output of all three invocations is displayed on the same page. This is illustrated in Figure 3.

    Listing 4 shows an invocation of the TicketServlet via its SSI file. The TicketServlet simply sends back a hard-coded response for the flight query. However, it illustrates some key points in this design. The output of this invocation is displayed in two separate sections of the resultant page. The first half (Flight request Parameters) shows the parameters passed into the servlet; the second half, the output from the servlet that comes back to the ColdFusion Custom Tag.

    Listing 4 represents the basis for the interaction between a ColdFusion application and the service exposed by the TicketServlet. In a real application this query could have gone across to another server, done some comparison shopping for airline tickets, and so on. The key thing is that the ColdFusion application is abstracted from all this. It basically submits a query and gets a price quote back.

    So What's the Big Deal?
    There's nothing that the CF_Servlet tag provides you that you couldn't have gotten by just typing the URL in the browser. However, what it does allow you to do is set up a basic communication between a ColdFusion template and a servlet residing in, perhaps, another tier of the application. The output from the servlet is going to be available in your template and can feed the front-end application.

    The protocol for communication between ColdFusion and Java servlets as demonstrated in this article is simple and string based. But let's stop and think for a minute. The server side of this equation is in Java. One of Java's primary features is dynamic class loading. What if object names were supplied to the servlet by ColdFusion templates? These objects could be instantiated on the fly, used and then discarded. Well-known and published services (such as CORBA/RMI services) could be accessed via this simple means of communication.

    Development Environment
    The code shown in this article was developed on NT 4.0. The servlets were tested in JRun Pro 2.2. The version of ColdFusion used was 4.0. The JDK version for the Java classes was 1.17B, and JSDK 2.0 (Java Servlet Development Kit) was used for the servlets.

    The following files are available at www. ColdFusionJournal.com. The ".java" files will need to be installed in JRun in order to run the ColdFusion templates:
    Listing 1: ServletURL.cfm
    Listing 2: Servlet.cfm
    Listing 3: invokeHelloColdFusionServlet.cfm
    Listing 4:invokeTicketServlet.cfm
    Listing 5: HelloColdFusionServlet.java
    Listing 6: HelloColdFusionServlet.shtml
    Listing 7: TicketServlet.java
    Listing 8: TicketServlet.shtml

    A Microsoft Access database file is also available for the reader to download: cfservlets.mdb.

    The Online Airline Ticket Store
    In subsequent articles in this series we'll use the foundation built here to develop an example e-business store. The Online Ticket Store is an Internet-based application that allows an Internet user to log in and purchase tickets via a browser. It also offers an online store to purchase items normally offered in duty-free shops in the regular international airports. In the next article we'll build some of the basic components of the store such as a shopping cart and a profile manager. We'll also add some intelligence to our queries for purchasing tickets and getting some meaningful quotes.

    References
    Servlets: Hunter, J., and Crawford, W. (1999). Java Servlet Programming. O'Reilly and Associates.
    ColdFusion Custom Tags: Forta, B., et al. (1999). Advanced ColdFusion 4.0 Application Development, pp. 114-132.

  • More Stories By Ajit Sagar

    Ajit Sagar is Associate VP, Digital Transformation Practice at Infosys Limited. A seasoned IT executive with 20+ years experience across various facts of the industry including consulting, business development, architecture and design he is architecture consulting and delivery lead for Infosys's Digital Transformation practice. He was also the Founding Editor of XML Journal and Chief Editor of Java Developer's Journal.

    Comments (0)

    Share your thoughts on this story.

    Add your comment
    You must be signed in to add a comment. Sign-in | Register

    In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


    @ThingsExpo Stories
    With several hundred implementations of IoT-enabled solutions in the past 12 months alone, this session will focus on experience over the art of the possible. Many can only imagine the most advanced telematics platform ever deployed, supporting millions of customers, producing tens of thousands events or GBs per trip, and hundreds of TBs per month. With the ability to support a billion sensor events per second, over 30PB of warm data for analytics, and hundreds of PBs for an data analytics archive, in his session at @ThingsExpo, Jim Kaskade, Vice President and General Manager, Big Data & Ana...
    In the consumer IoT, everything is new, and the IT world of bits and bytes holds sway. But industrial and commercial realms encompass operational technology (OT) that has been around for 25 or 50 years. This grittier, pre-IP, more hands-on world has much to gain from Industrial IoT (IIoT) applications and principles. But adding sensors and wireless connectivity won’t work in environments that demand unwavering reliability and performance. In his session at @ThingsExpo, Ron Sege, CEO of Echelon, will discuss how as enterprise IT embraces other IoT-related technology trends, enterprises with i...
    When it comes to the Internet of Things, hooking up will get you only so far. If you want customers to commit, you need to go beyond simply connecting products. You need to use the devices themselves to transform how you engage with every customer and how you manage the entire product lifecycle. In his session at @ThingsExpo, Sean Lorenz, Technical Product Manager for Xively at LogMeIn, will show how “product relationship management” can help you leverage your connected devices and the data they generate about customer usage and product performance to deliver extremely compelling and reliabl...
    The Internet of Things (IoT) is causing data centers to become radically decentralized and atomized within a new paradigm known as “fog computing.” To support IoT applications, such as connected cars and smart grids, data centers' core functions will be decentralized out to the network's edges and endpoints (aka “fogs”). As this trend takes hold, Big Data analytics platforms will focus on high-volume log analysis (aka “logs”) and rely heavily on cognitive-computing algorithms (aka “cogs”) to make sense of it all.
    One of the biggest impacts of the Internet of Things is and will continue to be on data; specifically data volume, management and usage. Companies are scrambling to adapt to this new and unpredictable data reality with legacy infrastructure that cannot handle the speed and volume of data. In his session at @ThingsExpo, Don DeLoach, CEO and president of Infobright, will discuss how companies need to rethink their data infrastructure to participate in the IoT, including: Data storage: Understanding the kinds of data: structured, unstructured, big/small? Analytics: What kinds and how responsiv...
    Since 2008 and for the first time in history, more than half of humans live in urban areas, urging cities to become “smart.” Today, cities can leverage the wide availability of smartphones combined with new technologies such as Beacons or NFC to connect their urban furniture and environment to create citizen-first services that improve transportation, way-finding and information delivery. In her session at @ThingsExpo, Laetitia Gazel-Anthoine, CEO of Connecthings, will focus on successful use cases.
    Sensor-enabled things are becoming more commonplace, precursors to a larger and more complex framework that most consider the ultimate promise of the IoT: things connecting, interacting, sharing, storing, and over time perhaps learning and predicting based on habits, behaviors, location, preferences, purchases and more. In his session at @ThingsExpo, Tom Wesselman, Director of Communications Ecosystem Architecture at Plantronics, will examine the still nascent IoT as it is coalescing, including what it is today, what it might ultimately be, the role of wearable tech, and technology gaps stil...
    The true value of the Internet of Things (IoT) lies not just in the data, but through the services that protect the data, perform the analysis and present findings in a usable way. With many IoT elements rooted in traditional IT components, Big Data and IoT isn’t just a play for enterprise. In fact, the IoT presents SMBs with the prospect of launching entirely new activities and exploring innovative areas. CompTIA research identifies several areas where IoT is expected to have the greatest impact.
    Wearable devices have come of age. The primary applications of wearables so far have been "the Quantified Self" or the tracking of one's fitness and health status. We propose the evolution of wearables into social and emotional communication devices. Our BE(tm) sensor uses light to visualize the skin conductance response. Our sensors are very inexpensive and can be massively distributed to audiences or groups of any size, in order to gauge reactions to performances, video, or any kind of presentation. In her session at @ThingsExpo, Jocelyn Scheirer, CEO & Founder of Bionolux, will discuss ho...
    Roberto Medrano, Executive Vice President at SOA Software, had reached 30,000 page views on his home page - http://RobertoMedrano.SYS-CON.com/ - on the SYS-CON family of online magazines, which includes Cloud Computing Journal, Internet of Things Journal, Big Data Journal, and SOA World Magazine. He is a recognized executive in the information technology fields of SOA, internet security, governance, and compliance. He has extensive experience with both start-ups and large companies, having been involved at the beginning of four IT industries: EDA, Open Systems, Computer Security and now SOA.
    The industrial software market has treated data with the mentality of “collect everything now, worry about how to use it later.” We now find ourselves buried in data, with the pervasive connectivity of the (Industrial) Internet of Things only piling on more numbers. There’s too much data and not enough information. In his session at @ThingsExpo, Bob Gates, Global Marketing Director, GE’s Intelligent Platforms business, to discuss how realizing the power of IoT, software developers are now focused on understanding how industrial data can create intelligence for industrial operations. Imagine ...
    Operational Hadoop and the Lambda Architecture for Streaming Data Apache Hadoop is emerging as a distributed platform for handling large and fast incoming streams of data. Predictive maintenance, supply chain optimization, and Internet-of-Things analysis are examples where Hadoop provides the scalable storage, processing, and analytics platform to gain meaningful insights from granular data that is typically only valuable from a large-scale, aggregate view. One architecture useful for capturing and analyzing streaming data is the Lambda Architecture, representing a model of how to analyze rea...
    SYS-CON Events announced today that Vitria Technology, Inc. will exhibit at SYS-CON’s @ThingsExpo, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. Vitria will showcase the company’s new IoT Analytics Platform through live demonstrations at booth #330. Vitria’s IoT Analytics Platform, fully integrated and powered by an operational intelligence engine, enables customers to rapidly build and operationalize advanced analytics to deliver timely business outcomes for use cases across the industrial, enterprise, and consumer segments.
    The explosion of connected devices / sensors is creating an ever-expanding set of new and valuable data. In parallel the emerging capability of Big Data technologies to store, access, analyze, and react to this data is producing changes in business models under the umbrella of the Internet of Things (IoT). In particular within the Insurance industry, IoT appears positioned to enable deep changes by altering relationships between insurers, distributors, and the insured. In his session at @ThingsExpo, Michael Sick, a Senior Manager and Big Data Architect within Ernst and Young's Financial Servi...
    SYS-CON Events announced today that Open Data Centers (ODC), a carrier-neutral colocation provider, will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place June 9-11, 2015, at the Javits Center in New York City, NY. Open Data Centers is a carrier-neutral data center operator in New Jersey and New York City offering alternative connectivity options for carriers, service providers and enterprise customers.
    The explosion of connected devices / sensors is creating an ever-expanding set of new and valuable data. In parallel the emerging capability of Big Data technologies to store, access, analyze, and react to this data is producing changes in business models under the umbrella of the Internet of Things (IoT). In particular within the Insurance industry, IoT appears positioned to enable deep changes by altering relationships between insurers, distributors, and the insured. In his session at @ThingsExpo, Michael Sick, a Senior Manager and Big Data Architect within Ernst and Young's Financial Servi...
    PubNub on Monday has announced that it is partnering with IBM to bring its sophisticated real-time data streaming and messaging capabilities to Bluemix, IBM’s cloud development platform. “Today’s app and connected devices require an always-on connection, but building a secure, scalable solution from the ground up is time consuming, resource intensive, and error-prone,” said Todd Greene, CEO of PubNub. “PubNub enables web, mobile and IoT developers building apps on IBM Bluemix to quickly add scalable realtime functionality with minimal effort and cost.”
    Sensor-enabled things are becoming more commonplace, precursors to a larger and more complex framework that most consider the ultimate promise of the IoT: things connecting, interacting, sharing, storing, and over time perhaps learning and predicting based on habits, behaviors, location, preferences, purchases and more. In his session at @ThingsExpo, Tom Wesselman, Director of Communications Ecosystem Architecture at Plantronics, will examine the still nascent IoT as it is coalescing, including what it is today, what it might ultimately be, the role of wearable tech, and technology gaps stil...
    SYS-CON Events announced today that GENBAND, a leading developer of real time communications software solutions, has been named “Silver Sponsor” of SYS-CON's WebRTC Summit, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. The GENBAND team will be on hand to demonstrate their newest product, Kandy. Kandy is a communications Platform-as-a-Service (PaaS) that enables companies to seamlessly integrate more human communications into their Web and mobile applications - creating more engaging experiences for their customers and boosting collaboration and productiv...
    From telemedicine to smart cars, digital homes and industrial monitoring, the explosive growth of IoT has created exciting new business opportunities for real time calls and messaging. In his session at @ThingsExpo, Ivelin Ivanov, CEO and Co-Founder of Telestax, shared some of the new revenue sources that IoT created for Restcomm – the open source telephony platform from Telestax. Ivelin Ivanov is a technology entrepreneur who founded Mobicents, an Open Source VoIP Platform, to help create, deploy, and manage applications integrating voice, video and data. He is the co-founder of TeleStax, a...