Fri, Jul
2 New Articles

Reusing Legacy Code in Business Applications for the Web

Web Languages
  • Smaller Small Medium Big Bigger
  • Default Helvetica Segoe Georgia Times

Rather than rewrite older business applications, consider using a method such as APIs, stored procedures, or UDFs to access legacy app functions

By Laura Ubelhor and Christian Hur

Editor’s note: This article is excerpted from chapter 7 of Developing Business Applications for the Web: With HTML, CSS, JSP, PHP, ASP.NET, and JavaScript, by Laura Ubelhor and Christian Hur.

Making the decision to include Web applications as part of your business systems doesn’t mean you have to scrap the applications already in use. It might make sense to leave some of these applications as they are, and only deploy select applications on the Web. Many organizations already have applications in which they have invested considerable resources, time, and money. Many of these applications are stable and still well suited to the business requirements. There is no reason to rewrite all your applications unless a business need requires a change.

It’s wise to consider whether legacy code can be reused. Doing so might well affect the design, choice of tools, and framework for Web application development. It isn’t always feasible to rewrite legacy code or maintain two different versions of programs that do the same thing. If you have existing applications that include detailed and complicated logic, it is possible to include these applications without a complete rewrite. There are many ways you can reuse legacy code. We discuss a few options here.


An application program interface (API) enables one program to communicate with another. For example, an API can be used from within a PHP, JSP, or ASP.NET application program to execute and share data with a legacy application. APIs were developed in response to the need to exchange information between two or more different software applications. APIs have been around for a long time, and most systems can use them. Stored procedures and user-defined functions are two types of APIs.

Stored Procedures

A stored procedure is a subroutine available to applications that make use of a RDBMS. Stored procedures are typically used for data validation, access control, or to trigger execution of a legacy application. Stored procedures are used to consolidate and centralize logic that was originally implemented in applications. Stored procedures must be invoked using a call statement (unlike user-defined functions, which can be used like any other expression within SQL statements). Here is an example of a call statement:

CALL procedurename(parm1, parm2)

Stored procedures can be used to return data result sets or may be used as a method to initiate another application to execute. Stored procedures may also receive and return variables, making it possible to pass parameters between the Web application and the stored procedure. While the call to the stored procedure is quite simple, you need information specific to your platform and DBMS to create the stored procedure.

On most platforms, a stored procedure can only be used to execute SQL statements and directives. Stored procedures are cataloged in the SQL system catalog using the CREATE PROCEDURE statement. On an IBM i system, however, the rules for stored procedures are relatively relaxed; the stored procedure can be written in several languages, including RPG, COBOL, FORTRAN, PL/I, REXX, CL, and C. Stored procedures written in a language other than SQL are usually referred to as external stored procedures. External stored procedures do not necessarily have to include embedded SQL statements, and they do not need to be cataloged. Other platforms provide similar functionality. You will need to verify the platform that you are using provides this functionality.

One example of how a stored procedure can enable reuse legacy code is to create a stored procedure that executes a legacy application. You pass required parameters within the stored procedure call within the Web application. This enables you to access and use the complicated code or extensive business logic of the legacy application without a rewrite.

Figure 1 provides an example of creating a stored procedure using SQL on an IBM i to initiate running an RPGLE program. In this example, a stored procedure named MYSTRPRC is created in library MYLIB. The procedure created references the RPG program named MYRPGPGM in the library MYLIBRARY. In this example, no parameters are passed.

Step 1: Create the stored procedure on the IBM i










Step 2: Call the stored procedure from a Web application

CallableStatement cstmt = connection.prepareCall("CALL MYLIBRARY.MYSTOREDRPROC");

Figure 1: Using a stored procedure to call an IBM i RPGLE program

Figure 2 shows another example of creating a stored procedure using SQL on an IBM i to run a CL program. This example is very similar to the one in Figure 1, except it calls a CL program rather than an RPGLE program. Also, two parameters are passed: PARMIN and PARMOUT. The call statement is from a Java program.

Step 1: Create the stored procedure









Step 2: Call the stored procedure

CallableStatement cstmt = connection.prepareCall("CALL LUBELHOR/HITACHICLP (?, ?)");

Figure 2: Using a stored procedure to call an iSeries CL program

User-defined Functions

User-defined functions (UDFs) are another possible option to reuse legacy code with minimal or no changes to the code. Most database management applications with SQL roots allow the use of UDFs. Calling legacy code is not the sole purpose of UDFs, but it is one of the possible uses.

Like a stored procedure, a UDF is executed by a call statement. The main difference between stored procedures and UDFs is that a stored procedure must be invoked using a call statement, while a UDF can be used like any other expression within a SQL statement.

Figure 3 is an example of how to create a DB2 UDF on an IBM i for referencing an RPGLE program. (The syntax for other database systems and platforms will vary slightly.) In the example, an integer variable is passed and will return a 15,0 decimal value. Once created, this function can be executed within PHP, JSP, or ASP.NET.














Figure 3: Creating a UDF

While stored procedures can have input and output parameters, UDFs have only input parameters. An output parameter must be returned as a return value. However, just because UDFs return a single value does not mean they can’t include applications with complex logic.

Some DBMSs with roots in SQL may allow use of user-defined table functions (UDTFs). A UDTF is a UDF that returns a virtual table instead of a single value. Using a UDTF, you can return a set of values. Like a stored procedure, a UDTF allows code reuse with minimal changes, enabling you to use legacy applications in coordination with Web applications.

The create function statement in Figure 4 identifies the function name in this example, MYFUNCTION, within the library MYLIBRARY. The external name keyword specifies the ILE CL program the function calls. In this example, it is MYUDTFPGM, found in the library MYLIBRARY. The example uses two parameters: PARM1 is a character value, and PARM2 is a decimal value.



PARM1     CHAR   (10)

, PARM2     DECIMAL (5, 0)















Figure 4: Creating a UDFT

If you want to reuse legacy code within Web applications, research the possibility of using a UDF or UDTF. The syntax is usually pretty similar from platform to platform. The answer to the question “how to” likely can be found within your DBMS documentation. Which one you use is best answered after thoroughly reviewing the documentation specific to your platform. The Web is another good resource for research. UDFs have been used in many organizations for legacy code reuse. If the DBMS you are using provides for UDFs or UDTFs, you’ll easily be able to find examples of them on the Web.

Conversion Tools

Many platforms provide software applications that can be used to convert legacy programs from one language to another. Sometimes, the conversion tools are referred to as migration tools. On some platforms, the tools may be provided for free to encourage the use of newer technology. In other instances, the tools must be purchased. If you’d like to keep legacy code but don’t want to rewrite applications, it is worth researching conversion tools. The work required to complete the conversion may be done by in-house staff or by an outside service provider. Conversion may also be used to move software from one platform to another in a format that can be used on the new platform.

Conversion likely will not be worthwhile if you only need to reuse a select few applications. If you need to reuse a large system or all your applications, however, a conversion tool might well be the right solution.

About the Authors

Laura Ubelhor owns and operates Consultech Services, Inc., a Rochester, Michigan-based technology consulting company. She is an author of HTML for the Business Developer (MC Press, 2008) and many technology articles. She also helped write the COMMON certification RPG and Business Computing Professional exams.

Laura has been involved in the Southeast Michigan iSeries User group since 1988, and has served as group president for over 15 years and as lead organizer for the group’s annual MITEC conference. She is also a longtime volunteer for COMMON, the IBM i and Power Systems user group, and has spent much of her career advocating for IT professional education.

Christian Hur is an IT-Web Instructor at Gateway Technical College in Racine, Wisconsin, where he teaches courses in Web Development and Microsoft SharePoint. Christian also manages Gateway’s Ubuntu (Linux) Web server, which runs on an IBM Power 8. Christian has a BLS from the University of Wisconsin-Oshkosh and is an MSCIS candidate at Boston University.

Christian has more than 20 years’ experience in Web development and has built many websites and Web applications using HTML, CSS, JavaScript, PHP, and ASP/ASPX. He has managed dedicated Web servers and maintained websites using various CMS applications. He is also an entrepreneur who cofounded two companies.

Laura Ubelhor
Laura Ubelhor owns and operates Consultech Services, Inc., a Rochester, Michigan-based technology consulting company. She has written many technology articles and is co-author of Developing Business Applications for the Web and HTML for the Business Developer. Laura also helped write the COMMON certification RPG and Business Computing Professional exams. She has been involved in the Southeast Michigan iSeries User group since 1988 and has served as group president for over 15 years, as well as lead organizer for the group’s annual MITEC conference. Laura is also a longtime volunteer for COMMON, the IBM i and Power Systems user group, and has spent much of her career advocating for IT professional education.

MC Press books written by Laura Ubelhor available now on the MC Press Bookstore.

Developing Business Applications for the Web Developing Business Applications for the Web
Gain the knowledge you need to build Web browser front-end applications that let users interact with business data.
List Price $79.95

Now On Sale

HTML for the Business Developer HTML for the Business Developer
Learn how to develop and deploy robust, data-driven, Web-based interfaces for your business applications.
List Price $49.95

Now On Sale



Support MC Press Online


Book Reviews

Resource Center

  • SB Profound WC 5536 Have you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application. You can find Part 1 here. In Part 2 of our free Node.js Webinar Series, Brian May teaches you the different tooling options available for writing code, debugging, and using Git for version control. Brian will briefly discuss the different tools available, and demonstrate his preferred setup for Node development on IBM i or any platform. Attend this webinar to learn:

  • SB Profound WP 5539More than ever, there is a demand for IT to deliver innovation. Your IBM i has been an essential part of your business operations for years. However, your organization may struggle to maintain the current system and implement new projects. The thousands of customers we've worked with and surveyed state that expectations regarding the digital footprint and vision of the company are not aligned with the current IT environment.

  • SB HelpSystems ROBOT Generic IBM announced the E1080 servers using the latest Power10 processor in September 2021. The most powerful processor from IBM to date, Power10 is designed to handle the demands of doing business in today’s high-tech atmosphere, including running cloud applications, supporting big data, and managing AI workloads. But what does Power10 mean for your data center? In this recorded webinar, IBMers Dan Sundt and Dylan Boday join IBM Power Champion Tom Huntington for a discussion on why Power10 technology is the right strategic investment if you run IBM i, AIX, or Linux. In this action-packed hour, Tom will share trends from the IBM i and AIX user communities while Dan and Dylan dive into the tech specs for key hardware, including:

  • Magic MarkTRY the one package that solves all your document design and printing challenges on all your platforms. Produce bar code labels, electronic forms, ad hoc reports, and RFID tags – without programming! MarkMagic is the only document design and print solution that combines report writing, WYSIWYG label and forms design, and conditional printing in one integrated product. Make sure your data survives when catastrophe hits. Request your trial now!  Request Now.

  • SB HelpSystems ROBOT GenericForms of ransomware has been around for over 30 years, and with more and more organizations suffering attacks each year, it continues to endure. What has made ransomware such a durable threat and what is the best way to combat it? In order to prevent ransomware, organizations must first understand how it works.

  • SB HelpSystems ROBOT GenericIT security is a top priority for businesses around the world, but most IBM i pros don’t know where to begin—and most cybersecurity experts don’t know IBM i. In this session, Robin Tatam explores the business impact of lax IBM i security, the top vulnerabilities putting IBM i at risk, and the steps you can take to protect your organization. If you’re looking to avoid unexpected downtime or corrupted data, you don’t want to miss this session.

  • SB HelpSystems ROBOT GenericCan you trust all of your users all of the time? A typical end user receives 16 malicious emails each month, but only 17 percent of these phishing campaigns are reported to IT. Once an attack is underway, most organizations won’t discover the breach until six months later. A staggering amount of damage can occur in that time. Despite these risks, 93 percent of organizations are leaving their IBM i systems vulnerable to cybercrime. In this on-demand webinar, IBM i security experts Robin Tatam and Sandi Moore will reveal:

  • FORTRA Disaster protection is vital to every business. Yet, it often consists of patched together procedures that are prone to error. From automatic backups to data encryption to media management, Robot automates the routine (yet often complex) tasks of iSeries backup and recovery, saving you time and money and making the process safer and more reliable. Automate your backups with the Robot Backup and Recovery Solution. Key features include:

  • FORTRAManaging messages on your IBM i can be more than a full-time job if you have to do it manually. Messages need a response and resources must be monitored—often over multiple systems and across platforms. How can you be sure you won’t miss important system events? Automate your message center with the Robot Message Management Solution. Key features include:

  • FORTRAThe thought of printing, distributing, and storing iSeries reports manually may reduce you to tears. Paper and labor costs associated with report generation can spiral out of control. Mountains of paper threaten to swamp your files. Robot automates report bursting, distribution, bundling, and archiving, and offers secure, selective online report viewing. Manage your reports with the Robot Report Management Solution. Key features include:

  • FORTRAFor over 30 years, Robot has been a leader in systems management for IBM i. With batch job creation and scheduling at its core, the Robot Job Scheduling Solution reduces the opportunity for human error and helps you maintain service levels, automating even the biggest, most complex runbooks. Manage your job schedule with the Robot Job Scheduling Solution. Key features include:

  • LANSA Business users want new applications now. Market and regulatory pressures require faster application updates and delivery into production. Your IBM i developers may be approaching retirement, and you see no sure way to fill their positions with experienced developers. In addition, you may be caught between maintaining your existing applications and the uncertainty of moving to something new.

  • LANSAWhen it comes to creating your business applications, there are hundreds of coding platforms and programming languages to choose from. These options range from very complex traditional programming languages to Low-Code platforms where sometimes no traditional coding experience is needed. Download our whitepaper, The Power of Writing Code in a Low-Code Solution, and:

  • LANSASupply Chain is becoming increasingly complex and unpredictable. From raw materials for manufacturing to food supply chains, the journey from source to production to delivery to consumers is marred with inefficiencies, manual processes, shortages, recalls, counterfeits, and scandals. In this webinar, we discuss how:

  • The MC Resource Centers bring you the widest selection of white papers, trial software, and on-demand webcasts for you to choose from. >> Review the list of White Papers, Trial Software or On-Demand Webcast at the MC Press Resource Center. >> Add the items to yru Cart and complet he checkout process and submit

  • Profound Logic Have you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application.

  • SB Profound WC 5536Join us for this hour-long webcast that will explore:

  • Fortra IT managers hoping to find new IBM i talent are discovering that the pool of experienced RPG programmers and operators or administrators with intimate knowledge of the operating system and the applications that run on it is small. This begs the question: How will you manage the platform that supports such a big part of your business? This guide offers strategies and software suggestions to help you plan IT staffing and resources and smooth the transition after your AS/400 talent retires. Read on to learn: