13
Wed, Nov
5 New Articles

Practical RPG: Using Data Queues, Part 1

RPG
Typography
  • Smaller Small Medium Big Bigger
  • Default Helvetica Segoe Georgia Times

This article moves past the basics of data queues to the practical application of these lightweight communication marvels.

 

In previous articles on data queues and on keyed data queues, I presented the basics of how to create them and how to program for them. I went into some detail about the commands used to manage data queues and the RPG code required to access them. In these next articles, I'm going to go a slightly different direction and present you with the actual business case for using data queues in a robust multi-user (and even multi-platform) architecture.

First, a Conceptual Overview

Queues can be used to perform a number of functions. For example, queues serve as a way for a process on one platform to communicate with a process on another platform, regardless of whether the two processes are running at the same time. They can act as a buffer, allowing a faster process to send data to a slower process without having to wait. Or they can be used in one of my favorite roles, that of acting as a pipeline between different programming languages, specifically RPG and Java.


"Wait," you say, "ILE allows any languages to talk to one another!" And you are correct; the Integrated Language Environment (ILE) of the IBM i does allow any languages to directly call one another, passing parameters and effortlessly crossing the language barrier. But that integration isn't entirely uniform, and in fact in one case it's somewhat awkward and inefficient. Specifically, I'm talking about calling Java from RPG. While you can indeed call a Java class directly from an RPG program, it isn't exactly simple and it most definitely isn't efficient. The inefficiency arises from the nature of Java as a virtual machine; Java doesn't compile to machine code that is executed by the hardware; it's converted to bytecode that must run within a virtual machine. IBM has done a wonderful job of making that interaction as seamless as possible, but the implementation still requires any job that invokes RPG to have its very own JVM. Thus, a machine that has 100 users running an RPG program that calls Java has 100 JVMs. There are some other technical issues that together lead to an inexorable conclusion: the best way to use Java from an RPG program is through a Java server.

Java Servers and Data Queues

So that brings us to the actual implementation of a data queue architecture. Let's start with a simple picture. This image shows you the way a single data queue acts as the conduit between a Java server application and as many RPG clients as you need.

 

070214PlutaImage1

Figure 1: Here, the data queue is the conduit between one Java server application and multiple RPG clients.

 

Each of the RPG clients communicates only with the data queue, which is serviced by the Java server application. This is a keyed data queue, and the key is very simple: an ID representing the receiver. In a practical environment, I use a six-character ID field that is either a hard-coded value that represents the server or the six-digit job number of the client. Note that theoretically this would allow me to do this:

 

070214PlutaImage2

Figure 2: Alternatively, you could have multiple Java server applications.

 

I could have multiple Java servers, each with its own six-character ID value. Each RPG client could request a service from either server simply by putting an entry on the queue with the key of the desired server. What would the request look like? Something like this:

 

Key Value

  Server ID

  Client Job Number

  Request ID

Data

  Application-specific Request

 

The entry would be placed on the queue using the Server ID as the key. The appropriate server, in this case Java Server 1 or Java Server 2, would pop the entry and process the request. The response would then be placed on the same queue, except this time with the client job number as the key:

 

Key Value

  Server ID

  Client Job Number

  Request ID

Data

  Application-specific Response

 

Note that the two messages are exactly identical. The varying part, of course, is the application-specific data. The message to the server would contain the parameters for the request, while the response message sent back to the client would contain the results. Note that I haven't specified the size of the message; that's because it's very application-dependent. Some applications have messages that vary very little from one request to another, so it's relatively easy to identify the optimal size of the message. Others don't have the luxury of consistency, so you have to be a little more creative in how you design your infrastructure.

Practical Application

A design like this has practical application whenever Java is a better vehicle for a service function than RPG is. I've seen many example of it over the years, although I find two scenarios occur with some frequency.

 

First is the situation in which an entire Java library is used for a business function, typically some kind of open-source package like JasperReports. JasperReports is a fantastically powerful reporting package that allows you to generate PDFs, Excel spreadsheets, and all sorts of other documents programmatically from SQL databases, XML documents, and all sorts of other inputs. The package is so robust that you simply can't reprogram it in RPG, and the Java interface is dead simple to use. Stick the JasperReports interface into a server and your RPG programs leap from spooled files to multi-media juggernauts.

 

A second situation is when you have some sort of tool that generates Java code that you then need to use in a business environment. One typical environment is web services. Several tools exist that will take a standard Web Services Definition Language (WSDL) document and generate code to easily access that web service. However, the most standard of the tools tend to generate Java code and wrapping that Java code or otherwise altering it to efficiently interface directly to RPG would be difficult at best. Instead, the best approach is to put the generated code into a server and communicate between the Java and RPG via data queue.

 

Web services, of course, bring us back to the issue of data length. While many services provide a simple limited-length request/response interface, others are used to retrieve arbitrary lists of data. Those services require an infrastructure a bit more robust than the single-queued approach here, and in the next installment of this series I'll show you how to add a second queue to support any arbitrary amount of data. Until then, start thinking about situations in which you might want to invoke a Java function from your RPG code and use this article as a foundation for that design.

 

Joe Pluta

Joe Pluta is the founder and chief architect of Pluta Brothers Design, Inc. He has been extending the IBM midrange since the days of the IBM System/3. Joe uses WebSphere extensively, especially as the base for PSC/400, the only product that can move your legacy systems to the Web using simple green-screen commands. He has written several books, including Developing Web 2.0 Applications with EGL for IBM i, E-Deployment: The Fastest Path to the Web, Eclipse: Step by Step, and WDSC: Step by Step. Joe performs onsite mentoring and speaks at user groups around the country. You can reach him at This email address is being protected from spambots. You need JavaScript enabled to view it..


MC Press books written by Joe Pluta available now on the MC Press Bookstore.

Developing Web 2.0 Applications with EGL for IBM i Developing Web 2.0 Applications with EGL for IBM i
Joe Pluta introduces you to EGL Rich UI and IBM’s Rational Developer for the IBM i platform.
List Price $39.95

Now On Sale

WDSC: Step by Step WDSC: Step by Step
Discover incredibly powerful WDSC with this easy-to-understand yet thorough introduction.
List Price $74.95

Now On Sale

Eclipse: Step by Step Eclipse: Step by Step
Quickly get up to speed and productivity using Eclipse.
List Price $59.00

Now On Sale

BLOG COMMENTS POWERED BY DISQUS

LATEST COMMENTS

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: