Integrating from an iSeries Platform using ILE-based Languages
Web Services encompass a rather new and rapidly-evolving set of technologies. Many development platforms have native support to permit offering and consuming web services. Examples include .NET, J2EE, and others.
At its most basic level, web service consumption involves formatting a request in SOAP/XML, and sending that request over an HTTP port to a remote server. The server then replies with a formatted SOAP/XML response.
As of yet, IBM's iSeries platform offers no native support for web service consumption. Operating-system-level utilities exist to perform rudimentary HTTP actions, like POST and GET, but higher-level functions which construct or parse SOAP or XML do not exist.
Basic Concepts
Note: throughout these pages, "RPG" is referenced many times. Be aware that any ILE-based language can be used in place of "RPG".
RPG programs can serve as web service clients through a number of mechanisms.
- RPG can invoke logic contained in Java classes. The Java classes can then invoke the web service. Object oriented languages like Java tend to have better native support for web services. A brief discussion of this mechanism can be found here: Using RPG with Java JAR Files
- RPG can invoke logic contained in C++ classes. Object oriented languages like C++ tend to have better native support for web services. While an Omnitracs example does not exist, further reading can be done here: Using RPG with ILE C++
- At the most basic level, invoking a web service is nothing more than constructing an appropriate XML string, and submitting it to the proper URL. Therefore RPG can make use of native OS/400 utilities which can send HTTP requests to URLs. This approach is attractive because of its straightforward nature, however the complexity involved in constructing and parsing intricate XML documents adds significant effort to the process.
Examples include this, and this.
Portal Integration Toolkit
To fill this gap and simplify the process of consuming web services from within RPG, Omnitracs offers its Portal Integration Toolkit