The contents of the payload field are structured as a list of field name and value pairs. Although this may be directly accessed as a string within EPL, Apama provides the Payload Extraction plug-in to make extraction and manipulation of specific fields more straightforward.

The Payload Extraction plug-in is available as libPayloadPlugin.so in the lib directory on UNIX. On Microsoft Windows it is available as PayloadPlugin.dll in the bin directory.

The following EPL, which should be located within the monitor that requires the plug-in’s functions, loads the Payload Extraction plug-in and assigns it the alias payloadMgr:

The plug-in provides a suite of methods that allow extraction of named fields from the payload field.

There are two groups of these functions, the direct access functions, and the indirect access functions.