JES2 is designed to be customized to meet your system's job processing requirements. You can complete basic customization when you create the JES2 initialization data set, and then use JES2 exits and table pairs to change additional JES2 functions and processes.

To modify JES2 processing beyond the capability provided by initialization statements, you can provide installation-written code and isolate it from IBM source code. Changes to JES2 processing implemented through direct source code modification are error prone, counter-productive during migration to future releases, and can prove to be very time consuming when debugging, diagnosing, and applying IBM-written program temporary fixes (PTFs) and authorized program analysis report (APARs) fixes to code. Furthermore, alteration of JES2 processing in this manner complicates IBM® service assistance. Therefore, JES2 provides the means to customize processing without direct source code modification.

Recommended methods for customizing JES2 processing include JES2 table pairs, IBM-defined exits, and installation-defined exits. A general discussion of each is provided in this section. See z/OS JES2 Installation Exits for a complete description of each IBM-defined exit.