OWSM custom step development requires following jars to be used at a minimum to compile the project - saaj.jar and coresv-4.0.jar
Only specific versions of these jars should be used for compiling the project which can be found at
ORACLE_HOME/owsm/lib/extlib/saaj.jar and
ORACLE_HOME/owsm/lib/coresv-4.0.jar
If any other saaj.jar is used then you may get the following exception in your logs.
org.apache.axis.message.SOAPBody.getElementsByTagName(Ljava/lang/String;)Lorg/w3c/dom/NodeList;