If a model has any expressions defined, the Connect CDC Kernel calls the Expression Handler when a model is loaded and the Connect CDC Director client calls it when you select the “Validate” button. The Connect CDC Director calls the Expression Handler to parse (that is, to check the expression syntax) and validate an expression that you enter into the model.
To obtain access to the necessary Java executable code (omni.jar file), the Connect CDC Director’s omnient.ini file contains a parameter
Classpath=d:\v56\classes\omni.jar;d:\v56\classes\log4j-1.2.8.jar;that indicates where the Connect CDC executable is located. This is the same .jar file that is used to start the Connect CDC Listener on a host. Note that in addition to the reference to omnijar, there must also be a reference to the log4j.jar (log4j-1.2.8.jar), which controls logging of output.
To parse an expression, the Expression Handler only needs the expression string as input, but to do validation (that is, to check that the references to columns are correct and that they are columns that belong to the source table associated with the expression), the Expression Handler needs metadata (that is, table and column information). The Connect CDC Director passes the expression string along with metadata to the Handler.
The Connect CDC Director logs useful debugging information to its log, the omnidir.log. In addition, the Expression Handler writes its own log, omnijvm.log, which contains useful information about expression processing.