7 Extending and Customizing Products

RPASCE allows the extension of the calculation capabilities of the Server component through the creation of custom calculation expressions. Calculations that modify customer data in the system are defined in an expression language; when processing customer data, a component of the Server known as the Calculation Engine performs updates according to the expressions defined within the application.The expression language contains a predefined set of calculation primitives, such as arithmetic operations, and a set of predefined functions that perform more complex operations on the data. It is possible for a customer to extend this set of functions to provide unique methods for evaluating expressions and performing calculations through the creation of a Java Special Expression.In order to maintain the security of the system, the execution of Java Special Expressions is tightly constrained. JVMs in which these expressions are run are created with the Java Security Manager installed with a security policy that grants no privileges to externally supplied code.As a result, any operation attempted by externally supplied code that attempts to access any privileged resource, such as the file system, network, or even internal JVM resources such as class loaders, execution threads and executor services, or internal system properties will be vetoed by the Java Security Manager and will result in a SecurityException.This exception will prevent the execution of the privileged action and should an exception halt the execution of externally authored code result in the halting of a Java Special Expression, a notification to the application monitoring team will be generated by the system.Details about the security policy imposed on Java Special Expressions can be found within the Oracle Retail Predictive Application Server RPASCE Extension Development Guide.