When you develop an application, you can take advantage of existing Java code in multiple ways.
When your application needs to send requests to an external EJB application, use an EJB connector (Rule-Connect-EJB).
When your application is to send requests to an external Java-based application that is not an EJB, or interact with an external Java class that is maintained outside of Pega Platform, use a Java connector (Rule-Connect-Java).
By using a connector rule to call an external Java class, you can reuse the connector rule in multiple places, while maintaining the Java code the connector interacts with in a single place. Additionally, when connector rules run, they set Performance tool timers for the external connections. If a performance issue or question arises, you can determine how much time the external Java class spends processing the connector's request. You can also track connector rules in the Tracer tool, which can record the start and end of connector operations.
To access the external application or Java class, place the .jar or class files in the compile time and runtime class paths.
While a Java step in an activity can call external Java classes, as a best practice, use Java connectors. Pegasystems design and development guardrails encourage you to use Java steps in activities sparingly. Don't use Java in an activity step when you can use a rule to accomplish the processing goal.
However, there are specific and limited cases when you do need to use Java in an activity.
For example, use a Java step to call a Java method in the Public API. Specifically, to create custom authentication activities, use Java steps to call the setSecurityProfile() and setUserAuthenticated() Java methods of the PRAuthentication interface.
If the existing Java code that you want to use is a procedural method or routine that does not use member variables, refer to other Java classes, or maintain state, you can create a function rule (Rule-Utility-Function rule type) and store the code in the rule. That way you can maintain the code within the PegaRULES database as a rule that is subject to versioning, which means the correct version of the function rule is selected at runtime based on a user´s RuleSet list. However, the SmartBuild design and development guardrails encourage you to use custom Java sparingly.
Function rules typically perform simple computations or transformations. You can use them in activity preconditions and transitions, when rules, expressions, and so on. You can update them and recompile them without stopping and restarting the system.