How can you implement the ability to enable and disable certain parts of business logic in an existing application?

To enable and disable parts of business logic in a Java application, several approaches can be used:

1. Feature Flags — store boolean values in settings that control the execution of specific code.

if (featureToggle.isEnabled("newFeature")) {
    // new logic
} else {
    // old logic
}

2. Strategy Pattern — encapsulate different implementations of logic into separate classes and select the appropriate one at runtime.

3. Using Spring Profiles — enable or disable beans using @Profile annotations.

4. Configuration Files — change application behavior through externalized configuration (e.g., application.properties).

This approach allows flexible management of functionality without the need to change and rebuild the entire code.