Struts 2 is a popular web application framework for building Java-based applications. It provides a set of core components that developers can use to develop applications quickly and easily. Some of the key Struts 2 core components are:

1. Action: An action is a Java class that processes a user request and produces a result. It can receive data from a user, perform business logic, and then return a result. An action can be defined as a class that extends the ActionSupport class or implements the Action interface.

2. Interceptor: An interceptor is a Java class that provides cross-cutting functionality for an action. It intercepts the user request and performs some pre-processing or post-processing. Struts 2 provides a set of built-in interceptors for logging, exception handling, validation, and security. You can also create your own custom interceptors.

3. Result: A result is a Java class that generates the output of an action. It can be a JSP page, a FreeMarker template, a PDF file, or any other type of output. Struts 2 provides a set of built-in results for common output types, and you can also create your own custom results.

4. Value Stack: The value stack is a data structure that holds the data of an action. It is a hierarchical structure that allows you to access the data of an action and its associated objects. The value stack is also used to render the output of an action.

5. Action Mapping: An action mapping is a configuration that maps a user request to an action. It defines the URL pattern that triggers the action, the HTTP method that the action supports, and the parameters that are passed to the action.

6. Configuration: The Struts 2 configuration is a set of XML files that define the application settings and dependencies. It includes the struts.xml file, which defines the action mappings, interceptors, and results, and other configuration files for specific features such as validation and localization.

Overall, these core components are the building blocks of a Struts 2 application. They work together to handle user requests, perform business logic, and generate output. Struts 2 provides a powerful and flexible framework that allows developers to create robust and scalable web applications.