The Java Struts framework is a popular open-source framework used to build web applications in Java. It is built on top of the Java Servlet API and provides a Model-View-Controller (MVC) architecture for building web applications. The Struts framework provides a set of components and tools that simplify the process of building web applications.

The Struts framework is based on the following core components:

1. Action: An Action is a Java class that performs the business logic of the application. It is responsible for processing the user requests and producing the appropriate response.

2. ActionForm: An ActionForm is a Java class that is used to represent the data that is submitted by the user. It contains the properties and methods required to capture and validate user input.

3. ActionMapping: An ActionMapping is a Java class that maps the user requests to the appropriate Action class.

4. ActionForward: An ActionForward is a Java class that specifies the target view for the user after the Action is processed.

5. ActionServlet: An ActionServlet is a Java class that is responsible for managing the Action objects and forwarding the user requests to the appropriate Action class.

The Struts framework also provides several other components and features, such as validators, form beans, plug-ins, and tag libraries, that can be used to build complex web applications. The Struts framework has been widely adopted and is used in many enterprise-level applications.