Take the development of a credit project as an example. The system use case model shows the function examples to be developed by the system. With the use case and detailed description of the use case, the system analysis model should be established, that is, various use cases should be created in the form of analysis class diagrams. In general, the analysis of a system use case can start from the distinction between the system interface class and the system control class. As shown in the following figure: after an analysis model is created, you need to create a system design model, and create and analyze a truly runable class. To ensure system testability, the design model of the system to be established in the first step is irrelevant to the environment. The environment mentioned here refers to specific J2EE technologies, such as web containers and EJB containers. We need to establish a business framework that only depends on JDK (or as little as possible. After establishing a business framework, we can use various testing technologies to test the framework and write tests. ProgramSimulate a user or system interface to initiate a call to the business framework.