面向领域驱动设计的 Go 开发者：构建真正执行业务规则的实体

In many Go applications, the rule 'an expired token cannot be used' is often implemented in multiple places, such as middleware functions, repository methods, and handler guards. This scattered implementation leads to the need for modifications in several locations when the rule changes, and testing requires checking multiple areas as well. By adopting Domain-Driven Design, this rule can be centralized in one location: the <code>Token</code> entity's <code>IsValid()</code> method. This method consists of only five lines of code, and every piece of code that needs to check token validity calls it. Consequently, there is only one test for the rule, which is a straightforward Go test without the need for a database, HTTP server, or mocks. This approach significantly enhances the maintainability and testability of the code.