自 IT 系统诞生以来，单体架构风格一直主导着企业应用。从本质上讲，这种风格将应用程序分解为多个逻辑模块或服务，并将其作为单个应用程序进行构建和部署。这些服务提供可被外部客户端调用的端点。端点提供安全性和输入验证，然后将请求委托给共享业务逻辑，业务逻辑则通过数据访问对象（DAO）层访问持久存储。图 9-1是一个大学管理系统的设计示例，该系统具有处理学生课程分配和时间表、房间安排、缴费以及教师和顾问互动的功能。
这种架构鼓励在上创建可重复使用的业务逻辑和 DAO，这些逻辑和 DAO 可在不同的服务实现中共享。DAO 被映射到数据库实体，所有服务实现共享一个数据库。
IBM WebSphere 和 Microsoft .NET 等流行平台可将所有服务作为一个可执行包进行构建和部署。这就是 "单体 "一词的由来--完整的应用程序。应用程序接口（API）、业务逻辑、数据访问等都封装在一个单一的部署工件中。
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