What is POJOs?
What is POJO? POJO stands for “Plain Old Java Object.” It is a term used to describe a Java object that is not “polluted” by any special requirements from a framework or a library. It is a simple Java object that does not have any special restrictions or requirements. In the context of Clean Architecture and DDD, a POJO is an object that: Doesn’t extend a specific class (e.g., extends HttpServlet or extends BaseEntity). Doesn’t implement a specific interface from a library (e.g., implements Serializable is often okay, but implements org.hibernate.Entity is not). Doesn’t use “heavy” annotations that tie it to a technology (like @Entity from JPA or @Table from SQL). Why use POJOs in your Domain (Domain Driven Diagram)? Technology Independence: Your business logic doesn’t care if you use PostgreSQL, MongoDB, or even if you’re running on a Web Server or a CLI. Easier Testing: You can test a POJO with simple Unit Tests without needing to start a Spring Context or a database. Future Proofing: If you decide to switch from JPA to another database technology later, your core business logic (the POJOs) won’t have to change at all. Example comparison: POJO (Clean/DDD style): public class User { private String username; // Pure Java logic } NOT a POJO (Infrastructure-coupled style): @Entity // Tied to JPA @Table(name = "users") // Tied to SQL public class User { @Id // Tied to JPA private Long id; } Notes: By keeping your domain.entities as POJOs, you are ensuring that your “Business Truth” remains pure and independent! ...