How MyBatis Leverages 10+ Design Patterns to Simplify Complex Scenarios

MyBatis’s extensive source code (over 20,000 lines) makes extensive use of design patterns to decouple complex scenarios, forming the core of the framework’s architecture.

Factory Pattern (Creational)

SqlSessionFactory serves as a factory for creating sessions; each MyBatis operation opens a new session. It gathers environment configuration, builds transaction factories, and creates SQL executors before returning a session implementation.

The factory method in the parent class creates objects, allowing subclasses to decide the concrete type.

Singleton Pattern (Creational)

Configuration is a large singleton that spans the entire session lifecycle; it initializes all configuration objects (mappings, caches, parameters, interceptors, factories, etc.) during the SqlSessionFactoryBuilder construction phase.

The singleton ensures a class has only one instance and provides a global access point.

Builder Pattern (Creational)

ResultMap uses a builder pattern; multiple simple objects are assembled step‑by‑step into a complex object, isolating object construction from business logic.

Adapter Pattern (Structural)

MyBatis defines a unified logging interface to adapt various logging frameworks (Log4j, Log4j2, SLF4J), enabling them to work together despite incompatible APIs.

Proxy Pattern (Structural)

MapperProxy implements DAO interfaces, intercepting method calls and delegating them to executors, thus providing a placeholder that controls access to the actual implementation.

Composite Pattern (Structural)

MyBatis XML dynamic SQL provides nine tags (trim, where, set, foreach, if, choose, when, otherwise, bind) that can be combined into a tree‑like structure, representing part‑whole hierarchies.

Decorator Pattern (Structural)

Second‑level cache decorates the simple executor, adding caching behavior without altering the executor’s core logic.

Template Method Pattern (Behavioral)

BaseExecutor defines a fixed algorithm framework for SQL execution; subclasses override specific steps while the overall process remains unchanged.

Strategy Pattern (Behavioral)

TypeHandler implementations provide separate strategies for handling different Java types, avoiding extensive conditional logic during JDBC result processing.

Iterator Pattern (Behavioral)

PropertyTokenizer iterates over object properties in MyBatis’s MetaObject, enabling traversal without exposing underlying collection details.