Deep Dive into MyBatis: Architecture, Execution Flow, Plugins, Caching, and Spring Integration

MyBatis is a powerful persistence framework that abstracts JDBC operations by allowing developers to write SQL in XML or annotations. The framework builds a three‑layer architecture (API, data processing, and support layers) and creates a SqlSessionFactory from the configuration file.

When a mapper method is invoked, MyBatis generates a dynamic proxy ( MapperProxy) that implements InvocationHandler. The proxy retrieves a cached MapperMethod or creates a new one, determines the SQL command type (INSERT, UPDATE, DELETE, SELECT), and delegates execution to the appropriate Executor implementation (Simple, Reuse, Batch, or Caching).

The execution flow involves the Executor creating a StatementHandler, which wraps a ParameterHandler and a ResultSetHandler. The StatementHandler prepares the PreparedStatement, sets parameters, executes the query, and the ResultSetHandler maps results to Java objects.

MyBatis supports plugins that can intercept calls to Executor, ParameterHandler, ResultSetHandler, and StatementHandler. Plugins are defined in the configuration, instantiated, and applied via the InterceptorChain, which wraps target objects with dynamic proxies.

Caching in MyBatis consists of a session‑level first‑level cache (enabled by default) and an optional second‑level cache. The second‑level cache is built using the CacheBuilder and a series of decorator classes (e.g., LoggingCache, SynchronizedCache, SerializedCache) following the Builder and Decorator patterns. Queries first check the second‑level cache before hitting the database.

Spring integrates MyBatis by registering a FactoryBean that creates mapper proxies. The MapperFactoryBean (or a custom factory) implements FactoryBean, returning a proxy instance in getObject(). An ImportBeanDefinitionRegistrar scans specified packages, registers a bean definition for each mapper, and supplies the mapper interface class to the factory bean. The @MapperScan annotation simplifies this process, allowing Spring to manage MyBatis mappers as regular beans.