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Hibernate / MyBatis Interview questions

Explain the execution flow of a MyBatis query from mapper call to result?

A single mapper method call moves through several internal MyBatis layers before returning a mapped Java result, each responsible for a distinct part of translating a typed Java call into an executed SQL statement and back.

flowchart TD A[Application calls mapper.selectUserById 1] --> B[MapperProxy intercepts, resolves MappedStatement] B --> C[SqlSession delegates to configured Executor] C --> D{Result already in first-level cache?} D -- Yes --> E[Return cached result immediately] D -- No --> F[Executor obtains a StatementHandler] F --> G[ParameterHandler binds #{} parameters into PreparedStatement] G --> H[Statement executed against the database via JDBC] H --> I[ResultSetHandler maps raw ResultSet to Java objects per resultMap/resultType] I --> J[Result stored in first-level cache] J --> K[Mapped result returned to application]

After the MapperProxy resolves which MappedStatement corresponds to the called method, the SqlSession hands off to the configured Executor, which first checks the first-level cache before doing any real work; on a cache miss, it obtains a StatementHandler, which in turn uses a ParameterHandler to bind parameters and, after the JDBC driver executes the statement, a ResultSetHandler to map the raw ResultSet back into typed Java objects according to the statement's resultMap or resultType.

This layered pipeline — Executor, StatementHandler, ParameterHandler, ResultSetHandler — is also exactly where MyBatis's plugin/interceptor mechanism hooks in, since each of these four interfaces is a valid target for a custom plugin to intercept and modify behavior at a specific stage of query execution.

What is checked before the Executor does any real query work?
What component maps the raw ResultSet back into typed Java objects?

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