Replacing MyBatis with MyBatis‑Plus: Version Compatibility, Debugging, and Lessons Learned

Background: an old project uses MySQL 5.7, MyBatis 3.5.0, and mysql‑connector‑java 5.1.26. A new developer finds MyBatis cumbersome and decides to replace it with MyBatis‑Plus 3.1.1 while keeping the connector version unchanged.

Initial Demo: a simple tbl_order table is created with two rows to illustrate the migration.

Running com.qsl.OrderTest#orderListAllTest after the switch throws an exception: Conversion not supported for type java.time.LocalDateTime . The stack trace points to the JDBC driver, which does not support the new Java 8 date‑time types in version 5.1.26.

Solution Part 1 – Upgrade the JDBC driver: upgrading mysql‑connector‑java to 5.1.37 adds support for LocalDateTime , LocalDate , and LocalTime . After the upgrade the test runs without errors and returns correct results.

Root‑Cause Analysis: MyBatis 3.5.1 stopped handling Java 8 date‑time conversions internally and delegated them to the JDBC driver, which in versions prior to 5.1.37 cannot process those types. Therefore the combination of MyBatis 3.5.1 + MyBatis‑Plus + an old connector caused the failure.

Further Issues – After fixing the conversion problem, a new bug appears when inserting a record with INSERT INTO tbl_order VALUES (3, 'asdfgh', NULL, '2024-02-21 20:01:31.111', '2024-02-21 20:02:56.764'); . The test again fails, this time due to a NullPointerException caused by a null timestamp. The investigation shows that the underlying cause is the same driver limitation, which is finally resolved by upgrading the driver to 5.1.42.

Lesson Learned: component upgrades can have cascading effects; always verify compatibility of all dependent libraries and perform thorough testing before pushing changes to production.

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