MyBatis-Plus 3.5.15: Spring Boot 4.0 & Jackson 3.0 Support Explained

What MyBatis-Plus Does

MyBatis-Plus adds a layer of common capabilities on top of MyBatis without changing its core behavior. It eliminates repetitive boilerplate: single-table CRUD via BaseMapper, type-safe conditional queries with LambdaQueryWrapper (e.g., User::getUsername), automatic pagination SQL, and a code generator that produces Entity, Mapper, and Service classes from table schemas.

Key Changes in 3.5.15

The release focuses on two major compatibilities:

Spring Boot 4.0 support — Spring Boot 4 changes starter Maven coordinates. The old mybatis-plus-spring-boot3-starter does not work with Boot 4 because auto-configuration classes differ. Version 3.5.15 introduces mybatis-plus-spring-boot4-starter.

Jackson 3 support — Jackson 3 moved its core package from com.fasterxml.jackson to tools.jackson. The existing JacksonTypeHandler still targets Jackson 2. A new Jackson3TypeHandler is provided for projects already on Jackson 3.

Minor fixes include metadata adjustments in the code generator, a fix for Enjoy template XML generation, and CrudRepository batch operations now close connections more promptly when not in a transaction.

Integrating with Spring Boot 4

Starter Version Mapping

Starter artifacts are bound to specific Spring Boot major versions; mixing them causes auto-configuration failures.

Spring Boot 2.x → mybatis-plus-boot-starter Spring Boot 3.x → mybatis-plus-spring-boot3-starter Spring Boot 4.x →

mybatis-plus-spring-boot4-starter

Maven Dependency

<parent>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-parent</artifactId>
  <version>4.0.0</version>
</parent>
<dependencies>
  <!-- Note: this is boot4, not boot3 -->
  <dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-spring-boot4-starter</artifactId>
    <version>3.5.15</version>
  </dependency>
  <dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
  </dependency>
</dependencies>

DataSource Configuration

spring:
  datasource:
    url: jdbc:mysql://127.0.0.1:3306/db_demo?useUnicode=true&characterEncoding=utf8&serverTimezone=Asia/Shanghai
    username: root
    password: 123456

mybatis-plus:
  configuration:
    map-underscore-to-camel-case: true
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
  global-config:
    db-config:
      id-type: auto

Entity, Mapper, and Query Example

The following maps to table t_user without Lombok.

/**
 * User entity, maps to table t_user
 */
@TableName("t_user")
public class User {
    /** Primary key */
    @TableId(type = IdType.AUTO)
    private Long id;

    /** Username */
    private String username;

    /** Password, plaintext for demo */
    private String password;

    /** Gender, default male */
    private String gender;

    /** Creation time */
    private LocalDateTime createTime;

    // getters and setters omitted for brevity
}

/**
 * User table Mapper
 */
public interface UserMapper extends BaseMapper<User> {
}

/**
 * Query user by username
 */
@Service
public class UserService {
    private final UserMapper userMapper;

    public UserService(UserMapper userMapper) {
        this.userMapper = userMapper;
    }

    /**
     * Use method reference for condition, avoids typos in column names
     */
    public User findByUsername(String username) {
        return userMapper.selectOne(new LambdaQueryWrapper<User>()
                .eq(User::getUsername, username)
                .last("LIMIT 1"));
    }
}

The only required change from a Boot 3 project is replacing the starter dependency with mybatis-plus-spring-boot4-starter; @MapperScan and the main application class remain unchanged.

JSON Fields with Jackson 3

Many tables store extension data in a JSON column (e.g., user city and tags) to avoid extra tables. Previously JacksonTypeHandler handled Jackson 2; now Jackson3TypeHandler handles Jackson 3. It serializes objects to JSON strings on write and deserializes on read.

Extension Info Class

/**
 * User extension info, stored as JSON in t_user.extra_info
 */
public class ExtraInfo {
    /** City */
    private String city;

    /** Tag list */
    private List<String> tags;

    // getters and setters omitted
}

Attach to Entity Field

A critical detail: @TableName must include autoResultMap = true. Without it, the JSON column bypasses the type handler, resulting in null or raw string values.

/**
 * User entity with JSON extension field
 */
@TableName(value = "t_user", autoResultMap = true)
public class User {
    @TableId(type = IdType.AUTO)
    private Long id;

    private String username;

    /**
     * Read/write extra_info column using Jackson 3
     */
    @TableField(typeHandler = Jackson3TypeHandler.class)
    private ExtraInfo extraInfo;

    // getters and setters omitted
}

Insert Example

/**
 * Save user with JSON extension info
 */
public void saveUser() {
    ExtraInfo extraInfo = new ExtraInfo();
    extraInfo.setCity("Shanghai");
    extraInfo.setTags(Arrays.asList("vip", "spring-boot4"));

    User user = new User();
    user.setUsername("admin");
    user.setPassword("123456");
    user.setGender("Male");
    user.setExtraInfo(extraInfo);
    userMapper.insert(user);
}

The extra_info column then contains:

{"city":"Shanghai","tags":["vip","spring-boot4"]}

Reuse Spring's ObjectMapper

If the project already configures a custom Jackson 3 ObjectMapper (date formats, ignore nulls, etc.), inject it into the handler at startup to avoid a second default instance:

/**
 * Reuse Spring container's ObjectMapper
 */
@Configuration
public class Jackson3Config {
    public Jackson3Config(ObjectMapper objectMapper) {
        Jackson3TypeHandler.setObjectMapper(objectMapper);
    }
}

Package name caution: Jackson 3's ObjectMapper resides in tools.jackson.databind. Accidentally importing com.fasterxml.jackson.databind.ObjectMapper (Jackson 2) may compile but cause runtime type-handler mismatches.

Common Upgrade Pitfalls

1. Wrong Starter

Most frequent issue: using mybatis-plus-spring-boot3-starter in a Boot 4 project. The dependency resolves but auto-configuration fails, often with obscure errors not directly pointing to MyBatis-Plus.

2. JSON Handler and Jackson Version Mismatch

If the entity declares Jackson3TypeHandler, the classpath must contain Jackson 3. Legacy projects on Jackson 2 should keep using JacksonTypeHandler; no need to upgrade solely for the new handler name.

3. factoryBeanObjectType Error on Startup

Some users encountered:

Invalid value type for attribute 'factoryBeanObjectType': java.lang.String

Root cause: transitive mybatis-spring version too old for Boot 4. Fix by explicitly declaring org.mybatis:mybatis-spring:4.0.0 in the POM. Version 3.5.16 already upgrades this dependency in the Boot 4 starter, so a minor version bump is often simpler than manual exclusion.

4. Code Generator Changes

Metadata building was adjusted and Enjoy template XML generation bugs were fixed. After upgrading, regenerate a table's artifacts and compare with existing Mapper XML to catch discrepancies.