Mybatis自定义TypeHandler解决特殊类型转换问题详解

public class Role {
  private Integer id;
  private String name;
  private Integer[] accessIds; 
  private Date createTime;  
  // ... ignore get and set methods
}

DROP TABLE IF EXISTS `role`;
CREATE TABLE `role` (
 `id` int(11) NOT NULL AUTO_INCREMENT,
 `name` varchar(255) NOT NULL,
 `access_ids` varchar(255) DEFAULT NULL,
 `create_time` datetime NOT NULL,
 PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of role
-- ----------------------------
INSERT INTO `role` VALUES ('1', '测试角色', ',1,2,', '2019-11-14 13:43:14');

/**
 * Java Int数组与MySQL String转换器
 * 比如[1,2,3] --> ",1,2,3,"
 */
public class StringToIntArrayHandler extends BaseTypeHandler<Integer[]> {

  private static final String splitCharset = ",";

  @Override
  public void setNonNullParameter(PreparedStatement ps, int i, Integer[] objects, JdbcType jdbcType) throws SQLException {
    String str = arrayToString(objects);
    ps.setString(i, str);
  }

  @Override
  public Integer[] getNullableResult(ResultSet rs, String columnName) throws SQLException {
    String str = rs.getString(columnName);
    return stringToArray(str);
  }

  @Override
  public Integer[] getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
    String str = rs.getString(columnIndex);
    return stringToArray(str);
  }

  @Override
  public Integer[] getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
    String str = cs.getString(columnIndex);
    return stringToArray(str);
  }

  // --- private methods ---
  
  /**
   * Integer数组转String
   * 注：使用提前设定好的分隔符分割数组的每一项
   */
  private static String arrayToString(Integer[] array) {
    StringBuilder res = new StringBuilder();
    if (array != null && array.length > 0) {
      for (Object o : array) {
        res.append(splitCharset).append(o.toString());
      }
      res.append(splitCharset);
    }
    return res.length() > 0 ? res.toString() : null;
  }

    /**
   * 从String转Integer数组
   * 注：String是用分隔符分割的，使用String.split方法可以分解为数组
   */
  private static Integer[] stringToArray(String str) {
    List<Integer> list = new ArrayList<>();
    if (str != null) {
      String[] array = str.split(splitCharset);
      if (array.length > 0) {
        for (String o : array) {
          if (o != null && o.length() > 0) {
            list.add(Integer.parseInt(o));
          }
        }
      }
    }
    return list.toArray(new Integer[0]);
  }
}

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="com.example.model.dao.RoleDAO">

  <resultMap id="roleMap" type="com.example.model.bean.Role">
    <id property="id" column="id"/>
    <result property="name" column="name"/>
    <result property="accessIds" column="access_ids"
        typeHandler="ccom.example.model.dao.handler.StringToIntArrayHandler"/>
    <result property="createTime" column="create_time"/>
  </resultMap>

  <select id="findById" parameterType="map" resultMap="roleMap">
    SELECT id, name, access_ids, create_time
    FROM role
    WHERE id = #{id}
  </select>

  <insert id="insert" parameterType="com.example.model.bean.Role">
    <selectKey resultType="java.lang.Integer" order="AFTER" keyProperty="id">
      SELECT LAST_INSERT_ID()
    </selectKey>

    INSERT INTO role
    (name, create_time, access_ids)
    VALUES
    (#{name}, #{createTime}
    , #{accessIds, jdbcType=VARCHAR, typeHandler=com.example.model.dao.handler.StringToIntArrayHandler})
  </insert>

</mapper>