• 起因：
  • 今天在做公司的新项目的时候，公司使用了UUID作为数据库的部分字段，然后ORM使用的是Hibernate，在我新起项目的时候是用的Mybatis。然后在插入UUID字段的时候直接抛出了插入的数据太长的异常。（Hibernate中UUID可以使用binary(16)来存放）。

解决

• MyBatis给我们提供了TypeHandler来处理未知类型的转换。

  • UUID使用128位（16字节）存储，其中，uuid.getMostSignificantBits()返回高64位，uuid.getLeastSignificantBits()返回低64位。

• 具体代码如下：

  import org.apache.ibatis.type.BaseTypeHandler;
  import org.apache.ibatis.type.JdbcType;
  import org.apache.ibatis.type.MappedJdbcTypes;
  import org.apache.ibatis.type.MappedTypes;
  
  import java.sql.CallableStatement;
  import java.sql.PreparedStatement;
  import java.sql.ResultSet;
  import java.sql.SQLException;
  import java.util.UUID;
  
  @MappedJdbcTypes(JdbcType.BINARY)
  @MappedTypes(value = UUID.class)
  public class UUIDTypeHandler extends BaseTypeHandler<UUID> {
      @Override
      public void setNonNullParameter(PreparedStatement ps,
                                      int columnIndex, UUID uuid,
                                      JdbcType jdbcType) throws SQLException {
          long mostBit = uuid.getMostSignificantBits();
          byte[] bytes = new byte[16];
          bytes[0] = (byte) ((mostBit >> 56) & 0xFF);
          bytes[1] = (byte) ((mostBit >> 48) & 0xFF);
          bytes[2] = (byte) ((mostBit >> 40) & 0xFF);
          bytes[3] = (byte) ((mostBit >> 32) & 0xFF);
          bytes[4] = (byte) ((mostBit >> 24) & 0xFF);
          bytes[5] = (byte) ((mostBit >> 16) & 0xFF);
          bytes[6] = (byte) ((mostBit >> 8) & 0xFF);
          bytes[7] = (byte) (mostBit & 0xFF);
          //
          long leastBit = uuid.getLeastSignificantBits();
          bytes[8] = (byte) ((leastBit >> 56) & 0xFF);
          bytes[9] = (byte) ((leastBit >> 48) & 0xFF);
          bytes[10] = (byte) ((leastBit >> 40) & 0xFF);
          bytes[11] = (byte) ((leastBit >> 32) & 0xFF);
          bytes[12] = (byte) ((leastBit >> 24) & 0xFF);
          bytes[13] = (byte) ((leastBit >> 16) & 0xFF);
          bytes[14] = (byte) ((leastBit >> 8) & 0xFF);
          bytes[15] = (byte) (leastBit & 0xFF);
          //
          ps.setBytes(columnIndex, bytes);
      }
  
      @Override
      public UUID getNullableResult(ResultSet rs, String columnName) throws SQLException {
          byte[] bytes = rs.getBytes(columnName);
  
          long mostBit = ((((long) bytes[0] & 0xFF) << 56)
                  | (((long) bytes[1] & 0xFF) << 48)
                  | (((long) bytes[2] & 0xFF) << 40)
                  | (((long) bytes[3] & 0xFF) << 32)
                  | (((long) bytes[4] & 0xFF) << 24)
                  | (((long) bytes[5] & 0xFF) << 16)
                  | (((long) bytes[6] & 0xFF) << 8)
                  | (((long) bytes[7] & 0xFF)));
  
          long leastBit = ((((long) bytes[8] & 0xFF) << 56)
                  | (((long) bytes[9] & 0xFF) << 48)
                  | (((long) bytes[10] & 0xFF) << 40)
                  | (((long) bytes[11] & 0xFF) << 32)
                  | (((long) bytes[12] & 0xFF) << 24)
                  | (((long) bytes[13] & 0xFF) << 16)
                  | (((long) bytes[14] & 0xFF) << 8)
                  | (((long) bytes[15] & 0xFF)));
          return new UUID(mostBit, leastBit);
      }
  
  
      @Override
      public UUID getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
          // 略
          return null;
      }
  
      @Override
      public UUID getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
          // 略
          return null;
      }
  }

• SpringBoot项目中在application.properties中添加TypeHandler扫描的包，否则不生效。

  mybatis.type-handlers-package