1問題
uuid採用char(32)或char(36)存儲的話，須要佔用32或36個字節。爲節省存儲空間，改成binary(16)，佔用16字節。對於500W行的表，可節省7.4G的空間。java
mybatis中沒有默認的type handler來完成uuid類型<->binary類型的相互轉換，須要自定義一個type handler。下面就詳細地介紹如何實現。mysql
2 環境
mybatis 3.5.3sql
mysql 5.7.21session
java 8mybatis
3 自定義TypeHandler
1 public class UuidHandler extends BaseTypeHandler<UUID> { 2 4 @Override 5 public void setNonNullParameter(PreparedStatement ps, 6 int columnIndex, UUID uuid, 7 JdbcType jdbcType) throws SQLException { 8 9 long mostBit = uuid.getMostSignificantBits(); 10 byte[] bytes = new byte[16]; 11 bytes[0] = (byte) ((mostBit >> 56) & 0xFF); 12 bytes[1] = (byte) ((mostBit >> 48) & 0xFF); 13 bytes[2] = (byte) ((mostBit >> 40) & 0xFF); 14 bytes[3] = (byte) ((mostBit >> 32) & 0xFF); 15 bytes[4] = (byte) ((mostBit >> 24) & 0xFF); 16 bytes[5] = (byte) ((mostBit >> 16) & 0xFF); 17 bytes[6] = (byte) ((mostBit >> 8) & 0xFF); 18 bytes[7] = (byte) (mostBit & 0xFF); 19 // 20 long leastBit = uuid.getLeastSignificantBits(); 21 bytes[8] = (byte) ((leastBit >> 56) & 0xFF); 22 bytes[9] = (byte) ((leastBit >> 48) & 0xFF); 23 bytes[10] = (byte) ((leastBit >> 40) & 0xFF); 24 bytes[11] = (byte) ((leastBit >> 32) & 0xFF); 25 bytes[12] = (byte) ((leastBit >> 24) & 0xFF); 26 bytes[13] = (byte) ((leastBit >> 16) & 0xFF); 27 bytes[14] = (byte) ((leastBit >> 8) & 0xFF); 28 bytes[15] = (byte) (leastBit & 0xFF); 29 // 30 ps.setBytes(columnIndex, bytes); 31 } 32 33 @Override 34 public UUID getNullableResult(ResultSet rs, String columnName) throws SQLException { 35 byte[] bytes = rs.getBytes(columnName); 36 37 long mostBit = ((((long) bytes[0] & 0xFF) << 56) 38 | (((long) bytes[1] & 0xFF) << 48) 39 | (((long) bytes[2] & 0xFF) << 40) 40 | (((long) bytes[3] & 0xFF) << 32) 41 | (((long) bytes[4] & 0xFF) << 24) 42 | (((long) bytes[5] & 0xFF) << 16) 43 | (((long) bytes[6] & 0xFF) << 8) 44 | (((long) bytes[7] & 0xFF))); 45 46 long leastBit = ((((long) bytes[8] & 0xFF) << 56) 47 | (((long) bytes[9] & 0xFF) << 48) 48 | (((long) bytes[10] & 0xFF) << 40) 49 | (((long) bytes[11] & 0xFF) << 32) 50 | (((long) bytes[12] & 0xFF) << 24) 51 | (((long) bytes[13] & 0xFF) << 16) 52 | (((long) bytes[14] & 0xFF) << 8) 53 | (((long) bytes[15] & 0xFF))); 54 return new UUID(mostBit, leastBit); 55 } 56 57 58 @Override 59 public UUID getNullableResult(ResultSet rs, int columnIndex) throws SQLException { 60 // 略 61 return null; 62 } 63 64 @Override 65 public UUID getNullableResult(CallableStatement cs, int columnIndex) throws SQLException { 66 // 略 67 return null; 68 } 69 }
以 上代碼有2個關鍵點：app
一、在setNonNullParameter()方法中，將UUID轉換成byte[]。UUID使用128位（16字節）存儲，其中，uuid.getMostSignificantBits()返回高64位，uuid.getLeastSignificantBits()返回低64位。dom
二、在getNullableResult()方法中 , 將byte[]轉換成UUID。ide
4 測試
4.1 表
1 CREATE TABLE `user_uuid` ( 2 `id` binary(16) NOT NULL, 3 `name` varchar(10) DEFAULT NULL, 4 PRIMARY KEY (`id`) 5 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
4.2 實體
public class User { private UUID id; private String name; // 略 }
4.3 mapper
1 public interface UserMapper { 2 3 void insert(User record); 4 5 User selectByPrimaryKey(UUID id); 6 7 List<User> selectAll(); 8 9 }
1 <insert id="insert" parameterType="leo.domain.User"> 2 insert into user_uuid (id, name) 3 values (#{id}, #{name}) 4 </insert> 5 6 <select id="selectByPrimaryKey" resultType="leo.domain.User" 7 parameterType="java.util.UUID"> 8 select id, name 9 from user_uuid 10 where id = #{id} 11 </select> 12 13 14 <select id="selectAll" resultType="leo.domain.User"> 15 select id, name 16 from user_uuid 17 </select>
4.4 配置
1 <typeHandlers> 2 <typeHandler handler="leo.handler.UuidHandler"/> 3 </typeHandlers>
在typeHandlers節點中註冊UuidHandler
4.5 測試用例
1 @FixMethodOrder(MethodSorters.NAME_ASCENDING) 2 public class UserMapperTest { 3 4 SqlSession session; 5 UserMapper mapper; 6 7 @Before 8 public void init() { 9 InputStream inputStream = App3_uuid.class.getResourceAsStream("/mybatis-config.xml"); 10 SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); 11 session = sqlSessionFactory.openSession(); 12 mapper = session.getMapper(UserMapper.class); 13 } 14 15 16 @Test 17 public void test1Insert() { 18 // 插入用戶1 19 UUID uuid1 = UUID.fromString("0eaa9bf6-0c70-4678-8658-8737d3a5eba1"); 20 User user1 = new User(); 21 user1.setId(uuid1); 22 user1.setName("用戶1"); 23 mapper.insert(user1); 24 session.commit(); 25 26 // 插入用戶2 27 UUID uuid2 = UUID.fromString("0eaa9bf6-0c70-4678-8658-8737d3a5eba2"); 28 User user2 = new User(); 29 user2.setId(uuid2); 30 user2.setName("用戶2"); 31 mapper.insert(user2); 32 session.commit(); 33 34 } 35 36 @Test 37 public void test2SelectByPrimaryKey() { 38 UUID uuid1 = UUID.fromString("0eaa9bf6-0c70-4678-8658-8737d3a5eba1"); 39 User user1 = mapper.selectByPrimaryKey(uuid1); 40 System.out.println("user = " + user1); 41 } 42 43 @Test 44 public void test3SelectAll() { 45 List<User> list = mapper.selectAll(); 46 System.out.println("list = " + list); 47 48 } 49 }