Mapper系列六：類型處理器TypeHandler

簡單類型和複雜類型

通用 Mapper 默認情況下會忽略複雜類型，對複雜類型不進行“從類到表”的映射。
1、創建table_user表和數據

	CREATE TABLE `table_user` (
		`user_id` INT NOT NULL AUTO_INCREMENT,
		`user_name` VARCHAR (100) NULL,
		`address` VARCHAR (100) NULL,
		`season` VARCHAR (100) NULL,
		PRIMARY KEY (`user_id`)
	);

2、自定義類型轉換器

public class AddressTypeHandler extends BaseTypeHandler<Address> {

	@Override
	public void setNonNullParameter(PreparedStatement ps, int i, Address address, JdbcType jdbcType)
			throws SQLException {
		//1.對address對象進行驗證
		if(address == null) {
			return ;
		}
		//2.從address對象中取出具體數據
		String province = address.getProvince();
		String city = address.getCity();
		String street = address.getStreet();
		//3.拼裝成一個字符串
		//規則：各個值之間使用“,”分開
		StringBuilder builder = new StringBuilder();
		builder
			.append(province)
			.append(",")
			.append(city)
			.append(",")
			.append(street);
		String parameterValue = builder.toString();
		//4.設置參數
		ps.setString(i, parameterValue);
	}

	@Override
	public Address getNullableResult(ResultSet rs, String columnName) throws SQLException {
		//1.根據字段名從rs對象中獲取字段值
		String columnValue = rs.getString(columnName);
		//2.驗證columnValue是否有效
		if(columnValue == null || columnValue.length() == 0 || !columnValue.contains(",")) {
			return null;
		}
		//3.根據“,”對columnValue進行拆分
		String[] split = columnValue.split(",");
		//4.從拆分結果數組中獲取Address需要的具體數據
		String province = split[0];
		String city = split[1];
		String street = split[2];
		//5.根據具體對象組裝一個Address對象
		Address address = new Address(province, city, street);
		return address;
	}

	@Override
	public Address getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
		//1.根據字段名從rs對象中獲取字段值
		String columnValue = rs.getString(columnIndex);
		//2.驗證columnValue是否有效
		if(columnValue == null || columnValue.length() == 0 || !columnValue.contains(",")) {
			return null;
		}
		//3.根據“,”對columnValue進行拆分
		String[] split = columnValue.split(",");
		//4.從拆分結果數組中獲取Address需要的具體數據
		String province = split[0];
		String city = split[1];
		String street = split[2];
		//5.根據具體對象組裝一個Address對象
		Address address = new Address(province, city, street);
		return address;
	}

	@Override
	public Address getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
		//1.根據字段名從rs對象中獲取字段值
		String columnValue = cs.getString(columnIndex);
		//2.驗證columnValue是否有效
		if(columnValue == null || columnValue.length() == 0 || !columnValue.contains(",")) {
			return null;
		}
		//3.根據“,”對columnValue進行拆分
		String[] split = columnValue.split(",");
		//4.從拆分結果數組中獲取Address需要的具體數據
		String province = split[0];
		String city = split[1];
		String street = split[2];
		//5.根據具體對象組裝一個Address對象
		Address address = new Address(province, city, street);
		return address;
	}
}

3、註冊自定義類型轉換器
 方式1：字段級別：@ColumnType 註解

 方式2：全局級別：在 MyBatis 配置文件中配置 typeHandlers

<typeHandlers>
	<!-- handler屬性：指定自定義類型轉換器全類名 -->
	<!-- javaType屬性：指定需要使用“自定義類型轉換器”進行類型處理的實體類型 -->
	<typeHandler 
		handler="com.atguigu.mapper.handlers.AddressTypeHandler"
		javaType="com.atguigu.mapper.entities.Address"/>
		
</typeHandlers>

4、枚舉類型處理
 方式1：讓通用 Mapper 把枚舉類型作爲簡單類型處理 。Spring 配置文件中添加通用 Mapper 的配置項 enumAsSimpleType=true。本質上使用了 org.apache.ibatis.type.EnumTypeHandler<E>

<bean class="tk.mybatis.spring.mapper.MapperScannerConfigurer">
	<property name="basePackage" value="com.atguigu.mapper.mappers"/>
	<property name="properties">
		<value>
			enumAsSimpleType=true
		</value>
	</property>
</bean>

 方式2：：爲枚舉類型配置對應的類型處理器

5、枚舉類型處理器 ：
內置：
 org.apache.ibatis.type.EnumTypeHandler
   在數據庫中存儲枚舉值本身
 org.apache.ibatis.type.EnumOrdinalTypeHandler
   在數據庫中僅僅存儲枚舉值的索引
自定義：和AddressTypeHandler操作一樣
6、內置枚舉類型處理器註冊
 內置類型處理器不能使用@ColumnType 註解

 在 MyBatis 配置文件中配置 typeHandlers

<typeHandlers>
	<!-- handler屬性：指定自定義類型轉換器全類名 -->
	<!-- javaType屬性：指定需要使用“自定義類型轉換器”進行類型處理的實體類型 -->	
	<typeHandler 
		handler="org.apache.ibatis.type.EnumOrdinalTypeHandler"
		javaType="com.atguigu.mapper.entities.SeasonEnum"/>
		
</typeHandlers>

測試：

public class TypeHandlerTest {
	
	private UserService userService;
	
	{
		userService = new ClassPathXmlApplicationContext("spring-context.xml").getBean(UserService.class);
	}
	
	@Test
	public void testQueryUser() {
		Integer userId = 1;
		User user = userService.getUserById(userId);
		System.out.println(user);
	}
	
	@Test
	public void testSaveUser() {
		User user = new User(null, "tom08", new Address("AAA", "BBB", "CCC"), SeasonEnum.AUTUMN);
		userService.saveUser(user);
	}
}

Preparing: SELECT user_id,user_name,address,season FROM table_user WHERE user_id = ?   
Parameters: 1(Integer)  
Total: 1 
User [userId=1, userName=justin, address=Address [province=aaa, city=bbb, street=ccc], season=summer @_@]

Preparing: INSERT INTO table_user ( user_id,user_name,address,season ) VALUES( ?,?,?,? )   
Parameters: null, tom08(String), AAA,BBB,CCC(String), 2(Integer)  
Updates: 1