MyBatis枚举映射类讨论

前言

本篇需要对于MyBatis有一定的认识，而且只是针对于TypeHandler接口来讨论，暂不讨论其他方面的问题

TypeHandler概叙

      TypeHandler是MyBatis设计的一个用于参数的接口，你们会不会很好奇MyBatis是如何把整形，时间，字符串等映射到数据表字段的，实际上就是这个接口来做的，在TypeHandlerRegistry的构造器中初始化了很多处理器，如下

public TypeHandlerRegistry(Configuration configuration) {this.unknownTypeHandler = new UnknownTypeHandler(configuration);register(Boolean.class, new BooleanTypeHandler());register(boolean.class, new BooleanTypeHandler());register(JdbcType.BOOLEAN, new BooleanTypeHandler());register(JdbcType.BIT, new BooleanTypeHandler());register(Byte.class, new ByteTypeHandler());register(byte.class, new ByteTypeHandler());register(JdbcType.TINYINT, new ByteTypeHandler());register(Short.class, new ShortTypeHandler());register(short.class, new ShortTypeHandler());register(JdbcType.SMALLINT, new ShortTypeHandler());register(Integer.class, new IntegerTypeHandler());register(int.class, new IntegerTypeHandler());register(JdbcType.INTEGER, new IntegerTypeHandler());register(Long.class, new LongTypeHandler());register(long.class, new LongTypeHandler());register(Float.class, new FloatTypeHandler());register(float.class, new FloatTypeHandler());register(JdbcType.FLOAT, new FloatTypeHandler());register(Double.class, new DoubleTypeHandler());register(double.class, new DoubleTypeHandler());register(JdbcType.DOUBLE, new DoubleTypeHandler());register(Reader.class, new ClobReaderTypeHandler());register(String.class, new StringTypeHandler());register(String.class, JdbcType.CHAR, new StringTypeHandler());register(String.class, JdbcType.CLOB, new ClobTypeHandler());register(String.class, JdbcType.VARCHAR, new StringTypeHandler());register(String.class, JdbcType.LONGVARCHAR, new StringTypeHandler());register(String.class, JdbcType.NVARCHAR, new NStringTypeHandler());register(String.class, JdbcType.NCHAR, new NStringTypeHandler());register(String.class, JdbcType.NCLOB, new NClobTypeHandler());register(JdbcType.CHAR, new StringTypeHandler());register(JdbcType.VARCHAR, new StringTypeHandler());register(JdbcType.CLOB, new ClobTypeHandler());register(JdbcType.LONGVARCHAR, new StringTypeHandler());register(JdbcType.NVARCHAR, new NStringTypeHandler());register(JdbcType.NCHAR, new NStringTypeHandler());register(JdbcType.NCLOB, new NClobTypeHandler());register(Object.class, JdbcType.ARRAY, new ArrayTypeHandler());register(JdbcType.ARRAY, new ArrayTypeHandler());register(BigInteger.class, new BigIntegerTypeHandler());register(JdbcType.BIGINT, new LongTypeHandler());register(BigDecimal.class, new BigDecimalTypeHandler());register(JdbcType.REAL, new BigDecimalTypeHandler());register(JdbcType.DECIMAL, new BigDecimalTypeHandler());register(JdbcType.NUMERIC, new BigDecimalTypeHandler());register(InputStream.class, new BlobInputStreamTypeHandler());register(Byte[].class, new ByteObjectArrayTypeHandler());register(Byte[].class, JdbcType.BLOB, new BlobByteObjectArrayTypeHandler());register(Byte[].class, JdbcType.LONGVARBINARY, new BlobByteObjectArrayTypeHandler());register(byte[].class, new ByteArrayTypeHandler());register(byte[].class, JdbcType.BLOB, new BlobTypeHandler());register(byte[].class, JdbcType.LONGVARBINARY, new BlobTypeHandler());register(JdbcType.LONGVARBINARY, new BlobTypeHandler());register(JdbcType.BLOB, new BlobTypeHandler());register(Object.class, unknownTypeHandler);register(Object.class, JdbcType.OTHER, unknownTypeHandler);register(JdbcType.OTHER, unknownTypeHandler);register(Date.class, new DateTypeHandler());register(Date.class, JdbcType.DATE, new DateOnlyTypeHandler());register(Date.class, JdbcType.TIME, new TimeOnlyTypeHandler());register(JdbcType.TIMESTAMP, new DateTypeHandler());register(JdbcType.DATE, new DateOnlyTypeHandler());register(JdbcType.TIME, new TimeOnlyTypeHandler());register(java.sql.Date.class, new SqlDateTypeHandler());register(java.sql.Time.class, new SqlTimeTypeHandler());register(java.sql.Timestamp.class, new SqlTimestampTypeHandler());register(String.class, JdbcType.SQLXML, new SqlxmlTypeHandler());register(Instant.class, new InstantTypeHandler());register(LocalDateTime.class, new LocalDateTimeTypeHandler());register(LocalDate.class, new LocalDateTypeHandler());register(LocalTime.class, new LocalTimeTypeHandler());register(OffsetDateTime.class, new OffsetDateTimeTypeHandler());register(OffsetTime.class, new OffsetTimeTypeHandler());register(ZonedDateTime.class, new ZonedDateTimeTypeHandler());register(Month.class, new MonthTypeHandler());register(Year.class, new YearTypeHandler());register(YearMonth.class, new YearMonthTypeHandler());register(JapaneseDate.class, new JapaneseDateTypeHandler());// issue #273register(Character.class, new CharacterTypeHandler());register(char.class, new CharacterTypeHandler());}

所以我们平时不用设计什么就可以进行自动转换，而一种特殊情况下，我们需要自己定义，也就是枚举，这也是我们经常用的技术，比如有以下的对象

public class SysUser {/*** 用户名*/private String name;/*** 密码-加密模式*/private String password;/*** 数据状态,0-正常,1-删除*/private DataStateEnum deleted = DataStateEnum.NORMAL;
}package com.zxc.movie.common.enums;/*** 数据状态*/
public enum DataStateEnum implements BaseEnum<DataStateEnum>{NORMAL(0, "正常"),DELETE(1, "删除"),;private final Integer code;private final String desc;DataStateEnum(Integer code, String desc) {this.code = code;this.desc = desc;}@Overridepublic Integer getCode() {return code;}@Overridepublic String getDesc() {return desc;}
}

            那么我们如何进行转换呢，其实有很多种方式，下面一个个说下

常规方式

  直接继承BaseTypeHandler，然后实现就行，看下面的描述就很简单了

package com.zxc.movie.common.typehandler.common;import com.zxc.movie.common.enums.BaseEnumUtils;
import com.zxc.movie.common.enums.DataStateEnum;
import org.apache.ibatis.type.BaseTypeHandler;
import org.apache.ibatis.type.JdbcType;import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Objects;/**
* @author zxc_user
* @date 2023/8/7 19:15
* @version 1.0
* @description 数据状态返回
**/
public class DataStateEnumHandler extends BaseTypeHandler<DataStateEnum> {@Overridepublic void setNonNullParameter(PreparedStatement ps, int i, DataStateEnum parameter, JdbcType jdbcType) throws SQLException {ps.setInt(i, parameter.getCode());}@Overridepublic DataStateEnum getNullableResult(ResultSet rs, String columnName) throws SQLException {return getByCode(rs.getInt(columnName));}@Overridepublic DataStateEnum getNullableResult(ResultSet rs, int columnIndex) throws SQLException {return getByCode(rs.getInt(columnIndex));}@Overridepublic DataStateEnum getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {return getByCode(cs.getInt(columnIndex));}private DataStateEnum getByCode(Integer code) {DataStateEnum[] dataStateEnums = DataStateEnum.values();for (DataStateEnum baseEnum : dataStateEnums) {if(Objects.equals(baseEnum.getCode(), code)) {return baseEnum;}}}
}

这种方式很简单，但是如果有多个枚举类会存在大量的重复代码，所以我们可以把公用逻辑进行抽取，其实只要让枚举有统一的类型，并且获取到所有枚举就行了，那么怎么做呢，需要有以下的步骤

进阶方式      

  首先，要提供一个接口，然后所有枚举都实现这个接口，如下

/**
* @author zxc_user
* @date 2023/8/7 19:01
* @version 1.0
* @description 枚举基础类
**/
public interface BaseEnum<T>{Integer getCode();String getDesc();
}/*** 数据状态*/
public enum DataStateEnum implements BaseEnum<DataStateEnum>{NORMAL(0, "正常"),DELETE(1, "删除"),;private final Integer code;private final String desc;DataStateEnum(Integer code, String desc) {this.code = code;this.desc = desc;}@Overridepublic Integer getCode() {return code;}@Overridepublic String getDesc() {return desc;}
}

这样一来，所有枚举都属于BaseEnum类型

        其次提供了一个公用的TypeHandler处理器BaseEnumHandler，定义如下

package com.zxc.movie.common.typehandler;import com.zxc.movie.common.enums.BaseEnum;
import com.zxc.movie.common.enums.BaseEnumUtils;
import org.apache.ibatis.type.BaseTypeHandler;
import org.apache.ibatis.type.JdbcType;import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
/**
* @author zxc_user
* @date 2023/8/7 18:52
* @version 1.0
* @description 通用的枚举类解释器
**/
public abstract class BaseEnumHandler<T extends BaseEnum<T>> extends BaseTypeHandler<T> {//进一步优化protected abstract BaseEnum<T>[] getBaseEnumArray();//根据code获取对应的数据private BaseEnum<T> getBaseEnum(Integer code) {BaseEnum<T>[] baseEnumArray = getBaseEnumArray();for (BaseEnum<T> baseEnum : baseEnumArray) {if(Objects.equals(baseEnum.getCode(), code)) {return baseEnum;}}return null;}@Overridepublic void setNonNullParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException {ps.setInt(i, parameter.getCode());}@Overridepublic T getNullableResult(ResultSet rs, String columnName) throws SQLException {return (T) getBaseEnum(rs.getInt(columnName));}@Overridepublic T getNullableResult(ResultSet rs, int columnIndex) throws SQLException {return (T) getBaseEnum(rs.getInt(columnIndex));}@Overridepublic T getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {return (T) getBaseEnum(cs.getInt(columnIndex));}
}

原来的DataStateEnumHandler只需要继承上面的处理器，然后实现方法即可，如下

package com.zxc.movie.common.typehandler.common;import com.zxc.movie.common.enums.BaseEnum;
import com.zxc.movie.common.enums.DataStateEnum;
import com.zxc.movie.common.typehandler.BaseEnumHandler;/**
* @author zxc_user
* @date 2023/8/7 19:15
* @version 1.0
* @description 数据状态返回
**/
public class DataStateEnumHandler extends BaseEnumHandler<DataStateEnum> {@Overrideprotected BaseEnum<DataStateEnum>[] getBaseEnumArray() {return DataStateEnum.values();}
}

是不是很简单，到这里其实就已经很容易了，但是其实还能进一步优化，回看逻辑，其实我们只要有办法拿到所有枚举的对象就可以处理，那么有没有办法呢，其实是有的，可以通过反射，如下

最终方式

package com.zxc.movie.common.typehandler;import com.zxc.movie.common.enums.BaseEnum;
import org.apache.ibatis.type.BaseTypeHandler;
import org.apache.ibatis.type.JdbcType;import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Objects;/**
* @author zxc_user
* @date 2023/8/7 18:52
* @version 1.0
* @description 通用的枚举类解释器
**/
public abstract class BaseEnumHandler<T extends BaseEnum<T>> extends BaseTypeHandler<T> {private BaseEnum<T>[] baseArrayEnum;public BaseEnumHandler(){//获取泛型的类型Type genericSuperclass = this.getClass().getGenericSuperclass();if (genericSuperclass instanceof ParameterizedType){ParameterizedType parameterizedType = (ParameterizedType) genericSuperclass;Type[] actualTypeArguments = parameterizedType.getActualTypeArguments();for (Type actualTypeArgument : actualTypeArguments) {//获取枚举的所有对象，因为都实现了BaseEnum接口this.baseArrayEnum = (BaseEnum[]) ((Class)actualTypeArgument).getEnumConstants();}}}//根据code获取对应的数据private BaseEnum<T> getBaseEnum(Integer code) {for (BaseEnum<T> baseEnum : baseArrayEnum) {if(Objects.equals(baseEnum.getCode(), code)) {return baseEnum;}}return null;}@Overridepublic void setNonNullParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException {ps.setInt(i, parameter.getCode());}@Overridepublic T getNullableResult(ResultSet rs, String columnName) throws SQLException {return (T) getBaseEnum(rs.getInt(columnName));}@Overridepublic T getNullableResult(ResultSet rs, int columnIndex) throws SQLException {return (T) getBaseEnum(rs.getInt(columnIndex));}@Overridepublic T getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {return (T) getBaseEnum(cs.getInt(columnIndex));}
}

最重要的地方就是构造器里面通过反射获取到枚举所有类型，然后原来的处理器只需要直接继承就行了，如下

package com.zxc.movie.common.typehandler.common;import com.zxc.movie.common.enums.DataStateEnum;
import com.zxc.movie.common.typehandler.BaseEnumHandler;/**
* @author zxc_user
* @date 2023/8/7 19:15
* @version 1.0
* @description 数据状态返回
**/
public class DataStateEnumHandler extends BaseEnumHandler<DataStateEnum> {}

是不是变的很简单？唯一的缺点就是还是需要创建一个转换器，但是转换器已经不需要实现任何内容了，只需要提供一个类就行了

TypeHandler生效

老版本的MyBatis是通过xml文件注册的，这里就不说了，因为现在都是需要和Spring进行集成的，而且还是SpringBoot，所以这里只说SpringBoot的方式

第一种

在application.yml文件中配置如下内容，type-handlers-package为处理类所在包

mybatis-plus:
  type-handlers-package: com.zxc.movie.common.typehandler

第二种

往IOC容器中注入一个Bean,如下，这是MyBatis-PLUS提供的扩展点，是不是很方便？

/**
* @author zxc_user
* @date 2023/8/7 19:17
* @version 1.0
* @description mybatis-plus配置类
**/
@Configuration
public class MyBatisPlusConfig {/*** 自定义配置，看源码发现的* @return*/@Beanpublic ConfigurationCustomizer mybatisConfiguration() {return configuration -> {//注册解析器configuration.getTypeHandlerRegistry().register(DataStateEnumHandler.class);};}
}

这里顺便说一下，第二种方式的优先度比第一种的要高，这个逻辑需要在源码中查看或者官网介绍，源码逻辑在MybatisPlusAutoConfiguration.applyConfiguration中有所体现

总结

到这里本篇文章就结束了，其实并不复杂，主要是为了统一TypeHandler的处理逻辑，最妙的是通过反射获取的枚举列表方法，如下,虽然不难，不过也可以记录一下

    public BaseEnumHandler(){//获取枚举类型Type genericSuperclass = this.getClass().getGenericSuperclass();if (genericSuperclass instanceof ParameterizedType){ParameterizedType parameterizedType = (ParameterizedType) genericSuperclass;Type[] actualTypeArguments = parameterizedType.getActualTypeArguments();for (Type actualTypeArgument : actualTypeArguments) {this.baseArrayEnum = (BaseEnum[]) ((Class)actualTypeArgument).getEnumConstants();}}}