mybatis枚举类型转化

在MyBatis中，我们可以使用TypeHandler来处理Java中的枚举类型与SQL中的映射关系。具体操作如下：

1. 创建一个实现了TypeHandler接口的枚举类型转换器类。

public class MyEnumTypeHandler<E extends Enum<E>> implements TypeHandler<E> {

    private Class<E> type;

    public MyEnumTypeHandler(Class<E> type) {
        if (type == null)
            throw new IllegalArgumentException("Type argument cannot be null");
        this.type = type;
    }

    @Override
    public void setParameter(PreparedStatement ps, int i, E parameter, JdbcType jdbcType) throws SQLException {
        if (parameter == null) {
            ps.setNull(i, jdbcType.TYPE_CODE);
        } else {
            ps.setInt(i, parameter.ordinal());
        }
    }

    @Override
    public E getResult(ResultSet rs, String columnName) throws SQLException {
        int ordinal = rs.getInt(columnName);
        if (rs.wasNull()) {
            return null;
        } else {
            try {
                Method method = type.getMethod("values");
                Object[] objects = (Object[]) method.invoke(type);
                return (E) objects[ordinal];
            } catch (Exception e) {
                throw new IllegalArgumentException("Cannot convert " + ordinal + " to " + type.getSimpleName() + " by ordinal value.", e);
            }
        }
    }

    @Override
    public E getResult(ResultSet rs, int columnIndex) throws SQLException {
        int ordinal = rs.getInt(columnIndex);
        if (rs.wasNull()) {
            return null;
        } else {
            try {
                Method method = type.getMethod("values");
                Object[] objects = (Object[]) method.invoke(type);
                return (E) objects[ordinal];
            } catch (Exception e) {
                throw new IllegalArgumentException("Cannot convert " + ordinal + " to " + type.getSimpleName() + " by ordinal value.", e);
            }
        }
    }

    @Override
    public E getResult(CallableStatement cs, int columnIndex) throws SQLException {
        int ordinal = cs.getInt(columnIndex);
        if (cs.wasNull()) {
            return null;
        } else {
            try {
                Method method = type.getMethod("values");
                Object[] objects = (Object[]) method.invoke(type);
                return (E) objects[ordinal];
            } catch (Exception e) {
                throw new IllegalArgumentException("Cannot convert " + ordinal + " to " + type.getSimpleName() + " by ordinal value.", e);
            }
        }
    }
}

2. 在MyBatis的配置文件中注册这个TypeHandler。

<typeHandlers>
    <typeHandler handler="com.example.MyEnumTypeHandler" javaType="com.example.MyEnum"/>
</typeHandlers>

3. 在Java对象中使用枚举类型。

public class User {
    private Long id;
    private String name;
    private Gender gender;
    // getter and setter
}

4. 在SQL语句中使用枚举类型。

<select id="getUser" parameterType="long" resultType="com.example.User">
    select * from user where id = #{id}
</select>

这样，MyBatis就会自动将数据库中的值转换为Java对象中的枚举类型，或者将Java对象中的枚举类型转换为数据库中的值。