如何在 Mybatis 中优雅地使用枚举

前言

Mybatis 遇到字段为枚举时无法解析成我们想要的数据

MyBatis 内置枚举转换器

org.apache.ibatis.type.EnumTypeHandler 和 org.apache.ibatis.type.EnumOrdinalTypeHandler

EnumTypeHandler

Mybatis 中默认的枚举转换器，获取枚举中的 name 属性

EnumOrdinalTypeHandler

获取枚举中 ordinal 属性，相当于索引，从1开始

为了贴合业务开发，我们需要创建一个新的枚举转换器

1、枚举接口

枚举通用行为接口，此处的 value 属性为存储于数据库中的值

public interface BaseEnum<T extends Serializable> {

    /**
     * 枚举数据库存储值
     */
    T getValue();
}

让需要的枚举实现该接口，此方式不够灵活，只能使用存取value属性

@Getter
@AllArgsConstructor
public enum GenderEnum implements BaseEnum<Integer> {

    MALE(1, "男"),
    FEMALE(2, "女"),
    ;

    @JsonValue
    private Integer value;

    private String desc;

    @JsonCreator(mode = JsonCreator.Mode.DELEGATING)
    public static GenderEnum getByValue(int value) {
        for (GenderEnum genderEnum : values()) {
            if (genderEnum.getValue() == value) {
                return genderEnum;
            }
        }
        return null;
    }
}

2、枚举注解

/**
 * 支持普通枚举类字段, 只用在enum类的字段上
 * 当实体类的属性是普通枚举，且是其中一个字段，使用该注解来标注枚举类里的那个属性对应字段
 */
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD, ElementType.ANNOTATION_TYPE})
public @interface EnumValue {
}

 注解可以标记到想要的任何一个属性上

@Getter
@AllArgsConstructor
public enum GenderEnum {

    MALE(1, "男"),
    FEMALE(2, "女"),
    ;

    @JsonValue
    @EnumValue
    private int value;

    private String desc;

    @JsonCreator(mode = JsonCreator.Mode.DELEGATING)
    public static GenderEnum getByValue(int value) {
        for (GenderEnum genderEnum : values()) {
            if (genderEnum.getValue() == value) {
                return genderEnum;
            }
        }
        return null;
    }
}

3、自定义枚举属性转换器

MybatisEnumTypeHandler用于处理实现了BaseEnum的或者使用了@EnumValue的枚举

/**
 * 自定义枚举属性转换器
 **/
public class MybatisEnumTypeHandler<E extends Enum<E>> extends BaseTypeHandler<E> {

    private static final Map<String, String> TABLE_METHOD_OF_ENUM_TYPES = new ConcurrentHashMap<>();
    private static final ReflectorFactory REFLECTOR_FACTORY = new DefaultReflectorFactory();
    private final Class<E> enumClassType;
    private final Class<?> propertyType;
    private final Invoker getInvoker;

    public MybatisEnumTypeHandler(Class<E> enumClassType) {
        if (enumClassType == null) {
            throw new IllegalArgumentException("Type argument cannot be null");
        }
        this.enumClassType = enumClassType;
        MetaClass metaClass = MetaClass.forClass(enumClassType, REFLECTOR_FACTORY);
        String name = "value";
        if (!BaseEnum.class.isAssignableFrom(enumClassType)) {
            name = findEnumValueFieldName(this.enumClassType).orElseThrow(() -> new IllegalArgumentException(String.format("Could not find @EnumValue in Class: %s.", this.enumClassType.getName())));
        }
        this.propertyType = PrimitiveUtil.resolvePrimitiveIfNecessary(metaClass.getGetterType(name));
        this.getInvoker = metaClass.getGetInvoker(name);
    }

    /**
     * 查找标记标记EnumValue字段
     *
     * @param clazz class
     * @return EnumValue字段
     */
    public static Optional<String> findEnumValueFieldName(Class<?> clazz) {
        if (clazz != null && clazz.isEnum()) {
            String className = clazz.getName();
            return Optional.ofNullable(TABLE_METHOD_OF_ENUM_TYPES.computeIfAbsent(className, key -> {
                Optional<Field> fieldOptional = findEnumValueAnnotationField(clazz);
                return fieldOptional.map(Field::getName).orElse(null);
            }));
        }
        return Optional.empty();
    }

    private static Optional<Field> findEnumValueAnnotationField(Class<?> clazz) {
        return Arrays.stream(clazz.getDeclaredFields()).filter(field -> field.isAnnotationPresent(EnumValue.class)).findFirst();
    }

    @SuppressWarnings("Duplicates")
    @Override
    public void setNonNullParameter(PreparedStatement ps, int i, E parameter, JdbcType jdbcType)
        throws SQLException {
        if (jdbcType == null) {
            ps.setObject(i, this.getValue(parameter));
        } else {
            ps.setObject(i, this.getValue(parameter), jdbcType.TYPE_CODE);
        }
    }

    @Override
    public E getNullableResult(ResultSet rs, String columnName) throws SQLException {
        Object value = rs.getObject(columnName, this.propertyType);
        if (null == value && rs.wasNull()) {
            return null;
        }
        return this.valueOf(value);
    }

    @Override
    public E getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
        Object value = rs.getObject(columnIndex, this.propertyType);
        if (null == value && rs.wasNull()) {
            return null;
        }
        return this.valueOf(value);
    }

    @Override
    public E getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
        Object value = cs.getObject(columnIndex, this.propertyType);
        if (null == value && cs.wasNull()) {
            return null;
        }
        return this.valueOf(value);
    }

    private E valueOf(Object value) {
        E[] es = this.enumClassType.getEnumConstants();
        return Arrays.stream(es).filter((e) -> equalsValue(value, getValue(e))).findAny().orElse(null);
    }

    /**
     * 值比较
     *
     * @param sourceValue 数据库字段值
     * @param targetValue 当前枚举属性值
     * @return 是否匹配
     */
    protected boolean equalsValue(Object sourceValue, Object targetValue) {
        String sValue = String.valueOf(sourceValue).trim();
        String tValue = String.valueOf(targetValue).trim();
        if (sourceValue instanceof Number && targetValue instanceof Number
            && new BigDecimal(sValue).compareTo(new BigDecimal(tValue)) == 0) {
            return true;
        }
        return Objects.equals(sValue, tValue);
    }

    private Object getValue(Object object) {
        try {
            return this.getInvoker.invoke(object, new Object[0]);
        } catch (ReflectiveOperationException e) {
            throw new RuntimeException(e.getMessage());
        }
    }
}

工具类PrimitiveUtil

/**
 * 包装类型转换
 **/
public final class PrimitiveUtil {

    private static final Map<Class<?>, Class<?>> PRIMITIVE_TYPE_TO_WRAPPER_MAP = new IdentityHashMap<>(8);

    static {
        PRIMITIVE_TYPE_TO_WRAPPER_MAP.put(boolean.class, Boolean.class);
        PRIMITIVE_TYPE_TO_WRAPPER_MAP.put(byte.class, Byte.class);
        PRIMITIVE_TYPE_TO_WRAPPER_MAP.put(char.class, Character.class);
        PRIMITIVE_TYPE_TO_WRAPPER_MAP.put(double.class, Double.class);
        PRIMITIVE_TYPE_TO_WRAPPER_MAP.put(float.class, Float.class);
        PRIMITIVE_TYPE_TO_WRAPPER_MAP.put(int.class, Integer.class);
        PRIMITIVE_TYPE_TO_WRAPPER_MAP.put(long.class, Long.class);
        PRIMITIVE_TYPE_TO_WRAPPER_MAP.put(short.class, Short.class);
    }

    public static Class<?> resolvePrimitiveIfNecessary(Class<?> clazz) {
        return (clazz.isPrimitive() && clazz != void.class ? PRIMITIVE_TYPE_TO_WRAPPER_MAP.get(clazz) : clazz);
    }

}

4、将MybatisEnumTypeHandler注册成默认的枚举属性转换器

mybatis:
  configuration:
    # 自定义枚举属性转换器
    default-enum-type-handler: com.xxx.handler.MybatisEnumTypeHandler