Allow to customize default TypeHandler for Enum

[anson0370]

I want use a custom enum type handler. It always register an new instance for every enum class. Just like the EnumTypeHandler does here.

https://github.com/mybatis/mybatis-3/blob/master/src/main/java/org/apache/ibatis/type/TypeHandlerRegistry.java#L226-L229

      if (clazz.isEnum()) {
        jdbcHandlerMap = getJdbcHandlerMapForEnumInterfaces(clazz);
        if (jdbcHandlerMap == null) {
          register(clazz, new EnumTypeHandler(clazz)); // there is no way to use a custom enum type handler here now.
          return TYPE_HANDLER_MAP.get(clazz);
        }
      }

[harawata]

Hi @anson0370 ,
#947 does not help?
Could you show us your type handler implementation?

[anson0370]

Hi @kazuki43zoo , thanks for your great work!

Hi @harawata ,
In my case, I want mapping enum value use a annotation like @EnumValue in Ebean does (In fact I'm migrating some code from Ebean to Mybatis). And I noticed the EnumTypeHandler is hard coded in Mybatis.
I know interface can help but I think a hard coded enum type handler is not a good design, right?

There is my handler:

public class EnumValueHandler<E extends Enum<E>> extends BaseTypeHandler<E> {
    private Class<E> type;
    private Map<String, E> enums;
    private Map<E, String> values;

    public EnumValueHandler(Class<E> type) {
        if (type == null) {
            throw new IllegalArgumentException("Type argument cannot be null");
        }
        this.type = type;
        E[] constants = type.getEnumConstants();
        if (constants == null) {
            throw new IllegalArgumentException(type.getSimpleName() + " does not represent an enum type.");
        }
        this.enums = new HashMap<>();
        this.values = new HashMap<>();
        Arrays.stream(type.getEnumConstants()).forEach((e) -> {
            EnumValue enumValue = null;
            try {
                enumValue = type.getField(e.name()).getAnnotation(EnumValue.class);
            } catch (NoSuchFieldException e1) {
                // should never happen
                e1.printStackTrace();
            }
            if (enumValue == null) {
                throw new NullPointerException("No @EnumValue annotation found: " + type.getCanonicalName());
            }
            enums.put(enumValue.value(), e);
            values.put(e, enumValue.value());
        });
    }

    @Override
    public void setNonNullParameter(PreparedStatement ps, int i, E parameter, JdbcType jdbcType) throws SQLException {
        if (jdbcType == null) {
            ps.setString(i, values.get(parameter));
        } else {
            ps.setObject(i, values.get(parameter), jdbcType.TYPE_CODE); // see r3589
        }
    }

    @Override
    public E getNullableResult(ResultSet rs, String columnName) throws SQLException {
        String value = rs.getString(columnName);
        if (rs.wasNull()) {
            return null;
        } else {
            try {
                return enums.get(value);
            } catch (Exception ex) {
                throw new IllegalArgumentException("Cannot convert " + value + " to " + type.getSimpleName() + " by EnumValue.", ex);
            }
        }
    }

    @Override
    public E getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
        String value = rs.getString(columnIndex);
        if (rs.wasNull()) {
            return null;
        } else {
            try {
                return enums.get(value);
            } catch (Exception ex) {
                throw new IllegalArgumentException("Cannot convert " + value + " to " + type.getSimpleName() + " by EnumValue.", ex);
            }
        }
    }

    @Override
    public E getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
        String value = cs.getString(columnIndex);
        if (cs.wasNull()) {
            return null;
        } else {
            try {
                return enums.get(value);
            } catch (Exception ex) {
                throw new IllegalArgumentException("Cannot convert " + value + " to " + type.getSimpleName() + " by EnumValue.", ex);
            }
        }
    }
}

[kazuki43zoo]

@anson0370 like this ?

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface EnumValue {
    String value();
}

public enum MyEnum {
    @EnumValue("01")
    A,
    @EnumValue("02")
    B,
    @EnumValue("03")
    C;
}

[anson0370]

@kazuki43zoo yes! 👍 Ebean use an annotation just this way to mapping enum value. And I have many code need migrate from Ebean.

I find an issue a bit like my issue here. #42.
I agree Mybatis won't give an official implement but should give the possibility to do this.

[harawata]

@anson0370 ,
Thanks for the info!
Your explanation makes sense and @kazuki43zoo 's patch looks good.

[kazuki43zoo]

Hi @anson0370, I've fixed this via a238186. Please try the 3.4.5-SNAPSHOT.
About how to use snapshot see here.

Thanks.