如何在java中将一个枚举转换为另一个枚举？

Question

I have;

public enum Detailed {
    PASSED, INPROCESS, ERROR1, ERROR2, ERROR3;
}

and need to convert it to the following;

public enum Simple {
    DONE, RUNNING, ERROR;
}

So first PASSED -> DONE and INPROCESS -> RUNNING , but all errors should be: ERROR . Obviously it is possible to write cases for all values, but there may be a better solution?

Answer 1

Personally I would just create a Map<Detailed, Simple> and do it explicitly - or even use a switch statement, potentially.

Another alternative would be to pass the mapping into the constructor - you could only do it one way round, of course:

public enum Detailed {
    PASSED(Simple.DONE),
    INPROCESS(Simple.RUNNING),
    ERROR1(Simple.ERROR),
    ERROR2(Simple.ERROR),
    ERROR3(Simple.ERROR);

    private final Simple simple;

    private Detailed(Simple simple) {
        this.simple = simple;
    }

    public Simple toSimple() {
        return simple;
    }
}

(I find this simpler than Ted's approach of using polymorphism, as we're not really trying to provide different behaviour - just a different simple mapping.)

While you could potentially do something cunning with the ordinal value, it would be much less obvious, and take more code - I don't think there'd be any benefit.

Answer 2

One way is to define a method asSimple() in your Detailed enum:

public enum Detailed {
    PASSED {
        @Override
        Simple asSimple() {
            return DONE;
        }
    },
    INPROCESS {
        @Override
        Simple asSimple() {
            return RUNNING;
        }
    },
    ERROR1,
    ERROR2,
    ERROR3;
    public Simple asSimple() {
        return Simple.ERROR; // default mapping
    }
}

You can then simply call the method when you want to do the mapping:

Detailed code = . . .
Simple simpleCode = code.asSimple();

It has the advantage of putting the knowledge of the mapping with the Detailed enum (where perhaps it belongs). It has the disadvantage of having knowledge of Simple mixed in with the code for Detailed . This may or may not be a bad thing, depending on your system architecture.

Answer 3

Use EnumMap

I decouple my external xml interface from my internal domain model by implementing a transformation service. This includes mapping enums from jaxb generated code to domain model enums.

Using a static EnumMap encapsulates the concern of transformation within the class responsible for transformation. Its cohesive.

@Service
public class XmlTransformer {

    private static final Map<demo.xml.Sense, Constraint.Sense> xmlSenseToSense;
    static {
        xmlSenseToSense = new EnumMap<demo.xml.Sense, Constraint.Sense> (
            demo.xml.Sense.class);
        xmlSenseToSense.put(demo.xml.planningInterval.Sense.EQUALS, 
            Constraint.Sense.EQUALS);
        xmlSenseToSense.put(demo.xml.planningInterval.Sense.GREATER_THAN_OR_EQUALS, 
            Constraint.Sense.GREATER_THAN_OR_EQUALS);
        xmlSenseToSense.put(demo.xml.planningInterval.Sense.LESS_THAN_OR_EQUALS, 
            Constraint.Sense.LESS_THAN_OR_EQUALS);
    }
    ...
}

Answer 4

Ted's answer is very Javaly, but the expression

passed == PASSED ? DONE : ERROR

would do the job, too.

Answer 5

To me that sounds more like a conceptual problem than a programming problem. Why don't you just remove the "Simple" enum type and use the other one instead in all places in the program?

Just to make that more clear with another example: Would you really try to define an enum type for the work days in a week (Monday to Friday) and another enum for all days of a week (Monday to Sunday)?

Answer 6

Here is the simple enum mapper with test:

-- IMPLEMENTATION

-- ENUMS

public enum FirstEnum {

A(0), B(1);

private final int value;

private FirstEnum(int value) {
    this.value = value;
}

public int getValue() {
    return value;
}
}

public enum  SecondEnum {

C(0), D(1);

private final int valueId;

private SecondEnum(int valueId) {
    this.valueId = valueId;
}

public int getValueId() {
    return valueId;
}

}

--MAPPER

import java.lang.reflect.InvocationTargetException;
import java.util.HashMap;
import java.util.Map;

import org.apache.commons.beanutils.PropertyUtils;
import org.apache.commons.lang3.Validate;

import com.google.common.collect.Sets;

public class EnumPropertyMapping {

private final Map<?, ?> firstMap;
private final Map<?, ?> secondMap;

private final Class<?> firstType;
private final Class<?> secondType;

private EnumPropertyMapping(
        Map<?, ?> firstMap, Map<?, ?> secondMap, Class<?> firstType, Class<?> secondType) {

    this.firstMap = firstMap;
    this.secondMap = secondMap;
    this.firstType = firstType;
    this.secondType = secondType;
}

public static Builder builder() {
    return new Builder();
}

@SuppressWarnings("unchecked")
public <R> R getCorrespondingEnum(Object mappedEnum) {
    Validate.notNull(mappedEnum, "Enum must not be NULL");
    Validate.isInstanceOf(Enum.class, mappedEnum, "Parameter must be an Enum");

    if (firstType.equals(mappedEnum.getClass())) {
        return (R) firstMap.get(mappedEnum);
    }

    if (secondType.equals(mappedEnum.getClass())) {
        return (R) secondMap.get(mappedEnum);
    }

    throw new IllegalArgumentException("Didn't found mapping for enum value: " + mappedEnum);
}

public static class Builder {

    private final Map<Object, Object> firstEnumMap = new HashMap<>();
    private final Map<Object, Object> secondEnumMap = new HashMap<>();
    private Class<?> firstEnumType;
    private Class<?> secondEnumType;

    public <T extends Enum<T>> Builder addFirst(Class<T> enumType, String propertyName) {
        firstEnumType = enumType;
        initMap(firstEnumMap, enumType.getEnumConstants(), propertyName);
        return this;
    }

    public <T extends Enum<T>> Builder addSecond(Class<T> enumType, String propertyName) {
        secondEnumType = enumType;
        initMap(secondEnumMap, enumType.getEnumConstants(), propertyName);
        return this;
    }

    private void initMap(Map<Object, Object> enumMap, Object[] enumConstants, String propertyName) {
        try {
            for (Object constant : enumConstants) {
                enumMap.put(PropertyUtils.getProperty(constant, propertyName), constant);
            }
        } catch (InvocationTargetException | NoSuchMethodException | IllegalAccessException ex) {
            throw new IllegalStateException(ex);
        }
    }

    public EnumPropertyMapping mapEnums() {
        Validate.isTrue(firstEnumMap.size() == secondEnumMap.size());
        Validate.isTrue(Sets.difference(firstEnumMap.keySet(), secondEnumMap.keySet()).isEmpty());

        Map<Object, Object> mapA = new HashMap<>();
        Map<Object, Object> mapB = new HashMap<>();

        for (Map.Entry<Object, Object> obj : firstEnumMap.entrySet()) {
            Object secondMapVal = secondEnumMap.get(obj.getKey());
            mapA.put(obj.getValue(), secondMapVal);
            mapB.put(secondMapVal, obj.getValue());
        }
        return new EnumPropertyMapping(mapA, mapB, firstEnumType, secondEnumType);
    }
}

}

-- TEST

import org.junit.Test;

import com.bondarenko.common.utils.lang.enums.FirstEnum;
import com.bondarenko.common.utils.lang.enums.SecondEnum;

import static junit.framework.TestCase.assertEquals;

public class EnumPropertyMappingTest {

@Test
public void testGetMappedEnum() {
    EnumPropertyMapping mapping = EnumPropertyMapping.builder()
                                                                                                     .addSecond(SecondEnum.class, "valueId")
                                                                                                     .addFirst(FirstEnum.class, "value")
                                                                                                     .mapEnums();

    assertEquals(SecondEnum.D, mapping.getCorrespondingEnum(FirstEnum.B));
    assertEquals(FirstEnum.A, mapping.getCorrespondingEnum(SecondEnum.C));
}

}

Answer 7

Guava's Enums.getIfPresent() on Enum.name()

Our case was a particular specialization of this one. We do have two Enum : one we use in the application and another one we use in the core library. The core library is used by a handful of applications, by different teams. Each application views a subset of the whole functionality. The whole functionality is configured with the enums in order to switch on and off, throttle up or down, select strategies, etc.

So we ended up with:

1. one enum for the library, containing all the possible configurations, visible from the applications and also some library-specific
2. one enum for each application, containing the literals corresponding to what the application can see/touch in the library, and some application-specific

Then as we pass data down to the library, we adapt all data and also those configurations. We own all enums, so we can choose to call the same configuration with the same literal in different enums.

Enum LibraryConfig {
    FUNCTION_ONE,
    FUNCTION_TWO,
    FUNCTION_THREE,
    FUNCTION_FOUR;
}

Enum Aplication1Config {
    FUNCTION_ONE,
    FUNCTION_TWO,
    FUNCTION_THREE,
    APPL1_FUNCTION_ONE,
    APPL1_FUNCTION_TWO;
}

Enum Aplication2Config {
    FUNCTION_ONE,
    FUNCTION_TWO,
    FUNCTION_FOUR;
    APPL2_FUNCTION_ONE;
}

When we need to convert from one type to another (app --> lib or lib --> app) we use the getIfPresent() method from com.google.common.base.Enums in this way:

Aplication1Config config1App1 = FUNCTION_TWO;
LibraryConfig configLib = Enums.getIfPresent(LibraryConfig.class, config1App1.name()).orNull();

We check configLib for null value to see if there was successful conversion. This last step we use because of the APPX_FUNCTION_YYY, which are application-specific, and for the conversion on the direction lib --> app, not to pass configuration values library-specific ( FUNCTION_FOUR in the example).

maven's dependency management:

Just in case anyone needs it:

    <dependency>
        <groupId>com.google.guava</groupId>
        <artifactId>guava</artifactId>
        <version>20.0</version>
    </dependency>

Home grown version:

You can make your own conversion using the Enum methods, but you have to take care of the exception to detect when the conversion did not succeed:

try {
    Aplication1Config config1App1 = FUNCTION_TWO;
    LibraryConfig configLib = LibraryConfig.valueOf(config1App1.name());
} catch (IllegalArgumentException iae) {
    // if the conversion did not succeed
}