如何指定枚举对象数组的RESTful资源查询参数

Question

I have a RESTful resource which should take as a parameter a comma separated list of values.

http://host:port/path/to/resource?enums=abc,def,ghi

How do I make RestEasy and Jackson handle this?

@GET
public ResourceModel getResource( @QueryParam("enums") MyEnum[] values ) {
   return new ResourceModel( values );
}

I know I can make it a simple String with an internal parser. But I would much prefer to be able to specify the type so that Jackson does the conversion for me (returning appropriately numbered error codes if the input is bad, etc).

I've tried making values an array (as shown above), a List<MyEnum> and a custom MyList class extending List<MyEnum> with public static MyList fromString( String commaSeparatedValues ) method. Nothing seems to work.

There must be some way to introduce a custom converter for it?

Thanks. -Shadow

Answer 1

I found a work-around using something similar to the MyList variant mentioned above. For some reason RestEasy (or Jackson, I have no idea which) can't handle it if MyList extends ArrayList<MyEnum> . However it does seem to work if MyList implements Iterable<MyEnum> (renamed to MyEnums as it no longer is a List ).

public class MyEnums
   implements Iterable<MyEnum>
{
   @NotNull private final Collection<MyEnum> m_objects;

   public MyList ( @NotNull String stringValue )
   {
      m_objects = CSVEnums.getCommaSeparatedEnumValuesList( MyEnum.class, stringValue );
   }

   @NotNull
   @Override
   public Iterator<MyEnum> iterator ()
   {
      return m_objects.iterator();
   }
}

/** Used for deserializing lists of {@link Enum}s from a string of comma separated values. */
public abstract class CSVEnums
{
   @NotNull
   public static <T extends Enum<T>> Collection<T> getCommaSeparatedEnumValuesList (
      @NotNull Class<T> type,
      @Nullable String commaSeparatedValues )
   {
      if( commaSeparatedValues == null )
         return Collections.emptyList();

      Collection<T> collection = new ArrayList<T>();
      String[] splitStringValues = commaSeparatedValues.split( "," );
      for( String stringValue : splitStringValues )
         collection.add( getEnumValue( type, stringValue ) );
      return collection;
   }

   @NotNull
   private static <T extends Enum<T>> T getEnumValue (
      @NotNull Class<T> type,
      @NotNull String stringValue )
   {
      for( T possibleValue : type.getEnumConstants() )
      {
         if( possibleValue.name().equals( stringValue ) )
            return possibleValue;
      }
      throw new IllegalArgumentException( "Unexpected value '" + stringValue + "' found for type '" + type.getName() + "'" );
   }
}

This could probably be cleaned up a bit using Guava (Joiner/Splitter) libs, but this seems to work for me now.

@GET
@NotNull
public ResourceModel getResource( @QueryParam("enums") MyEnums values ) {
   ResourceModel model = new ResourceModel( values );
   for( MyEnum value : values )
      model.add( value );
   return model;
}

Again, the above could be cleaned up using Guava (Lists/Iterables) libs, but this works.