EnumParser

This is a utility for parsing a string to Enum constant. One common case is to parse a JSON data returned from a backend. In that case, you might want to convert it to Enum because writing below code in many places could bring a mistake because of a typo error.

"play".isEquals(modeString);

In order to convert, valueOf is widely used.

enum Mode {
  PLAY,
  PAUSE,
  SHUFFLE_PLAY
};

...

Mode mode = Mode.valueOf(modeString);

It works well in most cases. However, there are two problems. First, it is a case sensitive. If modeString is play, it returns null instead of PLAY. EnumParser support a case insensitive mapping. Thus, belows will match the same enum constant PLAY.

EnumParser<Mode> parser = EnumParser.forClass(Mode.class);
assertEquals(Mode.PLAY, parser.parser("play"));
assertEquals(Mode.PLAY, parser.parser("Play"));
assertEquals(Mode.PLAY, parser.parser("PLAY"));

Second, it doesn't support variations. One variation is about -. Enum doens't allow to have a - as a part of constant. _ is used intead of that. To make valueOf work, a backend should return modeString with _ even though - is more relevant in the backend side. Otherwise, we need to have this logic everytime.

Mode mode = Mode.valueOf(modeString.replaceAll("-", "_");

Moreover, some enums have a custom key, which can be used to parse. Unfortunately, valueOf only cares about its name. Finding a enum constant using its key is not that easy.

enum ModeWithKey {
  PLAY("music:play"),
  PAUSE("music:pause");

  private final String mKey;

  ModeWithKey(String key) {
    mKey = key;
  }

  public String getKey() {
    return mKey;
  }
}

EnumParser supports variations so both - and a custom key would be easily solved.

Function<Mode, String> dashVariation = new Function<Mode, String>() {
  @Override
  public String apply(Mode testEnum) {
    return testEnum.name().replaceAll("_", "-");
  }
};
EnumParser<Mode> enumParser = EnumParser.forClass(Mode.class).withVariation(dashVariation);
assertEquals(Mode.SHUFFLE_PLAY, enumParser.parse("shuffle-play"));

Function<ModeWithKey, String> customKeyVariation = new Function<ModeWithKey, String>() {
  @Override
  public String apply(ModeWithKey testEnum) {
    return testEnum.getKey();
  }
};
EnumParser<ModeWithKey> enumParser = EnumParser.forClass(ModeWithKey.class).withVariation(customKeyVariation);
assertEquals(Mode.PLAY, enumParser.parse("music:play"));

License

MIT License

Copyright (c) 2017 Sangsoo Nam

Permission is hereby granted, free of charge, to any person obtaining a copy
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