How can I lookup a Java enum from its String value?

with Java 8 you can achieve with this way:

public static Verbosity findByAbbr(final String abbr){
    return Arrays.stream(values()).filter(value -> value.abbr().equals(abbr)).findFirst().orElse(null);
}

Use the valueOf method which is automatically created for each Enum.

Verbosity.valueOf("BRIEF") == Verbosity.BRIEF

For arbitrary values start with:

public static Verbosity findByAbbr(String abbr){
    for(Verbosity v : values()){
        if( v.abbr().equals(abbr)){
            return v;
        }
    }
    return null;
}

Only move on later to Map implementation if your profiler tells you to.

I know it's iterating over all the values, but with only 3 enum values it's hardly worth any other effort, in fact unless you have a lot of values I wouldn't bother with a Map it'll be fast enough.

@Lyle's answer is rather dangerous and I have seen it not work particularly if you make the enum a static inner class. Instead I have used something like this which will load the BootstrapSingleton maps before the enums.

Edit this should not be a problem any more with modern JVMs (JVM 1.6 or greater) but I do think there are still issues with JRebel but I haven't had a chance to retest it.

Load me first:

   public final class BootstrapSingleton {

        // Reverse-lookup map for getting a day from an abbreviation
        public static final Map<String, Day> lookup = new HashMap<String, Day>();
   }

Now load it in the enum constructor:

   public enum Day { 
        MONDAY("M"), TUESDAY("T"), WEDNESDAY("W"),
        THURSDAY("R"), FRIDAY("F"), SATURDAY("Sa"), SUNDAY("Su"), ;

        private final String abbreviation;

        private Day(String abbreviation) {
            this.abbreviation = abbreviation;
            BootstrapSingleton.lookup.put(abbreviation, this);
        }

        public String getAbbreviation() {
            return abbreviation;
        }

        public static Day get(String abbreviation) {
            return lookup.get(abbreviation);
        }
    }

If you have an inner enum you can just define the Map above the enum definition and that (in theory) should get loaded before.

You're close. For arbitrary values, try something like the following:

public enum Day { 

    MONDAY("M"), TUESDAY("T"), WEDNESDAY("W"),
    THURSDAY("R"), FRIDAY("F"), SATURDAY("Sa"), SUNDAY("Su"), ;

    private final String abbreviation;

    // Reverse-lookup map for getting a day from an abbreviation
    private static final Map<String, Day> lookup = new HashMap<String, Day>();

    static {
        for (Day d : Day.values()) {
            lookup.put(d.getAbbreviation(), d);
        }
    }

    private Day(String abbreviation) {
        this.abbreviation = abbreviation;
    }

    public String getAbbreviation() {
        return abbreviation;
    }

    public static Day get(String abbreviation) {
        return lookup.get(abbreviation);
    }
}