Return enum array for a list of given strings contained in the enum using streams

I have an Enum of Strings like this:

public enum SomeEnum {

  STRING1("some value"),
  STRING2("some other value");
  STRING3("some third value");
  
  ...more strings...

  private String name;

  SomeEnum(String name) {
    this.name = name;
  }

  @Override
  public String toString() {
    return name;
  }

And I have a List<String> someStringList containing some Strings.

I want to iterate over someStringList and find the corresponding enums for it.

For example: The List contains the Strings "some value" and "some third value", then I would like to use the Java Stream-API to return me a List<SomeEnum> containing SomeEnum.STRING1 and SomeEnum.STRING3

Somehow I can't get this to work. I tried something like this:

    List<SomeEnum> enumList = Stream.of(someStringList).forEach( s -> Stream.of(SomeEnum.values()).filter(w -> w.toString().equalsIgnoreCase(s)).collect(Collectors.toList()));

but this doesn't compile because it doesn't return anything. Any ideas?

Build a map from the string to the corresponding SomeEnum value:

Map<String, SomeEnum> map = 
    Arrays.stream(SomeEnum.values()).collect(toMap(SomeEnum::toString, s -> s));

(This can be done once and stored)

Then you can look up in this:

List<SomeEnum> enumList = someStringList.stream().map(map::get).collect(toList());

(You may or may not want to handle the case where a string isn't found in the map: for example, you could throw an exception, or drop such elements).

In your SomeEnum you can build a Map<String, SomeEnum> from string name to enum and initialize it during class loading time. Then declare a public static method in your SomeEnum named fromString which returns an enum constant for a given string if one exists.

private static final Map<String, SomeEnum> stringToEnum = Arrays.stream(values())
	.collect(Collectors.toMap(SomeEnum::toString, e -> e));

public static SomeEnum fromString(String name) {
	return stringToEnum.get(name);
}

Then use it in your client code. Here's how it looks.

List<SomeEnum> enumList = someStringList.stream()
	.map(SomeEnum::fromString)
	.collect(Collectors.toList());