Here is what I do to populate my static map
public static final Map<String, FooBar> mapEnum =
Arrays.stream(FooBarEnum.values())
.collect(Collectors.toMap(e-> StringUtils.upperCase(e.name), e -> e));
I want to add another single key-value to this map.
mapEnum.put("xx", FooBar.A);
Here is the enum
public enum FooBar {
A("a"), B("b"), C("c");
}
My static map will look like this after map is constructed
{"a":FooBar.A, "b": FooBar.B, "c": FooBar.C, "xx": Foobar.A}
Is it possible to include the explicit put call into Collectors.toMap()?
I actually don't see the need to use Java Streams for that. You simply can use the static block to initialize mapEnum and put additional values in it:
public static final Map<String, FooBar> mapEnum;
static {
mapEnum = Arrays.stream(FooBar.values())
.collect(Collectors.toMap(FooBar::getName, Function.identity()));
mapEnum.put("xx", FooBar.A);
// ...
}
Collectors.toMap(): There are no guarantees on the type, mutability, serializability, or thread-safety of the {@code Map} returned.
To ensure the mutability of the Map returned by Collectors.toMap(), so you can use Map.put() afterwards better use this:
Arrays.stream(FooBar.values())
.collect(Collectors.toMap(Function.identity(), Function.identity(), (a, b) -> a, HashMap::new));
If you really want to use java streams you can use this:
public static final Map<String, FooBar> mapEnum = Stream.concat(
Stream.of(FooBar.values()).map(e -> Map.entry(e.getName(), e)),
Stream.of(Map.entry("xx", FooBar.A))
).collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
Or if you also want to add all names to the enum value itself you can change your class like this:
public static enum FooBar {
A("a", "xx"), B("b"), C("c");
private String[] names;
FooBar(String... names) {
this.names = names;
}
public String[] getNames() {
return names;
}
}
And use this to create the map:
public static final Map<String, FooBar> mapEnum = Stream.of(FooBar.values())
.flatMap(e -> Arrays.stream(e.getNames()).map(n -> Map.entry(n, e)))
.collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
Prior to Java 9 use new AbstractMap.SimpleEntry<>() instead of Map.entry(). If you need the map to be sorted use LinkedHashMap::new with Collectors.toMap().