Java 8 extracts the first key from the matching value in the map

Suppose I have a map with a given name and last name pair, and I want to find the given name of the first entry in the map with a last name matching a certain value

In my test case example below, I propose two methods

However, the first one (looking for the given name of the first person named "dongkey") will throw Java util. NoSuchElementException: no value exists, so it is unsafe

The second job, but it's not only difficult to read, but it's a little less useful

I just want to know that someone here will suggest that I use stream () or foreach () or both to achieve this, which is simpler

@Test
public void shouldBeAbleToReturnTheKeyOfTheFirstMatchingValue() throws Exception {
    Map<String,String> names = new LinkedHashMap<>();
    names.put("John","Doe");
    names.put("Fred","Flintstone");
    names.put("Jane","Doe");
    String keyOfTheFirst = names.entrySet().stream().filter(e -> e.getValue().equals("Doe")).findFirst().get().getKey();
    assertEquals("John",keyOfTheFirst);

    try {
        names.entrySet().stream().filter(e -> e.getValue().equals("Donkey")).findFirst().get();
    } catch (NoSuchElementException e){
        // Expected
    }

    Optional<Map.Entry<String,String>> optionalEntry = names.entrySet().stream().filter(e -> e.getValue().equals("Donkey")).findFirst();
    keyOfTheFirst = optionalEntry.isPresent() ? optionalEntry.get().getKey() : null;

    assertNull(keyOfTheFirst);
}

Thank you first

Solution

If it does not match, the default value is returned. Use optional #orelse

names.entrySet().stream()
  .filter(e -> e.getValue().equals("Donkey"))
  .map(Map.Entry::getKey)
  .findFirst()
  .orElse(null);