如何使用Optional进行null检查

Question

I have following method

public static String convertThreeLetterWordToUpper(String str) {
    String result = Arrays.stream(
            str.split(" ")).map(s-> checkLength(s)).collect(Collectors.joining(" "));
    return result;
}

How can I check if str is not null with out performing a null check and return Optional of result.

Answer 1

You can wrap the orignal string in Optional.ofNullable . Assuming checkLength returns a string, the return type of the below would be Optional<String> .

Optional.ofNullable(str)
    .map(s -> Arrays.stream(s.split(" "))
                .map(string -> checkLength(string)) 
                .collect(Collectors.joining(" ")));

If you have a default return value to return you can just chain orElse() or can throw an exception with orElseThrow() .

String result = Optional.ofNullable(str)
     .map(...)
     .orElse("someDefault");
     //.orElseThrow(() -> new RuntimeException()); Or whatever makes sense