convert a string to a list of object using Java 8

Question

I have a string

"Red apple, blue banana, orange".

How could I split it by ", " first then add "_" between two words (such as Red_apple but not orange) and capitalize all letters. I read a few posts and found a solution but it only has the split part and how could I also add "_" and capitalize all letters? :

   Pattern pattern = Pattern.compile(", ");
   List<Fruit> f = pattern.splitAsStream(fruitString)
  .map(Fruit::valueOf)
  .collect(Collectors.toList());

Fruit is a enum object. So basically if I am able to convert a string to a certain format and I am able get a Enum object based on a Enum name.

Answer 1

Use map(...) method to perform transformations on the original String. Instead of calling Fruit::valueOf through a method reference, split each string on space inside map(...), and construct a combined string when you get exactly two parts:

List<Fruit> f = pattern.splitAsStream("Red apple, blue banana, orange")
.map(s -> {
    String[] parts = s.split(" ");
    String tmp = parts.length == 2
    ? parts[0]+"_"+parts[1]
    : s;
    return Fruit.valueOf(tmp.toUpperCase());
}).collect(Collectors.toList());

Demo.

If you need to perform any additional transformations of the result, you can do them in the same lambda code block prior to the return statement.

Answer 2

Here is another sample:

f = pattern.splitAsStream(fruitString) 
        .map(s -> Arrays.stream(s.split(" ")).map(String::toUpperCase).collect(Collectors.joining("_"))) 
        .map(Fruit::valueOf).collect(Collectors.toList());

Or by StreamEx:

StreamEx.split(fruitString, ", ")
        .map(s -> StreamEx.split(s, " ").map(String::toUpperCase).joining("_"))
        .map(Fruit::valueOf).toList();

Answer 3

Your Enum

static enum Fruit {
    RED_APPLE, BLUE_BANANA, ORANGE
}

Main code:

public static void main(String[] ar) throws Exception {
    Pattern pattern = Pattern.compile(", ");
    List<Fruit> f = pattern.splitAsStream("Red apple, blue banana, orange")
            .map(YourClass::mapToFruit)
            .collect(Collectors.toList());
    System.out.println(f);
}

Helper method to offload dirty mapping part

private static Fruit mapToFruit(String input) {
    String[] words = input.split("\\s");
    StringBuilder sb = new StringBuilder();
    if (words.length > 1) {
        for (int i = 0; i < words.length - 1; i++) {
            sb.append(words[i].toUpperCase());
            sb.append("_");
        }
        sb.append(words[words.length - 1].toUpperCase());
    } else {
        sb.append(words[0].toUpperCase());
    }
    return Fruit.valueOf(sb.toString());
}