如何将 if 和 for each 转换为 java 流

Question

I have an enum class and method getColor , which returns a color depending on the index or black color when index doesn't exist. I would like to convert this method to Java Streams but I have a problem with how to do it.

My method:

public static Color getColor(String colorIndex) {
    if (StringUtils.isNotBlank(colorIndex)) {
        int i = Integer.parseInt(colorIndex);
        for (Color color : values()) {
            if (color.colorIndex == i) {
                return color;
            }
        }
    }
    return BLACK;
}

Answer 1

You can use the advantage of Optional :

public static Color getColor(String colorIndex) {

    return Optional.ofNullable(colorIndex)          // Optional colorIndex
        .map(Integer::parseInt)                     // as int
        .flatMap(i -> Arrays.stream(values())       // use the values()
            .filter(color -> color.colorIndex == i) // ... to find a color by the index
            .findFirst())                           // ... as Optional<Color>
        .orElse(BLACK);                             // if noone of the above, then BLACK
}

The reason of using Optional::flatMap is if Optional::map would be used, the result would be Optional<Optional<Color>> as long as Stream::findFirst / Stream::findAny returns Optional itself.

Answer 2

public static Color getColor(String colorIndex) {
    if (StringUtils.isNotBlank(colorIndex)) {
        int i = Integer.parseInt(colorIndex);
        Optional<Color> color = values().stream().filter(c -> c.colorIndex == i).findAny();
        if (color.isPresent())
            return color.get();
    }
    return BLACK;
}

Or

public static Color getColor(String colorIndex) {
    try {
        int i = Integer.parseInt(colorIndex);
        return values().stream().filter(c -> c.colorIndex == i).findAny().orElse(BLACK);
    } catch (NumberFormatException e) {
        return BLACK;
    }
}