Join list of string with commas and new lines-CodePudding

I need to join a list of strings with commas. But also I have a limit of line length. For example list I need to join a list of strings with commas should become : I, need, to, join, a, \n list, of, strings, with, \n commas.

I've already implemented a method for this:

private static String joinLabels(List<String> strings) {
    int rowLengthCounter = 0;
    StringBuilder result = new StringBuilder();
    for (String str : strings) {
        rowLengthCounter  = str.length();
        if (rowLengthCounter > 40) {
            result.append("\n");
            rowLengthCounter = str.length();
        }
        result.append(str);
        result.append(", ");
    }
    return result.substring(0, result.lastIndexOf(", "));
}

And it works. But maybe simple method exists, like String.join to join strings with specified delimiter, or stream API. Thanks for help.

CodePudding user response：

The code is quite complicated with streams but you can write it like that :

    public static String joinLabels2(final List<String> strings,) {
    final Optional<String> res = strings.stream()
            .map(s -> s   ", ")
            .reduce((s1, s2) ->
                    s1.contains("\n") && (s1   s2).length() - StringUtils.lastIndexOf(s1, "\n") > 40
                    ||
                    !s1.contains("\n") && (s1   s2).length() > 40
                    ?
                    s1   s2   "\n" : s1   s2)
            .map(s -> s.substring(0, s.length() - 2));
    return res.get();
}

Test by changing the max length from "40" to "10" :

@Test
public void test() {
    System.out.println(joinLabels2(Arrays.asList("I", "need", "to", "join", "a", "list", "of", "strings", "with", "commas")));
}

outputs :

I, need, to, 
join, a, list, 
of, strings, 
with, commas,

It would be great to write the reduce condition like that : (s1 s2).length() > 40 ? ... but after the first line break the condition would be always true because s1 contains the previous reduction.

NB: you need to fine tune that method if you want to compare the length without commas because I added them before the reduction but you didn't in your original code.

CodePudding user response：

I would do something like this. It eliminates the counter, so that is one less moving part.

Add commas to each string except the last one
try to add each token to the StringBuilder
- If adding next token to the the current line in the StringBuilder is more than max, add line break
- Add token

private static final int maxLength = 15;
private static final List<String> strings = Arrays.asList("I", "need", "to", "join", "a", "list", "of", "strings", "with", "commas");

public static void main(String[] args) {
    StringBuilder sb = new StringBuilder();

    IntStream.range(0, strings.size())
            .mapToObj(i -> strings.get(i)   (i<strings.size()-1 ?  ", " : ""))
            .forEach(s -> addToStringBuilder(s, sb));

    System.out.println(sb);
}

private static void addToStringBuilder(String s, StringBuilder sb) {
    int currentLineLength = sb.length() - sb.lastIndexOf("\n");
    if (currentLineLength   s.length() > maxLength) {
        sb.append("\n");
    }
    sb.append(s);
}

Output:

I, need, to, 
join, a, 
list, of, 
strings, 
with, commas

CodePudding user response：

you can use java 8's stream and collectors api to do like this,

private static String joinLables(List<String> lables) {
    final AtomicInteger counter = new AtomicInteger();
    final Integer chunkSize = 3;
    final String DELIMITER = ",";
    return lables.stream()
            .collect(Collectors.groupingBy(it -> counter.getAndIncrement() / chunkSize)).values()
            .stream()
            .map(s -> String.join(DELIMITER, s))
            .reduce((a, b) -> a   "\n"   b)
            .get();
}