如何在java中从右侧开始分割带有限制的字符串？

Question

Split without limits split the entire string but if you set a limit it splits up to that limit by the left. How can I do the same by the right?

"a.b.c".split("[.]", 2); // returns ["a", "b.c"]

I would want

"a.b.c".splitRight("[.]", 2); // to return ["a.b", "c"]

EDIT: I want a general solution that works just like splited but reversed so I add a more complex example

I would want

"a(->)b(->)c(->)d".splitRight("\\(->\\)", 3); // to return ["a(->)b", "c", "d"]

Answer 1

You may use look-ahead match:

"a.b.c".split("[.](?=[^.]*$)")

Here you say "I want to split by only that dot which has no other dots after it".

If you want to split by last N dots, you can generalize this solution in this (even more ugly way):

"dfsga.sdgdsb.dsgc.dsgsdfg.dsdg.sdfg.sdf".split("[.](?=([^.]*[.]){0,3}[^.]*$)");

Replace 3 with N-2 .

However I would write a short static method instead:

public static String[] splitAtLastDot(String s) {
    int pos = s.lastIndexOf('.');
    if(pos == -1)
        return new String[] {s};
    return new String[] {s.substring(0, pos), s.substring(pos+1)};
}

Answer 2

Despite that you said reversing would take to long, here´sa small programm that reveres the String and splits it by the limit;

static String[] leftSplit(String input, String regex, int limit) {
    String reveresedInput = new StringBuilder(input).reverse().toString();
    String[] output = reveresedInput.split(regex, limit);
    String tempOutput[] = new String[output.length];
    for(int i = 0;i<output.length;++i) {
        tempOutput[tempOutput.length-i-1] = new StringBuilder(output[i]).reverse().toString();
    }
    return tempOutput;
}

public static void main(String[] args) {
    System.out.println(Arrays.toString(leftSplit("a.b.c", "[.]", 2)));
    System.out.println(Arrays.toString(leftSplit("I want to. Split this. by the. right side", "[.]", 2)));
}

Answer 3

I would try with something like this:

public List<String> splitRight(String string, String regex, int limit) {
    List<String> result = new ArrayList<String>();
    String[] temp = new String[0];
    for(int i = 1; i < limit; i++) {
        if(string.matches(".*"+regex+".*")) {
            temp = string.split(modifyRegex(regex));
            result.add(temp[1]);
            string = temp[0];
        }
    }
    if(temp.length>0) { 
        result.add(temp[0]);
    }
    Collections.reverse(result);
    return result;
}

public String modifyRegex(String regex){
    return regex + "(?!.*" + regex + ".*$)";
}

The regular expression for split is wrapped by another, so for \\\\. , you will get: \\\\.(?!.*\\\\..*$) , to match and split on last occurance of delimiter. The string is splitted multiple time with this regex, the second element of result array is added to List, next split is done on first element of result array.

The effect of above method for your example string is as expected.