Multiple simultaneous substring replacements in Java

Question

(I come from the python world, so I apologise if some of the terminology I use jars with the norm.)

I have a String with a List of start/end indices to replace. Without getting too much into detail, consider this basic mockup:

String text = "my email is foo@bar.com and my number is (213)-XXX-XXXX"
List<Token> findings = SomeModule.someFnc(text);

And Token has the definition of

class Token {
    int start, end;
    String type;
}

This List represents start and end positions of sensitive data that I'm trying to redact.

Effectively, the API returns data that I iterate over to get:

[{ "start" : 12, "end" : 22, "type" : "EMAIL_ADDRESS" }, { "start" : 41, "end" : 54, "type" : "PHONE_NUMBER" }]

Using this data, my end goal is to redact the tokens in text specified by these Token objects to get this:

"my email is [EMAIL_ADDRESS] and my number is [PHONE_NUMBER]"

The thing that makes this question non-trivial is that the replacement substrings aren't always the same length as the substrings they're replacing.

My current plan of action is to build a StringBuilder from text, sort these IDs in reverse order of start indices, and then replace from the right end of the buffer.

But something tells me there should be a better way... is there?

Answer 1

This approach works:

import java.util.ArrayList;
import java.util.List;

public class Test {
    public static void main(String[] args) {
        String text = "my email is foo@bar.com and my number is (213)-XXX-XXXX";

        List<Token> findings = new ArrayList<>();
        findings.add(new Token(12, 22, "EMAIL_ADDRESS"));
        findings.add(new Token(41, 54, "PHONE_NUMBER"));

        System.out.println(replace(text, findings));
    }

    public static String replace(String text, List<Token> findings) {
        int position = 0;
        StringBuilder result = new StringBuilder();

        for (Token finding : findings) {
            result.append(text.substring(position, finding.start));
            result.append('[').append(finding.type).append(']');

            position = finding.end + 1;
        }

        return result.append(text.substring(position)).toString();
    }
}

class Token {
    int start, end;
    String type;

    Token(int start, int end, String type) {
        this.start = start;
        this.end = end;
        this.type = type;
    }
}

Output:

my email is [EMAIL_ADDRESS] and my number is [PHONE_NUMBER]

Answer 2

Ensure that all tokens are sorted by start index in ascending order:

List<Token> tokens = new ArrayList<>();
tokens.sort(Comparator.comparing(Token::getStart));

Now you can replace all strings starting from the end of the input text:

public String replace(String text, List<Token> tokens) {
    StringBuilder sb = new StringBuilder(text);
    for (int i = tokens.size() - 1; i >= 0; i--) {
        Token token = tokens.get(i);
        sb.replace(token.start, token.end + 1, "[" + token.type + "]");
    }
    return sb.toString();
}

Answer 3

Extract the substring between start and end, and split by it. Then you get an array of 2 elements, insert what you want in between. Next you have to move your next strings' to replace ids by the difference between the (previous string's that you replaced length) and (the string that you put in its place).

Code(in by case the 'end' in Token is exclusive):

public class Main {

    public static void main(String... args) {
        String text = "I want to replace AAA and B and scary wombat";
        Token[] tokens = {new Token(18, 21, "TEST"), new Token(26, 27, "TEST"), new Token(32, 44, "TEST")};
        int delta = 0;
        for (Token token : tokens) {
            String splitter = text.substring(token.start + delta, token.end + delta);
            System.out.println("Splitter: " + splitter);
            delta += token.replacement.length() - splitter.length();
            String[] beforeAndAfter = text.split(Pattern.quote(splitter));
            text = beforeAndAfter[0] + token.replacement + 
                    (beforeAndAfter.length == 2 ? beforeAndAfter[1] : ""); // in case where there are no more chars after splitter in text
        }
        System.out.println(text);
    }

    static class Token {
        public final int start, end;
        public final String replacement;

        public Token(int start, int end, String replacement) {
            this.start = start;
            this.end = end;
            this.replacement = replacement;
        }
    }
}