Java WildCard replacement

Question

I have a text field where a user is required to input information.

JTextField data = new JTextField();

I have a requirment that if a user enters in *. Then it should be treated as a regex wildcard for when I search for the data.

I am looping through a series of files and reading each line one by one.

for(int i = 0; i < files.length; i++) {
        BufferedReader reader = null;

        try {
            reader = new BufferedReader(new FileReader(files[i]));
            String text = null;

            while ((text = reader.readLine()) != null) {
                if(text.contains(data) return text; // Line that requires wildcard check
            }
        } catch(IOException e) {
            e.printStackTrace();
        } finally{
            try {
                if (reader != null) {
                    reader.close();
                }
            } catch (IOException e) {}
        }
    }

How could I achieve this wildcard check? I require to make the '*' become any character once entered by user.

Take the user input, loop through and if there is a star you replace it with "." as dot is wildcard for regex, then use that newly generated string as a regex for your search argument. Consider using StringBuilder as a variable type as a holder for user input if you plan on editing it. — , Nov 28 '17 at 00:00
Possible duplicate of [Difference between matches() and find() in Java Regex](https://stackoverflow.com/questions/4450045/difference-between-matches-and-find-in-java-regex) — Mahendra Kapadne, Nov 28 '17 at 01:59
You say “treated as a regex wildcard” but I assume you mean that the `*` by itself should be treated as a wildcard character, as in `dsc*.jpg`. Is that correct? — VGR, Nov 28 '17 at 12:56

score 1 · Accepted Answer · answered Nov 28 '17 at 23:46

The problem is that the search string may contain other characters which would be significant in a regular expression, so it isn’t safe to just blindly convert * to .*.

You’ll want to use Pattern.quote on all parts of the search string except for the asterisks:

String[] parts = data.split("\\*");
Pattern pattern = Pattern.compile(
    Stream.of(parts).map(Pattern::quote).collect(Collectors.joining(".*")));

if (pattern.matcher(text).find()) {
    return text;
}

Breaking down the above statement:

data.split("\\*") splits the string by a regular expression that literally matches the * character, into an array of substrings. Examples:
- "ab*cd" → { "ab", "cd" }
- "1*2345*67" → { "1", "2345", "67" }
Stream.of(parts) creates a Stream from the array of substrings.
map(Pattern:quote) replaces each element in the Stream with its quoted equivalent, so any regex metacharacters (other than *) will be treated as ordinary characters. Thus, "1+1" in the original user input would actually match those three characters in the searched files.
collect(Collectors.joining(".*")) reassembles the elements in the stream into a single String, with .* between each quoted part.

On a side note, you can avoid writing a finally block by placing your BufferedReader in a try-with-resources statement:

String[] parts = data.split("\\*");
Pattern pattern = Pattern.compile(
    Stream.of(parts).map(Pattern::quote).collect(Collectors.joining(".*")));
Matcher matcher = pattern.matcher("");

for (File file : files) {
    try (BufferedReader reader = new BufferedReader(new FileReader(file))) {
        String text;
        while ((text = reader.readLine()) != null) {
            if (matcher.reset(text).find()) {
                return text;
            }
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
}

Because BufferedReader implements AutoCloseable, an implicit finally block will be created which essentially does what you were doing: try to close the BufferedReader while suppressing any exception that might arise from the close attempt.

Java WildCard replacement

1 Answers1