java 34 lines · 9 steps

Streaming log redaction in Java

A file-to-file processor scrubs secrets and emails from logs line by line while counting how many lines changed.

Explained by highlit
Intermediate regex streaming-io try-with-resources data-sanitization
1public final class LogRedactor {
2 
3 private static final Pattern SECRET = Pattern.compile(
4 "(?i)(password|token|api[_-]?key|secret|authorization)\\s*[=:]\\s*\\S+");
5 
6 private static final Pattern EMAIL = Pattern.compile(
7 "[\\w.+-]+@[\\w-]+\\.[\\w.-]+");
8 
9 public long redact(Path source, Path target) throws IOException {
10 long redactedCount = 0;
11 try (BufferedReader reader = Files.newBufferedReader(source, StandardCharsets.UTF_8);
12 BufferedWriter writer = Files.newBufferedWriter(target, StandardCharsets.UTF_8,
13 StandardOpenOption.CREATE, StandardOpenOption.TRUNCATE_EXISTING)) {
14 
15 String line;
16 while ((line = reader.readLine()) != null) {
17 String sanitized = sanitize(line);
18 if (!sanitized.equals(line)) {
19 redactedCount++;
20 }
21 writer.write(sanitized);
22 writer.newLine();
23 }
24 }
25 return redactedCount;
26 }
27 
28 private String sanitize(String line) {
29 String result = SECRET.matcher(line).replaceAll(mr ->
30 Matcher.quoteReplacement(mr.group(1) + "=***REDACTED***"));
31 result = EMAIL.matcher(result).replaceAll("[email redacted]");
32 return result;
33 }
34}
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Compiling patterns once as static finals avoids recompiling regex on every line processed.
  2. 2Streaming line by line with buffered reader and writer keeps memory flat regardless of file size.
  3. 3Comparing sanitized output against the original is a cheap way to count how many lines were actually changed.

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