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

Space play ←→ step click any line
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.

Related explainers

rust 
use std::cmp::{Ordering, Reverse};
use std::collections::BinaryHeap;
use std::fs::File;
use std::io::{self, BufRead, BufReader, BufWriter, Lines, Write};

K-way merge of sorted logs in Rust

binary-heap k-way-merge streaming-io
Intermediate 8 steps
ruby 
class UserAgentParser
  BROWSERS = [
    [/Edg\/([\d.]+)/, "Edge"],
    [/OPR\/([\d.]+)/, "Opera"],

Parsing user-agent strings in Ruby

regex pattern-matching lookup-tables
Intermediate 8 steps
java 
@Component
@Converter
public class EncryptedStringConverter implements AttributeConverter<String, String> {
 

Transparent column encryption in Spring & JPA

encryption aes-gcm jpa-converter
Advanced 10 steps
java 
package com.acme.billing.config;
 
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.boot.context.properties.ConfigurationProperties;

Feature-flagged beans with Spring @ConditionalOnProperty

feature-flags conditional-beans strategy-pattern
Intermediate 5 steps
java 
public static Map<String, String> parseCookieHeader(String header) {
    Map<String, String> cookies = new LinkedHashMap<>();
    if (header == null || header.isBlank()) {
        return cookies;

Parsing an HTTP Cookie header in Java

string-parsing http url-decoding
Intermediate 6 steps
java 
public class TimedSocketReader {
 
    private static final int READ_TIMEOUT_MS = 5_000;
    private static final int CONNECT_TIMEOUT_MS = 3_000;

Reading a socket with connect and read timeouts

sockets timeouts io
Intermediate 8 steps

Share this explainer

Here's the card — post it anywhere.

Streaming log redaction in Java — share card
Made with highlit — turn any snippet into a walkthrough like this in about a minute.
Explain your code