Master Text Diff in Java with Diff Utils: Real‑World Spring Boot Examples

Introduction

In software development, comparing code and text versions is a common need. Traditional methods are inefficient, so the Java Diff Utils library offers a powerful solution for Java developers.

Key Features

Compute differences between two texts

Handle any type that implements hashCode() and equals() Apply and revert patches

Parse unified diff format

Generate readable diff output

Build inline diffs

Algorithms: Myers standard algorithm, space‑optimized Myers, HistogramDiff (via JGit)

Practical Examples

1. Add Dependency

<dependency>
  <groupId>io.github.java-diff-utils</groupId>
  <artifactId>java-diff-utils</artifactId>
  <version>4.16</version>
</dependency>

2. Compare String Lists

Create a utility class to compare two lists and obtain a Patch.

public class TextComparatorUtil {
  public static Patch<String> compare(List<String> original, List<String> revised) {
    return DiffUtils.diff(original, revised);
  }
}

Example usage:

var original = List.of("A", "B", "C");
var revised = List.of("A", "B", "D");
var patch = TextComparatorUtil.compare(original, revised);
System.err.printf("差异总数: %s%n", patch.getDeltas().size());
patch.getDeltas().forEach(delta -> {
  delta.getSource().getLines().forEach(System.out::println);
  System.err.println("=======================");
  delta.getTarget().getLines().forEach(System.out::println);
});

Output:

差异总数: 1
C
=======================
D

3. Generate Unified Diff

public class UnifiedDiffGeneratorUtil {
  public static List<String> generate(List<String> original, List<String> revised, String fileName) {
    var patch = DiffUtils.diff(original, revised);
    return UnifiedDiffUtils.generateUnifiedDiff(fileName, fileName + ".new", original, patch, 3);
  }
}

Example:

var original = List.of("x", "y", "z");
var revised = List.of("x", "y-modified", "z");
var diff = UnifiedDiffGeneratorUtil.generate(original, revised, "test.txt");
diff.forEach(System.out::println);

Result:

--- test.txt
+++ test.txt.new
@@ -1,3 +1,3 @@
 x
-y
+y-modified
 z

4. Apply Patch

public class PatchUtil {
  public static List<String> apply(List<String> original, List<String> revised) throws PatchFailedException {
    var patch = DiffUtils.diff(original, revised);
    return DiffUtils.patch(original, patch);
  }
}

Usage:

var original = List.of("alpha", "beta", "gamma");
var revised = List.of("alpha", "beta-updated", "gamma");
var result = PatchUtil.apply(original, revised);
result.forEach(System.out::println);

Output:

alpha
beta-updated
gamma

5. Side‑by‑Side View

public class SideBySideViewUtil {
  private static final Logger logger = LoggerFactory.getLogger(SideBySideViewUtil.class.getName());
  public static void display(List<String> original, List<String> revised) {
    var patch = DiffUtils.diff(original, revised);
    patch.getDeltas().forEach(delta -> {
      logger.info("Change: {}", delta.getType());
      logger.info("Original: {}", delta.getSource().getLines());
      logger.info("Revised: {}", delta.getTarget().getLines());
    });
  }
}

Example call:

List<String> original = List.of("line1", "line2", "line3");
List<String> revised = List.of("line1", "line2-modified", "line3", "line4");
SideBySideViewUtil.display(original, revised);

Sample log output:

SideBySideViewUtil Line: 16 - Change: CHANGE
SideBySideViewUtil Line: 17 - Original: [line2]
SideBySideViewUtil Line: 18 - Revised: [line2-modified]
SideBySideViewUtil Line: 16 - Change: INSERT
SideBySideViewUtil Line: 17 - Original: []
SideBySideViewUtil Line: 18 - Revised: [line4]

HTML Rendering Template

The article also provides a simple HTML template with CSS and JavaScript to render original and revised texts side by side, using the diff data generated by the library.