jar-comparator

Detect breaking API changes between two versions of any Maven artifact — in your browser or from the terminal.

Features

• Binary & source compatibility — powered by japicmp, the same engine used by many major open-source projects
• Web UI — paste two Maven coordinates and get a filterable, searchable HTML report in seconds
• CLI mode — pipe the output into your CI scripts; exits with code 1 on any incompatibility
• Source diff — view unified diffs of changed class sources side-by-side in the report
• Automatic download — fetches JARs (and sources) directly from Maven Central; no local Maven repo needed

Tech Stack

Layer	Technology
Runtime	Java 25 + Quarkus 3.35
CLI parsing	PicoCLI
REST / HTML	JAX-RS + Qute templates
Comparison engine	japicmp 0.25
Diff generation	java-diff-utils 4.12
Frontend	Bootstrap 5.3

Getting Started

Prerequisites: Java 25, Maven 3.9+

git clone https://github.com/danielferraz-git/jar-comparator.git
cd jar-comparator
mvn package -q

Web mode

java -jar target/jar-comparator-runner.jar
# Open http://localhost:8080

Enter two Maven coordinates (e.g. com.google.guava:guava:31.0-jre and com.google.guava:guava:33.0.0-jre) and click Compare.

CLI mode

java -jar target/jar-comparator-runner.jar \
  --old-version com.google.guava:guava:31.0-jre \
  --new-version com.google.guava:guava:33.0.0-jre

Exit code 0 = fully compatible. Exit code 1 = breaking changes found.

Save an HTML report

java -jar target/jar-comparator-runner.jar \
  --old-version org.springframework:spring-core:5.3.39 \
  --new-version org.springframework:spring-core:6.2.6 \
  --output-html report.html

Additional options

Flag	Default	Description
--access-modifier	PUBLIC	Minimum visibility to include (PUBLIC, PROTECTED, PACKAGE, PRIVATE)
--ignore-missing-classes	false	Skip classes not on the comparison classpath
--only-incompatible	false	Show only classes with breaking changes
--output-html	—	Write HTML report to this file

How It Works

Maven coordinates
      │
      ▼
MavenCentralDownloader  ──► repo1.maven.org (concurrent, cached)
      │
      ▼
JarComparisonService    ──► japicmp (binary + source analysis)
      │
      ▼
HtmlReportGenerator     ──► Qute template → HTML report

Both the web server and the CLI share the same service layer. The entry point (Main.java) selects the mode based on whether arguments are passed.

License

MIT