How do I share a JaCoCo HTML report?

Build it — `mvn jacoco:report` writes `target/site/jacoco/`, `gradle jacocoTestReport` writes `build/reports/jacoco/test/html/` — then drag the folder (or a zip) into Comma. `index.html` becomes the report body, the per-package and per-class pages upload alongside it, and relative links are rewritten so the drill-down still works.

Do the per-class source views with the red/green gutters survive?

Yes. JaCoCo's line highlighting is CSS classes on the rendered source, and the stylesheets and per-class pages travel with the bundle, so the report browses exactly as it does on your machine — including the sortable summary columns, which are script-driven and run inside the sandboxed iframe.

Can I publish coverage from Maven or Gradle CI?

Yes. PATCH the same report id with `target/site/jacoco/index.html` on every build and you get one permanent URL per module plus a revision per run, so 'did this PR move coverage' is a diff between two revisions rather than two numbers in two build logs.

What about a multi-module Maven build?

Publish one report per module, or use `jacoco:report-aggregate` to produce a single rolled-up site and publish that. A very large aggregate can exceed the 500-file asset count; per-module reports stay well inside it and are easier to actually read.

Can reviewers comment on a specific uncovered class?

Yes. Comment threads anchor to the rendered structure — the row in the summary table, the heading of a package — and stay attached across rebuilds, so 'this is deliberately untested, it's generated' gets recorded once instead of relitigated every sprint.

Share a JaCoCo coverage report

Java's coverage story ends one step early. JaCoCo produces a genuinely good artifact — a browsable site with per-class source views and the exact lines your tests never reached — and then Maven files it under target/site/, CI archives it as a build artifact, and the only thing that escapes into a human conversation is a single percentage in a Jenkins column.

That percentage is the least useful number in the whole report. "68%" starts an argument. "The retry path in PaymentGateway has never been executed" ends one.

Drop the folder in

mvn test jacoco:report          # → target/site/jacoco/
./gradlew test jacocoTestReport # → build/reports/jacoco/test/html/

Drag that folder — or a zip of it — into the app:

index.html becomes the report body, the page carrying the comment layer.
Package pages, per-class source views, the CSS and JaCoCo's icons upload as assets.
Relative href and src references are rewritten, so clicking from the summary into com.acme.billing into PaymentGateway.java works at the URL.

Scripts run inside a sandboxed iframe (allow-scripts, no allow-same-origin), so the sortable summary columns behave normally.

From CI, one stable URL per module

curl -fsS -X PATCH "https://commareports.com/api/v1/reports/$REPORT_ID" \
  -H "Authorization: Bearer $COMMA_API_TOKEN" \
  -H "Content-Type: application/json" \
  -d "$(jq -n --rawfile html target/site/jacoco/index.html \
        --arg title "Coverage — $GIT_BRANCH" '{title: $title, html: $html}')"

Use a scoped token with only reports:write. Each build appends a revision at the same URL, so the coverage question becomes a diff between two revisions instead of a trend line with no detail behind it.

Provider wiring: GitHub Actions, GitLab CI, Jenkins, Azure DevOps.

Multi-module builds

Two honest options:

jacoco:report-aggregate — one rolled-up site for the reactor. Simple link, but a big monorepo's aggregate can push past the 500-file asset count.
One report per module — a report id per module, PATCHed by that module's job. More ids to track, but each link is the one a specific team owns, and the review threads land with the people who can act on them.

The second is usually right for anything over a handful of modules.

Limits

Entry HTML: 5 MB. Assets: 25 MB per file, 250 MB and 500 files total.
Scripts run, sandboxed: no same-origin fetches.
60 requests/minute per token.

Try it

Comma is free — unlimited reports, unlimited commenters, unlimited revision history.

Publish a coverage report →

Share a coverage report — the Python/JS flavour
Share a JUnit report · Share an Allure report
Publish from CI · Comment on HTML