# Contributing to Apache Tomcat

Firstly, thanks for your interest in contributing! I hope that this will be a
pleasant experience for you, and that you will return to continue
contributing.

Please visit our [Get Involved page](https://tomcat.apache.org/getinvolved.html)
for more information on how to contribute.

## Code of Conduct

This project and everyone participating in it are governed by the Apache
software Foundation's
[Code of Conduct](https://www.apache.org/foundation/policies/conduct.html). By
participating, you are expected to adhere to this code. If you are aware of
unacceptable behavior, please visit the
[Reporting Guidelines page](https://www.apache.org/foundation/policies/conduct.html#reporting-guidelines)
and follow the instructions there.

## How Can I Contribute?

Most of the contributions that we receive are code contributions, but you can
also contribute to the documentation, wiki, etc., or simply report solid bugs
for us to fix.

### Reporting Bugs

Please review our [guide](https://tomcat.apache.org/bugreport.html) on how to
submit a bug report. This page also has links to other resources to assist
you.

### Reporting Translation improvements

Apache Tomcat project uses POEditor for managing the localization files.
Please see more at https://cwiki.apache.org/confluence/x/vIPzBQ

### Your First Code Contribution

### Trouble Deciding How to Contribute?

Unsure where to begin contributing to Tomcat? You can start by taking a look at
the issues marked 'Beginner', link below. Please note that the Beginner keyword
is pretty new to the project, so if there aren't any issues in the filter feel
free to ask on the [dev list](https://tomcat.apache.org/lists.html#tomcat-dev).

* [Beginner issues](https://bz.apache.org/bugzilla/buglist.cgi?bug_status=__open__&keywords=Beginner&keywords_type=allwords&product=Tomcat%209&product=Tomcat%2010&product=Tomcat%2011&query_format=advanced) -
issues which should only require a few lines of code, and a test or two to
resolve.

The list above shows all bugs that are marked 'Beginner' and are open in the
currently supported Tomcat versions (9.0, 10.1, 11.0 and 12.0).

If you prefer C over Java, you may also take a look at the tomcat-native and
Tomcat Connectors products in Bugzilla.

### How to Provide Your First Patch

Excited yet? This section will guide you through providing a patch to the
committers of the project for review and acceptance.

##### Choose Your Method of Submission

You can provide a patch in one of the following ways (in order of preference):

* GitHub Pull Request
* Patch attachment to the Bugzilla issue
* Email the patch to the developer list. This is not preferred, but if no bug
is associated with the patch, or you would like a developer review, an email
may be appropriate.

##### Get the Sources

Now that you've chosen how you want to submit a patch, you need to get the
source code.

###### Download The Source Distribution

This method works if you want to submit a patch via email, but
the difference in using the sources distribution and a VCS is that you have to
manually generate the patch file by using diff. If this is what you want, you
can download the sources from the "Source Code Distributions" section of the
Download Page. There is one such page for every major Tomcat version:

- [Tomcat 11](https://tomcat.apache.org/download-11.cgi)
- [Tomcat 10](https://tomcat.apache.org/download-10.cgi)
- [Tomcat 9](https://tomcat.apache.org/download-90.cgi)

##### Manual Patch Generation

If you have chosen to attach a patch to the Bugzilla issue (or email
one), then you'll need to download the sources as noted above, make your
desired changes and then manually generate your patch using diff (or any
other tool).

##### GitHub

To submit a GitHub Pull Request you'll need to fork the
[repository](https://github.com/apache/tomcat), clone your fork to do the work:

```
$ git clone https://github.com/$USERNAME/tomcat.git
```

and then push your changes, and submit a Pull Request via the GitHub UI.

#### Submitting Your Patch!

After you've chosen your method of submission, retrieved the sources, and
fixed the issue it's time to submit your work. At this point, just follow
the method of submission you chose earlier.

* GitHub PR - after resolving the issue in your local fork and pushing to your
copy of the repository, open a GitHub PR for review.
* Bugzilla attachment - attach the patch to the Bugzilla issue
* Email - again, not preferred, but you may send an email to the developer list
with a patch attached for review.

#### Waiting For Feedback

It may take a while for committers to review. Please be patient during this
time as all committers are volunteers on the project. If a significant amount
of time has lapsed since your submission, such as a couple of months, feel free
to either update your BZ, PR, or email the dev list with a message to bump your
issue. Sometimes things get lost in all the work and we need a reminder :smile:

## IDE Support

Special IDE support for
[Eclipse](https://www.eclipse.org/ide/),
[IntelliJ IDEA](https://www.jetbrains.com/idea/) and
[NetBeans](https://netbeans.org/)
is provided through special ant targets:

```bash
ant ide-eclipse
```
```bash
ant ide-intellij
```
```bash
ant ide-netbeans
```

Just execute the ant target for your IDE after checking out the sources
to set up the appropriate configuration files.
Also make sure to re-execute the target after switching branches or
after pulling upstream changes in order to keep your IDE configurations in sync.

## Style Guide

Apache Tomcat has very loosely defined coding conventions, but the following
guidelines will be useful:

* Use spaces for indenting, not tabs
* 100 char line width for Java source, 80 char line width for documentation
source (.txt, .xml)
* Java source: { at end of line, 4 space indents
* XML source: 2 space indents

## Changelog Entries

Every code change that affects functionality, behavior, or user-visible features should have a corresponding entry in `webapps/docs/changelog.xml`.

### When Changelog Entries Are Needed

Add a changelog entry for:
- New features or APIs
- Bug fixes
- Changes to defaults or existing behavior
- Removals or deprecations
- Significant refactoring that affects performance or behavior
- Documentation updates to public APIs

Skip changelog entries for:
- Test-only changes (unless fixing a test infrastructure issue)
- Build script maintenance
- Internal code cleanup with no user impact

### Entry Types

Use the appropriate XML element based on the nature of your change:

- `<add>` - New features, APIs, or capabilities. Start with "Add" or "Implement".
  Example: `Add support for Jakarta EE 12 XML schemas.`

- `<update>` - Changes to existing features, defaults, or removals. Start with "Change", "Remove", or "Update".
  Example: `Change the default for encodedSolidusHandling from decode to reject.`

- `<fix>` - Bug fixes. Start with "Fix". Include `<bug>NUMBER</bug>` if applicable.
  Example: `<bug>70000</bug>: Fix duplication of special headers in the response after commit.`

- `<scode>` - Internal refactoring or code structure changes. Explain the benefit, not just the change.
  Example: `Refactor generation of the remote user element in the access log to remove unnecessary code.`

- `<docs>` - Documentation-only updates (Javadoc, configuration docs).
  Example: `Add Javadoc for the Common Annotations API implementation.`

### Style and Formatting

- Write in present tense, imperative mood ("Add support" not "Added support")
- Keep entries concise (1-3 sentences)
- Use `<code>` tags for class names, method names, and configuration attributes
- Use `<bug>NUMBER</bug>` for Bugzilla references
- For default changes, show before -> after: "from `false` to `true`"
- End with attribution in parentheses: `(username)`
- For community patches: "Patch submitted by Name. (committer)"

### Subsection Placement

Place entries in the appropriate subsection following this order:
General, Catalina, Coyote, Jasper, Cluster, WebSocket, Web applications, Extras, Tribes, jdbc-pool, Other

### Common Pitfalls to Avoid

- Don't use past tense ("Fixed" -> use "Fix")
- Don't omit `<code>` tags for technical terms
- Don't forget attribution at the end
- Don't be vague ("Fix bug" -> "Fix NPE when processing empty request headers")
- Don't include implementation details unless relevant to users

## Did we miss something?

Have you reviewed this guide and found it lacking? Or are you confused about
some particular step? If so, please let us know! Or better yet, submit a PR to
address the issue :wink:
