Background

A consistent formatting is good regardless of specific project. There are lots of resources that explain why. Popular code style and code conventions documents often give a justification for each particular formatting decision.

ONAP

ONAP Java Code Style is based on Google Style with two modifications
 Line length  Indentation size

Link to onap code style: Java code style

Challenges

The challenge is to find a tool that would take care of code formatting automatically. Unfortunately, a generic tool never covers all possible cases of a particular style (e.g. Google’s).
We have tried the tools often mentioned in various forums, including the ONAP Wiki page above.
 The IntelliJ formatting for Google Java Style is for an old version of IntelliJ, and affects also the formatting of other languages (Python, JavaScript, etc.), which we want to avoid.  The Google Java Format plugin has the tab size and line length hard-coded, so that we had to fix and re-package it. Surprisingly, it also seems to contradict the Google Style Guide in some cases.

Solution

The home-built solution consists of two tools:
1. IntelliJ Checkstyle plugin coupled with a modified version of Checkstyle configuration for Google Style, which was made to comply with the ONAP requirements. 2. Thoroughly reviewed IntelliJ code formatting configuration for Java – aligned with the ONAP requirements as much as possible.
Setup
1. Save the attached onap_checkstyle_configuration.xml and onap_intellij_java_formatting.xml on your local disk.

2. Install https://plugins.jetbrains.com/plugin/1065-checkstyle-idea.

3. Go to File > Settings > Other Settings > Checkstyle.

4. Add a new Configuration File (green plus sign on the right).

5. Give it a name (e.g. “ONAP Checks”) and browse for the saved onap_checkstyle_configuration.xml.

6. Check the Active checkbox on the left.

7. Make sure “Only Java sources (including tests)” is selected for “Scan Scope” (top right).

8. Go to File > Settings > Editor > Code Style > Java.

9. Click the cogwheel to the right of “Scheme”, and select Import Scheme > IntelliJ IDEA code style XML.

10. Browse for the saved locally onap_intellij_java_formatting.xml; give the new configuration a new name, or leave it as is.
The base Checkstyle configuration used in the solution must merged once in a while with the original one, which may be updated: https://github.com/checkstyle/checkstyle/blob/master/src/main/resources/google_checks.xml

onap_intellij_java_formatting.xmlonap_checkstyle_8_23_configuration.xmlonap_checkstyle_8_24_configuration.xml
Usage

•  You will see a new Checkstyle toolbar around the edge of the IntelliJ window. 
• Results of running Analyze > Inspect Code… will now include a Checkstyle section. 
• Checkstyle violation will be highlighted in the editor.
•  Running Code > Reformat Code will apply the ONAP formatting.
• It can be run on a single file or an entire directory.
  Keep in mind that it is impossible to configure the IntelliJ formatting to cover 100% of cases, so sometimes you’ll have to format manually. Our goal was to make IntelliJ at least accept the manual formatting – if it complies with the ONAP style (and the Checkstyle configuration). Please contact me if you have encountered a situation when IntelliJ forces formatting that is not accepted by Checkstyle.