Code Style Guide (WIP)

Existing DSpace Java Style Guide

Per the Code Contribution Guidelines page (see "Coding Conventions" section), our existing style guide is listed as follows:

Your code needs to follow the Sun Java code conventions with the following minor modifications:

• Curly braces must be on new lines.
• Source files must have a copy of the copyright Duraspace notice and BSD license at the top (see Licensing of Contributions below). Also take a look at Copyright and Licensing.
• You must use 4-space tabulation.
• 'else' should be on a new line. 'else if' stays on one line.
• Users of the Eclipse IDE can have eclipse do the formatting automatically using this profile: - Dspace-eclipse-format.xml. See the Eclipse section below for details of how to apply this profile.

Your code should be well commented with Javadoc (including package and class overviews). All code contributions must come with Documentation. At a bare minimum, this should include Technical Documentation covering all configuration options and/or setup. See Documentation Contributions below for more details.

These existing style guidelines are based heavily on the Sun coding conventions (circa 1999) which are no longer maintained, but still available at http://www.oracle.com/technetwork/java/javase/documentation/codeconvtoc-136057.html

Because the Sun Java style guide is no longer maintained, it will not be keeping up with current Java style best practices, features, etc.  We should consider whether we continue to base our style off this outdated guide, use a more modern guide, or develop our own guide.

Proposed DSpace Java Style Guide (work-in-progress - not yet approved)

Bolded rules are a change from our current Style Guide.

1. 4-space indents for Java, and 2-space indents for XML. NO TABS ALLOWED.
   1.  Only exception is throws clause, which should be indented 8 spaces if on a new line

2. K&R style braces required. Braces required on all blocks.

   if (code) {
     // code
   } else {
     // code
   }

3. Do not use wildcard imports (e.g. import java.util.*). Duplicated or unused imports are also not allowed.
4. Write Javadocs for public methods and classes. Keep it short and to the point.
   
   1. Javadoc @author tags are optional, but should refer to an individual's name or handle (e.g. GitHub username) when included
      

5. Maximum length of lines is 120 characters.

6. No trailing spaces allowed (except in comments)
7. Tokens should be surrounded by whitespace, e.g. http://checkstyle.sourceforge.net/config_whitespace.html#WhitespaceAround

8. Each source file must contain the required license header, e.g.

   /**
    * The contents of this file are subject to the license and copyright
    * detailed in the LICENSE and NOTICE files at the root of the source
    * tree and available online at
    *
    * http://www.dspace.org/license/
    */

   
   

Other Java Style Guides

Google Java Style Guide

The Google Java Style Guide is at https://google.github.io/styleguide/javaguide.html

Some of the primary differences of this style include:

• Longer lines (100 characters vs the 80 chars required by Sun)
• K&R style brackets/braces (https://google.github.io/styleguide/javaguide.html#s4.1-braces). This is the same as the Sun style, but different from our style
• 2-space indentation (vs 4-space indentation): https://google.github.io/styleguide/javaguide.html#s4.2-block-indentation
• Requires UTF-8 encoding (no encoding required by Sun)

Fedora Java Style Guide

The Fedora project has its own style guide at https://wiki.duraspace.org/display/FF/Code+Style+Guide

Some of the primary differences of this style include:

• Longer lines (than both Google and Sun) at 120 characters
• K&R style brackets/braces
• 4-space indentation (same as our current guide, but different from Google)

Resources

Checkstyle verification

While not yet implemented, we likely would want to implement some verification of code style guidelines via Checkstyle.  Checkstyle is widely used in the Java world, and supports both Google and Sun Java conventions, as well as custom configurations. 

• A Maven plugin for checkstyle verification exists (which can validate styles on build): maven-checkstyle-plugin
• Existing Checkstyle configurations
  • The Fedora project has its own Checkstyle configuration (for its style guide): https://github.com/fcrepo4/fcrepo-build-tools/blob/master/src/main/resources/fcrepo-checkstyle/checkstyle.xml
  • A Google Checkstyle configuration is at: https://github.com/checkstyle/checkstyle/blob/master/src/main/resources/google_checks.xml
  • A Sun Checkstyle configuration is at: https://github.com/checkstyle/checkstyle/blob/master/src/main/resources/sun_checks.xml
• Early notes on enabling Checkstyle in DSpace codebase are available in this gist: https://gist.github.com/tdonohue/b51b919b87b5f08930fac4fd9d52b9ae
  • Note: Currently, it borrows heavily from the Fedora Checkstyle configuration (just as an example). We'd need to update the actual checkstyle.xml based on our final style guide.

Branches to enable Checkstyle on?

Which git branches would we want to enable Checkstyle on?

• Initially, likely just the master branch, and perhaps just specific modules (e.g. "dspace-spring-rest") on the master branch.
  • Enabling on master branch only may complicate cherry-picking of code changes from other branches (as line numbers, spacing, etc may change when the code is updated to use the latest DSpace Style Guide)
  • However, if we implement this module-by-module (starting with "dspace-spring-rest", the new DSpace 7 REST API), this may temporarily minimize the cherry-pick conflicts while also ensuring any new code meets the new style guidelines.
• Backporting to other branches (dspace-6_x, dspace-5_x, dspace-4_x) is yet to be determined.
  • Backporting might affect local checkouts/forks of these branches, as a large number of files will change at once. This has the potential to cause local merge conflicts to occur, if an institution has made Java code customizations.

IDE Support

Most major IDEs include plugins that support Checkstyle configurations. The plugin usually let you import an existing "checkstyle.xml" configuration to configure your IDE to use and/or validate against that style. (Please note: we have not tested all these plugins as of yet, so mileage may vary until we test/verify the plugin is usable)

• IntelliJ IDEA Checkstyle plugin: https://plugins.jetbrains.com/plugin/1065-checkstyle-idea  (Tested and works to format & validate code)
• Eclipse Checkstyle plugin: http://eclipse-cs.sourceforge.net/ (Tested and works to validate code. To format you must generate a formatter style following the steps here. It seems impossible to force eclipse to use braces on sinle-line if statement)
• NetBeans Checkstyle plugin: http://plugins.netbeans.org/plugin/3413/checkstyle-beans