Developing Drools and jBPM

If you want to build or contribute to a kiegroup project, read this document.

This document will save you and us a lot of time by setting up your development environment correctly. It solves all known pitfalls that can disrupt your development. It also describes all guidelines, tips and tricks. If you want your pull requests (or patches) to be merged into master, please respect those guidelines.

If you are reading this document with a normal text editor, please take a look at the more readable formatted version.

If you discover pitfalls, tips and tricks not described in this document, please update it using the markdown syntax.

Quick start

If you don't want to contribute to this project and you know git and maven, these build instructions should suffice:

To build 1 repository, for example guvnor:

$ git clone [email protected]:kiegroup/guvnor.git
$ cd guvnor
$ mvn clean install -DskipTests

To build all repositories:

$ git clone [email protected]:kiegroup/droolsjbpm-build-bootstrap.git
$ droolsjbpm-build-bootstrap/script/git-clone-others.sh
$ droolsjbpm-build-bootstrap/script/mvn-all.sh clean install -DskipTests

If you want to contribute to this project, read the rest of this file!

Source control with Git

Installing and configuring git

Install it in your OS:
- Linux: Install the package git
```
$ sudo apt-get install git
```
  Tip: Also install gitk to visualize your git log:
```
$ sudo apt-get install gitk
```
- Windows, Mac OSX: Download from the git website.
  
  Tip for Mac OSX: Also install gitx to visualize your git log.
- More info in GitHub's git installation instructions.
Check if git is installed correctly.
```
$ git --version
git version 1.7.1
```
Configure git correctly:
```
$ git config --global user.name "My Full Name"
$ git config --global user.email [email protected]
$ git config --global -l
user.name=Geoffrey De Smet
[email protected]
```
- Warning: the field user.name is your full name, not your username.
- Note: the field user.email should match an email address of your github account.
- More info on GitHub.
Get a github account
- And add your public key on github: Follow these instructions.
To learn more about git, read the free book Pro Git.

Getting the sources locally

Because you'll probably want to change our code, it's recommended to fork our code before cloning it, so it's easier to share your changes with us later. For more info on forking, read GitHub's help on forking.

First fork the repository you want to work on, for example guvnor:
- Surf to the blessed repositories on github and log in.
  - Note: Every git repository can be build alone. You only need to fork/clone the repositories you're interested in (guvnor in this case).
- Surf to the specific repository (guvnor)
- Click the top right button Fork
- Note: by forking the repository, you can commit and push your changes without our consent and we can easily review and then merge your changes into the blessed repository.
Clone your fork locally:
```
# First make a directory to hold all the kiegroup projects
$ mkdir kiegroup
$ cd kiegroup

# Then clone the repository you want to clone.
$ git clone [email protected]:MY_GITHUB_USERNAME/guvnor.git
$ cd guvnor
$ ls
```
- Warning: Always clone with the SSH URL, never clone with the HTTPS URL because the latter is unreliable.
- Note: it's highly recommended to name the cloned directory the same as the repository (which is the default), so the helper scripts work.
- By default you will be looking at the sources of the master branch, which can be very unstable.
  - Use git checkout to switch to a more stable branch or tag:
```
$ git checkout 5.2.0.Final
```
Add the blessed repository as upstream (if you've directly cloned the blessed repository, don't do this):
```
$ git remote add upstream [email protected]:kiegroup/guvnor.git
$ git fetch upstream
```

Working with git

First make a topic branch:
```
$ git checkout master
$ git checkout -b myFirstTopic
```
- Don't litter your local master branch: keep it equal to remotes/upstream/master
- 1 branch can have only 1 pull request, because the pull requests evolves as you add more commits on that branch.
Make changes, run, test and document them, then commit them:
```
$ git commit -m "Fix typo in documentation"
```
Push those commits on your topic branch to your fork
```
$ git push origin myFirstTopic
```
Get the latest changes from the blessed repository
- Set your master equal to the blessed master:
```
$ git fetch upstream
$ git checkout master
# Warning: this deletes all changes/commits on your local master branch, but you shouldn't have any!
$ git reset --hard upstream/master
```
- Start a new topic branch and set the code the same as the blessed master:
```
$ git fetch upstream && git checkout -b mySecondTopic && git reset --hard upstream/master
```
- If you have a long-running topic branch, merge master into it:
```
$ git fetch upstream
$ git merge upstream/master
```
  - If there are merge conflicts:
```
$ git mergetool
$ git commit
```
    or
```
$ git status
$ gedit conflicted-file.txt
$ git add conflicted-file.txt
$ git commit
```
    Many people get confused when a merge conflict occurs, because you're in limbo. Just fix the merge conflicts and commit (even if the git seems to contain many files), only then is the merge over. Then run git log to see what happened. The many files in the merge conflict resolving commit are a side effect of non-linear history.
You may delete your topic branch after your pull request is closed (first one deletes remotely, second one locally):
```
$ git push origin :myTopicBranch
$ git branch -D myTopicBranch
```
Tips and tricks
- To see the details of your local, unpushed commits:
```
$ git diff origin...HEAD
```
- To run a git command (except clone) over all repositories (only works if you cloned all repositories):
```
$ cd ~/projects/kiegroup
$ droolsjbpm-build-bootstrap/script/git-all.sh push
```
  - Note: the git-all.sh script is working directory independent.
  - Linux tip: Create a symbolic link to the git-all.sh script and place it in your PATH by linking it in ~/bin:
```
$ ln -s ~/projects/kiegroup/droolsjbpm-build-bootstrap/script/git-all.sh ~/bin/kiegroup-git
```
    For command line completion, add the following line in ~/.bashrc:
```
$ complete -o bashdefault -o default -o nospace -F _git kiegroup-git
```

Share your changes with a pull request

A pull request is like a patch file, but easier to apply, more powerful and you'll be credited as the author.

Creating a pull request
- Push all your commits to a topic branch on your fork on github (if you haven't already).
  - You can only have 1 pull request per branch, so it's advisable to use topic branches to avoid mixing your changes.
- Surf to that topic branch on your fork on github.
- Click the button Pull Request on the top of the page.
Accepting a pull request
- Surf to the pull request page on github.
- Review the changes
- Click the button Merge help on the bottom of the page and follow the instructions of github to apply those changes on the blessed master.
  - Or use the button Merge if there are no merge conflicts.

If the change being proposed is affecting more than a single repository, it will require creating a pull request for each of the repositories being affected; in this case, it is required for the topic branch to share the same name across all pull requests, in order for the CI build tool to include the necessary dependencies while performing the build with the proposed change. It is also highly recommended to use the github Autolinked references in the pull request comments, in order to make these depedencies explicit and emphasized during code reviews.

Building with Maven

All projects use Maven 3 to build all their modules.

Installing Maven

Get Maven
- Download Maven and follow the installation instructions.
Linux
- Note: the apt-get version of maven is probably not up-to-date enough.
- Linux trick to easily upgrade to future versions later:
  - Unzip maven to ~/opt/build
  - Create a version-independent link:
```
$ cd ~/opt/build/
$ ln -s apache-maven-3.3.9 apache-maven
```
    Next time you only have to remove the link and recreate the link to the new version.
  - Add this to your ~/.bashrc file:
```
export M3_HOME="~/opt/build/apache-maven"
export PATH="$M3_HOME/bin:$PATH"
```
- Give more memory to maven, so it can build the big projects too:
  - Add this to your ~/.bashrc file:
```
export MAVEN_OPTS="-Xms256m -Xmx1024m"
```
Windows:
- Give more memory to maven, so it can build the big projects too:
  - Open menu Configuration screen, menu item System, tab Advanced, button environment variables:
```
set MAVEN_OPTS="-Xms256m -Xmx1024m"
```
Check if maven is installed correctly.
```
$ mvn --version
Apache Maven 3.3.9 (...)
Java version: 1.8.0_112
```
Note: the enforcer plugin enforces a minimum maven and java version.

Running the build

Go into a project's base directory, for example guvnor:

$ cd ~/projects/kiegroup
$ ls
drools  droolsjbpm-build-bootstrap droolsjbpm-integration  droolsjbpm-knowledge  droolsjbpm-tools  optaplanner  guvnor
$ cd guvnor
$ ls
...  guvnor-repository  guvnor-webapp-drools  pom.xml

Notice you see a pom.xml file there. Those pom.xml files are the heart of Maven.

Run the build:
```
$ mvn clean install -DskipTests
```
The first build will take a long time, because a lot of dependencies will be downloaded (and cached locally).

It might even fail, if certain servers are offline or experience hiccups. In that case, you 'll see an IO error, so just run the build again.

If you consistently get Could not transfer artifact ... Connection timed out and you are behind a non-transparent proxy server, configure your proxy server in Maven.

After the first successful build, any next build should be fast and stable.
Try running a different profile by using the option -D<profileActivationProperty>:
```
$ mvn clean install -DskipTests -Dfull
```
There are 3 profile activation properties:
- none: Fast, for during development
- full: Slow, but builds everything (including documentation). Used by Jenkins and during releases.
- productized: activates branding changes for productized version
To run a maven build over all repositories (only works if you cloned all repositories):
```
$ cd ~/projects/kiegroup
$ droolsjbpm-build-bootstrap/script/mvn-all.sh -DskipTests clean install
```
- Note: the mvn-all.sh script is working directory independent.
Warning: The first mvn build of a day will download the latest SNAPSHOT dependencies of other kiegroup projects, unless you build all those kiegroup projects from source. Those SNAPSHOTS were build and deployed last night by Jenkins jobs.
- If you've pulled all changes (or cloned a repository) today, this is a good thing: it saves you from having to download and build all those other latest kiegroup projects from source.
- If you haven't pulled all changes today, this is probably a bad thing: you 're probably not ready to deal with those new snapshots.
  
  In that case, add -nsu (= --no-snapshot-updates) to the mvn command to avoid downloading those snapshots:
```
$ mvn clean install -DskipTests -nsu
```
  Note that using -nsu will also make the build faster.

Running tests

Guvnor uses Arquillian to run tests in a J2EE container and hence tests need to be ran differently to others.

Guvnor

$ cd ~/projects/kiegroup/guvnor/guvnor-webapp-drools
$ mvn integration-test [-Dtest=ATestClassName]

All other modules

$ cd ~/projects/kiegroup/drools
$ mvn test [-Dtest=ATestClassName]

Running code-coverage checks

JaCoCo plugin allows to measure code-coverage for any child of droolsjbpm-build-bootstrap. The check binds to the verify phase and for the plugin to run, the code-coverage profile has to be enabled.

From the module/project folder run command:
```
$ mvn clean verify -Pcode-coverage
```
The coverage report is then generated in ./target/site/jacoco/index.html

Running Pitest mutation coverage analysis

Mutation coverage is used to measure how good the tests are at making assertions about the tested code. It is a good idea to check the mutation coverage of tests added together with any changes, be it a newly developed feature or a bug fix. Code coverage is analyzed for free as part of the mutation analysis.

To analyze the complete module:

$ mvn verify -Dmutation-coverage

To limit analyzed classes to a sub-package:

$ mvn verify -Dmutation-coverage -DtargetClasses=org.drools*

The HTML report will be stored in local/pit-reports/ directory. Currently, it is not possible to get a report aggregated over multiple modules. Learn more about using Pitest.

Configuring Maven

To deploy snapshots and releases to nexus, you need to add this to the file ~/.m2/settings.xml:

<settings>
  ...
  <servers>
    <server>
      <id>jboss-snapshots-repository</id>
      <username>jboss.org_username</username>
      <password>jboss.org_password</password>
    </server>
    <server>
      <id>jboss-releases-repository</id>
      <username>jboss.org_username</username>
      <password>jboss.org_password</password>
    </server>
    </servers>
    ...
</settings>

Furthermore, you'll need nexus rights to be able to do this.

More info in the JBoss.org guide to get started with Maven.

Requirements for dependencies

Any dependency used in any KIE project must fulfill these hard requirements:

The dependency must have an ASL compatible license.
- Good: BSD, MIT, ASL
- Avoid: EPL, LGPL
  - Especially LGPL is a last resort and should be abstracted away or contained behind an SPI.
  - Test scope dependencies pose no problem if they are EPL or LPGL.
- Forbidden: no license, GPL, AGPL, proprietary license, field of use restrictions ("this software shall be used for good, not evil"), ...
  - Even test scope dependencies cannot use these licenses.
- To check the ALS compatibility license please visit these links:Similarity in terms to the Apache License 2.0 How should so-called "Weak Copyleft" Licenses be handled
The dependency shall be available in Maven Central or JBoss Nexus.
- Any version used must be in the repository Maven Central and/or JBoss (Nexus) Public repository group
  - Never add a <repository> element in a pom.xml.
  - Note: JBoss Public repository group mirrors java.net, codehaus.org, ... Most jars are available there.
- Why?
  - Build reproducibility. Any repository server we use, must still run 7 years from now.
  - Build speed. More repositories slow down the build.
  - Build reliability. A repository server that is temporary down can break builds.
- Workaround to still use a great looking jar as a dependency:
  - Get that dependency into JBoss Nexus as a 3rd party library.
The dependency must be able to run on any JVM 1.8 and higher.
- It must be compiled for Java target 1.8 or lower (even if it's compiled with JDK 7 or JDK 8).
- It must not use any JDK APIs that were not yet available in Java 1.8.
Do not release the dependency yourself (by building it from source).
- Why? Because it's not an official release, by the official release guys.
  - A release must be 100% reproducible.
  - A release must be reliable (sometimes the release person does specific things you might not reproduce).
No security issues (CVE's) reported on that version of the dependency
- We don't expect you to check this manually: The victims enforcer plugin will automatically fail the build if a known bad dependency is used.
The sources are publicly available
- We may need to rebuild the dependency from sources ourselves in future. This may be in the rare case when the dependency is no longer maintained, but we need to fix a specific CVE there. The other reason is that productisation needs to be able to easily rebuild the dependency internally.
- Make sure the dependency's pom.xml contains link to the source repository (scm tag).
The dependency needs to use reasonable build system
- Since we may need to rebuild the dependency from sources, we also need to make sure it is easily buildable. Maven or Gradle are acceptable as build systems.

Any dependency used in any KIE project should fulfill these soft requirements:

Use dependencies that are acceptable for the jboss-integration-platform-bom.
- Do not override versions in kie-parent's pom.xml unless an exception is granted
  - If a newer version of the ip-bom already uses the new version, it's of course fine to do a temporarily overwrite in kie-parent's pom.xml.
Prefer dependencies with the groupId org.jboss.spec over those with the groupId javax.*.
- Dependencies with the groupId javax.* are unreliable and are missing metadata. No one owns/maintains them consistently.
- Dependencies with the groupId org.jboss.spec are checked and fixed by JBoss.
Only use dependencies with an active community.
- Check for activity in the last year through Open Hub.
Less is more: less dependencies is better. Bloat is bad.
- Try to use existing dependencies if the functionality is available in those dependencies
  - For example: use poi instead of jexcelapi if poi is already a KIE dependency
Do not use fat jars, nor shading jars.
- A fat jar is a jar that includes another jar's content. For example: weld-se.jar which includes org/slf4j/Logger.class
- A shaded jar is a fat jar that shades that other jar's content. For example: weld-se.jar which includes org/weld/org/slf4j/Logger.class
- Both are bad because they cause dependency tree trouble. Use the non-fat jar instead, for example: weld-se-core.jar

There are currently a few dependencies which violate some of these rules. If you want to add a dependency that violates any of the rules above, get approval from the project leads.

Regenerating Protobuf Files

Some modules include Protobuf files (like drools-core and jbpm-flow). Every time a .proto file is changed, the java files have to be regenerated. In order to do that, on the module that contains the files to be regenerated, execute the following command:

$ mvn exec:exec -Dproto

After testing the regenerated files, don't forget to commit them.

IMPORTANT: before trying to regenerate the protobuf java files, you must install the protobuf compiler (protoc) in your machine. Please follow the instructions. You can download it from here: https://developers.google.com/protocol-buffers/docs/downloads.

For Linux/Mac, you have to compile it yourself as there are no binaries available. Follow the instructions in the README file for that.

Developing with Eclipse

Before running Eclipse

Do not use an Eclipse version older than 3.6 (helios).
Avoid an OutOfMemoryException and a StackOverflowError when building.

Open $ECLIPSE_HOME/eclipse.ini and add/change this: on openFile -vmargs:
```
openFile
-vmargs
...
-XX:MaxPermSize=512m
-Xms512m
-Xmx1024m
-Xss1024k
```

Configuring the project with the m2eclipse plugin

The m2eclipse plugin is a plugin in Eclipse for Maven. This is the new way (and compatible with tycho).

Open Eclipse
Follow the installation instructions of m2eclipse.
- Follow the link Installing m2eclipse at the bottom.
Click menu File, menu item Import, tree item Maven, tree item Existing Maven Projects.
Click button Browse, select a repository directory. For example ~/projects/kiegroup/guvnor.
Unfold Advanced, textfield Profiles: notSoaProfile,fullProfile.

For more information, see the m2eclipse book

Configuring the project with the deprecated maven-eclipse-plugin

The maven-eclipse-plugin plugin is a plugin in Maven for Eclipse. This is the old way (of which the development has stopped).

Run this command to generate .project and .classpath files:

$ mvn eclipse:eclipse

Open Eclipse
Menu item Import existing projects, navigate to the project base directory, select all the projects (= modules) it lists.

Important note: mvn eclipse:eclipse does not work for our eclipse plugins because it is not compatible with tycho (and never will be).

Configuring Eclipse

Force language level 8, to fail-fast when (accidentally) using features available only in newer Java versions.
- Open menu Window, menu item Preferences
- Click tree item Java, tree item Compiler, section JDK Compliance, combobox Compiler compliance level should be 1.8.
Remove the test resources Java Build Path exclusion filter to ensure JUnit tests ran inside Eclipse can find the necessary resources.
- Right-click the project
- Select menu item Build Path, sub-menu item Configure build path...
- On the Sources tab, scroll down to <project>\src\test\resources and expand tree
- Select Excluded and click Remove. The filter should show as (none)
Set the correct file encoding (UTF-8 except for properties files) and end-of-line characters (unix):
- Open menu Window, menu item Preferences.
- Click tree item General, tree item Workspace
  - Label Text file encoding, radiobutton Other, combobox UTF-8.
  - Label New text file delimiter, radiobutton Other, combobox Unix.
- Click tree item XML, tree item XML Files.
  - Combobox Encoding: ISO 10646/Unicode(UTF-8).
- Click tree item CSS, tree item CSS Files.
  - Combobox Encoding: ISO 10646/Unicode(UTF-8).
- Open tree item HTML, tree item HTML Files.
  - Combobox Encoding: ISO 10646/Unicode(UTF-8).
- Note: normal i18n properties files must be in ISO-8859-1 as specified by the java ResourceBundle contract.
  - Note on note: GWT i18n properties files override that and must be in UTF-8 as specified by the GWT contract.
Recommended: import our code style
- Set up formatter for edited code only: Open menu Window, menu item Preferences, click tree item Java, tree item Editor, and click Save actions. Enable Perform the selected actions on save: select Format source code (Format edited lines) and Organize imports
- If you don't do this, you need to set the number of spaces correctly manually.
- Use the one from droolsjbpm-build-bootstrap/ide-configuration
Set the correct number of spaces when pressing tab:
- Warning: If you imported the eclipse-formatter.xml file, you don't need to set it for Java, but you do need to set it for XML anyway!
- Open menu Window, menu item Preferences.
  - If you have project specific settings enabled instead, right click on the project and click the menu item Properties.
- Click tree item Java, tree item Code Style, tree item Formatter.
  - Click button Edit of the active profile, tab Indentation
  - Combobox Tab policy: spaces only
  - Textfield Indentation size: 4
  - Textfield Tab size: 4
  - Note: If it is a build-in profile, you 'll need to change its name with the textfield on top.
- Click tree item XML, tree item XML Files, tree item Editor.
  - Radiobutton Indent using space: on
  - Textfield Indentation size: 2
- Click tree item General, tree item Editors, tree item Text Editors.
  - Checkbox Insert spaces for tabs: on
  - Textfield Displayed tab width: 4
- Click tree item CSS Files, tree item Editor.
  - Radiobutton Indent using space: on
  - Textfield Indentation size: 4
Set the correct file headers (do not include @author or a meaningless javadoc):
- Open menu Window, menu item Preferences.
- Click tree item Java, tree item Code Style, tree item Code Templates.
- Click tree Configure generated code and comments, tree item Comments, tree item types.
- Remove the line @author Your Name.
  - We do not accept @author lines in source files, see FAQ below.
- Remove the entire javadoc as automatically templated data is meaningless.
Set the correct license header

Eclipse JEE Helios currently has no build-in support of license headers, but you can configure it for new files.
- Open menu Window, menu item Preferences.
  - If you have project specific settings enabled instead, right click on the project and click the menu item Properties.
- Click tree item Java, tree item Code Style, tree item Copy templates.
- Click tree item Comments, tree item Files.
- Replace the text area with the java multi-line comment version of droolsjbpm-build-bootstrap/ide-configuration/LICENSE-ASL-2.0-HEADER.txt:
```
/*
 * Copyright ${year} Red Hat, Inc. and/or its affiliates.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *     http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
```
- Note: Do not start or end with a newline character
- Note: Do not start with /**: it is not a valid javadoc.

Extra Eclipse plugins

Enable git support
- Open menu Help, menu item Install new software.
- Click combobox Update site Helios, tree item Collaboration, tree item Eclipse EGit.
GWT plugin
- Download and install the Eclipse GWT plugin
  - Note: it is recommended to use the same GWT SDK version like the GWT version it is used in droolsjbpm-build-bootstrap/pom.xml version.com.google.gwt property value.
- In Package Explorer, right click on the project guvnor-webapp, menu item Properties.
  - Enable the GWT aspect:
    - Click tree item Google, tree item Web Toolkit Settings...
    - Checkbox Use google Web Tookit: on
    - List Entry Point Modules should contain Guvnor - org.drools.guvnor (and optionally FastCompiledGuvnor too).
  - The gwt-dev jar needs to be first on the compilation classpath (the java.lang.NoSuchFieldError: warningThreshold problem)
    - Click tree item Java Build Path
    - Tab Libraries, button Add Library..., list item Google Web Toolkit, button Next, button Finish
    - Tab Order and Export, select GWT SDK ..., button Top
- Verify that you have a web browser configured in Eclipse:
  - Open menu Window, menu item Preferences.
  - Click tree General, tree item Web Browser, radiobutton Use external web browser.
  - Click button New..., textfield Name firefox, textfield Location /usr/bin/firefox, textfield Parameters %URL%, button OK.
  - Check the checkbox next to firefox.
- Run GWT in hosted mode
  - Open project context menu Properties, Google->Web application->
    - This project has a WAR directory, tick
    - WAR directory, target/guvnor-webapp-drools-5.4.0-SNAPSHOT (this will differ for different releases)
    - You will need to have completed a maven install, as explained above to generate the target/guvnor-webapp-drools-5.4.0-SNAPSHOT directory
    - Launch and deploy from this directory, tick
  - Open menu Run, menu item Run configurations...
  - In the list, select Web Application, button new launch configuration
  - Tab Main, Project: guvnor-webapp-drools
  - Tab Main, Ensure Main class is: com.google.gwt.dev.DevMode
  - Tab GWT, list Available Modules: Guvnor - org.drools.guvnor
  - Tab Arguments, Ensure Program Arguments are :
```
-war <path-to-war-folder> -remoteUI "${gwt_remote_ui_server_port}:${unique_id}" -startupUrl index.jsp -logLevel INFO -codeServerPort 9997 -port 8888 org.drools.guvnor.FastCompiledGuvnor org.drools.guvnor.Guvnor
```
    For example:
```
-war /home/manstis/workspaces/git/kiegroup/guvnor/guvnor-webapp-drools/target/guvnor-webapp-drools-5.4.0-SNAPSHOT -remoteUI "${gwt_remote_ui_server_port}:${unique_id}" -startupUrl index.jsp -logLevel INFO -codeServerPort 9997 -port 8888 org.drools.guvnor.FastCompiledGuvnor org.drools.guvnor.Guvnor
```
  - Tab Arguments, it is recommended to set VM Arguments to: -XX:MaxPermSize=512m -Xms512m -Xmx2048m. You might be able to try smaller values, but these are known to work.
  - Button Run.
- In your workspace, in the tab Development Mode, double click on the Guvnor URL.
- If you encounter a java.lang.NoSuchFieldError: warningThreshold error you need to follow the steps here, i.e.
  - Add GWT-SDK to your classpath (even though it is a Maven dependency)
  - On your Java Build Path, Order and Export tab, move GWT-SDK to the top

Eclipse plugin development

Installing a kiegroup eclipse plugin into a fresh Eclipse from a local update site.
- Follow the intructions in the description entity in the org.drools.updatesite pom.xml file.

Developing with IntelliJ

Before running IntelliJ

Avoid an OutOfMemoryException while editing or building.

Open $IDEA_HOME/bin/idea.vmoptions and change the first 3 values to this:
```
-Xms512m
-Xmx1024m
-XX:MaxPermSize=512m
```

Configuring the project with the maven integration

IntelliJ has very good build-in support for Maven.

Open IntelliJ.
Click menu File, menu item New project.
- Click radiobutton Create project from scratch, button Next
- Textfield name: kiegroup
- Textfield Project files location: ~/projects/kiegroup
- Checkbox Create module: off

Note: If you want to configure a main project that includes all projects you must create an empty project and add the projects as modules.

Click menu File, menu item New module
- Radiobutton Import from external model, button Next, button Next
- Textfield Root directory: ~/projects/kiegroup/guvnor
  - That is the directory that contains the multiproject pom.xml file from a project base directory.
- Button Next, check in the Selected profiles notSoaProfile and fullProfile, button Next, button Finish.
- Go grab a coffee while it's indexing.
- Repeat if you want to work on more than 1 kiegroup project.

Note: Don't use the maven-idea-plugin on the command line with mvn: it's dead.

Configuring IntelliJ

Force language level 8, to fail-fast when (accidentally) using features available only in newer Java versions.
- Open menu File, menu item Project Structure
- Click list item Modules, for each module, tab Sources, combobox Language level should be automatically set to 8.0 ...
Avoid that changes in some resources are ignored in the next run/debug (and you are forced to use mvn)
- Open menu File, menu item Settings
- Click tree item Compiler, textfield Resource patterns: change to !?*.java (remove other content)
Avoid a StackOverflowError when building
- Open menu File, menu item Settings
- Click tree item Compiler, tree item Java Compiler, textfield Additional command line parameters
- Add -J-Xss1024k so it becomes something like -target 1.8 -J-Xss1024k
Include files with non-default extensions in your searches and refactors
- Open menu File, menu item Settings
- Click tree item File Types, in the list Recognized File Types:
  - Next to list Recognized File Types, click on the button Add...
    - Textfield name: DRL files
    - Textfield Line comment: //
    - Textfield Block comment start: /*
    - Textfield Block comment end: */
    - Check the checkboxes Support paired braces, Support paired brackets and Support parens
    - Add some keywords: rule, when, then, end, ...
    - Click button ok
  - Next to the list Registered Patterns, use the button Add...:
    - For DRL files, add *.drl, *.mvel, *.drt, *.dslr
    - For Text files, add *.md
    - For Properties files, add *.dsl
    - For XML Files, add *.rf
Recommended: import our code style
- If you don't do this, you need to set the file encoding and number of spaces correctly manually.
- Use the one from droolsjbpm-build-bootstrap/ide-configuration
- Copy to ~/.IntelliJIdea*/config/codestyles/ (on mac: ~/Library/Preferences/IntelliJIdea*/config/codestyles/)
- Restart, open menu File, menu item Settings
- Click tree item Code Style and select it.
  - Note: IntelliJ IDEA doesn't format your code automatically. You have to press Ctrl+Alt+L keyboard combination to trigger auto formatting when coding is done. Another option is to commit your code directly from IntelliJ IDEA (open menu VCS, menu item Commit Changes...), and select the option Reformat Code, which will reformat all files changed in the commit.
Set the correct file encoding (UTF-8 except for properties files) and end-of-line characters (unix):
- Open menu File, menu item Settings
- Click tree item Code Style, tree item General
  - Combobox Line separator (for new files): Unix
- Click tree item File Encodings
  - Combobox IDE Encoding: UTF-8
  - Combobox Default encoding for properties files: ISO-8859-1
    - Note: normal i18n properties files must be in ISO-8859-1 as specified by the java ResourceBundle contract.
      - Note on note: GWT i18n properties files override that and must be in UTF-8 as specified by the GWT contract.
Set the correct number of spaces when pressing tab:
- Open menu File, menu item Settings
- Click tree item Code Style, tree item General
- Click tab Java
  - Checkbox Use tab character: off
  - Textfield Tab size: 4
  - Textfield Indent: 4
  - Textfield Continuation indent: 8
- Open tab XML
  - Checkbox Use tab character: off
  - Textfield Tab size: 2
  - Textfield Indent: 2
  - Textfield Continuation indent: 4
Set the correct file headers (do not include @author or a meaningless javadoc):
- Open menu File, menu item Settings
- Click tree item File templates, tab Includes, list item File Header
- Remove the line @author Your Name.
  - We do not accept @author lines in source files, see FAQ below.
- Remove the entire javadoc as automatically templated data is meaningless.

Set the correct license header

Open menu File, menu item Settings

Click tree item Copyright, tree item Copyright profiles

Click button + to add a Copyright profile
Textfield name: Red Hat, Inc. and/or its affiliates

Textarea with content:

Copyright $today.year Red Hat, Inc. and/or its affiliates.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

Note: Do not start or end with a newline character
Note: Do not start with /**: it is not a valid javadoc.

Click tree item Copyright
- Combobox Default project copyright: Red Hat, Inc. and/or its affiliates

Extra IntelliJ plugins

Enable git support
- Open menu File, menu item Other Settings, menu item Configure plugins.
- Check Git.
GWT plugin (to run in GWT hosted mode)
- Open menu File, menu item Project structure
  - For the module guvnor-webapp-drools, add the new aspect GWT if you haven't already.
    - Textfield Compiler maximum heap size (Mb): 512
- Open menu Run, menu item Edit configurations
  - Add new GWT configuration
    - Combobox Module: guvnor-webapp-drools
    - Combobox GWT Module to load: org.drools.guvnor.FastCompiledGuvnor
    - Textfield VM options: -Xmx1024m -XX:MaxPermSize=256m
    - Textfield Start page: org.drools.guvnor.Guvnor/Guvnor.html (Second entry, not the first)
  - Run that configuration.
Tomcat exploded war deployment
- Open menu File, menu item Project structure
  - Select tree item Artifacts, list item guvnor-webapp-drools:war exploded
    - Checkbox Build on make: on
- Open menu Run, menu item Edit configurations
  - Add new Tomcat server, local
    - Tab deployment, add Artifact guvnor-webapp-drools:war exploded.
    - Panel Before launch, checkbox Build 'guvnor-webapp-drools:war exploded' artifact: on
  - Run that configuration.

Linux inotify

We have encountered some issues with different Linux distribution's inotify when running any of the Workbench's in Super Dev Mode from within InteliJ.

Error message User limit of inotify instances reached or too many open files has been observed with both Ubuntu and Fedora. Should you encounter this issue you will need to reconfigure your inotify settings.

Add the following to /etc/sysctl.conf and then run sudo sysctl -p:

fs.inotify.max_user_watches = 524288

fs.inotify.max_user_instances = 524288

You may also need to add the following lines (replacing user-id with your User Id) to /etc/security/limits.conf:

user-id soft nofile 4096

user-id hard nofile 10240

Team communication

To develop a great project as a team, we need to communicate efficiently as a team.

Team workflows

Fixing a community issue in JIRA:
- Find/create the issue in JIRA (Drools, OptaPlanner, jBPM, Guvnor)
- Fix the issue and push those changes to the appropriate branch(es) on github.
  - If you don't have push permissions, create a pull request (PR). See Using pull requests for more info.
- Change the Status to Resolved.
  - When you file a PR, do not mark the issue as Resolved until the PR gets merged. Link the PR to the JIRA issue and wait till someone reviews the changes.
  - Once the reporter verifies the fix, he changes Status to Closed. Or we bulk change it to Closed after a year.
(Red Hat developers only) Fixing BRMS issues in Bugzilla:
- Find an issue in Bugzilla. Change Status to ASSIGNED and Assigned To to yourself.
- Fix the issue and push those changes to the appropriate branch(es) on github.
  - This will likely require back porting or forward porting, because the issue must be fixed on master too.
- Change the Status to MODIFIED.
  - Once the new product version is build, they change Status to ON_QA.
  - Once QA verifies the fix, they change Status to VERIFIED.

Knowing what's going on

Subscribe to the Drools Development Google Group and check it daily.
- Start a new topic for every important organizational or structural decision.
- If you (accidentally) push a change that can severely hinder or disrupt other developers (such as a compilation failure), notify the Development group.
Subscribe to the RSS feeds.
- It's recommend to subscribe at least to the RSS feeds of the project/repositories you're working on.
- Prefer an RSS reader which shows which RSS articles you've already read, such as:
  - Thunderbird
    - Open menu File, menu item Subscribe.
    - Tip: create a new, separate directory for each feed: some feeds (such as about the project you are working on) are more important to you than others.
  - Google Reader
- Subscribe to jira issue changes:
  - DROOLS
  - PLANNER
  - JBPM
  - GUVNOR
- Subscribe to github repository commits:
- Subscribe to Jenkins
  - with the Firefox plugin to easily see in your status bar which builds are failing (recommended):
    - After installation, right click on the Jenkins icon in the lower right corner.
    - Click menu item Preferences, tab Feed, textfield poll interval 30 minutes.
    - Click menu item Preferences, tab Display, combox Display latest build on status bar.
    - Go to the Jenkins job of the projects you're working on:
      - guvnor
    - Right click in the lower left corner on the All feed link, menu item Add link to Jenkins build monitor.
  - Otherwise, check the Jenkins website often.
    - Note: the public Jenkins is a mirror of the VPN internal Red Hat Jenkins and is sometimes stale.
      - If you think this can be the case, check the build times.
Join us on IRC: chat.freenode.net #drools #jbpm #guvnor #optaplanner

Writing documentation

Optionally install a DocBook editor to write documentation more comfortably, such as:
- oXygen
  - Open menu Options, menu item Preferences....
  - Click tree item Global
    - Combobox Line separator: Unix-like
  - Click tree item Format
    - Checkbox Detect indent on open: off
    - Checkbox Indent with tabs: off
    - Combobox Indent size: 2
    - Textfield Line width - Format and Indent: 120
- XMLmind
  - Open menu Options, menu item Preferences....
  - Click tree item Save
    - Combobox Encoding: UTF-8
    - Textfield Identation: 2
    - Textfield Max. line length: 120
    - Checkbox Before saving, make a backup copy of the file: off
      - To avoid committing backups to source control.
      - Source control history is better than backups.

To generate the html and pdf output run maven with -Dfull:

$ cd kiegroup
$ cd optaplanner/optaplanner-docs
$ mvn clean install -Dfull
...
$ firefox target/docbook/publish/en-US/html_single/index.html

Read and follow the documentation guidelines.
The Drools Expert manual uses railroad diagrams.

These are generated from a BNF file into images files with the application Ebnf2ps, Automatic Railroad Diagram Drawing

FAQ

Why do you not accept @author lines in your source code?
- Because the author tags in the java files are a maintenance nightmare
  - A large percentage is wrong, incomplete or inaccurate.
  - Most of the time, it only contains the original author. Many files are completely refactored/expanded by other authors.
  - Git is accurate, that is the canonical source to find the correct author.
- Because the author tags promote code ownership, which is bad in the long run.
  - If people work on a piece they perceive as being owned by someone else, they tend to:
    - only fix what they are assigned to fix, instead of everything that's broken
    - discard responsibility if that code doesn't work properly
    - be scared of stepping on the feet of the owner.
  - For more motivation, see this video on How to get a healthy open source project?
- Credit to the authors is given:
  - on the team page
    - Please contact Geoffrey (or any of us) if you want to add/change/expand your entry in the team page. Don't be shy!
  - on the blog
    - Write an article about the improvements you did! Contact us if you don't have write authorization on the blog yet.
  - with Open Hub which also has statistics
  - in the GitHub web interface.

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