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JMRI Code: Building with IntelliJ IDEA

IntelliJ IDEA Community Edition (available from makes a great platform for working with JMRI and Java on OS X, Windows and *nix.

JMRI developers use Git for source control. Source control using Git is including as part of the IntelliJ IDEA download. For more information for getting the JMRI source, see JMRI: Getting the Code.

These instructions were developed and tested using IntelliJ IDEA 15 and 16 Community Edition (free).

Installing IntelliJ IDEA


  1. Go to and create an account.
  2. In GitHub web, go to the JMRI/JMRI repo and "Fork" the JMRI repository to your own remote copy. To do this, log on to your account at and navigate to the JMRI repository In the upper right hand corner of the page you will find a button labeled "Fork". Press the "Fork" button to create your own repository of the JMRI source. (see Getting the Code).

After downloading and running the installer for your OS, configure the IntelliJ application as follows:

Set vmoptions


On Windows and *nix

If the IDEA_VM_OPTIONS environment variable is defined, or a *.vmoptions file exists, then this file is used instead of the file located in the IntelliJ IDEA installation folder.

More info on setting these important vmoptions is available on the Idea web site.
Note: If you have a hint how to set this at the Project level instead of tinkering with local application settings, please tell JMRI users at

Set Preferences

Start IntelliJ and choose "Preferences" from the application menu (OS X) or Edit menu (Win).

  1. From the Editor -> File Encodings tab, check "Transparent native-to-ascii conversion":
    IntelliJ encoding prefs
  2. From the Version Control -> GitHub tab, enter "" as the Host and enter your Login credentials:
    IntelliJ build Git Login prefs
  3. From the Build, Execution, Deployment -> Java Compiler tab, select "1.8" as the Project bytecode version:
    IntelliJ build java SDK prefs
  4. Click OK to close the Preferences.

Getting the JMRI Source using Git

To get the source code from GitHub into IntelliJ, follow these steps:

  1. Open IntelliJ.
  2. From the main menu bar select File -> New -> Project from Version Control -> GitHub
    IntelliJ Git import pane
  3. If prompted, enter your GitHub username (Login) and Password in the authentication fields and click "Login":
    IntelliJ git login
  4. The Clone Repository pane should now appear. Select a Git Repository URL from your account and point to your local repo folder as "Parent Directory":
    IntelliJ Git import pane3
    Optionally click "Test" at top right to check your connection:
    IntelliJ Git import pane3
  5. Click "Clone" and follow progress in the indicator at the bottom of the Project window:
    IntelliJ Git clone progress
  6. In the pane that opens after download is complete, check the location on disk,
    confirm the project name (like the original i.e. "JMRI") and click "Next":
    IntelliJ Git import pane1
  7. Select "Create project from existing sources" and click "Next" again:
    IntelliJ Git import pane2
  8. Click "Mark all" and then "Finish":
    IntelliJ Git import pane3

This will add JMRI to the IntelliJ Project window.

The Project window

After cloning is completed, the IntelliJ Project window should look like this (OS X example):
IntelliJ main project window

Along the edges of the window are several groups of tools, often used are:

  1. the Project tab on the left
  2. the JMRI directory in the left half
  3. the Ant Build tab on the right and
  4. the Version Control tab at the bottom.
  5. the Git: master at the bottom righthand corner, showing the current Branch ("master") with a menu to change to another Branch.

You can also access this panel from the main VCS -> Git -> Branches... menu or right clicking the JMRI Project folder and selecting Git -> Repository -> Branches...
IntelliJ Project Git context menu

To check out another Branch from the remote repo, select its name under "Remote Branches", right click and select "Checkout as new local branch":
IntelliJ checkout branch

When the information from the new Branch is downloaded, the Message Center will confirm:
IntelliJ checkout branch OK

Making Changes

To work on the JMRI code, always start a new Branch, so your own "master" will stay intact.
To create a new Branch in IntelliJ, from the Git Branches pane, select "New Branch":
IntelliJ main project window
Supply a name i.e. my-dialog-2 and click OK.
Note: Starting your Branch name with a unique two letter combination will make it stand out from the long list much better than a name like patch-1.

Building and running JMRI using Ant

We recommend that before you try to build and run one of the applications within IntelliJ, you run the Ant Build -> <Default target> first. This will create the necessary working directories, load some resource icons, and create needed Java files. To run the ant build.xml do the following:

  1. Ant needs a JDK (Java Development Kit) in order to run the supplied "build.xml" file. The IntelliJ IDEA 15 download comes with a JDK, but you have to configure ant to use the right JDK.
    To verify the JDK is set to java 1.8, open the Ant Build tab [1], click a file in the Ant Build list [3] and select the Properties button [2] at the top right of the pane:
    IntelliJ Ant menu
  2. Select 1.8 as "Run under JDK" if not yet set:
    IntelliJ Ant Settings
    Click "OK" and save your JMRI Project (Cmd-S/Ctrl-S).
  3. Select the <Default target> file in the Ant Build list, right click, and select "Run", or click the green triangle "Run" button at the top of the pane. This should start the ant build. Follow any messages in the Event Log that pops up from the bottom edge of the Project window.
  4. A new JMRI checkout should build cleanly. If not, please check with the JMRIusers or jmri-developers mailings lists for help.

If the ant build is successful, you can launch any of the JMRI applications from the Ant Build tab.

Building and running JMRI using IntelliJ

To run an application, either:

  1. From the main menubar open the "Build" menu and select a JMRI package like panelpro or
  2. open the Ant Build tab and from the "Ant Build" list, right click the desired package i.e. decoderpro and select "Run Target".

Note: The first two "JMRI" sets will build the English and French JHelpDev TOC & Index files respectively. Hover your mouse over them and read the tooltip to learn which is which.

The Message Center Console will list all steps of the build process, after which a Java icon will open with the application running including all your new edits.

Pushing changes to your GitHub branch

The standard practice for getting your changes included in the main JMRI code repository is to Commit them to your local repository periodically and, when ready to publish everything, "Push" an entire set of Commits to your own remote repository on GitHub, and finally make a Pull Request for the maintainers to "Pull" your changes into the main JMRI repository.
When working on more than one computer or different IDEs, Committing and Pushing makes your new edit available on the other computers.
See the JMRI: Git FAQ "Setting up a Git environment for JMRI Developers" for more information.


It is also good practice to "Pull" all of the recent changes from the main JMRI repository before performing your Commits. After a "pull" your workspace and eventually your remote GitHub repository will be in synch with the main JMRI repository and you will see recent work by others. To perform a "Pull":


Pushing to your GitHub Branch:

Before you can Push your changes to GitHub for the first time, you'll have to create your own GitHub repository (which you have already done in step 1).


We've documented the following steps to help you get started. (Note that step 4. as yet is not complete. When you know what to enter as the Main Class Path, please report on JMRI Users)

  1. In IntelliJ, start by opening Preferences > Build, Execution, Deployment and check "Generate debugging info":
  2. Then, doubleclick "jar-resources" in the Build tab to have IntelliJ build afresh .jar Java archive to use for our debugging.
  3. When that has run, choose "Debug..." from the Run menu.

    On the small "Debug" pane that appears, click "Edit Configurations..."
    Alternatively, on the top right, click on the downward triangle "Select Run/Debug Configuration" button and select the "Edit Configurations..." option from there:
  4. On the top left of the new pane that appears, click the + sign (Add New Configuration).

    Or simply type Command + N.
    Select "JAR Application" in the list.
  5. This opens the "Run/Debug Configurations" pane:

    • As the Name of this Configuration, enter "JMRI DP debug".
    • Make sure "Build" is visible in the "Before launch:" table, select "Run Ant target" and choose "jar-resources" from the build.xml list
    • Check "Activate tool window" near the bottom of the pane.
    • Enter "jmri.jar" as the "Path to JAR" or use the "..." button to navigate to the freshly built jmri.jar in your Project.
    • Make sure the prefilled "Working directory:" is showing your local path to JMRI (see example).
      Set "Default" as the "JRE:" choice.
    • Select "JMRI" using the "Search sources using module's classpath:" drop down.
    • Click "OK" to complete the configuration setup.
  6. To run your first debug session, start by opening a .java file and setting a Breakpoint on a line in your code by clicking in the left margin of the central edit pane:
  7. We're now ready to start a Debug session by clicking the Bug button at the top right, making sure our "JMRI debug" configuration is selected in the drop down to the left of it:
  8. After a short while, at the bottom of the main IntelliJ IDE interface, the Debug pane appears, stopping just before your Breakpoint (or some previous error):
  9. Inspect the current values of the active variables, and click the Step Into button to execute 1 line of code:

A further explanation of this pane and debugging in general can be found in the IntelliJ Help.
If your code has not been compiled before debugging, the source and class files might be out of sync, so be sure to build first. You could add that to your Debug Configuration too.


Edit .properties files

Make sure you have set up IntelliJ to convert special characters using lower case encoding strings, as only then will your changes be accepted for merging into JMRI.
The - not trivial - instructions to set this via vmoptions are at the top of this page.

To easily edit Resource Bundle .properties files, containing translations in different languages, right-click on one of these (closed) folders in the Project file list and select "Jump to Source":
IntelliJ Bundle edit menu

This will open a window with a list of coded keywords on the left and a text box for every translation to the right:
IntelliJ Bundle edit window

Error: Can't start Git

On macOS, when you run into this error, usually when starting IntelliJ for the first time after a system update:
IntelliJ Git error

  1. Quit and restart IntelliJ
  2. If that does not fix it, quit IntelliJ and start the Apple Xcode application.
    By this you be asked to agree with the licence agreement, and that will reenable the Git installation to be used inside IntelliJ too.
    IntelliJ Git error

Reset HEAD

When in testing your app you conclude that you would like to remove your last couple of Commits, IntelliJ gives you the option to graphically Reset your HEAD.
To do this, open the "Version Control" -> "Log" tab at the lower left of the Project window to view a "Track Plan" of the history of your Branch, all the way back to the different parts that made JMRI:
IntelliJ VCS tab

Click on any line to view the changes that were Committed at that point in time (listed to the right).
To reset your repo (HEAD) back to a certain point, right click on the corresponding line and select "Reset Current Branch to Here...".
IntelliJ History reset
Confirm the way you want to save or discard your Commits after that point in the dialog:
IntelliJ Reset HEAD dialog

Master password

To securely store your GitHub login, you might periodically be asked to unlock it:
IntelliJ Git Master Pwd dialog

Make a Pull Request

Finally, when ready, submit a "Pull Request" to the main JMRI code repository on the GitHub website so the maintainers of JMRI can study your proposed changes and merge them into the master JMRI repo.

To make a PR from within IntelliJ IDEA, select "Create Pull Request" from the "VCS" -> Git menu (that's the last item, supported by the Git plug in).
IntelliJ Git Create PR

To Make a PR from GitHub web - outside IntelliJ - start by signing on to the GitHub web site, selecting your repository & branch and clicking the Pull Request button. For more info, see the Git Developer Help page.

Testing with IntelliJ

When you create or edit a test (located in your Project at etc.) you can test it either as part of the alltest Ant Build (double click its name in the IntelliJ Ant Build right hand column to run) or run it on its own using test-single.
In the latter case, enter the name of your test in the Ant Build Properties by either clicking the Properties button at the top or right-clicking on any line in the Ant Build column, choosing "Properties". Open the "Properties" tab, click the + (Add) sign at lower left and enter "test.includes" in the Name column and the path to your test under Value, starting with either apps. or jmri. as shown:
IntelliJ Ant Property

More Help

See the IntelliJ IDEA web reference and other resources for more information on using this IDE.