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Tutorials >Hello GridWorld! > Part 1

Brew unlink maven && brew link maven-snapshot brew unlink maven-snapshot && brew link maven Take care though: these are really the latest bits, and they may or may not work. Those builds are not an official distribution of Maven and they are not supported in any way. How to install maven1. Install homebrew:go to and copy /usr/bin/ruby -e '$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/mas. I wanted to add, that the homebrew project has a tool to tell you how to fix Xcode tools related errors. Not all errors by 'doctor' need to be fixed, but the ones relating to xcode-select and softwareupdate will fix tools issues on supported versions. For the window while an OS is in pre-release and released-but-not-yet-supported, you will have to resort to answers like the ones here to.

1. The tap seems to work quite well and is automatically updated with newer snapshot builds of Maven as soon as they are built. Note that this tap conflicts with the regular, stable Maven that is installed with brew install maven. If you prefer a stable version of Maven, use that one.
2. Machine version swvers ProductName: Mac OS X ProductVersion: 10.10.1 BuildVersion: 14B25 brew.

You are viewing the tutorial for BURLAP 3 with Maven. If you'd like the BURLAP 2 tutorial, go here.

Introduction

In this tutorial we will walk you through getting started with BURLAP. We will assume that you have Maven installed for this process, since it will make management of dependencies very straightforward. If you do not already have Maven installed, you can probably get it from your favorite package manager. For example, on Debian systems, Or on Mac OS with homebrew: Alternatively, you can manually install it from https://maven.apache.org/download.cgi. Be sure to follow their installtion instructions.

To verify that you have maven installed try the following from the command line

We also highly recommend that you use an IDE for your work, which will make working with the library substantially easier. If you do not have an IDE we recommend either IntelliJ or Eclipse. Both will have tools for working with Maven projects. That said, for this tutorial we will give instructions using just the command line and your favorite text editor. You can probably follow along in an IDE if you prefer.

In this tutorial you will have two options. You can either build and install BURLAP from its source, or you can simply use the released version of BURLAP from Maven Central. The latter will require the least work, but if you'd like to be able to modify BURLAP at all or want to make sure you always have the most update to date version, it may be worth it to checkout out the code and manually compile it. If you prefer to simply use the Maven Central copy, skip the next section.

We will make use of the command line to test things out and compile everything. On the Mac and Linux you can just use the terminal. If you are on windows, you can use either use the command prompt something like Cygwin.

Compiling from Source

To compile the code from source, you will probably want to have git installed, or you can manually download the source from github. If you have git installed, navigate from your command line to a directory where you would like to place the code. Then type the following:

If you do not have git installed on your computer, then you can manually download the files by navigating to the website https://github.com/jmacglashan/burlap and clicking on 'download zip' to save it and unarchive it at a desired location.

Whether you used git to clone the source, or manually downloaded it, navigate into the directory with your command line. The directory should look something like the following:

Now we can compile using Maven, which you should have installed on the previous step. You can use the standard Maven methods for compilation. That is, to simply compile the code, use

To create a jar file and Java doc in the target directory (as well as jar file that includes all dependencies) use

And to install BURLAP to your local Maven repository, use

And if you want to skip the tests (which may take a while), use the command

That's it!

Hello GridWorld Project

Whether you compiled and installed BURLAP from source in the prior step or not, this next section is the same because BURLAP is available on Maven Central, which means Maven will automatically download it and install it if you did not compile it from source.

To begin our example project, create a directory somewhere on your file system where you will store the project code and navigate into it on your command line. If you've used Maven before, you may want to create your project by generating an archetype. Feel free to do so if you, like. However, we will manually set up the project from the command line and text editors here.

First create a file named pom.xml. With your favorite text editor, insert the following

<project><modelversion>4.0.0</modelversion><groupid>com.mycompany.app</groupid>myProj<version>1</version><dependencies><dependency><groupid>edu.brown.cs.burlap</groupid>burlap<version>3.0.0</version></dependency></dependencies><build><plugins><plugin><groupid>org.codehaus.mojo</groupid>exec-maven-plugin<version>1.2.1</version><executions><execution><goals><goal>java</goal></goals></execution></executions></plugin></plugins></build></project>

You should set the group id at the top to anything that seems relevant for you, and you can also rename the artifact id to something else if you prefer. Note the <dependencies> section with the BURLAP dependency, which tells Maven that your project depends on BURALP. As of writing this tutorial, the latest version of BURLAP is 3.1.0. However, you may want to change this value to whatever the latest is, or to a version you prefer (especially if you've installed your own custom version with its own version number). You can see the list of all release versions of BURLAP from here.

The plugin we added will also allow us to use Maven to easily run code that we write.

Now create the following directory tree: src/main/java/myProj. Inside the nested myProj folder, we will create two text files, HelloGridWorld.java and PlotTest.java.

HelloGridWorld.java should have the following contents.

And PlotTest.java should have the contents

Your directory structure should now look like the following.

We're now ready to compile and run! In the command line, make sure you're in the same directory as your pom.xml file. Then, to compile, run

Maven should download BURLAP (if you did not manually compile and install it) and other information, and then compile your two sources.

To run the HelloGridWorld code, use the following command

Running this code should launch a GUI with a grid world, similar to the image below. If you click on the image and then use the w-a-s-d keys, you'll be able to control the agent's movements. Note, however, that we made this a stochastic grid world in the code, which means some of the time you may find the agent going in a different direction than the one you intended!

We can similarly run our PlotTest code with

Which will run Q-learning on the same grid world 10 times, plotting the most recent trial and average performance. It should look something like the below image.

Conclusion

In this tutorial we walked you through compiling BURLAP and setting up your own Maven project that uses BURLAP. We used the command line to set everything up, but we strongly encourage you to use a full IDE for most projects, such as IntelliJ or Eclipse. You can initialize your projects the way we did here and then import the code into the IDE, or you can have these IDE's create a new Maven project themselves.

Now that you've completed this tutorial, you are encouraged to check out the other BURLAP tutorials that are available. Happy coding!

Recently, the Maven community decided to push forward and start workingtowards a 4.0.0 release.The first question after this announcement is of course: what can we expect Maven 4 to bring us?A lot - and in this post, we want to highlight some of the features that we are particularly excited about.

So without further ado, let’s dive into some of the new features that will ship with Maven 4.This post highlights a few, but the complete list is a lot longer and even more impressive.

Improved behaviour of reactor command-line arguments

Homebrew Mavericks

The first thing that will be making a lot of impact on the day-to-day use of Maven is a group of big improvements in the “Reactor”.It may be a part of Maven that you’re not aware of as an end-user, but it’s actually very important.When you invoke Maven, it’s the Reactors job to build the project structure, make sure all modules are built in the correct order and eventually build those projects.The Reactor made its way into Maven 3, which was a great improvement in the way Maven worked on multi-module projects.

As such, the improvements to this part of Maven are most relevant to those that use multi-module projects.A recent poll we did during our J-Fall 2020 talk shows that this feature is now wide-spread.

In the following paragraphs, let’s assume we have a Maven project with three modules: common, client and app.The modules depend on each other:

Homebrew Maven

Use --also-make together with --resume-from

The first improvement in the Reactor is a bug fix.Previously, if your project build failed on the client module, you would get a hint to resume the build with --resume-from :client.But if you did that, the build would break again: this time because Maven couldn’t find the common module.You might think that adding --also-make (or -am) would address this, but it wouldn’t.This long-standing bug is no longer there.If you combine --resume-from :client with --also-make, the Reactor will find all modules in your project and continue the build as you requested.

Automatically resume from the last point of failure

But chances are you will not notice.The thing with --resume-from :client is that it makes you think more than necessary.With Maven 4, you can make your life even easier and use --resume, or -r for short.It will automatically resume the build from the module that last failed.

But there’s more!Maybe you are using parallel builds.One sequence of modules was successfully built, while the build of another sequence of modules broke.In that scenario, using -r will skip the modules that were successful in the previous build.

The combination of these two features may well improve the time you need to build your large, enterprise software project!

Root-reactor aware subfolder builds

Imagine the app module in our earlier example is a web application.With Maven 3, when you wanted to start it to see if it works, you might use for example mvn jetty:run.But if you run that from the root project, it will run jetty:run in client and common as well.Since those modules do not contain a web application, it will fail.

Running mvn jetty:run inside the app module didn’t work either, because Maven would not be able to resolve the client and common modules.That’s why many people got into the bad habit of running mvn install first, as a workaround, so Maven would resolve client and common from the local repository.The same was true for selecting the project to build with mvn -f app/pom.xml - again, Maven would not be able to resolve the client and common modules.

This four-year-old improvement made it into Maven 4 as well.There are two ways in which you can use it:

1. Run mvn jetty:run inside the app module.When you navigate to the module with the web app and run mvn jetty:run, Maven will resolve the client and common modules from your workspace, just as you would expect.
2. Run mvn -f app/pom.xml jetty:run from the project root.In this scenario, Maven too will resolve the client and common modules from your workspace, just as you would expect.

Note that this requires a .mvn folder to be present in the root of your project.This folder does not have to contain any files, as long as it’s there.

Add --non-recursive option

This option is particularly interesting if your multi-module project is more than one or two levels deep.Take the Quarkus project as an example: each extension has at least two subprojects, deployment and runtime.

Earlier, if you wanted to build only the gRPC module and its five children, you would have needed something like mvn -pl extensions/grpc/codegen,extensions/grpc/deployment - and the list would go on and on…With Maven 4, you can use -pl extensions/grpc and build the grpc module plus all its child-modules in one go.So a “recursive” approach is now the default.If you don’t want this to happen, add --non-recursive to get back the old behaviour.

Detect errorless or warningless builds

But there’s more, not related to the Reactor and multi-module builds!

A warning is an error in the making.
– unknown author

Many tools send warnings to their users to, indeed, warn them about potential problems.Sometimes the developers of the tool use this to introduce stricter checks without breaking every project.So we prefer to have a build that does not contain any warnings - one day, they may become an error.

That’s why we are happy that with Maven 4, you can specify the --fail-on-severity or -fos parameter.By adding -fos WARN, the Maven build will break as soon as Maven itself or any plugin logs a warning message.

Consistent timestamp in multi-module builds

A recent improvement had to deal with a timestamp that Maven uses internally.That timestamp would end up in packaged archives, but in a multi-module build, each module would have a different timestamp.That’s a bit odd, and it can become annoying when determining when a bug was introduced.

Long story short: with Maven 4, all modules in the build have the same timestamp.

Automatic builds on GitHub actions

No matter whether you’re a veteran Maven contributor or somebody who passes by to fix a minor bug, the first thing you want to know is whether you broke something.The usual process was to pull the contribution to the Maven source code repository hosted at the Apache Software Foundation.There, it would be built with Jenkins and tested on various Windows and Linux versions.If you aren’t a Maven contributor yourself, you would need a “committer” on the project to do this for you.In our first experiences, before we became committers ourselves, this process could take a while.

But now, if you submit a pull request on GitHub, you don’t need to wait that long to have feedback.We’ve added GitHub Actions that perform a build and then test your changes in various environments.These provide you with instant feedback on the quality of your contribution - no human work involved.

As a bonus, those tests also run on macOS - this even showed a failing test that previously went undercover as it only failed on macOS.

But wait, there’s more!

Maven 4 will contain so much more, it’s too much to write in one article.To mention a few other things:

• Update the default plugin versions for the POM, JAR, EJB, WAR, EAR, RAR and Maven Plugin packaging types.
• If a downloaded file fails the checksum check, the build will break.This was previously a warning - see why we like -fos?
• Some of the current warnings will break your build.Again, see why we like -fos?You most like will need to fix your pom for these.
• Build/consumer implementation, explained in great detail in this video chat.
• Maven wrapper, just like Gradle has had for quite some time.There used to be a wrapper for a long time, but that was not part of the official Maven distribution.Now it is, and it will continue to be part of Maven.
• Automatic parent/dependency versioning

The full release notes contain all details, however big or small.

Wrapping up

We are truly happy to see a few major improvements coming with this new Maven release.Both of us have contributed some of them in time that our employer, Info Support, provided us with.We’re grateful for that time and we hope we used it to make Maven an even better tool than it already was.

If you want to give a try and you are working on macOS or Linux, there’s some good news for you.Using Brew, you can install the very latest bits and pieces of Maven 4.0 using this “tap”.

Your previously installed Maven is not gone if you do this.Using Brew, you can switch back & forth:

Take care though: these are really the latest bits, and they may or may not work.Those builds are not an official distribution of Maven and they are not supported in any way.But of course, they pass the extensive integration test suite.

Please try these builds!We appreciate early feedback on the quality and usability of Maven 4.0.0-alpha-1.You can submit a bug in JIRA (requires login, but you can create one in seconds).