Maven and the JOGL library?

Question

I've been studying Maven in my free time over the last several days but can't seem to figure out how to organize a project so that the JOGL libraries are used. I would preferably like the following:

1. Automatically download, if necessary, the OS-specific JOGL zip file from here (contains 4 jar files and some native library files (.so/.dll)); or depend on a Maven project which is a wrapper of one of the files.
2. Unzip that zip file appropriately, so that:
   1. the jar files are added to the classpath and deployed as necessary, and
   2. the native library files are added to the final jar file (would this enable them to be automatically used, or would I need something more involved?)

I think part of my problem is that I don't fully understand the use of JOGL, where to place the native libraries when running the code, etc. I need to go back to the basics and write a JOGL hello world, compile it from the command line and run it from the command line to see exactly what it requires as far as directory placement of the native libraries; I may go do that right now, actually.

With item 1, I've found some OS-specific features; Maven profiles can be activated based on properties of the system, which include the operating system. So then I could activate a Windows profile which has a dependency of the Windows-specific JOGL library, same for the Linux, and both having a 64-bit alter ego. (Activation official docs / unofficial docs.)

I have tried creating a Maven repository based on a JOGL jar file, and then adding the JOGL jar file project as a dependency of my project; the dependency is downloaded, but not used. I have no idea where the jar file goes or how to use it, unpack it, etc. Here is the command I used.

So, in short: JOGL consists of four .jar files and some native libraries. How can I integrate those files into my Maven project so that I can write a JOGL application with Maven handling my build process? Furthermore, how can I use a different set of files depending on the operating system, because of course the native libraries and even the .jar files differ between Windows, Linux and Mac.

Answer 1

When dealing with JNI and Maven, Projects With JNI is the reference one should start with. It covers a lot more than your current problem (which is "just" using a library that relies on JNI and native libraries) but, well, he who can do more can do less.

If you read it carefully, you'll see that one solution to use JNI libraries is to bundle them in architecture specific JARs so that you can depend on them like any other dependency from a Maven point of view. This is actually how JOGL version 1.1.1 is packaged in http://download.java.net/maven/2/net/java/dev/jogl/, there is one JAR artifact with the Java classes and several architecture specific JARs artifacts with the native libraries.

JNI library archived within the jar

The solution I ended up using was to store the compiled jni library in the jar alongside the class files.

This means either cross-compiling for all possible architectures, or more simply, having a different jar for each architecture. This latter fits quite well with our setup - where almost all of our machines are Linux-i386, with a smattering of win32 boxes.

Sadly System.load() can't cope with loading libraries from within a jar, so we'll therefore need a custom loader which extracts the library to a temporary file at runtime; this is obviously achievable, however.

Then, as explained, the idea is to use a custom library loader to load the native library. The good news is that such a loader is "provided" as explained below.

Library loader

We now have our JNI library on the class path, so we need a way of loading it. I created a separate project which would extract JNI libraries from the class path, then load them. Find it at http://opensource.mxtelecom.com/maven/repo/com/wapmx/native/mx-native-loader/1.2/. This is added as a dependency to the pom, obviously.

To use it, call com.wapmx.nativeutils.jniloader.NativeLoader.loadLibrary(libname). More information is in the javadoc for NativeLoader.

I generally prefer to wrap such things in a try/catch block, as follows:

public class Sqrt {
    static {
        try {
            NativeLoader.loadLibrary("sqrt");
        } catch (Throwable e) {
            e.printStackTrace();
            System.exit(1);
        }
    }
    /* ... class body ... */
}

We should now be at the point where our junit tests work from maven; a mvn test should work! It should also work fine from an IDE.

Now, to answer your questions, how to:

Automatically download, if necessary, the OS-specific JOGL zip file from here (contains 4 jar files and some native library files (.so/.dll)); or depend on a Maven project which is a wrapper of one of the files.

Sadly, JOGL 2.0 jars aren't available in the Maven repository of java.net so you'll have to deal with that and either make them available in a private repository or install them manually in the local repository of each developer. To do so, use mvn install:install-file as documented in the Guide to installing 3rd party JARs (and not mvn deploy:deploy-file as you did, this goal is used to install artifacts to a remote repository).

Personally, I would download JOGL 2.0 ZIPs from the URL you provided, package it as they did with JOGL 1.1.1 (one Java JAR and several specific JARs for native libraries) and install the JARs in each local repository for now. Then, declare a standard dependency on the Java artifact and, indeed, use profiles for the architecture specific dependency. Something like this:

<project>
  ...
  <dependencies> 
    <dependency>
      <groupId>net.java.dev.jogl</groupId>
      <artifactId>jogl</artifactId>
      <version>2.0-beta10</version>
    </dependency>
    ...
  </dependencies>
  ...
  <profiles>
    <profile>
      <id>linux-i586</id>
      <activation>
        <os>
          <arch>i386</arch>
          <family>unix</family>
          <name>linux</name>
        </os>
      </activation>
      <dependencies>
        <dependency>
          <groupId>net.java.dev.jogl.jogl-linux-i586</groupId>
          <artifactId>jogl-linux-i586</artifactId>
          <version>2.0-beta10</version>
        </dependency>
      </dependencies>
    </profile>
    ...
  </profiles>
  ...
</project>

Don't forget to add the repository required for the custom library loader and the dependency:

<project>
  <repositories>
    <repository>
      <id>opensource.mxtelecom.com</id>
      <url>http://opensource.mxtelecom.com/maven/repo</url>
    </repository>
    ...
  <repositories>
  ...
  <dependencies> 
    <dependency>
      <groupId>com.wapmx.native</groupId>
      <artifactId>mx-native-loader</artifactId>
      <version>1.2</version>
    </dependency>
    ...
  </dependencies>
  ...
</project>

Regarding the second part of your question:

Unzip that zip file appropriately, so that (...)

As I explained, you actually won't depend on ZIP files but on JARs and you won't need to uncompress them neither during development nor to distribute your project. For the distribution, you'll just need to create a jar including the dependencies. This can be done with the maven-assembly-plugin. See this answer for example for more details on this.