Java JNI and dependent libraries on Windows

java java-native-interface java.library.path
alkar picture alkar · Sep 24, 2012 · Viewed 8.5k times · Source

Long story short: I have an executable jar, that calls jni.dll which is dependent on lib.dll. And I'm getting the oh-so-dreaded UnsatisfiedLinkError.

This answer comes pretty close, yet it fails to solve the problem, from my experience. Even when the folder where the dll's reside is specified in java.library.path, it will not work. I have to change the Windows PATH environment variable as well. In fact, the default java.library.path on Windows seems to be PATH.

Is there any "pretty" way to fix this? I want to build an installer for Windows and I'm wondering how I would deal with this issue, so that the end-user will not have to do any manual work.

EDIT:

What I implemented is the following: the application ships with a folder called "native_libs" which has dynamic libraries for all supported architectures. The structure is the following:

/
+- native_libs/
   +- windows/
   |  +- x86/
   |  |  +- ...
   |  +- x64/
   |     +- ...
   |
   +- linux/
   |  +- x86/
   |  |  +- ...
   |  +- x64/
   |     +- ...
   |
   +- libs/
      +- ...

On runtime, while the application initializes, the correct JRE architecture and System OS are detected and the proper library files are copied to the libs/ folder. The java.library.path is being set on runtime as well using a common hack. Finally, the PATH environment variable for windows is set using a native launcher.

Any room for improvement? Maybe copying the dll's in the same directory as the jar file would negate the need for setting the java.library.path and PATH variables? I need to investigate loading the dll's with System.load() as well, which will negate the need to copy files.

Answer

Ingo Kegel picture Ingo Kegel · Sep 24, 2012

java.library.path specifies the directories where System.loadLibrary() looks for the dynamic library file. If you change the java.library.path system property in your code, it will not have any effect. There are hacks to make Java "forget" the initial value and re-evaluate the contents of the java.library.path system property.

However, the dependent library is not loaded by Java, it's loaded by Windows. Windows does not care about java.library.path, it only cares about the PATH environment variable. Your only option is to adjust PATH for your Java process. For example, if you start it from a batch file, change the PATH environment variable right before the java invocation.

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