6

Using JNA 4.0.0, on Linux, I am trying to load a native library (libmean.so), which is in the lib subdirectory (the library is just a trivial example that calculates the mean of two numbers).

I run the following code (within Eclipse), with -Djna.library.path=lib set in the run configuration.

import com.sun.jna.Library;
import com.sun.jna.Native;

public class Mean {
  public interface MeanLib extends Library {    
    MeanLib INSTANCE = (MeanLib) Native.loadLibrary("mean", MeanLib.class);
    double mean(double a, double b);
  }
  public static void main(String[] args) {          
    double result = MeanLib.INSTANCE.mean(1.0, 3.0);
    System.out.println(result);
  }
}

But this fails with the following exception:

Exception in thread "main" java.lang.UnsatisfiedLinkError: Can't obtain updateLastError method for class com.sun.jna.Native
at com.sun.jna.Native.initIDs(Native Method)
at com.sun.jna.Native.<clinit>(Native.java:139)
at com.sun.jna.examples.Mean$MeanLib.<clinit>(Mean.java:64)
at com.sun.jna.examples.Mean.main(Mean.java:72)

Through trial-and-error, I have discovered that the code starts working if I also set java.library.path.

However, it works regardless of the value of this property. For example, I can set -Djava.library.path=xxxxxxx and it continues to work. An empty value also works.

What is going on?

DNA
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3 Answers3

11

The root problem is that there is an older version of JNA installed on the system:

$ dpkg -l | grep -i jna
ii  libjna-java  3.2.7-4 Dynamic access of native libraries from Java without JNI

JNA starts up by trying to load its bootstrap native library. It searches for this in various places, as described in the documentation.

The problem is fixed by using the -Djna.nosys=true flag, which forces JNA to load the native library from your jna.jar, not from the system.

Setting the java.library.path to a nonsense value has a similar side-effect - it overwrites the normal java.library.path, preventing the system version of JNA from being loaded, and falling back on the version from your local jna.jar.

The debug setting -Djna.debug_load=true is also useful for diagnosing JNA problems.

DNA
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  • I am having same error...I have tried using -Djna.nosys=true in the VM option in project properties in Netbeans...and it gave following error at the time of execution `Exception in thread "main" java.lang.UnsatisfiedLinkError: The specified module could not be found.` –  Mar 15 '16 at 08:37
  • it really solve my headache whether I start my jenkins – Larry Cai Jan 18 '17 at 07:18
3
$ dpkg -l | grep -i jna

try this command and if u getting this output

ii  libjna-java  3.2.7-4 Dynamic access of native libraries from Java without JNI

or any other output then this u need to remove then that jna from the system because if program itself have jna jar with that then there is no need of system jna for the same. so do something like this.

sudo apt-get autoremove libjna-java

and try for restart that application again. it will run and it is not running then try to install new version of libwebkit-gtk.

hope this will help. this helped me.

Kishan Bheemajiyani
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1

I got this error when I'd installed Netbeans 7 via apt-get which pulled in libjna-java (3.2.7-4).

Since Netbeans 7 is old, I installed version 8 via their shell installer after removing the debian packages. Be sure and autoremove to get rid of libjna.

Jeff Rodriguez
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