Where does @executable_path point to in a Java program

问题

I'm trying to load a native library in Java on Mac OS X 10.10.5 like this:

System.loadLibrary("SgCore_wrap");

and it throws an exception:

Exception in thread "main" java.lang.UnsatisfiedLinkError: /Users/nyholku/sgCoreTest/libSgCore_wrap.dylib: dlopen(/Users/nyholku/sgCoreTest/libSgCore_wrap.dylib, 1): Library not loaded: @executable_path/../Frameworks/libsgCore64.dylib

So my question is where does @executable_path points to in case of a Java program and does this depend on weather I run from command line or within Eclipse?

And further, supposing the correct location is 'somewhere in the system' like say '/Library', what is the best strategy handle this in a distributable Mac OS bundle (.app) with embedded JVM?

This what my otool shows for the two libraries involved (functions in libSgCore_wrap.dylib call functions in libsgCore64.dylib) in question:

otool -L /Users/nyholku/sgCoreTest/libSgCore_wrap.dylib 
   /Users/nyholku/sgCoreTest/libSgCore_wrap.dylib:
      libSgCore_wrap.dylib (compatibility version 0.0.0, current version 0.0.0)
      /usr/lib/libstdc++.6.dylib (compatibility version 7.0.0, current version 104.1.0)
      @executable_path/../Frameworks/libsgCore64.dylib (compatibility version 1.0.0, current version 1.0.0)
      /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1213.0.0)

and here otool output for the

 tool -L /Users/nyholku/sgCoreTest/libsgCore64.dylib 
    /Users/nyholku/sgCoreTest/libsgCore64.dylib:
       @executable_path/../Frameworks/libsgCore64.dylib (compatibility version 1.0.0, current version 1.0.0)
       /System/Library/Frameworks/Carbon.framework/Versions/A/Carbon (compatibility version 2.0.0, current version 157.0.0)
       /usr/lib/libc++.1.dylib (compatibility version 1.0.0, current version 120.0.0)
       /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1197.1.1)
       /System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation (compatibility version 150.0.0, current version 855.14.0)

As a bonus question, why does libSgCore_wrap.dylib reference itself and what does it mean/effect as far where the library should be?

回答1:

Seems that you copy directly the .dylibs from some other application to your user folder and then you're trying to load it with Java.

The problem is that the references on these libraries are using @executable_path which is relative to the main executable (the other application) and when Java try to load these libraries the reference using @executable_path are not correct, so dlopen can not find the required dependencies.

A possible solution for your specific case is to use @loader_path instead since this variable is relative to the referring binary.

So if you only need this two libraries, and you can work with a copy of them without worrying about update on theirs etc, and both are on the same directory, then you can try to copy the libraries and change their references from @executable_path to @loader_path using install_name_tool.

As you show in your code I suppose that both libraries are in the same path /Users/nyholku/sgCoreTest/ and since you're using System.loadLibrary method you're setting correctly -Djava.library.path=/Users/nyholku/sgCoreTest/.

First, change the reference to libsgCore64.dylib inside libSgCore_wrap.dylib file using the follow command install_name_tool -change oldReference newReference dylibToChange, in your case:

install_name_tool -change @executable_path/../Frameworks/libsgCore64.dylib @loader_path/libsgCore64.dylib libSgCore_wrap.dylib

Then you must change the identifier of the libsgCore64.dylib itself, using install_name_tool -id newReference dylibToChange, in your case:

install_name_tool -id @loader_path/libsgCore64.dylib libsgCore64.dylib

Now you can use these modified libraries and they will load correctly in Java.

来源：https://stackoverflow.com/questions/40475065/where-does-executable-path-point-to-in-a-java-program

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