# Calling Julia from Java: Image Not Found

**URL:** <https://discourse.julialang.org/t/calling-julia-from-java-image-not-found/17265>\
**Category:** General Usage\
**Created:** [November 7, 2018, 4:07pm UTC](https://discourse.julialang.org/t/calling-julia-from-java-image-not-found/17265 "2018-11-07T16:07:48Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![peter.wolf](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/peter.wolf/32/6018_2.png) [@peter.wolf](https://discourse.julialang.org/u/peter.wolf)\
**Post date:** [November 7, 2018, 4:07pm UTC](https://discourse.julialang.org/t/calling-julia-from-java-image-not-found/17265/1 "2018-11-07T16:07:48Z")

</div>

Hello, I asked this on StackOverflow, but this is a better place 🙂

I am calling Julia from Java via JNI.

I have successfully compiled and linked my Julia into a dylib using instructions here:

> julia ~/dev/PackageCompiler.jl/juliac.jl -vas f.jl`

[https://docs.julialang.org/en/v1/manual/embedding/index.htm](https://docs.julialang.org/en/v1/manual/embedding/index.htm)

> **[GitHub - JuliaLang/PackageCompiler.jl: Compile your Julia Package](https://github.com/JuliaLang/PackageCompiler.jl)**
>
> Compile your Julia Package. Contribute to JuliaLang/PackageCompiler.jl development by creating an account on GitHub.

I link with a thin layer of C++ to implement the JNI interface. I got the flags from

> julia/share/julia/julia-config.jl --allflags

> JAVA\_LINK\_FLAGS = -shared
> 
> JULIA\_LINK\_LIBS = -Wl,-rpath,‘/Applications/Julia-1.0.app/Contents/Resources/julia/lib’ -Wl,-rpath,‘/Applications/Julia-1.0.app/C  
> ontents/Resources/julia/lib/julia’ -ljulia
> 
> libTest.jnilib: Test.o builddir/f.dylib  
> gcc $JAVA\_LINK\_FLAGS $JULIA\_LINK\_FLAGS -o libTest.jnilib Test.o builddir/f.dylib JULIA\_LINK\_LIBS
> 
> Test.o: Test.cpp  
> gcc -c JULIA\_C\_FLAGS JAVA\_C\_FLAGS Test.cpp

Everything compiles and links with no complaint, but when I try to call it from Java I get this

> Exception in thread “main” java.lang.UnsatisfiedLinkError:  
> /Users/xxx/dev/ie/julia/libTest.jnilib:  
> dlopen(/Users/xxx/dev/ie/julia/libTest.jnilib, 1): Library not  
> loaded: @rpath/f.dylib  
> Referenced from: /Users/xxx/dev/ie/julia/libTest.jnilib  
> Reason: image not found  
> at java.lang.ClassLoader$NativeLibrary.load(Native Method)  
> at java.lang.ClassLoader.loadLibrary0(ClassLoader.java:1941)  
> at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1861)  
> at java.lang.Runtime.loadLibrary0(Runtime.java:870)  
> at java.lang.System.loadLibrary(System.java:1122)  
> at Test.(Test.java:3)

I can’t find anything in the docs. I thought PackageCompiler and julia-config would take care of including everything I need. What am I missing?

Thanks Peter

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<div class="post-metadata">

**Author:** ![avik](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/avik/32/17_2.png) [@avik](https://discourse.julialang.org/u/avik)\
**Post date:** [November 7, 2018, 4:56pm UTC](https://discourse.julialang.org/t/calling-julia-from-java-image-not-found/17265/2 "2018-11-07T16:56:55Z")

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Is `f.dylib` in the same directory as `libTest.jnilib` ? Is that your current working directory?

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<div class="post-metadata">

**Author:** ![peter.wolf](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/peter.wolf/32/6018_2.png) [@peter.wolf](https://discourse.julialang.org/u/peter.wolf)\
**Post date:** [November 7, 2018, 5:14pm UTC](https://discourse.julialang.org/t/calling-julia-from-java-image-not-found/17265/3 "2018-11-07T17:14:15Z")

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No f.dylib is in builddir and libTest.jnilib is in my current dir. Should I cause them to be in the same place?

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<div class="post-metadata">

**Author:** ![avik](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/avik/32/17_2.png) [@avik](https://discourse.julialang.org/u/avik)\
**Post date:** [November 7, 2018, 5:20pm UTC](https://discourse.julialang.org/t/calling-julia-from-java-image-not-found/17265/4 "2018-11-07T17:20:44Z")

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> [@peter.wolf](#):
>
> No f.dylib is in builddir and libTest.jnilib is in my current dir. Should I cause them to be in the same place?

Well, the error message suggests that they should be in the same place: `@rpath/f.dylib`

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<div class="post-metadata">

**Author:** ![peter.wolf](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/peter.wolf/32/6018_2.png) [@peter.wolf](https://discourse.julialang.org/u/peter.wolf)\
**Post date:** [November 7, 2018, 6:00pm UTC](https://discourse.julialang.org/t/calling-julia-from-java-image-not-found/17265/5 "2018-11-07T18:00:30Z")

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That didn’t fix it. Can you explain @rpath? How is it set?

Also, am I correct in thinking that my libTest.jnilib is finding f.dylib like any other dylib. But on loading Julia is trying to load an ‘image’ which it is not finding? That image is inside f.dylib

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<div class="post-metadata">

**Author:** ![peter.wolf](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/peter.wolf/32/6018_2.png) [@peter.wolf](https://discourse.julialang.org/u/peter.wolf)\
**Post date:** [November 19, 2018, 9:13pm UTC](https://discourse.julialang.org/t/calling-julia-from-java-image-not-found/17265/6 "2018-11-19T21:13:46Z")

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For those that come after. I eventually found code that works. See below.

Two important items:

1. I was unable to get the .dylib to work, however PackageCompiler also generates a static .a library. I was able to link with this and run successfully

2. The example code with PackageCompiler did not work for me, neither did the documentation on calling from C++. Once I am less of a N00B perhaps I will write up something, but for now the code below seems to work

I hope this helps others who want to call Julia from C++/Python/Java etc

```julia
#include <jni.h> // JNI header provided by JDK                                                                                                                                                              
#include <stdio.h> // C Standard IO Header                                                                                                                                                                    
#include <julia.h> // Julia API                                                                                                                                                                               
#include "Test.h" // Generated                                                                                                                                                                               

#ifdef JULIA_DEFINE_FAST_TLS // only available in Julia v0.7 and above                                                                                                                                             
JULIA_DEFINE_FAST_TLS()
#endif

/*                                                                                                                                                                                                                 
 * Class: Test                                                                                                                                                                                                 
 * Method: f                                                                                                                                                                                                    
 * Signature: (I)I                                                                                                                                                                                                 
 */
JNIEXPORT jint JNICALL Java_Test_f(JNIEnv *env, jobject cls, jint x) {

  libsupport_init();

  jl_init_with_image("/Applications/Julia-1.0.app/Contents/Resources/julia/bin","/Users/peter.wolf/dev/ie/julia/builddir/f.dylib");

  // f(x::Int32)::Int32 = x + 3                                                                                                                                                                                    
  jl_function_t *func = jl_get_function(jl_main_module, "f");

  int y = 0;
  if(func) {
      jl_value_t *argument = jl_box_int32(3);
      jl_value_t *ret = jl_call1(func, argument);
      y = jl_unbox_int32(ret);
  }

  jl_atexit_hook(0);
  return y;
}

```