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Native library loader for extracting and loading native libraries from Java.

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scijava/native-lib-loader

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README.md

About native library loader

The native library loader is a utility that assists with loading native libraries from Java. It provides the ability to painlessly identify, extract and load the correct platform-specific native library from a JAR file.

Search Maven Central for latest version and add a dependency to your pom.xml.

dependency> groupId>org.scijavagroupId> artifactId>native-lib-loaderartifactId> version>x.y.zversion> dependency>

Native libraries should be packaged into a single jar file, with the following directory & file structure:

/natives /linux_32 libxxx[-vvv].so /linux_64 libxxx[-vvv].so /osx_32 libxxx[-vvv].dylib /osx_64 libxxx[-vvv].dylib /osx_arm64 libxxx[-vvv].dylib /windows_32 xxx[-vvv].dll /windows_64 xxx[-vvv].dll /windows_arm64 xxx[-vvv].dll /aix_32 libxxx[-vvv].so libxxx[-vvv].a /aix_64 libxxx[-vvv].so libxxx[-vvv].a 

Here «xxx» is the name of the native library and «-vvv» is an optional version number. Depending on the platform at runtime, a native library will be unpacked into a temporary file and will be loaded from there.

The version information will be grabbed from the MANIFEST.mf file from «Implementation-Version» entry. So it’s recommended to follow Java’s package version information convention.

If you want to load ‘awesome.dll’ (on Windows) or ‘libawesome.so’ (on Linux or AIX), simply do like this .

NativeLoader.loadLibrary("awesome");

About

Native library loader for extracting and loading native libraries from Java.

Источник

How should I load native libraries for JNI to avoid an UnsatisfiedLinkError?

I want to use JNI on Ubuntu 8.10, using Eclipse and gcc (the standard one with Ubuntu if there are flavours). I can’t seem to load my library despite the make file creating it successfully. The main Java class is as follows:

class Hello < public native void sayHello(); static < System.loadLibrary("hello.so"); >public static void main(String[] args) < Hello h = new Hello(); h.sayHello(); >> 

 all : hello.so hello.so : Hello.o gcc -shared -o hello.so Hello.o Hello.o : Hello.c Hello.h gcc -I/usr/lib/jvm/java-6-sun/include -I/usr/lib/jvm/java-6-sun/include/linux -c Hello.c -o Hello.o Hello.h : Hello.class javah -jni Hello clean : -del Hello.h -del Hello.o 

Exception in thread "main" java.lang.UnsatisfiedLinkError: no hello.so in java.library.path 

System.loadLibrary("/home/gavin/Work/workspace/JNI/hello.so"); 

Thanks very much for the help, your tips were all correct, my lack of reputation restricts me from noting them all as helpful. Cheers

5 Answers 5

As per Pax you should set the library path to where ever Java should look for the library. Your library name should be libhello.so. The call to load the library should then be:

Linux libraries are referenced by the convention libname.so and loaded based on the name. Here is a link about dynamic linking problems in Java from the SWIG documentation, although you are not using SWIG this section is still relevant.

The link is alright, but the note about using ‘-rpath’ is bogus. For ‘rpath to work, it would have to be specified when compiling that java virtual machine itself.

You’re calling System.loadLibrary() incorrect. The loadLibrary method takes a library name, e.g. «hello», and tries to load the corresponding shared object. On Unix, it will attempt to load «libhello.so», and on windows it will try to load «hello.dll». It will expect the file to be found in java.library.path .

The method you probably intend to be calling is System.load() which takes a fully qualified filename and loads it. This method should take a File as argument, but it takes a string instead. If you use load , you’ll have to handle local naming conventions manually, but you won’t have to rely on java.library.path to be set.

change your Java class to this:

class Hello < public native void sayHello(); static < System.loadLibrary("hello"); >public static void main(String[] args) < Hello h = new Hello(); h.sayHello(); >> 

And are you running it with something like:

java -Djava.library.path=/home/gavin/Work/workspace/JNI Hello 

You’ll need to make sure the shared object is in your library path.

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Java load native library linux

There are several ways to make it possible for the Java runtime to find and load a native shared library (.so) at runtime. I will list them briefly here, followed by examples with more explanation below.

1. Call System.load to load the .so from an explicitly specified absolute path.
2. Copy the shared library to one of the paths already listed in java.library.path
3. Modify the LD_LIBRARY_PATH environment variable to include the directory where the shared library is located.
4. Specify the java.library.path on the command line by using the -D option.

Note: To help resolve an UnsatisfiedLinkError Runtime Error, see How to Handle the UnsatisfiedLinkError Runtime Error in Java

1. Call System.load to load the shared library from an explicitly specified absolute path.

This choice removes all uncertainty, but embeds a hard-coded path within your Java application. Example:

import com.chilkatsoft.CkZip; public class Test < static < try < System.load("/home/joe/chilkatJava/libchilkat.so"); > catch (UnsatisfiedLinkError e) < System.err.println("Native code library failed to load.\n" + e); System.exit(1); >> public static void main(String argv[]) < CkZip zip = new CkZip(); System.out.println(zip.version()); >>

2. Copy the shared library to one of the paths already listed in java.library.path

To view the paths listed in java.library.path, run this Java code:

String property = System.getProperty(«java.library.path»); StringTokenizer parser = new StringTokenizer(property, «;»); while (parser.hasMoreTokens())

Note: The java.library.path is initialized from the LD_LIBRARY_PATH environment variable.

The loadLibrary method may be used when the directory containing the shared library is in java.library.path. To load «libchilkat.so», call System.loadLibrary(«chilkat»), as shown below.

import com.chilkatsoft.CkZip; public class Test < static < try < System.loadLibrary("chilkat"); > catch (UnsatisfiedLinkError e) < System.err.println("Native code library failed to load.\n" + e); System.exit(1); >> public static void main(String argv[]) < CkZip zip = new CkZip(); System.out.println(zip.version()); >>

3. Modify the LD_LIBRARY_PATH environment variable to include the path where the Chilkat shared library is located.

For Bourne Shell, K Shell or Bash, type:

export LD_LIBRARY_PATH=/home/joe/chilkatJava-9.1.1-x86_64-linux:$LD_LIBRARY_PATH

setenv LD_LIBRARY_PATH "/home/joe/chilkatJava-9.1.1-x86_64-linux:$LD_LIBRARY_PATH"

4. Specify the java.library.path on the command line by using the -D option.

java -Djava.library.path=".:/home/joe/chilkatJava-9.1.1-x86_64-linux" TestApp

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How to load native library (.dlls) from a java application running on linux?

I have a java application in ubuntu, java application uses a jar. This jar uses some native libraries(.dll). System.loadLibrary(«my_native_library») is used in the jar to load required libraries. In linux it tries to load an .so file means here my_native_library.so, but I have my_native_library.dll. So I am not able to run this java application. How should I proceed?

1 Answer 1

If your .jar file has included some .dll the problem is that it has several modules that use JNI (Java Native Interface) and solves something based on code that is not written in java, but in another system specific language.

Shared objects in Windows are packed in files with extension .dll while the equivalent in linux is a shared object, which is packed in a file with extension .so.xxx.yyy where xxx and yyy are numbers identifying the version of the shared object.

Linux and Windows executables are not interchangeable, what means you cannor run that .jar file in linux, most probably, except if the .jar file includes also .so files to cope with linux execution.

EDIT

Normally, if you want a JNI enabled jar file to be executable, you’ll need some installation before the jar is usable. Windows normally installs dlls in some windows directory, or if you have not done, it uses the PATH environment variable to locate the dll (so normally, programs leave dlls in the same place as the application executable) Linux has a fully documented way of searching shared objects (see ldconfig manpage for instructions, and ld.so manpage also) which involves system libraries and user shared objects.

Anyway, the jar file only uses the CLASSPATH environment to locate .class files, and you’ll need to make (extract from the jar) the shared objects visible to the system loader in use. So the best way to so install a JNI shared object, is to extract it from the .jar file and put it in a directory where it will be located by the O.S. search engine (which is different for both systems)

Beware that windows and linux JNI loaders require a common name for the library object, and they do the system dependant part to complete the shared object name. This means that for a shared object called like myshared , you’ll need to call the shared objects myshared.dll in a windows system, and myshared.so in linux (I’m not sure about this, but you’ll get it easily by trial and fail and looking the System class and System#loadLibrary(String) documentation)

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