如何修复 JNI 项目中的不满意 LinkError (无法找到依赖库)

I'm pretty sure the classpath and the shared library search path have little to do with each other. According to The JNI Book (which admittedly is old), on Windows if you do not use the java.library.path system property, the DLL needs to be in the current working directory or in a directory listed in the Windows PATH environment variable.

Update:

Looks like Oracle has removed the PDF from its website. I've updated the link above to point to an instance of the PDF living at University of Texas - Arlington.

Also, you can also read Oracle's HTML version of the JNI Specification. That lives in the Java 8 section of the Java website and so hopefully will be around for a while.

Update 2:

At least in Java 8 (I haven't checked earlier versions) you can do:

java -XshowSettings:properties -version

to find the shared library search path. Look for the value of the java.library.path property in that output.

I used to have exactly the same problem, and finally it was solved.

I put all the dependent DLLs into the same folder where mylib.dll was stored and make sure the JAVA Compiler could find it (if there is no mylib.dll in the compilation path, there would be an error reporting this during compiling). The important thing you need to notice is you must make sure all the dependent libs are of the same version with mylib.dll, for example if your mylib.dll is release version then you should also put the release version of all its dependent libs there.

Hope this could help others who have encountered the same problem.

I want to inform this interesting case, after tried all the above method, the error is still there. The weird thing is it works on a Windows 7 computer, but on Windows XP it is not. Then I use dependency walker and found on the Windows XP there is no VC++ Runtime as my dll requirement. After installing VC++ Runtime package here it works like a charm. The thing that disturbed me is it keeps telling Can't find dependent libraries, while intuitively the JNI dependent dll is there, however it finally turns out the JNI dependent dll requires another dependent dl. I hope this helps.

Did have identical problem with on XP machine when installing javacv and opencv in combination with Eclipse. It turned out that I was missing the following files:

• msvcp100.dll
• msvcr100.dll

Once these were installed, the project compiled and ran OK.

Please verify your library path is right or not. Of course, you can use following code to check your library path path: System.out.println(System.getProperty("java.library.path"));

You can appoint the java.library.path when launching a Java application:

java -Djava.library.path=path ...

You need to load your JNI library.

System.loadLibrary loads the DLL from the JVM path (JDK bin path).

If you want to load an explicit file with a path, use System.load()

See also: Difference between System.load() and System.loadLibrary in Java

If you load a 32 bit version of your dll with a 64 bit JRE you could have this issue. This was my case.

1. Go to http://tess4j.sourceforge.net/usage.html and click on Visual C++ Redistributable for VS2012
2. Download it and run VSU_4\vcredist_x64.exe or VSU_4\vcredist_x84.exe depending upon your system configuration
3. Put your dll files inside the lib folder, along with your other libraries (eg \lib\win32-x86\your dll files).

I had the same issue, and I tried everything what is posted here to fix it but none worked for me. In my case I'm using Cygwin to compile the dll. It seems that JVM tries to find the JRE DLLs in the virtual Cygwin path. I added the the Cygwin's virtual directory path to JRE's DLLs and it works now. I did something like:

SET PATH="/cygdrive/c/Program Files/Java/jdk1.8.0_45";%PATH%

In my situation, I was trying to run a java web service in Tomcat 7 via a connector in Eclipse. The app ran well when I deployed the war file to an instance of Tomcat 7 on my laptop. The app requires a jdbc type 2 driver for "IBM DB2 9.5". For some odd reason the connector in Eclispe could not see or use the paths in the IBM DB2 environment variables, to reach the dll files installed on my laptop as the jcc client. The error message either stated that it failed to find the db2jcct2 dll file or it failed to find the dependent libraries for that dll file. Ultimately, I deleted the connector and rebuilt it. Then it worked properly. I'm adding this solution here as documentation, because I failed to find this specific solution anywhere else.

• Short answer: for "can't find dependent library" error, check your $PATH (corresponds to bullet point #3 below)
• Long answer:
  1. Pure java world: jvm uses "Classpath" to find class files
  2. JNI world (java/native boundary): jvm uses "java.library.path" (which defaults to $PATH) to find dlls
  3. pure native world: native code uses $PATH to load other dlls

I found a great article by some friends at keepsafe that went through the same thing I did. It worked for me, so hopefully it helps you out as well! Have a read if you're interested (The Perils of Loading Native Libraries on Android) or just use

compile 'com.getkeepsafe.relinker:relinker:1.2.3'

and replace

System.loadLibrary("myLibrary");

with

ReLinker.loadLibrary(context, "mylibrary");

Creating static library worked for me, compiling using g++ -static. It bundles the dependent libraries along with the build.

installing Microsoft Visual C++ 2010 SP1 Redistributable Fixed it

place the required dlls in folder and set the folder path in PATH environment variable. make sure updated environment PATH variable is reflected.

I was facing same issue with ffmpeg library after merging two Android projects as one project.

Actually issue was arriving due to two different versions of ffmpeg library but they were loaded with same names in memory. One library was placed in JNiLibs while other was inside another library used as module. I was not able to modify the code of module as it was readonly so I renamed the one used in my own code to ffmpegCamera and loaded it in memory with same name.

System.loadLibrary("ffmpegCamera");

This resolved the issue and now both versions of libraries are loading well as separate name and process id in memory.

When calling System.loadLibrary(), the JVM will look on the java.library.path for your native library. However, if that native library declares any dependencies on other native libraries, then the operating system will be tasked with finding those native library dependencies.

Since the operating system has no concept of the java.library.path, it will not see any directories you place on the java.library.path. Instead, it will only search the directories on PATH environment variable of the operating system. This is totally fine if the native library dependency is an operating system native library because it will be found on the PATH. However, if the native library dependency is a native library that you or someone else created, then it will not be found on the PATH unless you place it there. This behavior is strange, unexpected, and not well documented, but it is documented in the OpenJDK issue tracker here. You can also find another StackOverflow answer reinforcing this explanation, here.

So, you have a couple of options. You could either load each native library in the correct dependency order using System.loadLibrary(), or you could modify the PATH to include the directories where your native libraries are stored.

I faced the same problem after migrating my CI into a new machine. I was still facing it even after applying all the above solutions.

The problem was in my new machine, there was Microsoft Visual C++ 2010 SP1 Redistributable x86 installed in it. But my new machine was having 64-bit CPU and operating system. So the fix was that i just updated and installed the 64 bit version from here .