Java Native Access

Java Native Access (JNA) is a community-developed library that provides Java programs easy access to native shared libraries without using the Java Native Interface (JNI). JNA's design aims to provide native access in a natural way with a minimum of effort. Unlike JNI, no boilerplate or generated glue code is required.

Since Java 22, the Foreign Function and Memory API was provided as a standard modern alternative.

The JNA library uses a small native library called foreign function interface library (libffi) to dynamically invoke native code. The JNA library uses native functions allowing code to load a library by name and retrieve a pointer to a function within that library, and uses libffi library to invoke it, all without static bindings, header files, or any compile phase. The developer uses a Java interface to describe functions and structures in the target native library. This makes it quite easy to take advantage of native platform features without incurring the high development overhead of configuring and building JNI code.

JNA is built and tested on macOS, Microsoft Windows, FreeBSD / OpenBSD, Solaris, Linux, AIX, Windows Mobile, and Android. It is also possible to tweak and recompile the native build configurations to make it work on most other platforms that run Java.

The following table shows an overview of types mapping between Java and native code and supported by the JNA library.^[2]

Note: The meaning of TCHAR changes between char and wchar_t according to some preprocessor definitions. LPCTSTR follows.

Native libraries have no standardized memory byte alignment flavor. JNA defaults to an OS platform specific setting, that can be overridden by a library specific custom alignment. If the alignment details are not given in the documentation of the native library, the correct alignment must be determined by trial and error during implementation of the Java wrapper.

The following program loads the local C standard library implementation and uses it to call the printf function.

Note: The following code is portable and works the same on Windows and POSIX (Linux / Unix / macOS) platforms.

importcom.sun.jna.Library;
importcom.sun.jna.Native;
importcom.sun.jna.Platform;
/** Simple example of native library declaration and usage. */
publicclass HelloWorld{
publicinterface CLibraryextendsLibrary{
CLibraryINSTANCE=(CLibrary)Native.loadLibrary(
(Platform.isWindows()?"msvcrt":"c"),CLibrary.class);
voidprintf(Stringformat,Object...args);
}
publicstaticvoidmain(String[]args){
CLibrary.INSTANCE.printf("Hello, World\n");
for(inti=0;i<args.length;i++){
CLibrary.INSTANCE.printf("Argument %d: %s\n",i,args[i]);
}
}
}

The following program loads the C POSIX library and uses it to call the standard mkdir function.

Note: The following code is portable and works the same on POSIX standards platforms.

importcom.sun.jna.Library;
importcom.sun.jna.Native;
/** Simple example of native C POSIX library declaration and usage. */
publicclass ExampleOfPOSIX{
publicinterface POSIXextendsLibrary{
publicintchmod(Stringfilename,intmode);
publicintchown(Stringfilename,intuser,intgroup);
publicintrename(Stringoldpath,Stringnewpath);
publicintkill(intpid,intsignal);
publicintlink(Stringoldpath,Stringnewpath);
publicintmkdir(Stringpath,intmode);
publicintrmdir(Stringpath);
}
publicstaticvoidmain(String[]args){
// It is possible to load msvcrt for its partial POSIX support on Windows...
POSIXposix=(POSIX)Native.loadLibrary("c",POSIX.class);
// but it will still fail on Windows due to /tmp being missing.
posix.mkdir("/tmp/newdir",0777);
posix.rename("/tmp/newdir","/tmp/renamedir");
}
}

The program below loads the Kernel32.dll and uses it to call the Beep and Sleep functions.

Note: The following code works only on Windows platforms.

importcom.sun.jna.Library;
importcom.sun.jna.Native;
/** Simple example of Windows native library declaration and usage. */
publicclass BeepExample{
publicinterface Kernel32extendsLibrary{
// FREQUENCY is expressed in hertz and ranges from 37 to 32767
// DURATION is expressed in milliseconds
publicbooleanBeep(intFREQUENCY,intDURATION);
publicvoidSleep(intDURATION);
}
publicstaticvoidmain(String[]args){
Kernel32lib=(Kernel32)Native.loadLibrary("kernel32",Kernel32.class);
lib.Beep(698,500);
lib.Sleep(500);
lib.Beep(698,500);
}
}

• JNAerator
• P/Invoke
• SWIG

• Java Native Access Web Page
• Java Native Access - Download page
• Java Native Access - User Mailing List
• Friesen, Jeff (5 February 2008). "Open source Java projects: Java Native Access". Open Source Java Tutorials. JavaWorld . Retrieved 2020年07月27日.
• Morris, Stephen B. (20 May 2009). "Protect Your Legacy Code Investment with JNA". today.java.net. Archived from the original on 2015年01月13日.
• Dasgupta, Sanjay (11 November 2009). "Simplify Native Code Access with JNA". today.java.net. Archived from the original on 2009年11月15日.
• Doubrovkine, Daniel (20 June 2011). "JNA is now a Githubber". code.dblock.org. Retrieved 2020年07月27日.
• Kiaer, Jesper (21 March 2010). "Calling the Lotus Domino C-API with JNA". Nevermind.dk. Retrieved 2020年07月27日.

• Java platform