Java Native Access: Javasite.org

Java Native Access
Latest release	3.0.9 / 30 October 2008; 70 days ago
Written in	C and Java
OS	Cross-platform
Size	606.9 KB (archived)
Type	Software Library
License	LGPL version 2.1 or later.
Website	https://jna.dev.java.net

Java Native Access provides Java programs easy access to native shared libraries without using the Java Native Interface. JNA's design aims to provide native access in a natural way with a minimum of effort. No boilerplate or generated glue code is required. While some attention is paid to performance, correctness and ease of use take priority. The JNA library uses a small native library called libffi to dynamically invoke native code. The libffi library allows code to load a library by name, retrieve a pointer to a function within that library, and 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 overhead of configuring and building JNI code.

1 Adoption
2 Mapping types
3 Example
4 References
5 See also
6 External links

Adoption

Java Native Access is known to be used in:

JRuby use JNA for POSIX functionality ^[1]
Freedom for Media in Java (FMJ) ^[2]
IntelliJ IDEA IDE by the company JetBrains
SVNKit pure Java Subversion client library.
Videolan JVLC Java Multimedia Library.

Mapping types

The following table shows the mapping of types between Java and native code and supported by the JNA library.

Native Type	Size	Java Language Type	Common Windows Types
char	8-bit integer	byte	BYTE, TCHAR
short	16-bit	short	short WORD
wchar_t	16/32-bit character	char	TCHAR
int	32-bit integer	int	DWORD
int	boolean value	boolean	BOOL
long	32/64-bit integer	NativeLong	LONG
long long, __int64	64-bit integer	long
float	32-bit FP	float
double	64-bit FP	double
char*	C string	String	LPTCSTR
void*	pointer	Pointer	LPVOID, HANDLE, LPXXX

Example

The following program loads the local C standard library implementation and uses it to call the printf function. Note that the code is portable and works the same on Windows and Linux / Unix / Mac OS X platforms.

import com.sun.jna.Library;
import com.sun.jna.Native;
import com.sun.jna.Platform;
 
/** Simple example of native library declaration and usage. */
public class HelloWorld {
	public interface CLibrary extends Library {
		CLibrary INSTANCE = (CLibrary) Native.loadLibrary(
				(Platform.isWindows() ? "msvcrt" : "c"), CLibrary.class);
 
		void printf(String format, Object... args);
	}
 
	public static void main(String[] args) {
		CLibrary.INSTANCE.printf("Hello, World\n");
		for (int i = 0; i < args.length; i++) {
			CLibrary.INSTANCE.printf("Argument %d: %s\n", i, args[i]);
		}
	}
}

The following program loads the the C POSIX library and uses it to call the standard mkdir function. Note that the code is portable and works the same on POSIX standards platforms.

import com.sun.jna.Library;
import com.sun.jna.Native;
 
/** Simple example of native C POSIX library declaration and usage. */
public class exampleOfPOSIX {
	public interface POSIX extends Library {
		public int chmod(String filename, int mode);
		public int chown(String filename, int user, int group);
		public int rename(String oldpath, String newpath);
		public int kill(int pid, int signal);
		public int link(String oldpath, String newpath);
		public int mkdir(String path, int mode);
		public int rmdir(String path);
	}
 
	public static void main(String[] args) {
		POSIX posix = (POSIX) Native.loadLibrary("c", POSIX.class);
		posix.mkdir("/tmp/newdir", 777);
		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.

import com.sun.jna.Library;
import com.sun.jna.Native;
 
/** Simple example of Windows native library declaration and usage. */
public class BeepExample {
	public interface Kernel32 extends Library {
                // FREQUENCY is expressed in hertz and ranges from 37 to 32767
                // DURATION is expressed in milliseconds
		public boolean Beep(int FREQUENCY, int DURATION);
		public void Sleep(int DURATION);
	}
	public static void main(String[] args) {
		Kernel32 lib = (Kernel32) Native.loadLibrary("kernel32", Kernel32.class);
		lib.Beep(698, 500);
		lib.Sleep(500);
		lib.Beep(698, 500);
	}
}