Usually the native libraries are passed to the VM with the property java.library.path. This is not pratical when we want to provide a single jar, and we cannot pass an URL to System#load(String).
Therefore we adopt the strategy to copy the native library contained in the jar (or simply classpath) in the system temporary folder and than we
pass this filename to System#load(String).
As for the standard JDK method, this one should be invoked at classloading:
static {
try {
loadLibrary("my.package", "HelloWorld");
} catch (IOException e) {
// handle this exception
}
}
This is our implementation:
/**
* Load native libraries packed in a jar.
*
* @param pkg
* The package where the shared library (for example .so or .ddl)
* is.
* @param libname
* The system indipendent name (for example HelloWorld for
* libHelloWorld.so under linux or HelloWorld.dll under windows).
* @throws IOException
*/
static public void loadLibrary(String pkg, String libname) throws IOException {
String syslibname = System.mapLibraryName(libname);
String tmpdir = System.getProperty("java.io.tmpdir");
File file = new File(tmpdir + File.separator + syslibname);
if (!file.exists()) {
String resourcename = "/" + pkg.replace('.', '/') + "/" + syslibname;
writeToFile(GtkVersion.class.getResourceAsStream(resourcename), file);
}
System.load(file.getAbsolutePath());
}
static private void writeToFile(InputStream stream, File file) throws IOException {
OutputStream os = null;
try {
os = new FileOutputStream(file);
byte buffer[] = new byte[4096];
int len = 0;
while ((len = stream.read(buffer)) > 0) {
os.write(buffer, 0, len);
}
} finally {
if (os != null) {
os.close();
}
stream.close();
}
}
