org.scijava.nativelib
Class NativeLoader

java.lang.Object
  org.scijava.nativelib.NativeLoader

public class NativeLoader
extends Object

Provides a means of loading JNI libraries which are stored within a jar.

The library is first extracted to a temporary file, and then loaded with System.load().

The extractor implementation can be replaced, but the default implementation expects to find the library in META-INF/lib/, with its OS-dependent name. It extracts the library underneath a temporary directory, whose name is given by the System property "java.library.tmpdir", defaulting to "tmplib".

This is complicated by the http://java.sun.com/javase/6/docs/technotes/guides/jni/jni-12.html#libmanage - specifically "The same JNI native library cannot be loaded into more than one class loader". In practice this appears to mean "A JNI library on a given absolute path cannot be loaded by more than one classloader". Native libraries that are loaded by the OS dynamic linker as dependencies of JNI libraries are not subject to this restriction.

Native libraries that are loaded as dependencies must be extracted using the library identifier a.k.a. soname (which usually includes a major version number) instead of what was linked against (this can be found using ldd on linux or using otool on OS X). Because they are loaded by the OS dynamic linker and not by explicit invocation within Java, this extractor needs to be aware of them to extract them by alternate means. This is accomplished by listing the base filename in a META-INF/lib/AUTOEXTRACT.LIST classpath resource. This is useful for shipping libraries which are used by code which is not itself aware of the NativeLoader system. The application must call extractRegistered() at some suitably early point in its initialization (before loading any JNI libraries which might require these dependencies), and ensure that JVM is launched with the LD_LIBRARY_PATH environment variable (or other OS-dependent equivalent) set to include the "tmplib" directory (or other directory as overridden by "java.library.tmpdir" as above).

Author:

Richard van der Hoff

Constructor Summary

NativeLoader()

Method Summary

static void	extractRegistered() Extract all libraries registered for auto-extraction by way of META-INF/lib/AUTOEXTRACT.LIST resources.
static JniExtractor	getJniExtractor()
static void	loadLibrary(String libname) Extract the given library from a jar, and load it.
static void	setJniExtractor(JniExtractor jniExtractor)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

NativeLoader

public NativeLoader()

Method Detail

loadLibrary

public static void loadLibrary(String libname)
                        throws IOException

Extract the given library from a jar, and load it.

The default jni extractor expects libraries to be in META-INF/lib/, with their platform-dependent name.

Parameters:

libname - platform-independent library name (as would be passed to System.loadLibrary)

Throws:

IOException - if there is a problem extracting the jni library

SecurityException - if a security manager exists and its checkLink method doesn't allow loading of the specified dynamic library

extractRegistered

public static void extractRegistered()
                              throws IOException

Extract all libraries registered for auto-extraction by way of META-INF/lib/AUTOEXTRACT.LIST resources. The application must call extractRegistered() at some suitably early point in its initialization if it is using libraries packaged in this way.

Throws:

IOException - if there is a problem extracting the libraries

getJniExtractor

public static JniExtractor getJniExtractor()

Returns:

the JniExtractor implementation object.

setJniExtractor

public static void setJniExtractor(JniExtractor jniExtractor)

Parameters:

jniExtractor - JniExtractor implementation to use instead of the default.