Adding New Paths for Native Libraries at Runtime in Java

Adding new paths for native libraries at runtime in Java

[This solution don't work with Java 10+]

It seems impossible without little hacking (i.e. accessing private fields of the ClassLoader class)

This blog provide 2 ways of doing it.

For the record, here is the short version.

Option 1: fully replace java.library.path with the new value)

public static void setLibraryPath(String path) throws Exception {
    System.setProperty("java.library.path", path);

    //set sys_paths to null so that java.library.path will be reevalueted next time it is needed
    final Field sysPathsField = ClassLoader.class.getDeclaredField("sys_paths");
    sysPathsField.setAccessible(true);
    sysPathsField.set(null, null);
}

Option 2: add a new path to the current java.library.path

/**
* Adds the specified path to the java library path
*
* @param pathToAdd the path to add
* @throws Exception
*/
public static void addLibraryPath(String pathToAdd) throws Exception{
    final Field usrPathsField = ClassLoader.class.getDeclaredField("usr_paths");
    usrPathsField.setAccessible(true);

    //get array of paths
    final String[] paths = (String[])usrPathsField.get(null);

    //check if the path to add is already present
    for(String path : paths) {
        if(path.equals(pathToAdd)) {
            return;
        }
    }

    //add the new path
    final String[] newPaths = Arrays.copyOf(paths, paths.length + 1);
    newPaths[newPaths.length-1] = pathToAdd;
    usrPathsField.set(null, newPaths);
}

How can I configure java.library.path at runtime?

First option is to set java.library.path to different value

/**
 * Sets the java library path to the specified path
 *
 * @param path the new library path
 * @throws Exception
 */
public static void setLibraryPath(String path) throws Exception {
    System.setProperty("java.library.path", path);

    //set sys_paths to null
    final Field sysPathsField = ClassLoader.class.getDeclaredField("sys_paths");
    sysPathsField.setAccessible(true);
    sysPathsField.set(null, null);
}

The second option is to append your path to java.library.path

/**
* Adds the specified path to the java library path
*
* @param pathToAdd the path to add
* @throws Exception
*/
public static void addLibraryPath(String pathToAdd) throws Exception{
    final Field usrPathsField = ClassLoader.class.getDeclaredField("usr_paths");
    usrPathsField.setAccessible(true);

    //get array of paths
    final String[] paths = (String[])usrPathsField.get(null);

    //check if the path to add is already present
    for(String path : paths) {
        if(path.equals(pathToAdd)) {
            return;
        }
    }

    //add the new path
    final String[] newPaths = Arrays.copyOf(paths, paths.length + 1);
    newPaths[newPaths.length-1] = pathToAdd;
    usrPathsField.set(null, newPaths);
}

Taken from fahd.blog

How to add native library to java.library.path with Eclipse launch (instead of overriding it)

Had forgotten this issue... I was actually asking with Eclipse, sorry for not stating that originally.
And the answer seems to be too simple (at least with 3.5; probably with older versions also):

Java run configuration's Arguments : VM arguments:

-Djava.library.path="${workspace_loc:project}\lib;${env_var:PATH}"

Must not forget the quotation marks, otherwise there are problems with spaces in PATH.

Java.library.path setting programmatically

No you can't. This property is a read only value. You can change it at JVM launchin time with:

-Djava.library.path=your_path

If you want to load a library from a specific location, you can use System.load(libraryPath) instead with the full path to the library.

How to set the java.library.path from Eclipse

Don't mess with the library path! Eclipse builds it itself!

Instead, go into the library settings for your projects and, for each jar/etc that requires a native library, expand it in the Libraries tab. In the tree view there, each library has items for source/javadoc and native library locations.

Specifically: select Project, right click -> Properties / Java Build Path / Libraries tab, select a .jar, expand it, select Native library location, click Edit, folder chooser dialog will appear)

Messing with the library path on the command line should be your last ditch effort, because you might break something that is already properly set by eclipse.

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