com.wolfram.jlink
Class JLinkClassLoader

java.lang.Object
  java.lang.ClassLoader
      java.security.SecureClassLoader
          java.net.URLClassLoader
              com.wolfram.jlink.JLinkClassLoader

public class JLinkClassLoader
extends java.net.URLClassLoader

This class loader does all the loading of classes requested via the Mathematica function LoadJavaClass[]. It also loads native libraries and resources used by classes that it loads. The directories and files it searches for classes and other resources are provided to it via the addLocations() method, which is called from Mathematica during every call to LoadJavaClass[]. The JLink Mathematica code manages the class path locations, including providing a default set of extra dirs. Directories are automatically searched for jar or zip files they contain, so you do not have to name jar files explicitly in addLocations(), although you can if you want to limit the search to a specific jar file in a directory.

Most uses of this class are internal to J/Link, and most programmers will never deal with it directly. One reason to use this class is if you want to load a class in Java code that is found in the special set of extra locations that this class loader knows about (such as Java subdirectories of Mathematica application directories). Each KernelLink has a JLinkClassLoader instance associated with it, which you can retrieve using the link's getClassLoader() method. Here is an example of loading a class from a special J/Link-specific directory.

 Class cls = Class.forName("Some.class.that.only.JLink.can.find", ml.getClassLoader());

You can add directories and jar files to the search path using the addLocations() method:

 // This is equivalent to calling AddToClassPath["/some/dir", "/another/dir"] in Mathematica.
 ml.getClassLoader().addLocations(new String[]{"/some/dir", "/another/dir"}, true);

If you using this class from a standalone Java program you should first call the KernelLink method enableObjectReferences() to initialize the class loader with the special Mathematica-specific locations for Java classes.

Another advanced reason to use this class is if you need the class loader to have a specific parent loader, because that parent loader has certain capabilities or can load classes from certain locations that J/Link would otherwise not know about.

 KernelLink ml = MathLinkFactory.createKernelLink(...);
 ml.discardAnswer();
 ml.setClassLoader(new JLinkClassLoader(mySpecialParentClassLoader));
 ml.enableObjectReferences();

The class has some static methods that are intended to be used from Mathematica code. Here is an example that loads a resource from a Mathematica application's Java subdirectory:

 (* Mathematica code *)
 LoadJavaClass["com.wolfram.jlink.JLinkClassLoader"];
 JLinkClassLoader`getInstance[]@getResource["myImage.gif"];

When using the class from Java, you will always have a specific link in hand, so instead of calling static methods you should obtain a JLinkClassLoader instance from the link using its getClassLoader() method and then call instance methods.

Since:

3.0

See Also:

KernelLink.getClassLoader(), KernelLink.setClassLoader(JLinkClassLoader)

Constructor Summary

JLinkClassLoader()
Constructs a new JLinkClassLoader instance.

JLinkClassLoader(java.lang.ClassLoader parent)
Constructs a new JLinkClassLoader instance that has the given class loader as its parent loader.

Method Summary

void	addLocations(java.lang.String[] locations, boolean searchForJars) Adds URLs, directories, and jar files in which this classloader will look for classes.
java.lang.Class	classFromBytes(java.lang.String className, byte[] bytes) Converts an array of bytes into an instance of class Class.
static java.lang.Class	classFromName(java.lang.String name) Loads the class with the given name using the JLinkClassLoader instance of the currently-active link.
protected java.lang.String	findLibrary(java.lang.String libName)
java.lang.String[]	getClassPath() Gives the set of locations in which this class loader will search for classes.
static JLinkClassLoader	getInstance() Retrieves the JLinkClassLoader instance being used by the currently-active link.

Methods inherited from class java.net.URLClassLoader

addURL, definePackage, findClass, findResource, findResources, getPermissions, getURLs, newInstance, newInstance

Methods inherited from class java.security.SecureClassLoader

defineClass, defineClass

Methods inherited from class java.lang.ClassLoader

clearAssertionStatus, defineClass, defineClass, defineClass, defineClass, definePackage, findLoadedClass, findSystemClass, getPackage, getPackages, getParent, getResource, getResourceAsStream, getResources, getSystemClassLoader, getSystemResource, getSystemResourceAsStream, getSystemResources, loadClass, loadClass, resolveClass, setClassAssertionStatus, setDefaultAssertionStatus, setPackageAssertionStatus, setSigners

Methods inherited from class java.lang.Object

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

Constructor Detail

JLinkClassLoader

public JLinkClassLoader()

Constructs a new JLinkClassLoader instance. Only advanced programmers will need to use this.

Since:

3.0

JLinkClassLoader

public JLinkClassLoader(java.lang.ClassLoader parent)

Constructs a new JLinkClassLoader instance that has the given class loader as its parent loader. Only advanced programmers will need to use this.

Since:

3.0

Method Detail

getInstance

public static JLinkClassLoader getInstance()

Retrieves the JLinkClassLoader instance being used by the currently-active link. This method is intended to be called only from Mathematica, where the "active link" is well-defined (it is the link on which the call is coming in on).

Since:

3.0

classFromName

public static java.lang.Class classFromName(java.lang.String name)
                                     throws java.lang.ClassNotFoundException

Loads the class with the given name using the JLinkClassLoader instance of the currently-active link. This method is intended to be called only from Mathematica, where the "active link" is well-defined (it is the link on which the call is coming in on).

Throws:

java.lang.ClassNotFoundException

Since:

3.0

addLocations

public void addLocations(java.lang.String[] locations,
                         boolean searchForJars)

Adds URLs, directories, and jar files in which this classloader will look for classes. The elements of the locations array must be full paths to directories or jar or zip files, or http URLs. The searchForJars parameter determines whether directories will be automatically searched for any jar files they contain.

Since:

3.0

getClassPath

public java.lang.String[] getClassPath()

Gives the set of locations in which this class loader will search for classes. Only the locations known by this loader, not its parent loader, are returned.

Since:

3.0

classFromBytes

public java.lang.Class classFromBytes(java.lang.String className,
                                      byte[] bytes)

Converts an array of bytes into an instance of class Class. This method is effectively a public export of the protected ClassLoader method defineClass(). It exists mainly for future internal uses within J/Link applications.

Since:

3.0

findLibrary

protected java.lang.String findLibrary(java.lang.String libName)

Overrides:

findLibrary in class java.lang.ClassLoader