| java.lang.Object
 java.lang.ClassLoader
edu.rice.cs.util.classloader.StickyClassLoader
| StickyClassLoader | | public class StickyClassLoader extends ClassLoader (Code) | | A
ClassLoader that works as the union of two classloaders, but always tries to delegate to the first of
these. The purpose for this class is to ensure that classes loaded transitively due to some class's loading are
also loaded with the right classloader. Here's the problem: Say that class A contains a reference to class B, but
the specific B is unknown to clients of class A. Class A is loadable by the standard classloader, but class B needs
to be loaded with a (known) custom classloader.
If A were loaded using the standard classloader, it would fail because this would cause the transitive loading of
B to be done by the system loader as well. If A were loaded with the custom loader, the same thing would happen --
the custom loader would delegate to the system loader to load A (since it doesn't load non-custom-loader-requiring
classes), but this would associate class A with the system classloader. (Every class is associated with the loader
that called
ClassLoader.defineClass to define it in the JVM.) This association would make B be loaded by
the standard loader!
To get around this problem, we use this class, which acts mostly as a union of two classloaders. The trick, however,
is that the StickyClassLoader has itself associated with all classes it loads, even though the actual work is done
by the two loaders it delegates to. (It does this by calling
ClassLoader.findResource on the subordinate
loaders to get the class data, but then by calling
ClassLoader.defineClass itself to preserve the
association.
version:
$Id: StickyClassLoader.java 4255 2007-08-28 19:17:37Z mgricken $ |
| Method Summary | |
| protected Class | _loadWithSecondary(String name)
Try to load the class with the given name with the secondary (new) loader. | | public URL | getResource(String name)
Gets the requested resource, looking first in the new loader and then in the old loader. | | protected Class | loadClass(String name, boolean resolve)
Loads the given class, delegating first to the new class loader and then second to the old class loader. |
| StickyClassLoader | | public StickyClassLoader(ClassLoader newLoader, ClassLoader oldLoader)(Code) | | Creates a sticky class loader with the given primary and secondary loaders to join together. All classes will be
attempted to be loaded with the primary loader, and the secondary will be used as a fallback.
Parameters:
newLoader - Primary loader
Parameters:
oldLoader - Secondary loader |
| StickyClassLoader | | public StickyClassLoader(ClassLoader newLoader, ClassLoader oldLoader, String[] classesToLoadWithOld)(Code) | | Creates a sticky class loader with the given primary and secondary loaders to join together. All classes will be
attempted to be loaded with the primary loader
(except for classes in classesToLoadWithOld),
and the secondary will be used as a fallback.
Parameters:
newLoader - Primary loader
Parameters:
oldLoader - Secondary loader
Parameters:
classesToLoadWithOld - All class names in this array will be loaded only with the secondary classloader. Thisis vital to ensure that only one copy of some classes are loaded, since two differently loaded versions ofa class act totally independently! (That is, they have different, incompatible types.) Often it'll be necessary to make key interfaces that are used between components get loaded via one standard classloader, to ensure that things can be cast to that interface. |
| _loadWithSecondary | | protected Class _loadWithSecondary(String name) throws ClassNotFoundException(Code) | | Try to load the class with the given name with the secondary (new) loader. Uses getResource to find the class.
Parameters:
name - Name of the class to load. |
| getResource | | public URL getResource(String name)(Code) | | Gets the requested resource, looking first in the new loader and then in the old loader.
Parameters:
name - Name of resource to find URL of the resource if found/accessible, or null if not. |
| loadClass | | protected Class loadClass(String name, boolean resolve) throws ClassNotFoundException(Code) | | Loads the given class, delegating first to the new class loader and then second to the old class loader. The
returned Class object will have its ClassLoader (
Class.getClassLoader ) set to be this. This is very
important because it causes classes that are loaded due to this class being loaded (ancestor classes/interfaces,
referenced classes, etc) to use the same loader. There are a few exceptions to this explanation:
- If the class is in java.* or javax.*, it will be loaded using
ClassLoader.getSystemClassLoader . This
is because only the system loader is allowed to load system classes! Also: sun.*.
- If the class name is in the list of classes to load with the old class loader (passed to constructor), the new
loader is not considered when trying to load the class. This is useful to make sure that certain classes (or
interfaces) only have one copy in the system, to ensure that you can cast to that
class/interface regardless of which loader loaded the other class.
|
| Methods inherited from java.lang.ClassLoader | public synchronized void clearAssertionStatus()(Code)(Java Doc)
final protected Class defineClass(byte[] b, int off, int len) throws ClassFormatError(Code)(Java Doc)
final protected Class defineClass(String name, byte[] b, int off, int len) throws ClassFormatError(Code)(Java Doc)
final protected Class defineClass(String name, byte[] b, int off, int len, ProtectionDomain protectionDomain) throws ClassFormatError(Code)(Java Doc)
final protected Class defineClass(String name, java.nio.ByteBuffer b, ProtectionDomain protectionDomain) throws ClassFormatError(Code)(Java Doc)
protected Package definePackage(String name, String specTitle, String specVersion, String specVendor, String implTitle, String implVersion, String implVendor, URL sealBase) throws IllegalArgumentException(Code)(Java Doc)
protected Class findClass(String name) throws ClassNotFoundException(Code)(Java Doc)
protected String findLibrary(String libname)(Code)(Java Doc)
final protected Class findLoadedClass(String name)(Code)(Java Doc)
protected URL findResource(String name)(Code)(Java Doc)
protected Enumeration<URL> findResources(String name) throws IOException(Code)(Java Doc)
final protected Class findSystemClass(String name) throws ClassNotFoundException(Code)(Java Doc)
protected Package getPackage(String name)(Code)(Java Doc)
protected Package[] getPackages()(Code)(Java Doc)
final public ClassLoader getParent()(Code)(Java Doc)
public URL getResource(String name)(Code)(Java Doc)
public InputStream getResourceAsStream(String name)(Code)(Java Doc)
public Enumeration<URL> getResources(String name) throws IOException(Code)(Java Doc)
public static ClassLoader getSystemClassLoader()(Code)(Java Doc)
public static URL getSystemResource(String name)(Code)(Java Doc)
public static InputStream getSystemResourceAsStream(String name)(Code)(Java Doc)
public static Enumeration<URL> getSystemResources(String name) throws IOException(Code)(Java Doc)
public Class loadClass(String name) throws ClassNotFoundException(Code)(Java Doc)
protected synchronized Class loadClass(String name, boolean resolve) throws ClassNotFoundException(Code)(Java Doc)
final protected void resolveClass(Class c)(Code)(Java Doc)
public synchronized void setClassAssertionStatus(String className, boolean enabled)(Code)(Java Doc)
public synchronized void setDefaultAssertionStatus(boolean enabled)(Code)(Java Doc)
public synchronized void setPackageAssertionStatus(String packageName, boolean enabled)(Code)(Java Doc)
final protected void setSigners(Class c, Object[] signers)(Code)(Java Doc)
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