diff options
Diffstat (limited to 'libjava/java/lang/ClassLoader.java')
| -rw-r--r-- | libjava/java/lang/ClassLoader.java | 124 |
1 files changed, 115 insertions, 9 deletions
diff --git a/libjava/java/lang/ClassLoader.java b/libjava/java/lang/ClassLoader.java index 1b3b310..ea6546c 100644 --- a/libjava/java/lang/ClassLoader.java +++ b/libjava/java/lang/ClassLoader.java @@ -13,7 +13,6 @@ package java.lang; import java.io.InputStream; import java.io.IOException; import java.net.URL; -import java.net.URLConnection; import java.security.AllPermission; import java.security.CodeSource; import java.security.Permission; @@ -23,13 +22,68 @@ import java.security.ProtectionDomain; import java.util.*; /** - * The class <code>ClassLoader</code> is intended to be subclassed by - * applications in order to describe new ways of loading classes, - * such as over the network. + * The ClassLoader is a way of customizing the way Java gets its classes + * and loads them into memory. The verifier and other standard Java things + * still run, but the ClassLoader is allowed great flexibility in determining + * where to get the classfiles and when to load and resolve them. For that + * matter, a custom ClassLoader can perform on-the-fly code generation or + * modification! * - * @author Kresten Krab Thorup + * <p>Every classloader has a parent classloader that is consulted before + * the 'child' classloader when classes or resources should be loaded. + * This is done to make sure that classes can be loaded from an hierarchy of + * multiple classloaders and classloaders do not accidentially redefine + * already loaded classes by classloaders higher in the hierarchy. + * + * <p>The grandparent of all classloaders is the bootstrap classloader, which + * loads all the standard system classes as implemented by GNU Classpath. The + * other special classloader is the system classloader (also called + * application classloader) that loads all classes from the CLASSPATH + * (<code>java.class.path</code> system property). The system classloader + * is responsible for finding the application classes from the classpath, + * and delegates all requests for the standard library classes to its parent + * the bootstrap classloader. Most programs will load all their classes + * through the system classloaders. + * + * <p>The bootstrap classloader in GNU Classpath is implemented as a couple of + * static (native) methods on the package private class + * <code>java.lang.VMClassLoader</code>, the system classloader is an + * instance of <code>gnu.java.lang.SystemClassLoader</code> + * (which is a subclass of <code>java.net.URLClassLoader</code>). + * + * <p>Users of a <code>ClassLoader</code> will normally just use the methods + * <ul> + * <li> <code>loadClass()</code> to load a class.</li> + * <li> <code>getResource()</code> or <code>getResourceAsStream()</code> + * to access a resource.</li> + * <li> <code>getResources()</code> to get an Enumeration of URLs to all + * the resources provided by the classloader and its parents with the + * same name.</li> + * </ul> + * + * <p>Subclasses should implement the methods + * <ul> + * <li> <code>findClass()</code> which is called by <code>loadClass()</code> + * when the parent classloader cannot provide a named class.</li> + * <li> <code>findResource()</code> which is called by + * <code>getResource()</code> when the parent classloader cannot provide + * a named resource.</li> + * <li> <code>findResources()</code> which is called by + * <code>getResource()</code> to combine all the resources with the + * same name from the classloader and its parents.</li> + * <li> <code>findLibrary()</code> which is called by + * <code>Runtime.loadLibrary()</code> when a class defined by the + * classloader wants to load a native library.</li> + * </ul> + * + * @author John Keiser + * @author Mark Wielaard + * @author Eric Blake + * @author Kresten Krab Thorup + * @see Class + * @since 1.0 + * @status still missing 1.4 functionality */ - public abstract class ClassLoader { /** @@ -73,12 +127,40 @@ public abstract class ClassLoader // Package visible for use by Class. Map classAssertionStatus; - private ClassLoader parent; + /** + * The classloader that is consulted before this classloader. + * If null then the parent is the bootstrap classloader. + */ + private final ClassLoader parent; + + /** + * All packages defined by this classloader. It is not private in order to + * allow native code (and trusted subclasses) access to this field. + */ private HashMap definedPackages = new HashMap(); + /** + * Returns the parent of this classloader. If the parent of this + * classloader is the bootstrap classloader then this method returns + * <code>null</code>. A security check may be performed on + * <code>RuntimePermission("getClassLoader")</code>. + * + * @throws SecurityException if the security check fails + * @since 1.2 + */ public final ClassLoader getParent () { - /* FIXME: security */ + // Check if we may return the parent classloader + SecurityManager sm = System.getSecurityManager(); + if (sm != null) + { + /* FIXME: security, getClassContext() not implemented. + Class c = VMSecurityManager.getClassContext()[1]; + ClassLoader cl = c.getClassLoader(); + if (cl != null && cl != this) + sm.checkPermission(new RuntimePermission("getClassLoader")); + */ + } return parent; } @@ -449,7 +531,8 @@ public abstract class ClassLoader else { InternalError e - = new InternalError ("unexpected exception during linking"); + = new InternalError ("unexpected exception during linking: " + + clazz.getName()); e.initCause (x); throw e; } @@ -521,6 +604,8 @@ public abstract class ClassLoader * null when the package is not defined by this classloader or one of its * parents. * + * @param name the package name to find + * @return the package, if defined * @since 1.2 */ protected Package getPackage(String name) @@ -546,6 +631,7 @@ public abstract class ClassLoader /** * Returns all Package objects defined by this classloader and its parents. * + * @return an array of all defined packages * @since 1.2 */ protected Package[] getPackages() @@ -577,6 +663,26 @@ public abstract class ClassLoader return allPackages; } + /** + * Called by <code>Runtime.loadLibrary()</code> to get an absolute path + * to a (system specific) library that was requested by a class loaded + * by this classloader. The default implementation returns + * <code>null</code>. It should be implemented by subclasses when they + * have a way to find the absolute path to a library. If this method + * returns null the library is searched for in the default locations + * (the directories listed in the <code>java.library.path</code> system + * property). + * + * @param name the (system specific) name of the requested library + * @return the full pathname to the requested library, or null + * @see Runtime#loadLibrary() + * @since 1.2 + */ + protected String findLibrary(String name) + { + return null; + } + /** * Returns a class found in a system-specific way, typically * via the <code>java.class.path</code> system property. Loads the |