Every {@link Class Class} object contains a {@link - * Class#getClassLoader() reference} to the ClassLoader that defined - * it. - * - *
Class objects for array classes are not created by class - * loaders, but are created automatically as required by the Java runtime. - * The class loader for an array class, as returned by {@link - * Class#getClassLoader()} is the same as the class loader for its element - * type; if the element type is a primitive type, then the array class has no - * class loader. - * - *
Applications implement subclasses of ClassLoader in order to - * extend the manner in which the Java virtual machine dynamically loads - * classes. - * - *
Class loaders may typically be used by security managers to indicate - * security domains. - * - *
The ClassLoader class uses a delegation model to search for - * classes and resources. Each instance of ClassLoader has an - * associated parent class loader. When requested to find a class or - * resource, a ClassLoader instance will delegate the search for the - * class or resource to its parent class loader before attempting to find the - * class or resource itself. The virtual machine's built-in class loader, - * called the "bootstrap class loader", does not itself have a parent but may - * serve as the parent of a ClassLoader instance. - * - *
Class loaders that support concurrent loading of classes are known as
- * parallel capable class loaders and are required to register
- * themselves at their class initialization time by invoking the
- * {@link
- * #registerAsParallelCapable ClassLoader.registerAsParallelCapable}
- * method. Note that the ClassLoader class is registered as parallel
- * capable by default. However, its subclasses still need to register themselves
- * if they are parallel capable.
- * In environments in which the delegation model is not strictly
- * hierarchical, class loaders need to be parallel capable, otherwise class
- * loading can lead to deadlocks because the loader lock is held for the
- * duration of the class loading process (see {@link #loadClass
- * loadClass} methods).
- *
- *
Normally, the Java virtual machine loads classes from the local file - * system in a platform-dependent manner. For example, on UNIX systems, the - * virtual machine loads classes from the directory defined by the - * CLASSPATH environment variable. - * - *
However, some classes may not originate from a file; they may originate - * from other sources, such as the network, or they could be constructed by an - * application. The method {@link #defineClass(String, byte[], int, int) - * defineClass} converts an array of bytes into an instance of class - * Class. Instances of this newly defined class can be created using - * {@link Class#newInstance Class.newInstance}. - * - *
The methods and constructors of objects created by a class loader may - * reference other classes. To determine the class(es) referred to, the Java - * virtual machine invokes the {@link #loadClass loadClass} method of - * the class loader that originally created the class. - * - *
For example, an application could create a network class loader to - * download class files from a server. Sample code might look like: - * - *
- * ClassLoader loader = new NetworkClassLoader(host, port);
- * Object main = loader.loadClass("Main", true).newInstance();
- * . . .
- * The network class loader subclass must define the methods {@link - * #findClass findClass} and loadClassData to load a class - * from the network. Once it has downloaded the bytes that make up the class, - * it should use the method {@link #defineClass defineClass} to - * create a class instance. A sample implementation is: - * - *
- * class NetworkClassLoader extends ClassLoader {
- * String host;
- * int port;
- *
- * public Class findClass(String name) {
- * byte[] b = loadClassData(name);
- * return defineClass(name, b, 0, b.length);
- * }
- *
- * private byte[] loadClassData(String name) {
- * // load the class data from the connection
- * . . .
- * }
- * }
- * Any class name provided as a {@link String} parameter to methods in - * ClassLoader must be a binary name as defined by - * The Java™ Language Specification. - * - *
Examples of valid class names include: - *
- * - * @see #resolveClass(Class) - * @since 1.0 - */ -public abstract class ClassLoader { - - @JavaScriptBody(args = {}, body = "") - private static native void registerNatives(); - static { - registerNatives(); - } - - // The parent class loader for delegation - // Note: VM hardcoded the offset of this field, thus all new fields - // must be added *after* it. - private final ClassLoader parent; - - - /** - * Creates a new class loader using the specified parent class loader for - * delegation. - * - *- * "java.lang.String" - * "javax.swing.JSpinner$DefaultEditor" - * "java.security.KeyStore$Builder$FileBuilder$1" - * "java.net.URLClassLoader$3$1" - *
If there is a security manager, its {@link - * SecurityManager#checkCreateClassLoader() - * checkCreateClassLoader} method is invoked. This may result in - * a security exception.
- * - * @param parent - * The parent class loader - * - * @throws SecurityException - * If a security manager exists and its - * checkCreateClassLoader method doesn't allow creation - * of a new class loader. - * - * @since 1.2 - */ - protected ClassLoader(ClassLoader parent) { - throw new SecurityException(); - } - - /** - * Creates a new class loader using the ClassLoader returned by - * the method {@link #getSystemClassLoader() - * getSystemClassLoader()} as the parent class loader. - * - *If there is a security manager, its {@link - * SecurityManager#checkCreateClassLoader() - * checkCreateClassLoader} method is invoked. This may result in - * a security exception.
- * - * @throws SecurityException - * If a security manager exists and its - * checkCreateClassLoader method doesn't allow creation - * of a new class loader. - */ - protected ClassLoader() { - throw new SecurityException(); - } - - // -- Class -- - - /** - * Loads the class with the specified binary name. - * This method searches for classes in the same manner as the {@link - * #loadClass(String, boolean)} method. It is invoked by the Java virtual - * machine to resolve class references. Invoking this method is equivalent - * to invoking {@link #loadClass(String, boolean) loadClass(name, - * false)}. - * - * @param name - * The binary name of the class - * - * @return The resulting Class object - * - * @throws ClassNotFoundException - * If the class was not found - */ - public Class loadClass(String name) throws ClassNotFoundException { - return loadClass(name, false); - } - - /** - * Loads the class with the specified binary name. The - * default implementation of this method searches for classes in the - * following order: - * - *Invoke {@link #findLoadedClass(String)} to check if the class - * has already been loaded.
Invoke the {@link #loadClass(String) loadClass} method - * on the parent class loader. If the parent is null the class - * loader built-in to the virtual machine is used, instead.
Invoke the {@link #findClass(String)} method to find the - * class.
If the class was found using the above steps, and the - * resolve flag is true, this method will then invoke the {@link - * #resolveClass(Class)} method on the resulting Class object. - * - *
Subclasses of ClassLoader are encouraged to override {@link - * #findClass(String)}, rather than this method.
- * - *Unless overridden, this method synchronizes on the result of - * {@link #getClassLoadingLock getClassLoadingLock} method - * during the entire class loading process. - * - * @param name - * The binary name of the class - * - * @param resolve - * If true then resolve the class - * - * @return The resulting Class object - * - * @throws ClassNotFoundException - * If the class could not be found - */ - protected Class loadClass(String name, boolean resolve) - throws ClassNotFoundException - { - synchronized (getClassLoadingLock(name)) { - // First, check if the class has already been loaded - Class c = findLoadedClass(name); - if (c == null) { - try { - if (parent != null) { - c = parent.loadClass(name, false); - } else { - c = findBootstrapClassOrNull(name); - } - } catch (ClassNotFoundException e) { - // ClassNotFoundException thrown if class not found - // from the non-null parent class loader - } - - if (c == null) { - // If still not found, then invoke findClass in order - // to find the class. - c = findClass(name); - -// // this is the defining class loader; record the stats -// sun.misc.PerfCounter.getParentDelegationTime().addTime(t1 - t0); -// sun.misc.PerfCounter.getFindClassTime().addElapsedTimeFrom(t1); -// sun.misc.PerfCounter.getFindClasses().increment(); - } - } - if (resolve) { - resolveClass(c); - } - return c; - } - } - - /** - * Returns the lock object for class loading operations. - * For backward compatibility, the default implementation of this method - * behaves as follows. If this ClassLoader object is registered as - * parallel capable, the method returns a dedicated object associated - * with the specified class name. Otherwise, the method returns this - * ClassLoader object.
- * - * @param className - * The name of the to-be-loaded class - * - * @return the lock for class loading operations - * - * @throws NullPointerException - * If registered as parallel capable and className is null - * - * @see #loadClass(String, boolean) - * - * @since 1.7 - */ - protected Object getClassLoadingLock(String className) { - Object lock = this; - return lock; - } - - /** - * Finds the class with the specified binary name. - * This method should be overridden by class loader implementations that - * follow the delegation model for loading classes, and will be invoked by - * the {@link #loadClass loadClass} method after checking the - * parent class loader for the requested class. The default implementation - * throws a ClassNotFoundException. - * - * @param name - * The binary name of the class - * - * @return The resulting Class object - * - * @throws ClassNotFoundException - * If the class could not be found - * - * @since 1.2 - */ - protected Class findClass(String name) throws ClassNotFoundException { - throw new ClassNotFoundException(name); - } - - /** - * Converts an array of bytes into an instance of class Class. - * Before the Class can be used it must be resolved. This method - * is deprecated in favor of the version that takes a binary name as its first argument, and is more secure. - * - * @param b - * The bytes that make up the class data. The bytes in positions - * off through off+len-1 should have the format - * of a valid class file as defined by - * The Java™ Virtual Machine Specification. - * - * @param off - * The start offset in b of the class data - * - * @param len - * The length of the class data - * - * @return The Class object that was created from the specified - * class data - * - * @throws ClassFormatError - * If the data did not contain a valid class - * - * @throws IndexOutOfBoundsException - * If either off or len is negative, or if - * off+len is greater than b.length. - * - * @throws SecurityException - * If an attempt is made to add this class to a package that - * contains classes that were signed by a different set of - * certificates than this class, or if an attempt is made - * to define a class in a package with a fully-qualified name - * that starts with "{@code java.}". - * - * @see #loadClass(String, boolean) - * @see #resolveClass(Class) - * - * @deprecated Replaced by {@link #defineClass(String, byte[], int, int) - * defineClass(String, byte[], int, int)} - */ - @Deprecated - protected final Class defineClass(byte[] b, int off, int len) - throws ClassFormatError - { - throw new SecurityException(); - } - - /** - * Converts an array of bytes into an instance of class Class. - * Before the Class can be used it must be resolved. - * - *This method assigns a default {@link java.security.ProtectionDomain - * ProtectionDomain} to the newly defined class. The - * ProtectionDomain is effectively granted the same set of - * permissions returned when {@link - * java.security.Policy#getPermissions(java.security.CodeSource) - * Policy.getPolicy().getPermissions(new CodeSource(null, null))} - * is invoked. The default domain is created on the first invocation of - * {@link #defineClass(String, byte[], int, int) defineClass}, - * and re-used on subsequent invocations. - * - *
To assign a specific ProtectionDomain to the class, use - * the {@link #defineClass(String, byte[], int, int, - * java.security.ProtectionDomain) defineClass} method that takes a - * ProtectionDomain as one of its arguments.
- * - * @param name - * The expected binary name of the class, or - * null if not known - * - * @param b - * The bytes that make up the class data. The bytes in positions - * off through off+len-1 should have the format - * of a valid class file as defined by - * The Java™ Virtual Machine Specification. - * - * @param off - * The start offset in b of the class data - * - * @param len - * The length of the class data - * - * @return The Class object that was created from the specified - * class data. - * - * @throws ClassFormatError - * If the data did not contain a valid class - * - * @throws IndexOutOfBoundsException - * If either off or len is negative, or if - * off+len is greater than b.length. - * - * @throws SecurityException - * If an attempt is made to add this class to a package that - * contains classes that were signed by a different set of - * certificates than this class (which is unsigned), or if - * name begins with "java.". - * - * @see #loadClass(String, boolean) - * @see #resolveClass(Class) - * @see java.security.CodeSource - * @see java.security.SecureClassLoader - * - * @since 1.1 - */ - protected final Class defineClass(String name, byte[] b, int off, int len) - throws ClassFormatError - { - throw new SecurityException(); - } - - /** - * Links the specified class. This (misleadingly named) method may be - * used by a class loader to link a class. If the class c has - * already been linked, then this method simply returns. Otherwise, the - * class is linked as described in the "Execution" chapter of - * The Java™ Language Specification. - * - * - * @param c - * The class to link - * - * @throws NullPointerException - * If c is null. - * - * @see #defineClass(String, byte[], int, int) - */ - protected final void resolveClass(Class c) { - resolveClass0(c); - } - - private native void resolveClass0(Class c); - - - /** - * Returns the class with the given binary name if this - * loader has been recorded by the Java virtual machine as an initiating - * loader of a class with that binary name. Otherwise - * null is returned. - * - * @param name - * The binary name of the class - * - * @return The Class object, or null if the class has - * not been loaded - * - * @since 1.1 - */ - protected final Class findLoadedClass(String name) { - if (!checkName(name)) - return null; - return findLoadedClass0(name); - } - - private native final Class findLoadedClass0(String name); - - /** - * Sets the signers of a class. This should be invoked after defining a - * class. - * - * @param c - * The Class object - * - * @param signers - * The signers for the class - * - * @since 1.1 - */ - protected final void setSigners(Class c, Object[] signers) { - //c.setSigners(signers); - throw new UnsupportedOperationException(); - } - - - // -- Resource -- - - /** - * Finds the resource with the given name. A resource is some data - * (images, audio, text, etc) that can be accessed by class code in a way - * that is independent of the location of the code. - * - *The name of a resource is a '/'-separated path name that - * identifies the resource. - * - *
This method will first search the parent class loader for the - * resource; if the parent is null the path of the class loader - * built-in to the virtual machine is searched. That failing, this method - * will invoke {@link #findResource(String)} to find the resource.
- * - * @param name - * The resource name - * - * @return A URL object for reading the resource, or - * null if the resource could not be found or the invoker - * doesn't have adequate privileges to get the resource. - * - * @since 1.1 - */ - public URL getResource(String name) { - URL url; - if (parent != null) { - url = parent.getResource(name); - } else { - url = getBootstrapResource(name); - } - if (url == null) { - url = findResource(name); - } - return url; - } - - /** - * Finds all the resources with the given name. A resource is some data - * (images, audio, text, etc) that can be accessed by class code in a way - * that is independent of the location of the code. - * - *The name of a resource is a /-separated path name that - * identifies the resource. - * - *
The search order is described in the documentation for {@link - * #getResource(String)}.
- * - * @param name - * The resource name - * - * @return An enumeration of {@link java.net.URL URL} objects for - * the resource. If no resources could be found, the enumeration - * will be empty. Resources that the class loader doesn't have - * access to will not be in the enumeration. - * - * @throws IOException - * If I/O errors occur - * - * @see #findResources(String) - * - * @since 1.2 - */ - public EnumerationThe search order is described in the documentation for {@link - * #getSystemResource(String)}.
- * - * @param name - * The resource name - * - * @return An enumeration of resource {@link java.net.URL URL} - * objects - * - * @throws IOException - * If I/O errors occur - - * @since 1.2 - */ - public static EnumerationThe search order is described in the documentation for {@link - * #getResource(String)}.
- * - * @param name - * The resource name - * - * @return An input stream for reading the resource, or null - * if the resource could not be found - * - * @since 1.1 - */ - public InputStream getResourceAsStream(String name) { - URL url = getResource(name); - try { - return url != null ? url.openStream() : null; - } catch (IOException e) { - return null; - } - } - - /** - * Open for reading, a resource of the specified name from the search path - * used to load classes. This method locates the resource through the - * system class loader (see {@link #getSystemClassLoader()}). - * - * @param name - * The resource name - * - * @return An input stream for reading the resource, or null - * if the resource could not be found - * - * @since 1.1 - */ - public static InputStream getSystemResourceAsStream(String name) { - URL url = getSystemResource(name); - try { - return url != null ? url.openStream() : null; - } catch (IOException e) { - return null; - } - } - - - // -- Hierarchy -- - - /** - * Returns the parent class loader for delegation. Some implementations may - * use null to represent the bootstrap class loader. This method - * will return null in such implementations if this class loader's - * parent is the bootstrap class loader. - * - *If a security manager is present, and the invoker's class loader is - * not null and is not an ancestor of this class loader, then this - * method invokes the security manager's {@link - * SecurityManager#checkPermission(java.security.Permission) - * checkPermission} method with a {@link - * RuntimePermission#RuntimePermission(String) - * RuntimePermission("getClassLoader")} permission to verify - * access to the parent class loader is permitted. If not, a - * SecurityException will be thrown.
- * - * @return The parent ClassLoader - * - * @throws SecurityException - * If a security manager exists and its checkPermission - * method doesn't allow access to this class loader's parent class - * loader. - * - * @since 1.2 - */ - public final ClassLoader getParent() { - throw new SecurityException(); - } - - /** - * Returns the system class loader for delegation. This is the default - * delegation parent for new ClassLoader instances, and is - * typically the class loader used to start the application. - * - *This method is first invoked early in the runtime's startup - * sequence, at which point it creates the system class loader and sets it - * as the context class loader of the invoking Thread. - * - *
The default system class loader is an implementation-dependent - * instance of this class. - * - *
If the system property "java.system.class.loader" is defined - * when this method is first invoked then the value of that property is - * taken to be the name of a class that will be returned as the system - * class loader. The class is loaded using the default system class loader - * and must define a public constructor that takes a single parameter of - * type ClassLoader which is used as the delegation parent. An - * instance is then created using this constructor with the default system - * class loader as the parameter. The resulting class loader is defined - * to be the system class loader. - * - *
If a security manager is present, and the invoker's class loader is - * not null and the invoker's class loader is not the same as or - * an ancestor of the system class loader, then this method invokes the - * security manager's {@link - * SecurityManager#checkPermission(java.security.Permission) - * checkPermission} method with a {@link - * RuntimePermission#RuntimePermission(String) - * RuntimePermission("getClassLoader")} permission to verify - * access to the system class loader. If not, a - * SecurityException will be thrown.
- * - * @return The system ClassLoader for delegation, or - * null if none - * - * @throws SecurityException - * If a security manager exists and its checkPermission - * method doesn't allow access to the system class loader. - * - * @throws IllegalStateException - * If invoked recursively during the construction of the class - * loader specified by the "java.system.class.loader" - * property. - * - * @throws Error - * If the system property "java.system.class.loader" - * is defined but the named class could not be loaded, the - * provider class does not define the required constructor, or an - * exception is thrown by that constructor when it is invoked. The - * underlying cause of the error can be retrieved via the - * {@link Throwable#getCause()} method. - * - * @revised 1.4 - */ - public static ClassLoader getSystemClassLoader() { - throw new SecurityException(); - } - - // Returns true if the specified class loader can be found in this class - // loader's delegation chain. - boolean isAncestor(ClassLoader cl) { - ClassLoader acl = this; - do { - acl = acl.parent; - if (cl == acl) { - return true; - } - } while (acl != null); - return false; - } - - private boolean checkName(String name) { - throw new UnsupportedOperationException(); - } - - private Class findBootstrapClassOrNull(String name) { - throw new UnsupportedOperationException(); - } - - private static URL getBootstrapResource(String name) { - throw new UnsupportedOperationException(); - } - - private static Enumeration