classloader.java

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   * @return the requested Class
   * @throws ClassNotFoundException when the class can not be found
   * @since 1.2
   */   
  protected Class findClass (String name)
    throws ClassNotFoundException
  {
    throw new ClassNotFoundException (name);
  }

  // Protection Domain definitions 
  // FIXME: should there be a special protection domain used for native code?
  
  // The permission required to check what a classes protection domain is.
  static final Permission protectionDomainPermission
    = new RuntimePermission("getProtectionDomain");
  // The protection domain returned if we cannot determine it. 
  static ProtectionDomain unknownProtectionDomain;
  // Protection domain to use when a class is defined without one specified.
  static ProtectionDomain defaultProtectionDomain;

  static
  {
    Permissions permissions = new Permissions();
    permissions.add(new AllPermission());
    unknownProtectionDomain = new ProtectionDomain(null, permissions);  

    CodeSource cs = new CodeSource(null, null);
    defaultProtectionDomain =
      new ProtectionDomain(cs, Policy.getPolicy().getPermissions(cs));
  }

  /** 
   * Defines a class, given the class-data.  According to the JVM, this
   * method should not be used; instead use the variant of this method
   * in which the name of the class being defined is specified
   * explicitly.   
   * <P>
   * If the name of the class, as specified (implicitly) in the class
   * data, denotes a class which has already been loaded by this class
   * loader, an instance of
   * <code>java.lang.ClassNotFoundException</code> will be thrown.
   *
   * @param     data    bytes in class file format.
   * @param     off     offset to start interpreting data.
   * @param     len     length of data in class file.
   * @return    the class defined.
   * @exception java.lang.ClassNotFoundException 
   * @exception java.lang.LinkageError
   * @see ClassLoader#defineClass(String,byte[],int,int) */
  protected final Class defineClass(byte[] data, int off, int len) 
    throws ClassFormatError
  {
    return defineClass (null, data, off, len, defaultProtectionDomain);
  }

  /**
   * Helper to define a class using a string of bytes without a
   * ProtectionDomain. Subclasses should call this method from their
   * <code>findClass()</code> implementation. The name should use '.'
   * separators, and discard the trailing ".class".  The default protection
   * domain has the permissions of
   * <code>Policy.getPolicy().getPermissions(new CodeSource(null, null))<code>.
   *
   * @param name the name to give the class, or null if unknown
   * @param data the data representing the classfile, in classfile format
   * @param offset the offset into the data where the classfile starts
   * @param len the length of the classfile data in the array
   * @return the class that was defined
   * @throws ClassFormatError if data is not in proper classfile format
   * @throws IndexOutOfBoundsException if offset or len is negative, or
   *         offset + len exceeds data
   * @throws SecurityException if name starts with "java."
   * @since 1.1
   */
  protected final Class defineClass(String name, byte[] data, int off, int len)
    throws ClassFormatError
  {
    return defineClass (name, data, off, len, defaultProtectionDomain);
  }
  
  /** 
   * Defines a class, given the class-data.  This is preferable
   * over <code>defineClass(byte[],off,len)</code> since it is more
   * secure.  If the expected name does not match that of the class
   * file, <code>ClassNotFoundException</code> is thrown.  If
   * <code>name</code> denotes the name of an already loaded class, a
   * <code>LinkageError</code> is thrown.
   * <p>
   * 
   * FIXME: How do we assure that the class-file data is not being
   * modified, simultaneously with the class loader running!?  If this
   * was done in some very clever way, it might break security.  
   * Right now I am thinking that defineclass should make sure never to
   * read an element of this array more than once, and that that would
   * assure the ``immutable'' appearance.  It is still to be determined
   * if this is in fact how defineClass operates.
   *
   * @param     name    the expected name.
   * @param     data    bytes in class file format.
   * @param     off     offset to start interpreting data.
   * @param     len     length of data in class file.
   * @param     protectionDomain security protection domain for the class.
   * @return    the class defined.
   * @exception java.lang.ClassNotFoundException 
   * @exception java.lang.LinkageError
   */
  protected final synchronized Class defineClass(String name,
						 byte[] data,
						 int off,
						 int len,
						 ProtectionDomain protectionDomain)
    throws ClassFormatError
  {
    if (data==null || data.length < off+len || off<0 || len<0)
      throw new ClassFormatError ("arguments to defineClass "
				  + "are meaningless");

    // as per 5.3.5.1
    if (name != null && findLoadedClass (name) != null)
      throw new java.lang.LinkageError ("class " 
					+ name 
					+ " already loaded");

    if (protectionDomain == null)
      protectionDomain = defaultProtectionDomain;

    try
      {
	Class retval = defineClass0 (name, data, off, len, protectionDomain);
	loadedClasses.put(retval.getName(), retval);
	return retval;
      }
    catch (LinkageError x)
      {
	throw x;		// rethrow
      }
    catch (VirtualMachineError x)
      {
	throw x;		// rethrow
      }
    catch (Throwable x)
      {
	// This should never happen, or we are beyond spec.  
      	InternalError r = new InternalError ("Unexpected exception "
					     + "while defining class "
					     + name);
	r.initCause(x);
	throw r;
      }
  }

  /** This is the entry point of defineClass into the native code */
  private native Class defineClass0 (String name,
				     byte[] data,
				     int off,
				     int len,
				     ProtectionDomain protectionDomain)
    throws ClassFormatError;

  /** 
   * Link the given class.  This will bring the class to a state where
   * the class initializer can be run.  Linking involves the following
   * steps: 
   * <UL>
   * <LI>  Prepare (allocate and internalize) the constant strings that
   *       are used in this class.
   * <LI>  Allocate storage for static fields, and define the layout
   *       of instance fields.
   * <LI>  Perform static initialization of ``static final'' int,
   *       long, float, double and String fields for which there is a
   *       compile-time constant initializer.
   * <LI>  Create the internal representation of the ``vtable''.
   * </UL>
   * For <code>gcj</code>-compiled classes, only the first step is
   * performed.  The compiler will have done the rest already.
   * <P>
   * This is called by the system automatically,
   * as part of class initialization; there is no reason to ever call
   * this method directly.  
   * <P> 
   * For historical reasons, this method has a name which is easily
   * misunderstood.  Java classes are never ``resolved''.  Classes are
   * linked; whereas method and field references are resolved.
   *
   * @param     clazz the class to link.
   * @exception java.lang.LinkageError
   */
  protected final void resolveClass(Class clazz)
  {
    resolveClass0(clazz);
  }

  static void resolveClass0(Class clazz)
  {
    synchronized (clazz)
      {
	try
	  {
	    linkClass0 (clazz);
	  }
	catch (Throwable x)
	  {
	    markClassErrorState0 (clazz);

	    LinkageError e;
	    if (x instanceof LinkageError)
	      e = (LinkageError)x;
	    else if (x instanceof ClassNotFoundException)
	      {
		e = new NoClassDefFoundError("while resolving class: "
					     + clazz.getName());
		e.initCause (x);
	      }
	    else
	      {
		e = new LinkageError ("unexpected exception during linking: "
				      + clazz.getName());
		e.initCause (x);
	      }
	    throw e;
	  }
      }
  }

  /** Internal method.  Calls _Jv_PrepareClass and
   * _Jv_PrepareCompiledClass.  This is only called from resolveClass.  */ 
  private static native void linkClass0(Class clazz);

  /** Internal method.  Marks the given clazz to be in an erroneous
   * state, and calls notifyAll() on the class object.  This should only
   * be called when the caller has the lock on the class object.  */
  private static native void markClassErrorState0(Class clazz);

  /**
   * Defines a new package and creates a Package object.
   * The package should be defined before any class in the package is
   * defined with <code>defineClass()</code>. The package should not yet
   * be defined before in this classloader or in one of its parents (which
   * means that <code>getPackage()</code> should return <code>null</code>).
   * All parameters except the <code>name</code> of the package may be
   * <code>null</code>.
   * <p>
   * Subclasses should call this method from their <code>findClass()</code>
   * implementation before calling <code>defineClass()</code> on a Class
   * in a not yet defined Package (which can be checked by calling
   * <code>getPackage()</code>).
   *
   * @param name The name of the Package
   * @param specTitle The name of the specification
   * @param specVendor The name of the specification designer
   * @param specVersion The version of this specification
   * @param implTitle The name of the implementation
   * @param implVendor The vendor that wrote this implementation
   * @param implVersion The version of this implementation
   * @param sealed If sealed the origin of the package classes
   * @return the Package object for the specified package
   *
   * @exception IllegalArgumentException if the package name is null or if
   * it was already defined by this classloader or one of its parents.
   *
   * @see Package
   * @since 1.2
   */
  protected Package definePackage(String name,
				  String specTitle, String specVendor,
				  String specVersion, String implTitle,
				  String implVendor, String implVersion,
				  URL sealed)
  {
    if (getPackage(name) != null)
      throw new IllegalArgumentException("Package " + name
					 + " already defined");
    Package p = new Package(name,
			    specTitle, specVendor, specVersion,
			    implTitle, implVendor, implVersion,
			    sealed);
    synchronized (definedPackages)
    {
      definedPackages.put(name, p);
    }
    return p;
  }

  /**
   * Returns the Package object for the requested package name. It returns
   * 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)
  {
    Package p;
    if (parent == null)
      // XXX - Should we use the bootstrap classloader?
      p = null;
    else
      p = parent.getPackage(name);

    if (p == null)
      {
        synchronized (definedPackages)
	{
	  p = (Package) definedPackages.get(name);
	}
      }

    return p;
  }

  /**
   * Returns all Package objects defined by this classloader and its parents.
   *
   * @return an array of all defined packages
   * @since 1.2
   */
  protected Package[] getPackages()
  {
    Package[] allPackages;

    // Get all our packages.
    Package[] packages;
    synchronized(definedPackages)
    {
      packages = new Package[definedPackages.size()];
      definedPackages.values().toArray(packages);
    }

    // If we have a parent get all packages defined by our parents.
    if (parent != null)