classloader.java

来自「This is a resource based on j2me embedde」· Java 代码 · 共 1,855 行 · 第 1/5 页

     *
     * @see  #defineClass(String, byte[], int, int)
     */
    protected final void resolveClass(Class c) {
	check();
	resolveClass0(c);
    }

    private native void resolveClass0(Class c);

    /**
     * Finds a class with the specified name, loading it if necessary.
     *
     * <p> This method loads the class through the system class loader (see
     * {@link #getSystemClassLoader()}).  The <tt>Class</tt> object returned
     * might have more than one <tt>ClassLoader</tt> associated with it.
     * Subclasses of <tt>ClassLoader</tt> need not usually invoke this method,
     * because most class loaders need to override just {@link
     * #findClass(String)}.  </p>
     *
     * @param  name
     *         The name of the class that is to be found
     *
     * @return  The <tt>Class</tt> object for the specified <tt>name</tt>
     *
     * @throws  ClassNotFoundException
     *          If the class could not be found
     *
     * @see  #ClassLoader(ClassLoader)
     * @see  #getParent()
     */
    protected final Class findSystemClass(String name)
	throws ClassNotFoundException
    {
	check();
	ClassLoader system = getSystemClassLoader();
	if (system == null) {
	    return loadBootstrapClass(name);
	}
	return system.loadClass(name);
    }

    /**
     * Used only by profiling code to load classes via reflections
     */
    private Class findBootstrapClass(String name)
	throws ClassNotFoundException {
	return loadBootstrapClass(name);
    }

    /**
     * Returns a bootstrap Class, or throws a ClassNotFoundException
     */
    static Class loadBootstrapClass(String name) 
	throws ClassNotFoundException {
	Class c = loadBootstrapClassOrNull(name);
	if (c == null)
                throw new ClassNotFoundException(name);
	return c;
    }

    /*
     * Returns a Class or null if class not found.
     * Can throw ClassNotFoundException for various other 
     * faux pas
     */
    private static Class loadBootstrapClassOrNull(String name) 
	throws ClassNotFoundException {
        if (!checkName(name))
                throw new ClassNotFoundException(name);
	synchronized(ClassLoader.class) {
	    Class c = loadBootstrapClass0(name);
	    if (c != null && !c.superClassesLoaded()) {
		c.loadSuperClasses();
	    }	
	    return c;
	}
    }

    private static native Class loadBootstrapClass0(String name)
	throws ClassNotFoundException;


    // Check to make sure the class loader has been initialized.
    private void check() {
	if (!initialized) {
	    throw new SecurityException("ClassLoader object not initialized");
	}
    }

    /**
     * Returns the class with the given name if this loader has been recorded
     * by the Java virtual machine as an initiating loader of a class with
     * that name.  Otherwise <tt>null</tt> is returned.  </p>
     *
     * @param  name
     *         The class name
     *
     * @return  The <tt>Class</tt> object, or <tt>null</tt> if the class has
     *          not been loaded
     *
     * @since  1.1
     */
    protected final Class findLoadedClass(String name) {
        check();
        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.  </p>
     *
     * @param  c
     *         The <tt>Class</tt> object
     *
     * @param  signers
     *         The signers for the class
     *
     * @since  1.1
     */
    protected final void setSigners(Class c, Object[] signers) {
        check();
	c.setSigners(signers);
    }


    // -- 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.
     *
     * <p> The name of a resource is a '<tt>/</tt>'-separated path name that
     * identifies the resource.
     *
     * <p> This method will first search the parent class loader for the
     * resource; if the parent is <tt>null</tt> 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.  </p>
     *
     * @param  name
     *         The resource name
     *
     * @return  A <tt>URL</tt> object for reading the resource, or
     *          <tt>null</tt> 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.
     *
     * <p>The name of a resource is a <tt>/</tt>-separated path name that
     * identifies the resource.
     *
     * <p> The search order is described in the documentation for {@link
     * #getResource(String)}.  </p>
     *
     * @param  name
     *         The resource name
     *
     * @return  An enumeration of {@link java.net.URL <tt>URL</tt>} 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 final Enumeration getResources(String name) throws IOException {
	Enumeration[] tmp = new Enumeration[2];
	if (parent != null) {
	    tmp[0] = parent.getResources(name);
	} else {
	    tmp[0] = getBootstrapResources(name);
	}
	tmp[1] = findResources(name);

	return new CompoundEnumeration(tmp);
    }

    /**
     * Finds the resource with the given name. Class loader implementations
     * should override this method to specify where to find resources.  </p>
     *
     * @param  name
     *         The resource name
     *
     * @return  A <tt>URL</tt> object for reading the resource, or
     *          <tt>null</tt> if the resource could not be found
     *
     * @since  1.2
     */
    protected URL findResource(String name) {
	return null;
    }

    /**
     * Returns an enumeration of {@link java.net.URL <tt>URL</tt>} objects
     * representing all the resources with the given name. Class loader
     * implementations should override this method to specify where to load
     * resources from.  </p>
     *
     * @param  name
     *         The resource name
     *
     * @return  An enumeration of {@link java.net.URL <tt>URL</tt>} objects for
     *          the resources
     *
     * @throws  IOException
     *          If I/O errors occur
     *
     * @since  1.2
     */
    protected Enumeration findResources(String name) throws IOException {
	return new CompoundEnumeration(new Enumeration[0]);
    }

    /**
     * Find 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()}).  </p>
     *
     * @param  name
     *         The resource name
     *
     * @return  A {@link java.net.URL <tt>URL</tt>} object for reading the
     *          resource, or <tt>null</tt> if the resource could not be found
     *
     * @since  1.1
     */
    public static URL getSystemResource(String name) {
	ClassLoader system = getSystemClassLoader();
	if (system == null) {
	    return getBootstrapResource(name);
	}
	return system.getResource(name);
    }

    /**
     * Finds all resources of the specified name from the search path used to
     * load classes.  The resources thus found are returned as an
     * {@link java.util.Enumeration <tt>Enumeration</tt>} of {@link
     * java.net.URL <tt>URL</tt>} objects.
     *
     * <p> The search order is described in the documentation for {@link
     * #getSystemResource(String)}.  </p>
     *
     * @param  name
     *         The resource name
     *
     * @return  An enumeration of resource {@link java.net.URL <tt>URL</tt>}
     *          objects
     *
     * @throws  IOException
     *          If I/O errors occur

     * @since  1.2
     */
    public static Enumeration getSystemResources(String name)
	throws IOException
    {
	ClassLoader system = getSystemClassLoader();
	if (system == null) {
	    return getBootstrapResources(name);
	}
	return system.getResources(name);
    }

    /**
     * Find resources from the VM's built-in classloader.
     */
    private static URL getBootstrapResource(String name) {
	URLClassPath ucp = getBootstrapClassPath();
	Resource res = ucp.getResource(name);
	return res != null ? res.getURL() : null;
    }

    /**
     * Find resources from the VM's built-in classloader.
     */
    private static Enumeration getBootstrapResources(String name)
	throws IOException
    {
	final Enumeration e = getBootstrapClassPath().getResources(name);
	return new Enumeration () {
	    public Object nextElement() {
		return ((Resource)e.nextElement()).getURL();
	    }
	    public boolean hasMoreElements() {
		return e.hasMoreElements();
	    }
	};
    }

    // Returns the URLClassPath that is used for finding system resources.
    static URLClassPath getBootstrapClassPath() {
	return sun.misc.Launcher.getBootstrapClassPath();
    }

    /**
     * Returns an input stream for reading the specified resource.
     *
     * <p> The search order is described in the documentation for {@link
     * #getResource(String)}.  </p>
     *
     * @param  name
     *         The resource name
     *
     * @return  An input stream for reading the resource, or <tt>null</tt>
     *          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()}).  </p>
     *
     * @param  name
     *         The resource name
     *
     * @return  An input stream for reading the resource, or <tt>null</tt>
     * 	        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 --