moduleclassloader.java

OSGI 的 源码实现,采用JAVA书写

                    // not be holding any locks before making the call.
                    URL url = m_mgr.getURLPolicy().createCodeSourceURL(
                        m_mgr, m_module);

                    // If we have a valid code source URL, then use it to
                    // define the class for security purposes, otherwise
                    // define the class without a code source.
                    if (url != null)
                    {
                        CodeSource cs = new CodeSource(url, (Certificate[]) null);
                        clazz = defineClass(name, bytes, 0, bytes.length, cs);
                    }
                    else
                    {
                        clazz = defineClass(name, bytes, 0, bytes.length);
                    }
                }
            }
        }

        if (clazz != null)
        {
            return clazz;
        }

        throw new ClassNotFoundException(name);
    }

    /**
     * <p>
     * This method is used by <tt>SearchPolicy</tt> instances when they want
     * to load a class from a module. The search policy is initially invoked when
     * <tt>ModuleClassLoader.loadClass()</tt> delegates a class loading
     * request to it. In general, the ultimate goal of the search policy is to
     * return a class from another module if possible. Unfortunately, if a search
     * policy tries to directly load a class from another module's class loader, an
     * infinite loop will result because the module's class loader will delegate the
     * request back to the search policy. To avoid this situation, search policies
     * must use this method when trying to load a class from a module.
     * </p>
     * @param name the name of the class to load.
     * @return the loaded class or <tt>null</tt>.
    **/
    public Class searchForClass(String name)
    {
        try
        {
            return findClass(name);
        } catch (Throwable th) {
            // Not much we can do.
// TODO: Do something with this error message.
//            System.err.println("ModuleClassLoader: " + th.getMessage());
        }
        return null;
    }

    /**
     * <p>
     * This method is nearly an exact copy of the ClassLoader.getResource()
     * method. The main difference is that it delegates to its associated
     * <tt>ModuleManager</tt>'s search policy before calling the
     * <tt>ClassLoader.findResource()</tt> method.
     * </p>
     * @param name the class to be loaded.
     * @return a URL to the resource or <tt>null</tt> if the resource was not found.
    **/
    public URL getResource(String name)
    {
        URL url = null;

        // First try the parent class loader.
        if (getParent() != null)
        {
            url = getParent().getResource(name);
        }
//        else
//        {
//            url = getBootstrapResource(name);
//        }

        // Then try the search policy.
        if (url == null)
        {
            // Try the search policy if no resource is
            // found in the parent or bootstrap loader.
            if (m_mgr.getSearchPolicy() != null)
            {
                try
                {
                    url = m_mgr.getSearchPolicy().findResource(m_module, name);
                }
                catch (ResourceNotFoundException ex)
                {
                    // We return null here because if SearchPolicy.findResource()
                    // throws an exception we interpret that to mean that the
                    // search should be stopped.
                    return null;
                }
            }
        }

        // Finally, look locally.
        if (url == null)
        {
            url = findResource(name);
        }

        return url;
    }

    /**
     * <p>
     * This method overriden from from <tt>ClassLoader</tt>.
     * It is implemented such that it loads resources from the set of
     * <tt>ResourceSource</tt>s from its associated module.
     * </p>
     * @param name the name of the resource to load.
     * @return the <tt>URL</tt> associated with the resource or <tt>null</tt>.
    **/
    protected URL findResource(String name)
    {
        // Remove leading slash, if present.
        if (name.startsWith("/"))
        {
            name = name.substring(1);
        }

        URL url = null;

        // Try to load the resource from the module's resource
        // sources.
        if (url == null)
        {
            ResourceSource[] sources = m_module.getResourceSources();
            for (int i = 0;
                (url == null) && (sources != null) && (i < sources.length);
                i++)
            {
                if (sources[i].hasResource(name))
                {
                    url = m_mgr.getURLPolicy().createResourceURL(m_mgr, m_module, i, name);
                }
            }
        }

        return url;
    }

    /**
     * <p>
     * This method is used by <tt>SearchPolicy</tt> instances when they want
     * to load a resource from a module. The search policy is initially invoked when
     * <tt>ModuleClassLoader.loadClass()</tt> delegates a resource loading
     * request to it. In general, the ultimate goal of the search policy is to
     * return a resource from another module if possible. Unfortunately, if a search
     * policy tries to directly load a resource from another module's class loader, an
     * infinite loop will result because the module's class loader will delegate the
     * request back to the search policy. To avoid this situation, search policies
     * must use this method when trying to load a resource from a module.
     * </p>
     * @param name the name of the resource to load.
     * @return a URL to the resource or <tt>null</tt>.
    **/
    public URL searchForResource(String name)
    {
        try
        {
            URL url = findResource(name);
            return url;
        }
        catch (Throwable th)
        {
            // Ignore and just return null.
        }
        return null;
    }

    protected Enumeration findResources(String name)
    {
        Vector v = new Vector();

        // Remove leading slash, if present.
        if (name.startsWith("/"))
        {
            name = name.substring(1);
        }

        // Try to load the resource from the module's resource
        // sources.

        ResourceSource[] sources = m_module.getResourceSources();
        for (int i = 0; (sources != null) && (i < sources.length); i++)
        {
            if (sources[i].hasResource(name))
            {
                v.addElement(m_mgr.getURLPolicy().createResourceURL(m_mgr, m_module, i, name));
            }
        }

        return v.elements();
    }

    /**
     * <p>
     * This method overriden from from <tt>ClassLoader</tt>. It maps a library
     * name to a library path by consulting the <tt>LibrarySource</tt>s of the
     * class loader's module.
     * </p>
     * @param name the name of the library to find.
     * @return the file system path of library or <tt>null</tt>
    **/
    protected String findLibrary(String name)
    {
        // Remove leading slash, if present.
        if (name.startsWith("/"))
        {
            name = name.substring(1);
        }

        LibrarySource[] sources = m_module.getLibrarySources();
        for (int i = 0;
            (sources != null) && (i < sources.length);
            i++)
        {
            String path = sources[i].getPath(name);
            if (path != null)
            {
                return path;
            }
        }

        return null;
    }
}