[jira] Commented: (MYFACES-2290) Add OSGi bundle information and bundle classloader / activator

["Leonardo Uribe (JIRA)" <de...@myfaces.apache.org>]

    [ https://issues.apache.org/jira/browse/MYFACES-2290?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12998711#comment-12998711 ] 

Leonardo Uribe commented on MYFACES-2290:
-----------------------------------------

Unfortunately, the patch has some problems. I see some code already committed, but fortunately it does not contains too much changes. 

Let's start with the idea of MyFacesClassLoader. Look this code:

    @Override
    public URL getResource(String s)
    {
        // context classloader
        URL url = super.getResource(s);

        if (url == null)
        {
            // try api
            url = apiClassLoader.getResource(s);

            if (url == null)
            {
                // try impl
                url = implClassLoader.getResource(s);
            }

It is ok, but note if we are using myfaces-bundle, we'll scan on the same classloader twice (because api and impl are the same bundle classloader)

This code will not work correctly:

    @Override
    public Enumeration<URL> getResources(String s) throws IOException
    {
        // use all 3 classloaders and merge without duplicates
        Set<URL> urls = new HashSet<URL>(); // no duplicates

        // context classloader
        urls.addAll(Collections.list(super.getResources(s)));

        // api classlaoder
        urls.addAll(Collections.list(apiClassLoader.getResources(s)));

        // impl classlaoder
        urls.addAll(Collections.list(implClassLoader.getResources(s)));

        return Collections.enumeration(urls);

Why? the class loader IS NOT unique per class. Really it depends on the environment. In some scenarios, the same classloader is returned from different classes. In OSGi case, since it is expected myfaces-bundle is used we are adding the same resources 2 times, and if the TCCL can locate resources of myfaces bundle jar, the final result is have 3 times the same files.

Look this issue: MYFACES-3055 META-INF/faces-config.xml files in JARs are loaded twice . The problem is caused because somebody decide to do the same the patch here is proposing. 

Unfortunately, by the previous reason it is not possible to use a MyFacesClassLoader. The best we can do here is let the code as we had before, so we can differentiate between use TCCL and class ClassLoader. Instead, it is better to have utility methods that handle the case we require (retrieve resource from TCCL and myfaces-bundle CL). There is no need to worry about myfaces-api/myfaces-impl, because that's one reason to have just one jar file in OSGi case (myfaces-bundle).

Really there is one problem about MyFaces and OSGi. Sometimes, MyFaces requires to instantiate/load resources or classes inside/outside MyFaces. For example, I have one JSF component library that has some resources under META-INF/resources/my.custom.library and MyFaces requires to serve this resource on a page. First MyFaces should scans on its bundle classloader and it does not found the files required. Then, it uses the TCCL to locate the files, and that one "contacts" the custom JSF component library jar to see if this bundle has the files and if that so it serves the required resources.

Right now, MyFaces REQUIRES the TCCL to work as expected. That was one lesson learned trying to close MYFACES-2290. The problem in that time was FactoryFinder imposes that restriction. Note right now, it is probably we'll commit soon a solution to override FactoryFinder behavior. But the problem we need to think is if there is other way in OSGi to make MyFaces load some resource files in a web context or app context. For now, it is supposed the TCCL do the job (and it does fine), but we don't have any report indicating it is necessary to suppose the opposite. 

> Add OSGi bundle information and bundle classloader / activator
> --------------------------------------------------------------
>
>                 Key: MYFACES-2290
>                 URL: https://issues.apache.org/jira/browse/MYFACES-2290
>             Project: MyFaces Core
>          Issue Type: New Feature
>          Components: General
>    Affects Versions: 1.2.8-SNAPSHOT
>         Environment: OSGi (Equinox, Apache Felix, ...)
>            Reporter: Felix Röthenbacher
>            Assignee: Leonardo Uribe
>            Priority: Critical
>         Attachments: MYFACES-2290-no-activator-2.patch, MYFACES-2290-no-activator.patch, allow-ee6-versioned-apis.diff, myfaces-core.diff.txt, myfaces-shared.diff.txt, myfaces-test-helloworld-osgi-pax-web.zip, myfaces-test-helloworld-osgi-springdm.zip
>
>
> The provided patch will add OSGi information to bundle manifest. A bundle activator class makes the MyFaces framework aware that it is running in a bundle environment. A bundle classloader is used to load classes and resources from the bundle classpath. The patch doesn't require any new runtime dependencies and doesn't affect class loading in a non-OSGi environment. Though, small modifications to classloading were needed. This was mainly replacing Thread.currentThread.getContextClassLoader() with ClassUtils methods.
> To run MyFaces in an OSGi environment both bundles (myfaces-api and myfaces-impl) have to be started in the OSGi container. Additionally, the myfaces-impl bundle has to be made available to myfaces-api. Use a fragment bundle with myfaces-api as Fragment-Host and myfaces-impl as Required-Bundle.

-- 
This message is automatically generated by JIRA.
-
For more information on JIRA, see: http://www.atlassian.com/software/jira