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From Ivan <xhh...@gmail.com>
Subject Re: Questions on yoko Util class in yoko-rmi-spec should use the interface class as the key?
Date Tue, 11 Jan 2011 14:20:20 GMT
Hmm, I have to say that I know little about corba, just from the codes of
UtilLoader.loadClass, the first part of that method is trying to load an
implementation of the SPI, but the left part is just to load the SPI itself,
is it the expected behavior ?
If we need to look up a specific provider for an interface, maybe it is
better to use the similar method suggested by you. which passing both the
SPI and defaultImpl class, then we might first try to look up the impl by
ProviderLocator, if failed, try to load the default impl by context
classloader or stack classloader...
Thanks.

2011/1/11 Rick McGuire <rickmcg@gmail.com>

> On 1/11/2011 8:45 AM, Ivan wrote:
>
>> That makes sense, also it is better to remove the codes
>> ProviderLocator.loadClass from the UtilLoader.loadClass method, or that
>> makes the function of loadClass method ambigurous.
>>
>
> For other reasons, I believe it is still necessary to have
> ProviderLocator.loadClass() part of the loadClass() searches.  This is a
> different, internal situation where we're looking for a specific provider
> for an interface.
>
> Rick
>
>
>> 2011/1/11 Rick McGuire <rickmcg@gmail.com <mailto:rickmcg@gmail.com>>
>>
>>
>>    On 1/11/2011 7:35 AM, Ivan wrote:
>>
>>>    I agree with Forrest that those code logic might need to be
>>>    updated. From the codes fragment below of UtilLoader
>>>    In the loadClass method, it will first try the
>>>    ProviderLocator.loadClass, but what ProviderLocation.loadClass
>>>    expect is an interface class name, like javax.rmi.CORBA.Util.
>>>    So those codes in the static block of Util, it should first try
>>>    to load it from ProviderLocator with service provider interface.
>>>    Comments ?
>>>
>>
>>    I think the static code in the Util class should be something like:
>>
>>
>>    // Initialize delegate StringdelegateName=
>>
>>  (String)AccessController.doPrivileged(newGetSystemPropertyAction("javax.rmi.CORBA.UtilClass",
>>
>>    defaultDelegate)); try{ // this is a little bit recursive, but
>>    this will use the full default search order for locating // this.
>>                 delegate  =
>> (UtilDelegate)UtilLoader.loadServiceClass(delegateName,
>> Delegate.class).newInstance();
>>    } catch(Throwablee) { org.omg.CORBA.INITIALIZEex=
>>    neworg.omg.CORBA.INITIALIZE("Can not create Util delegate:
>>
>>    "+delegateName); ex.initCause(e); throwex; }
>>
>>    Where UtilLoader.loadServiceClass() is a method that functions
>>    like UtilLoader.loadClass(), but takes both an interface class
>>    name that is used to qualify the lookup.
>>
>>    Rick
>>
>>     -->
>>>    static public Class loadClass(String name, String codebase,
>>>    ClassLoader loader)
>>>                throws ClassNotFoundException {
>>>            Class result = null;
>>>
>>>            try {
>>>                return ProviderLocator.loadClass(name, null, loader);
>>>            } catch (ClassNotFoundException e) {
>>>                //skip
>>>            }
>>>
>>>            ClassLoader stackLoader = null;
>>>            ClassLoader thisLoader = UtilLoader.class.getClassLoader();
>>>            Class[] stack = _secman.getClassContext();
>>>            for (int i = 1; i < stack.length; i++) {
>>>                ClassLoader testLoader = stack[i].getClassLoader();
>>>                if (testLoader != null && testLoader != thisLoader)
>>>                {
>>>                    stackLoader = thisLoader;
>>>                    break;
>>>                }
>>>            }
>>>            ......
>>>    <---
>>>
>>>
>>>
>>>
>>>
>>>    2011/1/11 Rick McGuire <rickmcg@gmail.com <mailto:rickmcg@gmail.com>>
>>>
>>>
>>>        On 1/11/2011 4:46 AM, Forrest Xia wrote:
>>>
>>>            Hi,
>>>
>>>            When I debug a corba related application, I managed to
>>>            trace into a piece of yoko code like this:
>>>
>>>            public class Util {
>>>               private static UtilDelegate delegate = null;
>>>               private static final String defaultDelegate =
>>>            "org.apache.yoko.rmi.impl.UtilImpl";
>>>
>>>               // To hide the default constructor we should implement
>>>            empty private constructor
>>>               private Util() {}
>>>
>>>               static {
>>>                   // Initialize delegate
>>>                   String delegateName =
>>>            (String)AccessController.doPrivileged(new
>>>            GetSystemPropertyAction("javax.rmi.CORBA.UtilClass",
>>>            defaultDelegate));
>>>                   try {
>>>
>>>                       // this is a little bit recursive, but this
>>>            will use the full default search order for locating
>>>                       // this.
>>>            delegate = (UtilDelegate)Util.loadClass(delegateName,
>>>            null, null).newInstance();
>>>                   } catch (Throwable e) {
>>>                       org.omg.CORBA.INITIALIZE ex = new
>>>            org.omg.CORBA.INITIALIZE("Can not create Util delegate:
>>>            "+delegateName);
>>>                       ex.initCause(e);
>>>                       throw ex;
>>>                   }
>>>               }
>>>            ...
>>>
>>>            According to another code in
>>>            ProviderRegistryImpl$SPIRegistry(the id's value is the
>>>            delegateName variable as highlighted above), while the
>>>            registry hashmap's key is "javax.rmi.CORBA.UtilClass",
>>>            that will lead CNF exception.
>>>            private synchronized BundleProviderLoader
>>>            getLoader(String id) {
>>>                       // synchronize on the registry instance
>>>                       if (registry != null) {
>>>                           log.fine("registry: " + registry);
>>>                           // return the first match, if any
>>>                           List<BundleProviderLoader> list =
>>>            registry.get(id);
>>>                           if (list != null && !list.isEmpty()) {
>>>                               return list.get(0);
>>>                           }
>>>                       }
>>>                       // no match here
>>>                       return null;
>>>                   }
>>>
>>>            So my question is should we change the Util code to pass
>>>            the interface class name to load class? Please advise.
>>>
>>>        I'm not sure I understand the question.  The target class in
>>>        question here is a concrete delegate instance, so I don't
>>>        understand why you think an interface is needed here.  The
>>>        loading in question here is just for the delegate class that
>>>        is used for the rmi util class.
>>>
>>>        In any event, you cannot change any of the method signatures
>>>        for the javax.rmi.CORBA.Util class.  That is a standard API
>>>        class and you can't add that.
>>>
>>>        I think I understand what you wish to do here, and I'd
>>>        recommend adding a loadServiceClass() method to the
>>>        UtilLoader class and change the initializer in Util to use
>>>        that directly rather than recursively calling Util.loadClass().
>>>
>>>        Rick
>>>
>>>
>>>            Forrest
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>    --     Ivan
>>>
>>
>>
>>
>>
>> --
>> Ivan
>>
>
>


-- 
Ivan

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