Re: Service Provider mechanism and javax.imageio.spi.ServiceRegistry

Dunno, having a SAX/DOM for .properties files strikes me as being a
bit heavyweight approach...

Anyway, the service implementation files aren't required to conform to
the full .properties file format IIRC (there are provisions for
multiline values and escaping in the properties file format that a
parser for service files shouldn't care about). It'd be quite trivial
to write a loop around BufferedReader.readLine() and ignore empty
lines and those starting with # character if you really cared about
ordering.

Attila.

On 2007.11.07., at 18:54, Dilum Ranatunga wrote:

> Speaking of properties files, ordering and comments, does anyone know
> of a readily available SAX handler-like or DOM-like parser for
> properties files? (Seems like the right way to have written that code
> in the first place...)
>
> On 11/3/07, Attila Szegedi <[email protected]> wrote:
>> It's easy to dicover and process these files with a bit of custom
>> code. I
>> have it in few places, most notably here:
>>
>> <http://dynalang.svn.sourceforge.net/viewvc/dynalang/trunk/dynalang/src/org/dynalang/mop/impl/AutoDiscovery.java?view=markup
>> >
>>
>> Something like this'll return you a list of service instances for all
>> declared services within a ClassLoader's scope:
>>
>> <T> static List<T> getServices(Class<T> serviceItf, ClassLoader cl)
>> throws IOException, InstantiationException, IllegalAccessException,
>> ClassNotFoundException {
>>     List<T> list = new LinkedList<T>();
>>     String path = "/META-INF/services/" +
>> serviceItf.getClass().getName();
>>     Enumeration<URL> urls;
>>     if(cl == null) {
>>         urls = ClassLoader.getSystemResources(path);
>>     }
>>     else {
>>         urls = cl.getResources(path);
>>     }
>>     for(;urls.hasMoreElements();) {
>>         URL url = urls.nextElement();
>>         InputStream in = url.openStream();
>>         try {
>>             Properties props = new Properties();
>>             props.load(in);
>>            for (Object className : props.keySet()) {
>>                 T serviceInstance = (T)Class.forName(
>>                     className.toString(), true, cl).newInstance());
>>             list.add(serviceInstance);
>>         }
>>         finally {
>>             in.close();
>>         }
>>     }
>>     return list;
>> }
>>
>> I'm using Properties object 'cause I get skipping of empty lines and
>> handling of # comments for free. It does not guarantee you that
>> you'll
>> instantiate the objects in the order they were declared in individual
>> files though, but I can live with that...
>>
>> That's it :-)
>>
>> BTW, it stinks that java.util.Properties doesn't extend
>> Hashtable<String,
>> String>...
>>
>> Attila.
>>
>> On Wed, 31 Oct 2007 15:03:49 +0100, Bertrand Delacretaz
>> <[email protected]> wrote:
>>
>>> On 10/31/07, Bertrand Delacretaz <[email protected]> wrote:
>>>
>>>> ...But it feels a bit weird to have this in javax.imageio.spi, is
>>>> there
>>>> a
>>>> better alternative?...
>>>
>>> Someone mentioned off-list the java.util.ServiceLoader class, which
>>> looks like what I'm looking for, but it's available starting with
>>> Java
>>> 1.6 only.
>>>
>>> -Bertrand
>>>
>> --
>> home: http://www.szegedi.org
>> weblog: http://constc.blogspot.com
>>
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