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

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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