How to get list of classes from a package

[Ulf Zibis]

Am 16.02.2009 21:35, Rémi Forax schrieb:
> Tom Hawtin a écrit :
>> David M. Lloyd wrote:
>>> On 02/16/2009 10:22 AM, Ulf Zibis wrote:
>>>>
>>>> can anybody tell me, how I could get al list or enumeration of the 
>>>> classes, which belong to a package.
>>>> I can't see any appropriate method in java.lang.Package :-(
>>>
>>> This isn't really possible at run time, since one doesn't know 
>>> whether a class exists until one tries to load it.  The classloader 
>>> might not even know.  Also, a package can span classloaders, adding 
>>> more complexity to the problem.
>>
>> IIRC, you will get a different Package for each class loader, for a 
>> given package name. Certainly classes with the same package name will 
>> not have Java access to default/protected 
>> members/classes/interface/constructors from different class loaders.
>>
>> But yes, a list of classes is not necessarily complete. Also, IIRC, 
>> Proxy dynamically inserts classes into packages as well.
>>
>> Tom Hawtin
> Ulf, if you can create an agent, you can get all loaded classes:
> http://download.java.net/jdk7/docs/api/java/lang/instrument/Instrumentation.html#getAllLoadedClasses() 
>
>
> But if you want thoses classes to find some that implement an interface,
> java.util.ServiceLoader is your friend:
> http://download.java.net/jdk7/docs/api/java/util/ServiceLoader.html
>
> cheers,
> Rémi
>

Hi David, Tom and Rémi,

very much thanks for your hints. They were really valuable. :-)
I just finished to code a tricky solution:

package sun.nio.cs;

import java.io.*;
import java.net.*;
import java.nio.charset.*;
import java.util.*;
import java.util.jar.*;

/**
 *
 * @author Ulf Zibis <Ulf.Zibis at CoSoCo.de>
 */
public class LegacyCharsets {

    private static StandardCharsets standChars = new StandardCharsets();
    // Maps lowered canonical names to legacy class names
    static final Map<String,String> legacyClassNameMap;

    static {
        legacyClassNameMap = new HashMap(256);
        collectLegacyClassNames("StandardCharsets.class");
        collectLegacyClassNames("ext/DelegatableDecoder.class");
    }

    @SuppressWarnings("static-access")
    private static void collectLegacyClassNames(String searchAnchor) {
        String[] paths = 
LegacyCharsets.class.getResource(searchAnchor).getPath().split("!");
        paths[1] = paths[1].substring(paths[1].indexOf('/')+1, 
paths[1].lastIndexOf('/'));
        try {
            Enumeration<JarEntry> en = new JarFile(new File(new 
URI(paths[0]))).entries();
            while (en.hasMoreElements()) {
                String name = en.nextElement().getName();
                int extPos;
                if (name.indexOf('$') < 0 && name.startsWith(paths[1]) 
&& (extPos = name.indexOf(".class")) > 0) {
                    Class c = Class.forName(name.substring(0, 
extPos).replace('/', '.'),
                                true, 
LegacyCharsets.class.getClassLoader());
                    if (Charset.class.isAssignableFrom(c)) try {
                        
legacyClassNameMap.put(standChars.toLower(((Charset)c.newInstance()).name()),
                                
c.getName().substring("sun.nio.cs.".length()));
                    } catch (IllegalAccessException iae) {
                    } catch (InstantiationException ie) {}
                }
            }
        } catch (Exception ex) {
            System.err.println(ex);
        }
    }

    @SuppressWarnings("static-access")
    static Charset legacyCharset(String canonicalName) {
        return 
standChars.newCharsetForClassName(legacyClassNameMap.get(standChars.toLower(canonicalName)));
    }
}