Re: How to get list of classes from a package

16 Feb 2009

      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....)
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)));
    }
}