How to get list of classes from a package

[Martin Buchholz]

Ulf,

This kind of solution is likely to be brittle.
For example, you appear to assume that the code
you are looking for is in a jar file.  But it might not be;
in jdk "developer mode", they are likely to be in
a "classes" directory.

Martin

On Mon, Feb 16, 2009 at 13:30, Ulf Zibis <Ulf.Zibis at gmx.de> wrote:
> 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)));
>   }
> }
>
>
>