Which class file is loaded by the classloader ?

nivek (Kevin Gaudin) — Fri, 23 Mar 2007 11:38:37 GMT

When using lots of third-party libraries, one problem might be that 2 of them package different versions of the same class, producing errors when method version conflicts happen.

Here is a simple way to know the exact location used by the classloader to get your class :



URL myClassURL = MyMysteryClass.class.getProtectionDomain().getCodeSource().getLocation();

Functional JarClassLoader - warning, really awful

DRMacIver (David R. MacIver) — Thu, 15 Feb 2007 09:55:37 GMT

Some really awful functional style Java...

Note that this depends on a bunch of other classes in the playground namespace. If you actually want to use it ask me and I'll send you the source - I didn't really feel like snippetting all the needed code.



package playground.library.classloader;



import java.io.ByteArrayOutputStream;

import java.io.IOException;

import java.io.InputStream;

import java.util.ArrayList;

import java.util.HashSet;

import java.util.Iterator;

import java.util.List;

import java.util.Set;

import java.util.jar.JarEntry;

import java.util.jar.JarFile;

import playground.library.functional.FunctionalUtils;

import playground.library.functional.Pair;

import playground.library.functional.iterator.FilterIterator;

import playground.library.functional.iterator.IteratorTransformer;

import playground.library.functional.Predicate;

import playground.library.functional.Transformer;

import playground.library.functional.iterator.DelegatingIterator;

import playground.library.functional.iterator.LinkingIterator;

import playground.library.jar.JarEntryIterator;

import playground.library.utils.IteratorUtils;

import playground.library.utils.IOUtils;



/**

 * ClassLoader for loading from Jar files.

 *

 * @author david

 */

public class JarClassLoader extends ClassLoader

{

    public JarClassLoader(ClassLoader parent) { super(parent); }    

    public JarClassLoader()                   { super(); }

    

    private final List     files = new ArrayList();

    

    /**

     * Provides an iterator over all pairs of (file, entry) of JarFiles associated

     * with this class loader and entries of those jar files.

     */

    private Iterator> getResources(){

        return new LinkingIterator>(

            new IteratorTransformer>>(

                new Transformer>>(){

                public Iterator> transform(JarFile file){

                    return FunctionalUtils.merge(file, new JarEntryIterator(file));}})

           .transform(JarClassLoader.this.files.iterator()));}

    

    /**

     * Searches through the available jar files to try and find a class with the given name.

     */

    @Override

    protected Class findClass(String name) throws ClassNotFoundException{

        final Iterator> resources = this.getResources();

        while (resources.hasNext()){

            final Pair resource = resources.next();

                if(resource.second.getName().equals(name)){

                    try { return this.load(resource.first.getInputStream(resource.second));}

                    catch (IOException e) { e.printStackTrace(); }}}

        throw new ClassNotFoundException();}

    

    /**

     * Loads the contents of the InputStream as a class. This doesn't validate

     * the contents, so will fail messily if you pass it something that isn't a

     * valid class file.

     */

    private Class load(final InputStream input){

        try {

            final ByteArrayOutputStream output = new ByteArrayOutputStream();

            final byte[] bytes = IOUtils.copy(input, new ByteArrayOutputStream()).toByteArray();

            return this.defineClass(null, bytes, 0, bytes.length); }

        catch (IOException e){ throw new RuntimeException(e); }

        finally{

            try{ input.close(); }

            catch (IOException e){ throw new RuntimeException(e);}}}

        

    /**

     * Provides an iterator which lazily loads the contents of the jar file as

     * classes. Will also register the jar file with the class loader's file list.

     * When the iterator is exhausted the jar file will be removed from the file list.

     */

    public Iterator> load(final JarFile file) throws IOException{

        this.files.add(file);

                

        return  

            new DelegatingIterator>(

                new IteratorTransformer>(

                    new Transformer>(){

                        public Class transform(JarEntry stream){

                            InputStream fileStream = null;



                            try{return JarClassLoader.this.load(fileStream = file.getInputStream(stream)); }

                            catch(IOException e){throw new RuntimeException(e);}

                            finally{IOUtils.close(fileStream); }}})

                .transform(

                    new FilterIterator( 

                       new Predicate(){ 

                           public boolean satisfies(JarEntry entry){

                               return entry.getName().endsWith(".class");}},

                       new JarEntryIterator(file)))){

                @Override

                public Class next(){

                    final Class clazz = super.next();

                    if (!this.hasNext()) JarClassLoader.this.files.remove(file);                    

                    return clazz;}

                

                @Override

                public boolean hasNext(){

                    final boolean hasNext = super.hasNext();

                    if (!hasNext) JarClassLoader.this.files.remove(file);

                    return hasNext;}};}



    /**

     * Loads all class files from the jar and returns a set of them.

     */

    public Set> loadAll(final JarFile file) throws IOException

    {

        return IteratorUtils.fill(new HashSet>(), this.load(file));

    }

}

DZone Snippets: classloader code

Which class file is loaded by the classloader ?

Functional JarClassLoader - warning, really awful