WasWebJarAssetLocator

import java.io.IOException;
import java.net.URL;
import java.util.Enumeration;
import java.util.HashSet;
import java.util.ServiceLoader;
import java.util.Set;
import java.util.SortedMap;
import java.util.TreeMap;
import java.util.regex.Pattern;

import org.webjars.WebJarAssetLocator;
import org.webjars.urlprotocols.UrlProtocolHandler;

public class WasWebJarAssetLocator extends WebJarAssetLocator {
    // WAS webjars protocol (normally is jar)
    private static final String WEBJARS_PROTOCOL = "wsjar";

    // WAS wants resources path trailing slash
    public static final String WEBJARS_PATH_PREFIX = "META-INF/resources/webjars/";

    public WasWebJarAssetLocator() {
        super(getWasFullPathIndex(Pattern.compile(".*"),
                WasWebJarAssetLocator.class.getClassLoader()));
    }

    public static SortedMap<String, String> getWasFullPathIndex(
            final Pattern filterExpr, final ClassLoader... classLoaders) {

        final Set<String> assetPaths = getWasAssetPaths(filterExpr, classLoaders);

        final SortedMap<String, String> assetPathIndex = new TreeMap<String, String>();
        for (final String assetPath : assetPaths) {
            assetPathIndex.put(reverseWasPath(assetPath), assetPath);
        }

        return assetPathIndex;
    }

    private static Set<String> getWasAssetPaths(final Pattern filterExpr, final ClassLoader... classLoaders) {
        final Set<String> assetPaths = new HashSet<String>();
        final Set<URL> urls = listParentWasURLsWithResource(classLoaders, WEBJARS_PATH_PREFIX);

        ServiceLoader<UrlProtocolHandler> urlProtocolHandlers = ServiceLoader.load(UrlProtocolHandler.class);
        for (final URL url : urls) {
            for (UrlProtocolHandler urlProtocolHandler : urlProtocolHandlers) {
                if (WEBJARS_PROTOCOL.equals(url.getProtocol()) || urlProtocolHandler.accepts(url.getProtocol())) {
                    Set<String> assetPathSet = urlProtocolHandler.getAssetPaths(url, filterExpr, classLoaders);
                    if (assetPathSet != null) {
                        assetPaths.addAll(assetPathSet);
                        break;
                    }
                }
            }
        }

        return assetPaths;
    }

    private static String reverseWasPath(String assetPath) {
        final String[] assetPathComponents = assetPath.split("/");
        final StringBuilder reversedAssetPath = new StringBuilder();
        for (int i = assetPathComponents.length - 1; i >= 0; --i) {
            reversedAssetPath.append(assetPathComponents[i]);
            reversedAssetPath.append('/');
        }

        return reversedAssetPath.toString();
    }

    private static Set<URL> listParentWasURLsWithResource(final ClassLoader[] classLoaders, final String resource) {
        final Set<URL> urls = new HashSet<URL>();
        for (final ClassLoader classLoader : classLoaders) {
            try {
                final Enumeration<URL> enumeration = classLoader.getResources(resource);
                while (enumeration.hasMoreElements()) {
                    urls.add(enumeration.nextElement());
                }
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        return urls;
    }
}