add findClass() to servlet class loader (used in YaCyDefaltServlet)

In the 2 cases where servlet calls servlet the jvm classloader chain is
invoked and servlet class loaded by jvm loader (successful while requiring 
htroot in system classpath). This patch uses the standard override design
for loaders to handle these cases (making in not longer crucial to have htroot 
in system classpath, as this classLoader is mainly used for servlets and
looks in this case for the class in the configured path).
+ As the default classloader is parallelcapable we should register this too.

source/net/yacy/server/serverClassLoader.java

@@ -25,10 +25,16 @@ import java.io.File;
 import java.io.IOException;
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
+import net.yacy.cora.util.ConcurrentLog;
 
 import net.yacy.kelondro.util.FileUtils;
+import net.yacy.search.Switchboard;
+import net.yacy.search.SwitchboardConstants;
 
-
+/**
+ * Class loader for servlet classes
+ * (findClass looking in default htroot directory)
+ */
 public final class serverClassLoader extends ClassLoader {
     /**
      * directory of class files
@@ -38,18 +44,47 @@ public final class serverClassLoader extends ClassLoader {
     public serverClassLoader() {
         //super(ClassLoader.getSystemClassLoader());
     	super(Thread.currentThread().getContextClassLoader());
+        if (!registerAsParallelCapable()) { // avoid blocking
+            ConcurrentLog.warn("ClassLoader", "registerAsParallelCapable failed");
+        }
         this.classes = new ConcurrentHashMap<File, Class<?>>(100);
     }
 
     public serverClassLoader(final ClassLoader parent) {
         super(parent);
+        if (!registerAsParallelCapable()) {
+            ConcurrentLog.warn("ClassLoader", "registerAsParallelCapable failed");
+        }
         this.classes = new ConcurrentHashMap<File, Class<?>>(100);
     }
 
-    public Package[] packages() {
-        return super.getPackages();
+    /**
+     * Find servlet class in default htroot directory
+     * but use the internal loadClass(File) methode to load the class same way
+     * (e.g. caching) as direct call to loadClass(File)
+     * This methode is mainly to avoid classpath conflicts for servlet to servlet calls
+     * making inclusion of htroot in system classpath not crucial
+     *
+     * @param servletname (delivered by parent loader without ".class" file extension
+     * @return class in htroot
+     * @throws ClassNotFoundException
+     */
+    @Override
+    protected Class<?> findClass(String classname) throws ClassNotFoundException {
+        // construct path to htroot for a servletname
+        File cpath = new File (Switchboard.getSwitchboard().getDataPath(SwitchboardConstants.HTROOT_PATH, SwitchboardConstants.HTROOT_PATH_DEFAULT),classname+".class");
+        return loadClass(cpath);
     }
 
+    /**
+     * A special loadClass using file as argument to find and load a class
+     * This methode is directly called by the application and not part of the
+     * normal loadClass chain (= never called by JVM)
+     *
+     * @param classfile
+     * @return loaded an resolved class
+     * @throws ClassNotFoundException
+     */
     public Class<?> loadClass(final File classfile) throws ClassNotFoundException {
         // take the class out of the cache, denoted by the class file
         Class<?> c = this.classes.get(classfile);