7u21 mixed code warning java.lang.ClassNotFoundException

Question

Initially with Java 7u21 when I tried to invoke the browser dialog when trying to import records through applet I got the following error:
"Liveconnect call for Applet ID 1 is not allowed in this JVM instance"
It used to work fine with earlier versions of Java.
In order to fix it I have updated manifest file of applet, added the following entry for mixed code warning:
Trusted-library: true
I am self - signing the jars. It runs fine if I donot sign the jars, but if I self sign the jars
then I see the following exception in Java console:
Protocol: https
codeBase.getPort(): -1
appletConfig.getPort(): 443
Exception in thread "Thread-15" java.lang.NoClassDefFoundError: com/l2fprod/common/swing/JDirectoryChooser
     at com.sjm.pcs.sneakernet.applet.ScanApplet$JavaScriptEventListener.run(ScanApplet.java:803)
     at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.ClassNotFoundException: com.l2fprod.common.swing.JDirectoryChooser
     at sun.plugin2.applet.Applet2ClassLoader.findClass(Unknown Source)
     at sun.plugin2.applet.Plugin2ClassLoader.loadClass0(Unknown Source)
     at sun.plugin2.applet.Plugin2ClassLoader.loadClass(Unknown Source)
     at sun.plugin2.applet.Plugin2ClassLoader.loadClass(Unknown Source)
     at java.lang.ClassLoader.loadClass(Unknown Source)
     ... 2 moreAny idea what might be going wrong.
Any idea what is going wrong?
Thanks!

Answer 1

This is confirmed by the  post  https://forums.oracle.com/thread/2280127
and it is confirmed by Oracle http://docs.oracle.com/javase/7/docs/technotes/guides/jweb/mixed_code.html#trusted_library
"Code in a jar file that is to be marked with the Trusted-Library manifest attribute may need to be modified slightly if it uses calls that are class loader dependent [...]
Code in a Trusted-Library can look up the normal loader by invoking Thread.currentThread().getContextClassLoader().[...]
Generally, care must be taken to ensure that the code in the trusted library is written in a careful and secure manner and is otherwise compatible with being loaded in a separate class loader instance from any remaining jars which are part of the application and are loaded by the normal loader."
"Thread.currentThread().getContextClassLoader().[...]" 
I just did a simple test to call a method from a trusted jar into sandbox jar, I used reflection to do that and it worked.
It seems for every usage of any sandbox jar file classes in the trusted jar file, we have to use reflection ( load the class, invoke the required method ). Is this the way forward. Can somebody confirm this.
private void useReflection()
      try
           // using normal class loader
         Class<?> clazz = Class.forName("com.abc.bla.bla.SandBox", true, Thread.currentThread().getContextClassLoader());
         Constructor<?> constructor = clazz.getConstructor();
         Object obj = constructor.newInstance(new Object[] {});
         Method method = clazz.getMethod("sayHello", new Class[] {});
         method.invoke(obj, new Object[] {});
      catch (Exception ex)
         ex.printStackTrace();