Get Java runtime classes as byte array while filtering out local classes

I want to get any java runtime classes as a byte array. Currently I am looking them up using ClassLoader.getSystemClassLoader().getResourceAsStream(...) to get the class as an input stream and then convert it to a byte array. How can I ensure that the classes loaded are only runtime classes of Java itself (Object.class etc.), while classes that are application specific (stored in the JAR file / classpath) are blocked due to security reasons?