Java becomes the first choice due to its inherent advantages of platform independence, object serialization and dynamic class loading.

The dynamic loading of Java classes at runtime, especially the reflection mechanism, and some correlative design patterns, such as, factory method and prototype pattern are introduced with the application of dynamic loading technology in design pattern.

Its key technologies such as thread-pool in Java 5,dynamic loading a class,message queue,which make the collector efficient,all-purpose,modularized,extensible and replantable,are discussed in detail.

We present a fully formal, machine-checked specification of the bytecode verification and dynamic class loading, which are important parts in Java's security architecture.