Integration Server runs in the Java Virtual Machine (JVM). When Integration Server, or any Java application, needs access to a class, the JVM locates the executable bytecode of the class and brings it into the JVM. This process is referred to as loading the class and is handled by class loaders. The class loaders in Integration Server and the JVM are designed to load classes from different locations.

During server initialization, at the point when Integration Server loads packages, Integration Server also loads all classes that contain Java services. A Java service contains statements that reference other Java classes. To execute these statements, the referenced classes must be loaded into the JVM.

If you are using your own classes developed by your company or classes from a third-party library, you can control the visibility and loading order of these classes. Class visibility refers to whether the classes and jar files will be or need to be visible to all the classes in Integration Server or to a particular package only.