Load-Time Structural Reflection in Java

The standard reflection API of Java provides the ability to introspect a program but not to alter program behavior. This paper presents an extension to the reflection API for addressing this limitation. Unlike other extensions enabling behavioral reflection, our extension called Javassist enables structural reflection in Java. For using a standard Java virtual machine (JVM) and avoiding a performance problem, Javassist allows structural reflection only before a class is loaded into the JVM. However, Javassist still covers various applications including a language extension emulating behavioral reflection. This paper also presents the design principles of Javassist, which distinguish Javassist from related work.