Aspect-Oriented Programming (AOP) is a new paradigm that allows you to organize and layer your software applications in ways that are impossible with traditional object-oriented approaches. Aspects allow you to transparently glue functionality together so that you can have a more layered design. AOP allows you to intercept any event in a Java program and trigger functionality based on those events.

JBoss Aop is an open-source Aop framework library developed by JBoss. It is 100% Java based and can be run either as a standalone or inside an application server environment. More details can be found at www.jboss.com. PojoCache uses JBoss Aop library in two ways. It uses JBoss Aop firstly for its own interceptor-based architecture and secondly to realize the fine-grained replication aspects.

Dynamic Aop is a feature of JBoss Aop that provides a hook so that a caller can insert event interception on the POJO at runtime. PojoCache currently uses this feature to perform field level interception.

JGroups is a reliable Java group messaging library that is open-source and LGPL. In addition to reliable messaging transport, it also performs group membership management. It has been a de facto replication layer used by numerous open-source projects for clustering purposes. It is also used by JBossCache for replication layer.

Core Cache is a tree-structured, clustered, transactional cache. Simple and Serializable java types are stored as key/value pairs on nodes within the tree using a collection-like API. It also provides a number of configurable aspects such as node locking strategies, data isolation, eviction, and so on. POJO Cache leverages Core Cache as the underlying data-store in order to provide the same capabilities.

Plain old Java object.

Annotation is a new feature in JDK5.0. It introduces metadata along side the Java code that can be accessed at runtime. PojoCache currently uses JDK50 annotation to support POJO instrumentation (JDK1.4 annotation has been deprecated since release 2.0).

Prepare is a keyword in JBoss Aop pointcut language used to specify which POJO needs to be instrumented. It appears in a pojocache-aop.xml file. However, if you can use annotation to specify the POJO instrumentation, there is no need for a pojocache-aop.xml listing. Note that When a POJO is declared properly either through the xml or annotation, we consider it "aspectized".

Instrumentation is an Aop process that basically pre-processes (e.g., performing byte-code weaving) on the POJO. There are two modes: compile- or load-time. Compile-time weaving can be done with an Aop precompiler (aopc) while load-time is done to specify a special classloader in the run script. This step is necessary for an Aop system to intercept events that are interesting to users.