Learning Java

BeanContext and BeanContextServices

So far we’ve talked about some sophisticated mechanisms for connecting Java Beans together at design time and runtime. However, we haven’t talked at all about the environment in which JavaBeans live. To build advanced, extensible applications we need a way for Java Beans to find each other or “rendezvous” at run time. The java.beans.beancontext package provides this kind of container environment It also provides a generic “services” lookup mechanism for Beans that wish to advertise their capabilities.

Beans that implement the BeanContextChild interface (or a subinterface) are passed a reference to the container’s BeanContext, which is the source for all container-related information. The BeanContext implements many useful interfaces that describe the Bean environment. (To use it, cast it to the appropriate interface.) The two interfaces that we will talk about here are Collection and BeanContextServices.

A bean collection is an object that implements the java.util.Collection interface. It can be used to enumerate the Bean instances in the container. A corresponding listener interface lets Beans find out when Beans are added or removed. The BeanContextServices interface provides a means for looking up Beans that provide services, either by the Bean’s class type or through a list of the currently available service Beans. There is a corresponding listener interface for being informed of new services and revoked services.

Doing much with these classes ...