Contexts and Dependency Injection (CDI) defines a powerful set of complementary services that help improve the structure of application code. CDI is a Java EE specification.

JBoss Weld is one of the implementations of the CDI specification. https://docs.jboss.org/weld/reference/latest/en-US/html/index.html

Context is an isolated environment of a process, such as running an application, handling a HTTP request, handling a HTTP session or handling a conversation. Each of a processes has their own context which is application context, request context, session context and conversation context respectively. Each context internally can only contain object with a scope supported by that context (@ApplicationScoped bean in application context, @RequestScoped in request context.)

The most fundamental services provided by CDI are as follows:

• Contexts: The ability to bind the lifecycle and interactions of stateful components to well-defined but extensible lifecycle contexts
• Dependency injection: The ability to inject components into an application in a typesafe way, including the ability to choose at deployment time which implementation of a particular interface to inject

CDI provides:

• an improved lifecycle for stateful objects, bound to well-defined contexts
• a typesafe approach to dependency injection
• object interaction via an event notification facility
• a better approach to binding interceptors to objects, along with a new kind of interceptor, called a decorator, that is more appropriate for use in solving business problems, and