Containers

This figure provides a closer look at the compositional hierarchy of the container components, their nested components, and their request processing pipelines and valves.

The outermost container represents the Catalina servlet engine and is the subject of this chapter.

Note

An engine cannot be contained by any component other than its service. Adding an engine as a child of any other container will cause an IllegalArgumentException to be thrown.

Note that while the Service component does contain other components, it is not considered a container, and is instead classified as a Top Level Component.

An Engine contains one or more children that are of type Host, each of which is a virtual host. In turn, a Host contains a number of Contexts, each of which represents a single web application. A context may optionally contain Wrapper components, where each wrapper represents an individual servlet.

Some child containers, such as the Host, Context, and Wrapper can have more than one instance...