WebSphere Application Server - IBM Redbooks

The servlet configuration
This object must implement the ServletConfig interface and is provided by the
servlet container as a parameter of the init method of the servlet. The servlet
container is responsible for providing a ServletConfig object.
The servlet container uses this object to pass configuration information to its
servlet instances, such as the name and the value of a parameter located in the
servlet container. The ServletConfig object is accessible to the servlet through its
getServletConfig() method. Moreover, a ServletConfig object allows the access
to a ServletContext object.
The servlet context
This object implements the ServletContext interface and is provided to the servlet
within the ServletConfig object. During its life cycle, a servlet can access its
servlet context through the getServletContext() method.
The servlet container is also responsible for providing an implementation of this
interface.
The servlet context provides information about its environment to a servlet. It can
be shared by a group of servlets and provides access to the following:
► A set of attributes: a set of name/object pairs that can be shared between
servlets and other components to maintain persistency. A servlet can either
add or remove an attribute or simply change its content. A servlet can also
access its init parameters, which are name/value pairs.
► Resources: servlets sharing the same context can also share resources such
as files. They can access these resources via their servlet context.
► A log file: a servlet can write a set of events to a log file.
► A request dispatcher: this object, created and managed by the servlet
container, allows a servlet to forward its request to another servlet or to
include the content of another servlet into its own response. It allows servlets
sharing the same context to communicate with each other.
There can be several servlet context objects in a servlet container at the same
time, each managing its pool of servlets. Each servlet instance is running in one
of these contexts and all the servlet instances running in the same context will
share the same resources. Following that, a servlet class may have more than
one instance in a container, with each of these instances attached to a different
servlet context.
Finally, the servlet context is the way for the servlet to interact with its
environment (its container, but also other resources) without having to reconsider
its own logic. Every servlet container has at least a default servlet context.
Chapter 7. Working with servlets 219