关于servlet mapping

servlet 2.4 specification中说，
Upon receipt of a client request, the Web container determines the Web application
to which to forward it. The Web application selected must have the the longest
context path that matches the start of the request URL. The matched part of the URL
is the context path when mapping to servlets.
The Web container next must locate the servlet to process the request using
the path mapping procedure described below.
The path used for mapping to a servlet is the request URL from the request
object minus the context path and the path parameters. The URL path mapping
rules below are used in order. The first successful match is used with no further
matches attempted:
1. The container will try to find an exact match of the path of the request to the
path of the servlet. A successful match selects the servlet.

2. The container will recursively try to match the longest path-prefix. This is done
by stepping down the path tree a directory at a time, using the ’/’ character as
a path separator. The longest match determines the servlet selected.

3. If the last segment in the URL path contains an extension (e.g. .jsp), the servlet
container will try to match a servlet that handles requests for the extension.
An extension is defined as the part of the last segment after the last ’.’ character.

4. If neither of the previous three rules result in a servlet match, the container will
attempt to serve content appropriate for the resource requested. If a "default"
servlet is defined for the application, it will be used.

谁能给我讲讲这是什么意思？
我找遍了所有的书，包括Sun和O'REILLY的，没有一本书上讲过这些内容。看规范又不太明白，真是太累了。
谁能帮帮我，在这里先谢谢了！