The welcome files mechanism allows you to specify a list of files that the web container will use for appending to a request for a URL (called a valid partial request) that is not mapped to a web component.
For example, suppose you define a welcome file welcome.html. When a client requests a URL such as host:port/webapp/directory, where directory is not mapped to a servlet or XHTML page, the file host:port/webapp/directory/welcome.html is returned to the client.
If a web container receives a valid partial request, the web container examines the welcome file list and appends to the partial request each welcome file in the order specified and checks whether a static resource or servlet in the WAR is mapped to that request URL. The web container then sends the request to the first resource in the WAR that matches.
If no welcome file is specified, the Enterprise Server will use a file named index.xhtml as the default welcome file. If there is no welcome file and no file named index.xhtml, the Enterprise Server returns a directory listing.