要配置Weblogic8.1的缺省应用，需要为相应的Web Application的WEB-INF目录下加上相应的配置文件信息。

1、对于以ear形式发布的web application,在application.xml中加入：
<web>
  <web-uri>yourAppName</web-uri>
  <context-root>/</context-root>
</web>

2、对于以目录形式发布的web application,可以在weblogic.xml里面配置：

<!DOCTYPE weblogic-web-app PUBLIC "-//BEA Systems, Inc.//DTD Web Application 8.1//EN" "http://www.bea.com/servers/wls810/dtd/weblogic810-web-jar.dtd">

<weblogic-web-app>
  <container-descriptor>
    <index-directory-enabled>true</index-directory-enabled>
  </container-descriptor>
  <context-root>/</context-root>
</weblogic-web-app>

注意：application.xml里面的配置将会覆盖掉weblogic.xml的配置信息(Note that the application.xml context-root takes precedent over the weblogic.xml value.)

bea关于default web application的说明：

http://e-docs.bea.com/wls/docs81/ConsoleHelp/web_applications.html

Designating a Default Web Application

The default Web Application is presented to clients who do not specify a URI (or specify "/" as the URI). To deploy a Web Application as a default Web Application, set the value of the context-root element to "/" in its deployment descriptor.

You can specify the context-root element in the weblogic.xml deployment descriptor for Web Applications that are packaged as a .war archive or exploded .war directory. If you package the Web Application as part of an Enterprise Application (.ear archive or exploded .ear), specify the context-root in application.xml. Note that the application.xml context-root takes precedent over the weblogic.xml value.

Deploy the application using the instructions in Deploying a New Web Application.

To deploy a Web Application as part of an .ear archive or exploded .ear, see Deploying WebLogic Server Applications.