What is name of Weblogic's default data source?

I'm trying to get Weblogic's default data source using the Java code below, but I don't know what to set strDefaultDataSource to. In JBoss, the string is "java:DefaultDS", and in WebSphere the string is "DefaultDatasource".

String strDefaultDataSource = ?;
InitialContext initialContext = new InitialContext();
DataSource dataSource = (DataSource)initialContext.lookup(strDefaultDataSource);