As per bug 18178560, WebLogic Server provides a non-blocking IO muxer implementation as the default muxer configuration. On 12.1.2 or after, non-blocking IO muxer is default implementation of Muxer. In default configuration, MuxerClass is set to "weblogic.socket.NIOSocketMuxer".
 
     Native Muxers and Java Muxer are old and deprecated. Bug 18178560 also suggests that switching to the native muxer may improve performance on some platforms like windows

     Native muxers use platform-specific native binaries to read data from sockets. The majority of all platforms provide some mechanism to poll a socket for data. For example, Unix systems use the poll system call and the Windows architecture uses completion ports. Native muxers provide superior scalability because they implement a non-blocking thread model. When a native muxer is used, the server creates a fixed number of threads dedicated to reading incoming requests.

    Currently it is just deprecated which means it is still supported at this point in time but may not be in the future To enable these muxers, muxer class name needs to be explicitly configured in MuxerClass.