Using XFileOutputStream, I Write Data, But It Never Appears in the File. Why?

This is probably due to the write buffering. When you write data to an NFS server using XRandomAccessFile or XFileOutputStream the writes are buffered. When the buffer becomes full (NFS v2 8k, NFS v3 32k) the data is written to the server. If the Java application exits without calling the close() method then the last incomplete buffer will not be written to the server. It is important to call close() when you have finished writing data to a file!