Which book are you referring to? I originally thought you might be referring to the book I wrote with Terry (hence A&T SCJD 5), but my book details are lining up with your questions. According to me, it is chapter 6 (not 5) that discusses RMI, and page 187 is showing part of the DBClient interface.
So if it is the book I wrote with Terry, can you please re-check your references, or provide a little more contextual information so I can try to track the example down?
Is it better to close all the stream one by one OR closing the "external" one is enough. (like in ObjectOuputStream description)
If you check the source for ObjectOutputStream you will find that it is quite safe to do as Sun demonstrate in the example code. However I personally feel that this can cause confusion for junior programmers, so it should be avoided.
note for the authors: the first finally block cant see oos, the second finally block cant see ois and fis. (p187)