Once again another excellent O'Reilly book.
O'Reilly have for some time been publishing a series of Java programming books. These are split into different areas of interest, of which Java Security is one.
With there being concern over using both the Internet and Java for secure transactions, a book such as this is needed to dispel the myths. It is designed for programmers to implement security within their Java programs and thus ensure any data and users are 'safe'. The author, a Sun employee, accomplishes this by covering the basics of the Java security model and the classes needed to implement it. By the end you should be able to manage all the security features within Java from threads through to encryption of the actual data being transmitted.
Once again another excellent O'Reilly book. There may be others that cover similar territory, but this will match all the other O'Reillys on the shelf.