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Advanced Java 
Apache Jakarta Commons: Reusable Java Components (Will Iverson)
Java Application Development on Linux (Carl Albing/Michael Schwarz)
Introduction To Design Patterns with Java (Bob Tarr) Java Server Technologies (Bob Tarr)
Processing XML with Java (E.R. Harold) [Mirror] Sun Certified Java Programmer Pre-Exam Essentials [Mirror]
Securing Java (G. McGraw, E. Felten) Java Data Objects (by R.M. Roos, in PDF)
Concurrent Programming Using Java (S.J. Hartley) Java Design Pattern: A Tutorial (J.W. Cooper)
Interface Design: Best Practices in Object-Oriented API Design in Java (by Bill Venners)
Design Patterns Dictionary (in C++ and Java) [in C#] Advanced Programming for the Java 2 Platform
Thinking in Patterns with Java [PDF] [Mirror] [Mirror] [Mirror] [Download]
Java Reference Guide (S. Haines) SUN's Java Developer Bookshelf
JavaBoutique Tutorials Java Open Source Tools Tutorials
O'Reilly® Java Books Chapters Using JAAS for Authorization and Authentication
The Java Native Interface Programmer's Guide and Specification [Download]
A Comparison of the C# Programming Language to the JAVA Programming Language
Integrating Java with Existing Data and Applications on OS/390 (Alex Louwe, et al)
Coding Conventions for Java [Mirror] Finite-state Automata in Java (Bradley Kjell)
Objects and Java: Building Object-Oriented, Multi-Threaded Applications with Java
Getting Started with JDBC API [1.4] [1.3] JAAS Developer's Guide [Reference]
Java Platform Performance: Strategies and Tactics (by S. Wilson and J. Kesselman)
330 Java Tips (Download) Java Performance
Working with Java and XML The JNDI Tutorial (Rosanna Lee)
Practical Artificial Intelligence Programming in Java (Mark Watson)
Java Application Development for CICS Extend Eclipse's Java Development Tools
Java Language Specification, 2nd Edition, (by James Gosling, Bill Joy, Guy Steele, Gilad Bracha)
Java Virtual Machine Specification, 2nd edition (Tim Lindholm and Frank Yellin)
Java Expert Solutions The Official Gamelan Java Directory