External Documentation

Java
Java 1.7 Javadoc

Spring MVC
Introduction to Spring Web MVC framework
Spring Expression Language (SpEL)
Spring Security 1
Spring Security 2
Spring 3 Javadoc
Spring Framework Reference Documentation

Validation
Validation, Data Binding, and Type Conversion
Using Bean Validation
Hibernate Validator

Thymeleaf
Thymeleaf
Thymeleaf - Spring Security 3 integration module

JPA
Introduction to the Java Persistence API
javax.persistence Javadoc
Wikibooks - Java Persistence
Google JPA tutorial

Joda Time
Joda Time - Java date and time API