Knowledge of HTTP, Servlets and Servers

We will be focussing on learning about web services with HTTP as the transport protocol and will be deploying web services on web containers as well as application servers . So a decent knowledge about these are good to have.

You can learn more about these @ http://javajee.com/java-ee-web-components-part1-http-and-servlets.

Monitoring Tools

Monitoring and seeing the actual requests and responses sent over wire will give a better understanding of the underlying protocol and message structure. 

You can learn about such monitoring and analyzing tools @ http://javajee.com/monitoring-and-analyzing-tools.

Core Java

Since we are developing web services using Java programming language, decent knowledge about Java is required.

You can start learning about Java @ http://javajee.com/beginning-java-book.

Knowledge of multithreading

Knowledge of multithreading is good to have, to write good multithreaded web services.

You can learn more about multithreading @ http://javajee.com/java-multithreading-book.

Knowledge of Collections

Knowledge of collections is good to have, to write good model classes for web services.

You can learn more about collections @ http://javajee.com/generics-and-collections.