As you saw yesterday, there are many ways of integrating existing and third-party applications and components with J2EE applications. However, the plethora of integration mechanisms has long been an issue. It would be better if there were a more consistent way of integrating applications. Additionally, expectations have increased around the capability to integrate applications that span organizations—particularly across the common communication medium of the Internet. Web Services provide a flexible and powerful integration mechanism that can be used to expose existing functionality and components to other organizations or new applications. Today and tomorrow, you will see how you can use Web Service protocols to build bridges between J2EE application components and any other platforms, applications, or components that support those Web Service protocols.

Web Services are seen by many as the next wave of the Internet revolution. The vision is of a Web as rich with functionality as the current Web is with information. The challenge is to expose this functionality in a consistent and usable way.

Today, you learn about

• The concepts underlying Web Services and how Web Services fit with J2EE

• Implementing RPC-style Web Service clients and servers

• Exposing session EJBs as Web Services

First, you need to understand why you would use Web Services.

The aim of the last two days was to describe how to use J2EE technologies to implement and access a Web Service. This chapter will give an overview of how Web Service interactions work and will show how you can use JAX-RPC to generate and consume SOAP messages based on a WSDL interface.

Note - Before proceeding further, please be aware that the subject of Web Services is in itself very large, and there are many books dedicated to this popular topic. Today and tomorrow are intended to give you a start into using Web Services in Java and with J2EE technologies. However, it is not possible to answer every question or pursue every topic. If you would like to find out more about Java and Web Services after you have read through the material in this book, try the following URLs:

• Sun Java Web Services—http://java.sun.com/webservices/

• IBM DeveloperWorks—http://www-106.ibm.com/developerworks/webservices/

• Apache XML—http://xml.apache.org/

• ZapThink—http://www.zapthink.com/

• Web Services Articles and Information—http://www.webservices.org

• ebXML home and resources—http://www.ebxml.org

This chapteris fromTeach Yourself J2EE in 21 Days, second edition, byMartin Bond et. al.(Sams, 2004, ISBN: 0-672-32558-6). Check it out at your favorite bookstore today. Buy this book now.