Book excerpt: As simple Web access to data housed on corporate mainframes is fast becoming a core business requirement, mainframe programmers need to learn how to develop Java applications to keep pace with growing corporate needs. Focusing on concepts familiar to mainframe programmers, this book gives step-by-step guidance on how to use Java to access file and database structures common to mainframe environments. After comparing Java and mainframe languages such as COBOL and PL/I, Marco goes on to cover Java implementations for IBM's OS/390 and advanced Java programming techniques, including Java classes and EJB. A must-read for anyone who needs to provide users with access to business data via a Web interface, this book is a logical companion to System 390 JCL (0-471-28309-6), our bestselling mainframe programming book now in its fourth edition.