Personal computing continues to become more “personal” in that computers are becoming increasingly accessible anytime, anywhere. At the forefront of this advancement are handheld devices that are transforming into computing platforms. Mobile phones are no longer just for talking—they have been capable of carrying data and video for some time. More signifi-cantly, the mobile device is now becoming so capable of general-purpose computing that it’s destined to become the next PC. It is also anticipated that a number of manufacturers such as ASUS, HP, and Dell will be producing netbooks based on the Android OS. So the battle lines of operating systems, computing platforms, programming languages, and development frame-works are being shifted and reapplied to mobile devices. We are also expecting a surge in mobile programming in the IT industry as more and more IT applications start to offer mobile counterparts. To help you profit from this trend, we’llshow you how to use Java to write programs for devices that run on Google’s Android Platform (http://code.google.com/android/), an open source platform for mobile development. We are excited about Android because it is an advanced platform that introduces a number of new paradigms in framework design. In this chapter, we’ll provide an…

Enterprise Concurrency The most dramatic difference between an enterprise system and a "regular" application is the number of users it must serve. As a result, enterprise applications face problems that don't often occur on the desktop. A word processor, for example, doesn't have to handle two users making changes to one paragraph at the same time—at the most, it might have to notify the second user that the document is already in use. Of course, all data-centric applications, whether they serve one user or 10,000, need to concern themselves with the validity of their data. An action that seems simple to the user ("Order a book") may require complex, choreographed activities within the application ("Check inventory, reserve stock, charge credit cards, arrange shipping, etc."). The more operations an application performs, the more likely one of those activities will fail—and when it does, the system must be able to carry on. Providing for this capability is easy in standalone applications: just don't save your changes if the mail merge fails. But if other users have been modifying the same databases at the same time, the brute-force approach to data integrity won't pan out. A lot of ink has been spilled on…

Database and Data Patterns Storage is the one constant in enterprise development. Enterprise systems are, essentially, information management systems. To the user, the value of these applications comes from the centralization of information resources, which allows broader access and more flexible interaction. Of course, you can maintain an entire information model in memory, but that's not the best method: if someone trips over the cord, your business is back to square one. So production applications implement persistence, storing information to reliable media. This chapter focuses on patterns for implementing and optimizing persistent storage in the business tier. The first section introduces some basic patterns for accessing persistent resources: the Data Access Object (DAO) pattern and the Procedure Access Object (PAO) pattern. The rest of the chapter focuses on solving recurring problems in database-backed applications. Since Java object graphs generally store relations between objects directly, we need to translate Java's direct object-to-object relationships into something that we can store in a database. The solution is a primary key: a unique identifier associated with each logical entity in the database, which can be used to represent the relationships between objects. Since unique primary keys are so important to the database side of…

Tier Communications This chapter focuses on managing the communications between tiers using data transfer patterns. Our goal is to provide a basic vocabulary for talking about exchanging data between different components of the business tier and between the business tier and the presentation tier. Ultimately, we want to be able to do this in a well-structured, efficient, and flexible way.   7.1 Data Transfer Patterns In an ideal world, every time we send data from one place to another, we would include all the information required for the current activity, with no waste and no need for the recipient to come back with questions. Anyone who has worked technical support is familiar with the situation: it's much easier to have the user explain the entire problem at once, with all the relevant detail, rather than have to ask a series of questions to determine whether the computer is on, if an error message was displayed, if the software was actually installed, and so forth. A single support person can handle more problems with fewer headaches. In Java terms, this ideal could involve transferring a single object containing a complete bug report, rather than transmitting several individual objects for each aspect…