Java Reference Guide. Hosted by Steven Haines. Guide Contents. PDF JavaBean; Ganymed SSH-2 for Java. Model-Driven Architecture; Enterprise Messaging with ActiveMQ. World Architecture Screensaver features well done images of old-time construction, buildings, mansions, and ancient and modern houses. You'll also see Eastern and Western architecture including splendid cathedrals, and. JavaBeans - a new component architecture: OVERVIEW Features. JAVABEANS VS ACTIVEX What is ActiveX? How. Not only is the JavaBean architecture portable across platforms, it's portable across other languages! Conclusion. This describes JavaBeans as present in JDK 1.1. This minor revision fixes some errors and omissions in the JavaBeans 1.00-A spec, adds some clarifications, and defines some extra (optional) conventions.
Enterprise JavaBeans Fundamentals Presented by developerWorks. attention to the role of Enterprise JavaBean components in distributed-computing scenarios. and PDF files. JavaBeans and Software Architecture Nenad Medvidovic, Ph. D. Assistant Professor SAL 338, Department of Computer Science. while notifications behave identically as JavaBean events. JAVA AND ARCHITECTURE-BASED SOFTWARE. Enterprise JavaBeans is a component architecture for creating scalable. A beginner's guide to Enterprise JavaBeans. More like this. News and New Product Briefs. An Enterprise JavaBean is a component.
A beginner's guide to Enterprise Java. Beans. Enterprise Java. Beans (EJB) has generated a great deal of excitement since the March 1. Enterprise Java. Beans Specification Version 1. Companies such as Oracle, Borland, Tandem, Symantec, Sybase, and Visigenic, among many others, have announced and/or delivered products that adhere to the EJB specification.
EJB Architecture and Design CS486 Global Knowledge Networks Instructor : Dr. V. Juggy Presentation by: Aravind Vinnakota What is EJB? An EJB is just a collection of Java classes and XML file, bundled into a single unit. The.
This month, we'll take a high- level look at what exactly Enterprise Java. Beans is. We'll go over how EJB differs from the original Java. Beans component model, and discuss why EJB has generated such an enormous amount of interest. But first, an advisory: we won't be looking at source code or how- to topics this month. This article isn't a tutorial; rather it's an architectural overview. EJB covers a lot of territory, and without first understanding the basic concepts involved, code snippets and programming tricks are meaningless.
If there's interest on the part of Java. World's readers, future articles may cover the specifics of using the Enterprise Java. Beans API to create your own Enterprise Java. Beans. In order to understand why EJB is so attractive to developers, we need some historical background.
First, we'll look at the history of client/server systems, and at the current state of affairs. Then, we'll discuss the various parts of an EJB system: EJB components - - which live on an EJB container running inside an EJB server - - and EJB objects, which the client uses as a kind of "remote control" of EJB components. We'll go over the two types of EJBs: session and entity objects. You'll also read about home and remote interfaces, which create EJB instances and provide access to the EJB's business methods, respectively. By the end of the article, you'll have an idea of how extensible servers can be built using Enterprise Java. Beans. But first, a look back in time. Client/server history.
Ancient history In the beginning, there was the mainframe computer. And it was good. (Or as good as it got, anyway.) The state of the art in information processing through the 1. Minicomputers and timesharing in the 1. The first personal computers in the 1.
Client/server to the rescue The client/server architecture is one of the most common solutions to the conundrum of how to handle the need for both centralized data control and widespread data accessibility. In client/server systems, information is kept relatively centralized (or is partitioned and/or replicated among distributed servers), which facilitates control and consistency of data, while still providing access to the data users need. Client- server systems are now commonly composed of various numbers of tiers. The standard old mainframe or timesharing system, where the user interface runs on the same computer as the database and business applications, is known as single tier. Such systems are relatively easy to manage, and data consistency is simple because data is stored in only one place. Unfortunately, single- tier systems have limited scalability and are prone to availability hazards (if one computer's down, your whole business goes down), particularly if communication is involved. The first client/server systems were two- tier, wherein the user interface ran on the client, and the database lived on the server.
Such systems are still common. One garden- variety type of two- tier server performs most of the business logic on the client, updating shared data by sending streams of SQL to the server. This is a flexible solution, since the client/server conversation occurs at the level of the server's database language. In such a system, a properly designed client can be modified to reflect new business rules and conditions without modifying the server, as long as the server has access to the database schema (tables, views, and so forth) needed to perform the transactions. The server in such a two- tier system is called a database server, as shown below.
Figure 1. A database server. Database servers have some liabilities, though. Often the SQL for a particular business function (for example, adding an item to an order) is identical, with the exception of the data being updated or inserted, from call to call. A database server ends up parsing and reparsing nearly identical SQL for each business function. For example, all SQL statements for adding an item to an order are likely to be very similar, as are the SQL statements for finding a customer in the database. The time this parsing takes would be better spent actually processing data.
There are remedies to this problem, including SQL parse caches and stored procedures.) Another problem that arises is versioning the clients and the database at the same time: all machines must shut down for upgrades, and clients or servers that fall behind in their software version typically aren't usable until they're upgraded. Application servers An application server architecture (see the next image) is a popular alternative to a database server architecture because it solves some of the problems database servers have.
Figure 2. An application server. A database server environment usually executes business methods on the client, and uses the server mostly for persistence and enforcing data integrity. In an application server, business methods run on the server, and the client requests that the server execute these methods. In this scenario, the client and server typically will use a protocol that represents a conversation at the level of business transactions, instead of at the level of tables and rows.
Such application servers often perform better than their database counterparts, but they still suffer from versioning problems. Both database and application systems can be enhanced by adding additional tiers to the architecture. So- called three- tier systems place an intermediate component between the client and the server. An entire industry - - middleware - - has cropped up to address the liabilities of two- tier systems.
A transaction- processing monitor, one type of middleware, receives streams of requests from many clients, and may balance the load between multiple servers, provide failover when a server fails, and manage transactions on a client's behalf. Other types of middleware provide communications protocol translation, consolidate requests and responses between clients and multiple heterogeneous servers (this is particularly popular in dealing with legacy systems in business process reengineering), and/or provide service metering and network traffic information. Multiple tiers provide a flexibility and interoperability that has resulted in systems with more than these three layers of service. For example, n- tier systems are generalizations of three- tier systems, each layer of software providing a different level of service to the layers above and beneath it. The n- tier perspective considers the network to be a pool of distributed services, rather than simply the means for a client to accesses a single server. As object- oriented languages and techniques have come into vogue, so have client/server systems increasingly moved toward object- orientation. CORBA (Common Object Request Broker Architecture) is an architecture that allows objects within applications - - even objects written in different languages - - to run on separate machines, depending on the needs of a given application.
Applications written years ago can be packaged as CORBA services and interoperate with new systems. Enterprise Java. Beans, which is designed to be compatible with CORBA, is another entry into the object- oriented application- server ring. The purpose of this article is not to provide a tutorial on client/server systems, but it was necessary to provide some background in order to define context.
Now let's look at what EJB has to offer. Enterprise Java. Beans and extensible application servers.
Now that we've looked at a bit of history and have an understanding of what application servers are, let's look at Enterprise Java. Beans and see what it offers in that context. The basic idea behind Enterprise Java. Beans is to provide a framework for components that may be "plugged in" to a server, thereby extending that server's functionality. Enterprise Java. Beans is similar to the original Java. Beans only in that it uses some similar concepts.
EJB technology is governed not by the Java. Beans Component Specification, but by the entirely different (and massive) Enterprise Java. Beans Specification. See Resources for details on this spec.) The EJB Spec calls out the various players in the EJB client/server system, describes how EJB interoperates with the client and with existing systems, spells out EJB's compatibility with CORBA, and defines the responsibilities for the various components in the system. Enterprise Java. Beans goals The EJB Spec tries to meet several goals at once: EJB is designed to make it easy for developers to create applications, freeing them from low- level system details of managing transactions, threads, load balancing, and so on.
Application developers can concentrate on business logic and leave the details of managing the data processing to the framework. For specialized applications, though, it's always possible to get "under the hood" and customize these lower- level services. The EJB Spec defines the major structures of the EJB framework, and then specifically defines the contracts between them. The responsibilities of the client, the server, and the individual components are all clearly spelled out. We'll go over what these structures are in a moment.) A developer creating an Enterprise Java. Bean component has a very different role from someone creating an EJB- compliant server, and the specification describes the responsibilities of each.
EJB aims to be the standard way for client/server applications to be built in the Java language. Just as the original Java.