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14 Chapter 1 Access another system. Examples include calling a high-performing CICS legacy system written in COBOL that computes the risk factor for a new insurance account, calling a legacy VSAM data store, or calling SAP R/3. Enterprise beans can integrate with an existing application through the J2EE Connector Architecture (JCA), which we will talk about in detail in Chapter 17. Thus, EJB components are not presentation tier components; rather, they sit behind the presentation tier components (or clients) and do all the hard work. Examples of the clients that can connect to enterprise beans include the following: Thick clients. Thick clients execute on a user s desktop. They could connect through the network with EJB components that live on a server. These EJB components may perform any of the tasks listed previously (business logic, database logic, or accessing other systems). Thick clients in Java include applets and applications. Dynamically generated Web pages. Web sites that are transactional and personalized in nature need their Web pages generated specifically for each request. For example, the home page for Amazon.com is completely different for each user, depending on the user s profile. Core technologies such as Java servlets and JavaServer Pages (JSP) are used to dynamically generate such specific pages. Both servlets and JSPs live within a Web server and can connect to EJB components, generating pages differently based upon the values returned from the EJB layer. Web Service clients. Some business applications require no user interface at all. They exist to interconnect with other business partners applications that may provide their own user interface. For example, consider a scenario where Dell Computer Corporation needs to procure Intel chips to assemble and distribute desktop computers. Here, Intel could expose an Order Parts Web Service that enables the Dell Web Service client to order chips. In this case, the Intel system does not provide a graphical user interface per se, but rather provides a Web Service interface. This scenario is shown in Figure 1.4.
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Overview 13 Cross-platform. Java runs on any platform. Since EJB is an application of Java, this means EJB should also easily run on any platform. This is valuable for customers who have invested in a variety of powerful hardware, such as Win32, UNIX, and mainframes. They do not want to throw away these investments. If you don t want to go the EJB route, you have two other choices: Lightweight open source Java frameworks such as Spring. In Chapter 11 we discuss when to use EJB versus such non-standard frameworks. Microsoft .NET managed components, part of the Microsoft .NET platform EJB as a Business Tier Component The real difference between presentation tier components such as thick clients, dynamically generated Web pages, or Web Service clients and enterprise beans is the domain in which they operate. Presentation components are well suited to handle client-side operations, such as rendering GUIs, executing client-side validations, constructing appropriate SOAP messages to send them to Web Service, and so on. They deal directly with the end user or business partner. Enterprise beans, on the other hand, are not intended for the client side; they are server-side components. They are meant to perform server-side operations, such as executing complex algorithms or performing high-volume business transactions. The server side has different kinds of needs than GUI clients do. Server-side components need to run in a highly available (24/7), fault-tolerant, transactional, and multiuser secure environment. The application server provides this high-end server-side environment for the enterprise beans, and it provides the runtime containment necessary to manage enterprise beans. Specifically, EJB is used to help write logic that solves business problems. Typically, EJB components (enterprise beans) can perform any of the following tasks: Perform business logic. Examples include computing the taxes on the shopping cart, ensuring that the manager has authority to approve the purchase order, or sending an order confirmation e-mail using the Java- Mail API. Access a database. Examples include submitting an order for books, transferring money between two bank accounts, or calling a stored procedure to retrieve a trouble ticket in a customer support system. Enterprise beans can achieve database access using the Java Database Connectivity (JDBC) API.
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12 Chapter 1 Rapid application development. Your application can be constructed faster because you get middleware infrastructure services such as transactions, pooling, security, and so on from the application server. There s also less of a mess to maintain. Note that while EJB does have these virtues, there are also scenarios in which EJB is overkill. See Chapters 11 and 16 for best practices and discussion surrounding the issue of when to (and when not to) use EJB. Physically, EJB is actually two things in one: A specification. This is a 640-plus-page Adobe Acrobat PDF file, freely downloadable from http://java.sun.com/products/ejb/docs.html. This specification lays out the rules of engagement between components and application servers. It constricts how you code enterprise beans to enable write once, run anywhere behavior for your EJB application. A set of Java interfaces. Components and application servers must conform to these interfaces. Since all components are written to the same interfaces, they all look the same to the application server. The application server therefore can manage anyone s components. Why Java? EJB architecture has supported only the Java language thus far. Though this sounds a bit restrictive, the good news is that Java is one of the best-suited languages for building components for the following reasons. Interface/implementation separation. We need a language that supports clean separation between the interface and implementation mainly to keep the component upgrades and maintenance to minimum. Java supports this separation at a syntactic level through the interface and class keywords. Safe and secure. The Java architecture is much safer than traditional programming languages. In Java, if a thread dies, the application stays up. Pointers are no longer an issue. Memory leaks occur much less often. Java also has a rich library set, so that Java is not just the syntax of a language but a whole set of prewritten, debugged libraries that enable developers to avoid reinventing the wheel in a buggy way. This safety is extremely important for mission-critical applications. Sure, the overhead required to achieve this level of safety might make your application slower, but 90 percent of all business programs are glorified graphical user interfaces (GUIs) to databases. That database is going to be your number one bottleneck, not Java.
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Overview 11 A corporate finance personnel uses treasury management system through company portal Rather than building a treasury management application from scratch, the business buys treasury management system, built as a service, from outside. All company employees use a central company portal application to access various services HTTP SOAP/HTTP Company Portal Application Corporate IT RMI/IIOP Corporate Treasury Management Web Service Wrapper EJBs providing treasury management logic Figure 1.3 Reusable services built using EJB. Introducing Enterprise JavaBeans EJB is a standard for building server-side components in Java. It defines an agreement (contract) between components and application servers that enables any component to run in any application server. EJB components (called enterprise beans) are deployable, and can be imported and loaded into an application server, which hosts those components. The top three propositions of EJB are as follows: It is agreed upon by the industry. Those who use EJB will benefit from its widespread use. Because everyone will be on the same page, in the future it will be easier to hire employees who understand your systems (since they may have prior EJB experience), learn best practices to improve your system (by reading books like this one), partner with businesses (since technology will be compatible), and sell software (since customers will accept your solution). The concept of train once, code anywhere applies. Portability is easier. The EJB specification is published and available freely to all. Since EJB is a standard, you do not need to gamble on a single, proprietary vendor s architecture. And although portability will never be free, it is cheaper than without a standard.
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10 Chapter 1 Why just stop at corporate ITs? Even ISVs are thinking of providing their software as services. Prime examples of software as a service include Sales force.com and Siebel. Both these companies have made their enterprise soft ware available to customers as hosted services. Many other businesses such as Amazon.com and Google provide their core business services, E-commerce, and Web searching, as reusable services to customers and end-users. Reusable services are a very powerful concept, because: Businesses can focus on strategic software development. In cases where software functionality is horizontal and cuts across multiple business domains, it should be treated as commodity and hence procured from a specialized ISV in the form of services. For example, each business requires a corporate treasury management and cash management system. For such a commodity business need, it is best to acquire software from an outside vendor than to build it. This will relieve the IT staff from having to deal with complex treasury functions involving millions of regulations; it anyway does not have direct relevance to the business s core function. The business processes can be assembled faster. The autonomous and loosely coupled nature of services makes it easy to assemble them into business processes. This strength makes services the chosen paradigm for encapsulating business logic. There is a lower total cost of ownership. Businesses that build their software as services end up with a lower total cost of ownership in the long term because they are building software such that it can be easily reusable and assembled into business processes. This is a definite plus when businesses are required to adapt business processes to address the changing market demands or when they are required to support new customers and their IT systems. Businesses that sell software as services, on the other hand, can benefit their customers by offering flexible software licensing options, such as per-month billing or per-year billing, thereby enabling their customers to lower total cost of ownership. Remember that these services can and should be built using components. Therefore, the component architectures are very much here to stay. Figure 1.3 depicts such a Treasury management service built using EJB components. With this introduction to SOA and their relevance to EJB, let us further explore the EJB technology.
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Overview on. At the time of this writing, WSDL 2.0 is well on its way to becoming a W3C standard. Thus, Web Services present a powerful solution for distributed but loosely coupled, coarse-grained SOA wherein services are described using WSDL and accessed via SOAP. In fact, one of the main reasons for using Web Services to realize SOA is the ubiquitous support for XML, SOAP, and WSDL technologies on disparate platforms, ranging from mainframes to mobile devices. This is the main reason why Web Services provide a true solution for interoperability between applications deployed on these disparate platforms. We will spend some more time explaining fundamental concepts in Chapter 5; however, explaining Web Services and related technologies in their entirety is outside the scope of this book. If you are new to Web Services, there are many books and online papers that you can refer to get started with Web Services conceptually. Given the solid adoption of this stack by the industry, we suggest that you familiarize yourself properly with Web services. SOA and Component Architectures SOA is not a replacement for component architecture; rather it neatly complements the component architecture. While component architectures enhance reusability at a finer grain level, SOA can enhance reusability at a coarser grained level. Hence, from an implementation standpoint, a given service might very well be developed using well-defined component frameworks such as EJB. The latest EJB standard, therefore, has in-built support for Web Services, the most popular stack for building SOA. So EJB is still very much in demand! Chapter 5 covers Web Services support in EJB framework in detail. Divide and Conquer to the Extreme with Reusable Services We have been seeing a slow but steady shift in the build-from-scratch trend, for years now. More and more businesses want CIOs to stretch their IT dollars to the maximum. Naturally, this has led the IT departments to think of reuse; reuse in terms of systems as well as software. What better candidate than highly functional and autonomous services to fulfill this promise of reuse? SOA offers maximum reuse, especially when implemented using ubiquitous protocols such as those supported by Web services. Architects want to design their software as a composition of services such that these services can be used from any platform through well-defined service interfaces.
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Chapter 1 Service-Oriented Architectures At the core of a service-oriented architecture lies the concept of service. A simplistic definition of service is a group of related components that carry out a given business process function, for example transferring funds between banks or booking an itinerary. A service-oriented architecture (SOA) thus is a paradigm focusing on development of services rather than piecemeal components such that these services provide a higher level of abstraction from a functional standpoint. Of course, there are more properties to SOA than mere coarse-granularity. One such characteristic property of SOA is that they are autonomous in nature. These independent entities can interact with others in spite of differences in the way they have been implemented or the platform they have been deployed on. The notion of putting together (integrating) such autonomous and loosely coupled services to address the changing business needs has a huge value proposition and it is well on its way to realization with the emergence of various choreography, orchestration and collaboration technologies such as WS-BPEL, EbXML BPSS, and WS Choreography. SOA and Web Services The terms Web Services and SOA are often used interchangeably and wrongly so. SOA is a paradigm. There are many possible ways of building software so that it implements salient features of SOA, mainly coarse granularity and loose coupling. One such way is Web services. Web Services are a group of XML technologies, which can be used for implementing SOA. Core Web service technologies mainly SOAP and WSDL form the basis of most of these Web service implementations today. Simple Object Access Protocol (SOAP) is an XML-based application-level protocol intended for exchanging information in a distributed network. SOAP supports both the models of distributed computing: RPC as well as document- style messaging. RPC style SOAP allows remote invocation of operations. Parameters and return in/out values of these operations are serialized in XML. Whereas, in document-style SOAP because an operation s input and output are XML, serialization of parameters and return value to XML is not needed. Although most of the Web service applications use SOAP over HTTP today, the standard does not preclude using SOAP over other IP protocols, such as SMTP. SOAP 1.2 is a W3C recommendation at the time of this writing. Web Service Description Language (WSDL) is an XML-based metadata standard that is used to describe the service interface in terms of the operations it supports, the parameters that the operations accept, and their return values in case of SOAP RPC, the XML schema that the input and output messages to the operations in case of document-style SOAP as well as service binding information in terms of the communication protocols, ports, service URL, and so

Overview Component Architectures It has been a number of years since the idea of multitier server-side deployments surfaced. Since then, more than 50 application servers have appeared on the market. At first, each application server provided component services in a nonstandard, proprietary way. This occurred because there was no agreed definition of what a component should be or how it should be provided with services or how should it interact with the application server. The result? Once you bet on an application server, your code was locked into that vendor s solution. This greatly reduced portability and was an especially tough pill to swallow in the Java world, which promotes openness and portability. What we need is an agreement, or set of interfaces, between application servers and components. This agreement will enable any component to run within any application server. This will allow components to be switched in and out of various application servers without having to change code or potentially even recompile the components themselves. Such an agreement is called component architecture and is shown in Figure 1.2. If you re trying to explain components to a nontechie, try these analogies: Any CD player can play any compact disc because of the CD standard. Think of an application server as a CD player and components as compact discs. In the United States, any TV set can tune into any broadcast because of the NTSC standard. Think of an application server as a TV set and components as television broadcasts. Application Server agreed-upon interfaces specified by component architecture Components Figure 1.2 A component architecture.
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Chapter 1 THINGS TO CONSIDER WHEN BUILDING LARGE BUSINESS SYSTEMS (continued) . Clean shutdown. If you need to shut down a server, can you do it in a smooth, clean manner so that you don t interrupt service to clients who are currently using the server? . Logging and auditing. If something goes wrong, is there a log that you can consult to determine the cause of the problem? A log would help you debug the problem so it doesn t happen again. . Systems management. In the event of a catastrophic failure, who is mon- itoring your system? You want monitoring software that paged a system administrator if a catastrophe occurred. . Threading. Now that you have many clients connecting to a server, that server is going to need the capability of processing multiple client re- quests simultaneously. This means the server must be coded to be multi- threaded. . Message-oriented middleware. Certain types of requests should be message-based where the clients and servers are very loosely coupled. You need infrastructure to accommodate messaging. . Object life cycle. The objects that live within the server need to be cre- ated or destroyed when client traffic increases or decreases, respectively. . Resource pooling. If a client is not currently using a server, that server s precious resources can be returned to a pool to be reused when other clients connect. This includes sockets (such as database connections) as well as objects that live within the server. . Security. The servers and databases need to be shielded from saboteurs. Known users must be allowed to perform only operations that they have rights to perform. . Caching. Let s assume there is some database data that all clients share and make use of, such as a common product catalog. Why should your servers retrieve that same catalog data from the database over and over again? You could keep that data around in the servers memory and avoid costly network roundtrips and database hits. . And much, much, much more. Each of these issues is a separate service that needs to be addressed for serious server-side computing. These services are needed in any business problem and in any vertical industry. And each of these services requires a lot of thought and a lot of plumbing to resolve. Together, these services are called middleware.
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Overview In the past, most companies built their own middleware. For example, a financial services firm might build some of the middleware services above to help them put together a stock trading system. These days, companies that build their own middleware risk setting themselves up for failure. High-end middleware is hideously complicated to build and maintain, requires expert-level knowledge, and is completely orthogonal to most companies core business. Why not buy instead of build? The application server was born to let you buy these middleware services, rather than build them yourself. Application servers provide you with common middleware services, such as resource pooling, networking, and more. Application servers enable you to focus on your application and not worry about the middleware you need for a robust server-side deployment. You write the code specific to your vertical industry and deploy that code into the runtime environment of an application server. You ve just solved your business problem by dividing and conquering. THINGS TO CONSIDER WHEN BUILDING LARGE BUSINESS SYSTEMS By now you should have a decent list of things you d have to worry about when building large business systems. Here s a short list of the big things we came up with. Don t worry if you don t understand all of them yet you will. . Remote method invocations. We need logic that connects a client and server via a network connection. This includes dispatching method re- quests, brokering parameters, and more. . Load balancing. Clients must be directed to the server with the lightest load. If a server is overloaded, a different server should be chosen. . Transparent fail-over. If a server crashes, or if the network crashes, can clients be rerouted to other servers without interruption of service? If so, how fast does fail-over happen? Seconds? Minutes? What is acceptable for your business problem? . Back-end integration. Code needs to be written to persist business data into databases as well as integrate with legacy systems that may already exist. . Transactions. What if two clients access the same row of the database si- multaneously? Or what if the database crashes? Transactions protect you from these issues. . Clustering. What if the server contains state when it crashes? Is that state replicated across all servers, so that clients can use a different server? . Dynamic redeployment. How do you perform software upgrades while the site is running? Do you need to take a machine down, or can you keep it running? (continued)
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