1. Write in brief about the J2EE enterprise edition? Java is one of the most commonly used and mature programming languages for building enterprise applications. Java development has evolved from small applets run on a Web browser to large enterprise distributed applications run on multiple servers. Now, Java has three different platforms, or flavors, and each addresses certain programming requirements: 1. The Java 2 Platform, Standard Edition (J2SE) 2. The Java 2 Platform, Enterprise Edition (J2EE) 3. The Java 2 Platform, Micro Edition (J2ME) The Java 2 Platform, Standard Edition (J2SE) It is the underlying base platform for the J2EE. The J2SE platform consists of the Java 2 Software Development Kit (SDK) and the Java 2 Runtime Environment (JRE). J2SE includes tools and application programming interfaces (APIs) for developing client applications with graphical user interfaces (GUIs), database access, directory access, Common Object Request Broker Architecture (CORBA), fine-grained security, input/output functions, and many other functions. It s the most widely used Java platform. The Java 2 Platform, Micro Edition (J2ME) It helps with building Java applications for micro-devices with limited display and memory requirements (the entire API fits into 1KB), such as wireless devices, PDAs, and network devices. The Java 2 Platform, Enterprise Edition (J2EE) It is a platform for building server-side components and applications. It provides the infrastructure needed for these applications through a set of common services. The Java 2 Platform, Enterprise Edition (J2EE) defines the standard for developing multitier enterprise applications. The J2EE platform simplifies enterprise applications by basing them on standardized, modular components, by providing a complete set of services to those components, and by handling many details of application behavior automatically, without complex programming. The J2EE platform takes advantage of many features of the Java 2 Platform, Standard Edition (J2SE), such as "Write Once, Run Anywhere" portability, JDBC API for database RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 1
access, CORBA technology for interaction with existing enterprise resources, and a security model that protects data even in internet applications. Building on this base, the Java 2 Platform, Enterprise Edition adds full support for Enterprise JavaBeans components, Java Servlets API, JavaServer Pages and XML technology. The J2EE standard includes complete specifications and compliance tests to ensure portability of applications across the wide range of existing enterprise systems capable of supporting the J2EE platform. In addition, the J2EE specification now ensures Web services interoperability through support for the WS-I Basic Profile. J2EE architecture supports component-based development of multi-tier enterprise applications. A J2EE application system typically includes the following tiers: Client tier: In the client tier, Web components, such as Servlets and JavaServer Pages (JSPs), or standalone Java applications provide a dynamic interface to the middle tier. Middle tier: In the server tier, or middle tier, enterprise beans and Web Services encapsulate reusable, distributable business logic for the application. These server-tier components are contained on a J2EE Application Server, which provides the platform for these components to perform actions and store data. Enterprise data tier: In the data tier, the enterprise's data is stored and persisted, typically in a relational database. J2EE applications are comprised of components, containers, and services. Components are application-level components. Web components, such as Servlets and JSPs, provide dynamic responses to requests from a Web page. EJB components contain server-side business logic for enterprise applications. Web and EJB component containers host services that support Web and EJB modules. J2EE platform and its common services : J2EE is a platform and an industry-accepted standard that enables solutions for developing and deploying multitier enterprise applications. It provides a unified platform for building distributed, server-centric systems. J2EE is a set of standard APIs that is offered by a vendor through products and tools to be used by the enterprise. It was developed to meet recent enterprise requirements, such as diversity of both applications and data, in addition to the complexity of business processes. The J2EE standard is defined through a set of related specifications, such as the J2EE specification, the Enterprise JavaBeans specification, the Java Servlet specification, and the JavaServer Pages (JSP) specification. RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 2
The J2EE platform offers the following benefits to the enterprise and to product vendors: Establishes standards for database connectivity, Web components, business logic components, message-oriented middleware (MOM), communication protocols, and interoperability. Decreases time-to-market because much of the infrastructure and common services are provided by vendors products that are implemented according to the standard J2EE specification. IT organizations can get out of the middleware business and concentrate on building applications for their business. Increases developer productivity because Java programmers can relatively easily learn J2EE technologies based on the Java language. All enterprise software development can be accomplished under the J2EE platform, using Java as the programming language. Promotes interoperability within existing heterogeneous systems, such as CORBA and J2EE. Enables developers to focus on supporting business process requirements rather than building the in-house application infrastructure. The application server handles the complex tasks of multithreading, synchronization, transactions, resource allocation, and life cycle management. In general, the J2EE platform helps the enterprise to overcome certain issues such as programming productivity, application reliability, availability, security, scalability, and integration with existing systems. 2. Explain the Java 2 Enterprise Edition Architecture RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 3
Sun released its J2EE specification which provided a comprehensive view of the Java middle tier solution. J2EE uses a 4-level model for web development. The browser runs on the client displaying HTML and optionally runs JavaScript. The middle tier is comprised of two layers: a Presentation Layer and a Business Logic Layer. The data manages persistent data in a database and, where appropriate, legacy data stores. J2EE implements the Presentation Layer with Servlets and, more recently, Java provides the option to generate webpages with dynamic content using JavaServer Pages (JSP). Servlets/JSP generate webpages with dynamic content (typically originating from the database). They also parse webpages submitted from the client and pass them to Enterprise JavaBeans for handling. Servlets and JSPs run inside a Web Server. J2EE implements the Business Logic layer with Enterprise JavaBeans (EJB). Enterprise JavaBeans are responsible for logic like validation and calculations as well as provided data access (e.g. database I/O) for the application. Enterprise JavaBeans run inside an Application Sever. Under J2EE, EJBs access a database through one of two means: using a JDBC interface which requires a lower level of coding RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 4
using SQLJ which provides a higher level interface to the database In addition to these components for web application, J2EE provides for access by nonweb clients to the business logic layer. A standalone Java application (IIOP client) can access an EJB directly using J2EE s Remote Method Invocation (RMI) API. The advantages of a 3-tiered or n-tiered application: 3-tier or multi-tier architectures force separation among presentation logic, business logic and database logic. Let us look at some of the key benefits: Manageability: Each tier can be monitored, tuned and upgraded independently and different people can have clearly defined responsibilities. Scalability: More hardware can be added and allows clustering (i.e. horizontal scaling). Maintainability: Changes and upgrades can be performed without affecting other components. Availability: Clustering and load balancing can provide availability. Extensibility: Additional features can be easily added. Supporting J2EE APIs J2EE provides a number of supporting APIs. The purpose of most of these APIs is to enable interaction between the main software layers/components in the J2EE architecture. Remote Method Interface (RMI) Java Servlets JSP EJB Java Naming and Directory Interface (JNDI) Java Message Service (JMS) Java Transaction API (JTA) Java Database Connectivity (JDBC) / SQLJ JavaMail /JMC JAAS XML Remote Method Interface (RMI) RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 5
RMI is an important API used for supporting distributed computing and has been supported in core Java since version 1.1. RMI allows a Java client application to communicate with a Java server application by invoking methods on that remote object. With RMI, the client gets a reference to a server object and then it can invoke methods on that object as if it were a local object within the same virtual machine. For server objects developed in other languages, you must employ other techniques like using Java IDL with CORBA or RMI/IIOP to access the server object. Java Servlets Servlets are the Java platform technology of choice for extending and enhancing web servers. Servlets provide a component-based, platform-independent method for building webbased applications, without the performance limitations of CGI programs. Servlets have access to the entire family of Java APIs, including the JDBC TM API to access enterprise databases. JSP (Java Server Pages) JavaServer Pages technology uses XML-like tags and scriptlets written in the Java programming language to encapsulate the logic that generates the content for the page. Any and all formatting (HTML or XML) tags are passed directly back to the response page. EJB (Enterprise Java Beans) Enterprise JavaBeans TM is the server-side component architecture for the J2EE TM platform. EJB TM enables rapid and simplified development of distributed, transactional, secure and portable Java applications. Java Naming and Directory Interface (JNDI) JNDI allows Java programs to use name servers and directory servers to look up objects or data by name. This important feature allows a client object to locate a remote server object or data. RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 6
JNDI is a generic API that can work with any name or directory servers. Server providers have been implemented for many common protocols (e.g. NIS, LDAP and NDS) and for CORBA object registries. Of particular interest to users of J2EE, JNDI is used to locate Enterprise JavaBean (EJB) components on the network. Java Message Service (JMS) JMS is an API for using networked messaging services. Data sent in a message is often intended as a sort of event notification (e.g. a Email-handling process may need to be notified when a request is enqueued). Another common use for messaging (thus JMS) is for interfacing with external, third party or legacy applications, typically via a Message Oriented Middleware product like IBM s MQ Series (now WebSphere MQ). It can be complex/risky to use RPC/RMI to directly invoke remote applications while a messaging solution can provide a simpler and more reliable interconnection. Java Transaction API (JTA) JTA is used for managing distributed transactions (e.g. updates to multiple databases that must be handled in a single transaction). JTA is a low-level API and associated coding is complex and error-prone. Fortunately, EJB containers (or application servers) generally provide support for distributed transactions using JTA. For this reason, the EJB developer is able to gain the benefit of distributed transaction while leaving the complex implementation details to the provider of the EJB container. Java Database Connectivity (JDBC) / SQLJ In principle, JDBC serves the same purpose as ODBC. JDBC provides a databaseindependent protocol for accessing relational databases from Java. JDBC supports Data Manipulation Language (DML) statements like insert, update, delete, select. It also includes Data Definition Language (DDL) statements like Create Table, Alter Table, etc. JDBC was included in core Java starting with version 1.1. With JDBC, the SQL is always dynamically generated at runtime and sent to the database. RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 7
An easier-to-use industry standard for Java database access has emerged and is called SQLJ. SQLJ allows static SQL to be used and it requires less cumbersome syntax than JDBC. Other SQLJ advantages over JDBC include better code quality (due to compile-time syntax checking) and better performance (due to compile-time optimization). James Woodger co-authored an in-depth article on SQLJ for the November 2000 issue of Java Enterprise Developer. 3. Write notes on the Multi-Tier Architecture The J2EE platform uses a multitiered distributed application model. Application logic is divided into components according to function, and the various application components that make up a J2EE application are installed on different machines depending on the tier in the multitiered J2EE environment to which the application component belongs. Client-tier components run on the client machine. J2EE multi-tiered applications are generally considered to be three-tiered applications because they are distributed over three different locations Client machines The J2EE server machine The database or legacy machines at the back end RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 8
Multitiered Applications Web-tier components run on the J2EE server. Business-tier components run on the J2EE server. Enterprise information system (EIS)-tier software runs on the EIS server. Although a J2EE application can consist of the three or four tiers shown, J2EE multitiered applications are generally considered to be three-tiered applications because they are distributed over three different locations: client machines, the J2EE server machine, and the database or legacy machines at the back end. Three-tiered applications that run in this way extend the standard two-tiered client and server model by placing a multithreaded application server between the client application and back-end storage. J2EE Components J2EE applications are made up of components. A J2EE component is a self-contained functional software unit that is assembled into a J2EE application with its related classes and files and that communicates with other components. The J2EE specification defines the following J2EE components: Application clients and applets are components that run on the client. Java Servlet and JavaServer Pages (JSP) technology components are Web components that run on the server. Enterprise JavaBeans (EJB) components (enterprise beans) are business components that run on the server. RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 9
J2EE components are written in the Java programming language and are compiled in the same way as any program in the language. The difference between J2EE components and "standard" Java classes is that J2EE components are assembled into a J2EE application, verified to be well formed and in compliance with the J2EE specification, and deployed to production, where they are run and managed by the J2EE server. J2EE Clients Web Clients A J2EE client can be a Web client or an application client. A Web client consists of two parts: dynamic Web pages containing various types of markup language (HTML, XML, and so on), which are generated by Web components running in the Web tier, and a Web browser, which renders the pages received from the server. A Web client is sometimes called a thin client. Thin clients usually do not do things like query databases, execute complex business rules, or connect to legacy applications. When you use a thin client, heavyweight operations like these are off-loaded to enterprise beans executing on the J2EE server where they can leverage the security, speed, services, and reliability of J2EE server-side technologies. Applets A Web page received from the Web tier can include an embedded applet. An applet is a small client application written in the Java programming language that executes in the Java virtual machine installed in the Web browser. However, client systems will likely need the Java Plug-in and possibly a security policy file in order for the applet to successfully execute in the Web browser. Web components are the preferred API for creating a Web client program because no plug-ins or security policy files are needed on the client systems. Application Clients A J2EE application client runs on a client machine and provides a way for users to handle tasks that require a richer user interface than can be provided by a markup language. It typically has a graphical user interface (GUI) created from Swing or Abstract Window Toolkit (AWT) APIs, but a command-line interface is certainly possible. Application clients directly access enterprise beans running in the business tier. RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 10
However, if application requirements warrant it, a J2EE application client can open an HTTP connection to establish communication with a servlet running in the Web tier. 4. Write about the best practices in J2EE? A Best Practice is a proven technique for achieving a desired result. It is a repeatable technique that has been successful in real life situations, and can be broadly applied across many problems. Best practices in two major sections: 1. Best practices in theory. 2. Best practices in practice. DEVELOPMENT LIFE CYCLE The most critical element of any application development philosophy is the methodology that defines the entire application development cycle. Since methodologies used to make modern J2EE applications are so diverse, we will not endorse any particular methodology. Instead, we will define five relatively generic steps that any significant development method will need to support. The best practices under each can then be integrated into your development cycle. RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 11
The above figure shows the major steps in a development cycle, and the areas in which Best Practices can be applied for each step. Development life cycle Attack risk as early as possible The risk associated with application development seems to rise exponentially with complexity. reducing risk in three ways: Improving knowledge. The biggest risks will always be associated with the unknown. Earlier knowledge will allow you to make more informed decisions and better schedules through the remainder of development cycle. Allowing recovery time. If you re going to fail, it s better to fail early, while there s still time to recover. Involving the customer early. Your customer s response to a user interface or key capability can dramatically impact the direction of a project. Inspiring confidence early improves your relationships. DESIGN Design for change with dynamic domain model Use a standard modeling language UML (Unified Modeling Language) Recycle your resources DEVELOP Use proven design patterns Automate the build process Integrate often Optimize communication costs TEST RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 12
Build test cases first Create a testing framework Automate testing DEPLOY Use j2ee standard packaging specification Use tools to help in deployment Back up your production data and environment TUNE Build a performance plan Manage memory and plug leaks Focus on priorities ENVIRONMENTS Do not restrict deployment options at design time Create a responsive development environment RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 13
4. Comparison between J2EE and.net There are many similarities between.net and J2EE.We are considering the models but in the real world, J2EE is a programming model based on the Java language, having a concept of a container (typically application server) that provides services like lifecycle management and support for declarative transactions. J2EE is based on object oriented design principles; it is a specification owned by Sun Microsystems, however, Sun does involve the community in building the specification through the Java Community Process. The core J2EE specification is supported by multiple vendors most notably Sun Microsystems, BEA and IBM and other vendors build applications that run on J2EE applications servers. In addition to the 'write once, deploy on multiple operating systems' feature of Java, J2EE also defines layers of abstractions in the forms of APIs that provide some level of decoupling between your application and the underlying infrastructure and resources e.g. as in case of JMS and JDBC APIs. In the real world,.net is a programming model that supports multiple languages; it provides object oriented design principles. The.NET specifications and the core APIs are developed by Microsoft, however, Microsoft involves the community by actively getting feedback through multiple channels and uses that feedback to decide the new features of the framework, the.net frame work is supported by a large ecosystem of ISVs that develop solutions that utilize the.net APIs. The applications developed using the.net model are typically deployable on the Windows platform only, however, they can interoperate with applications running on other platforms using a variety of mechanisms that I will be discussing in my future posts. The new version of.net,.net 2.0, introduces the concept of providers which decouples your application from the underlying resources like the database and security-credential provider. Both J2EE and.net have concepts of Virtual Machines and Just-in-time compilation, J2EE has a Java Virtual Machine (JVM) that facilities platform choice and.net has Common Language Runtime (CLR) that facilitates choice of programming languages, the conceptual architecture for both the models looks quiet similar. RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 14
Keeping all the prejudices aside, it is possible to develop good IT solutions using either model of programming, there is nothing inherently wrong with.net or J2EE, those who claim that a reliable system cannot be developed in Java or that it is not possible to develop a highly secure and reliable system in.net have not done their homework or are not current in their research. It is true that both J2EE and.net have had their set of issues in the past years, however both programming models have passed through radical changes and many of the issues have been resolved some time ago, e.g. I recently corresponded with someone that was concerned about the inherent capability of.net to support his enterprise mission critical application consisting of 100 transactions per second in a system where a 150 million dollars exchanges take place in an year. It came as news to him that their are many absolutely mission critical applications running on.net, including applications that support 3000 transactions per second with over 5 trillion dollars changing hands (at a stock exchange). Similarly, we have seen a very complex and large airline reservation system successfully developed and running on J2EE. The inherent capability of the programming models is only one of the factors and the architects and technical decision makers need to look at other criteria for making an objective decision. 6. Explain with diagram the features of.net and J2EE? Development model of J2EE and.net: RAJIV GANDHI COLLEGE OF ENGINEERING & TECHNOLOGY/CSE Page 15
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