responses. JSP pages are text-based documents that execute as servlets but allow a more natural approach to creating static content.
What is the container? - Containers are the interface between a component and the low-level platform specific functionality that supports the component. Before a Web, enterprise bean, or application client component can be executed, it must be assembled into a J2EE application and deployed into its container.
What are container services? - A container is a runtime support of a system-level entity. Containers provide components with services such as lifecycle management, security, deployment, and threading.
What is the web container? - Servlet and JSP containers are collectively referred to as Web containers. It manages the execution of JSP page and servlet components for J2EE applications. Web components and their container run on the J2EE server.
What is Enterprise JavaBeans (EJB) container? - It manages the execution of enterprise beans for J2EE applications.
Enterprise beans and their container run on the J2EE server.
Enterprise beans and their container run on the J2EE server.
What is Applet container? - IManages the execution of applets. Consists of a Web browser and Java Plugin running on the client together.
How do we package J2EE components? - J2EE components are packaged separately and bundled into a J2EE application for deployment. Each component, its related files such as GIF and HTML files or server-side utility classes, and a deployment descriptor are assembled into a module and added to the J2EE application. A J2EE application is composed of one or more enterprise bean,Web, or application client component modules. The final enterprise solution can use one J2EE application or be made up of two or more J2EE applications, depending on design requirements. A J2EE application and each of its modules has its own deployment descriptor. A deployment descriptor is an XML document with an .xml extension that describes a component’s deployment settings.
What is a thin client? - A thin client is a lightweight interface to the application that does not have such operations like query databases, execute complex business rules, or connect to legacy applications.
What are types of J2EE clients? - Following are the types of J2EE clients:
o Applets
o Application clients
o Java Web Start-enabled rich clients, powered by Java Web Start technology.
o Wireless clients, based on Mobile Information Device Profile (MIDP) technology.
What is deployment descriptor? - A deployment descriptor is an Extensible Markup Language (XML) text-based file with an .xml extension that describes a component’s deployment settings. A J2EE application and each of its modules has its own deployment descriptor. For example, an enterprise bean module deployment descriptor declares transaction attributes and security authorizations
for an enterprise bean. Because deployment descriptor information is declarative, it can be changed without modifying the bean source code. At run time, the J2EE server reads the deployment descriptor and acts upon the component accordingly.
for an enterprise bean. Because deployment descriptor information is declarative, it can be changed without modifying the bean source code. At run time, the J2EE server reads the deployment descriptor and acts upon the component accordingly.
What is the EAR file? - An EAR file is a standard JAR file with an .ear extension, named from Enterprise ARchive file. A J2EE application with all of its modules is delivered in EAR file.
What is JTA and JTS? - JTA is the abbreviation for the Java Transaction API. JTS is the abbreviation for the Jave Transaction Service. JTA provides a standard interface and allows you to demarcate transactions in a manner that is independent of the transaction manager implementation. The J2EE SDK implements the transaction manager with JTS. But your code doesn’t call the JTS methods directly. Instead, it invokes the JTA methods, which then call the lower-level JTS routines. Therefore, JTA is a high level transaction interface that your application uses to control transaction. and JTS is a low level transaction interface and ejb uses behind the scenes (client code doesn’t directly interact with JTS. It is based on object transaction service(OTS) which is part of CORBA.
What is JAXP? - JAXP stands for Java API for XML. XML is a language for representing and describing text-based data which can be read and handled by any program or tool that uses XML APIs. It provides standard services to determine the type of an arbitrary piece of data, encapsulate access to it, discover the operations available on it, and create the appropriate JavaBeans component to perform those operations.
What is J2EE Connector? - The J2EE Connector API is used by J2EE tools vendors and system integrators to create resource adapters that support access to enterprise information systems that can be plugged into any J2EE product. Each type of database or EIS has a different resource adapter. Note: A resource adapter is a software component that allows J2EE application components to access and interact with the underlying resource manager. Because a resource adapter is specific to its resource manager, there is typically a different resource adapter for each type of database or enterprise information system.
What is JAAP? - The Java Authentication and Authorization Service (JAAS) provides a way for a J2EE application to authenticate and authorize a specific user or group of users to run it. It is a standard Pluggable Authentication Module (PAM) framework that extends the Java 2 platform security architecture to support user-based authorization.
What is Java Naming and Directory Service? - The JNDI provides naming and directory functionality. It provides applications with methods for performing standard directory operations, such as associating attributes with objects and searching for objects using their attributes. Using JNDI, a J2EE application can store and retrieve any type of named Java object. Because JNDI is independent of any specific implementations, applications can use JNDI to access multiple naming and directory services, including existing naming and
directory services such as LDAP, NDS, DNS, and NIS.
directory services such as LDAP, NDS, DNS, and NIS.
What is Struts? - A Web page development framework. Struts combines Java Servlets, Java Server Pages, custom tags, and message resources into a unified framework. It is a cooperative, synergistic platform, suitable for development teams, independent developers, and everyone between.
How is the MVC design pattern used in Struts framework? - In the MVC design pattern, application flow is mediated by a central Controller. The Controller delegates requests to an appropriate handler. The handlers are tied to a Model, and each handler acts as an adapter between the request and the Model. The Model represents, or encapsulates, an application’s business logic or state. Control is usually then forwarded back through the Controller to the appropriate View. The forwarding can be determined by consulting a set of mappings, usually loaded from a database or configuration file. This provides a loose coupling between the View and Model, which can make an application significantly easier to create and maintain. Controller: Servlet controller which supplied by Struts itself; View: what you can see on the screen, a JSP page and presentation components; Model: System state and a business logic JavaBeans.
A great deal has transpired in the Java space since we first attended Java One in 1998. The latest batch of Java 2 Platform Enterprise Edition (J2EE) 1.4 compliant application servers is strong proof of the technological advancements that have taken place during this time period. These server-side offerings adhere to the J2EE three-tier model, while providing a solid foundation for deploying both Web services and service-oriented architectures (SOAs). Regarding Web services, there are currently two main development paths that include J2EE and .NET for creating and deploying these types of services.
Each has garnered the support of industry leaders. For example, J2EE has gained strong support from the Java community (e.g., BEA, IBM, Oracle, Sun, etc.) and .NET spearheads the Web services effort for Microsoft. While development paths may differ, the aforementioned vendors have been strong proponents of Web services and open-standards that include WSDL, ebXML/UDDI and SOAP.
The J2EE Multitiered Model
J2EE multitiered applications are usually considered to be three-tiered applications because they are distributed over three locations (client machine, J2EE server and database server or legacy systems at the back end). It is important to note that although a J2EE application may consist of three tiers (client tier, business tier and EIS tier) or four tiers (client tier, Web tier, business tier and EIS tier), J2EE multitiered applications are generally considered to be three applications. Application logic is divided into components according to function. Accordingly, 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 belongs. The following are the three tiers that comprise the J2EE multitiered model.
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Client Machine (Client Tier)
The J2EE client tier is divided into two main categories that include Web-based clients and application clients.
Web-based client (a.k.a thin client) executes in a standard Web browser such as Microsoft Internet Explorer (IE) and Mozilla Firefox. A Web-based client is comprised of two main parts that include: 1) dynamic Web pages containing various types of markup languages (e.g., HTML, XML, etc.) which are generated by Web components (JSPs and servlets) on the Web tier and 2) a Web browser which renders the pages received from the server. Web-based clients typically do not execute complex business rules, query databases and/or connect to legacy systems. Normally, heavyweight operations are offloaded to Enterprise Java Beans (EJBs) executing on the J2EE server where they may leverage the reliability, security and speed of J2EE-server-side technologies.
Biggest Advantage: Available on a majority of client machines (e.g., laptops, PCs, Tablet, etc.).
Biggest Disadvantage: Limited to the capabilities of HTML, JavaScript and other related Web-scripting languages.
Biggest Disadvantage: Limited to the capabilities of HTML, JavaScript and other related Web-scripting languages.
Application clients are Java applications that run in a Java virtual machine (JVM), and provide a way for users to handle tasks that require a richer user interface (UI) that can be provided by markup languages. Application clients can directly access EJBs running on the business tier. Alternatively, if required, an application client may also open an HTTP connection to establish communication with a servlet running in the Web tier.
Biggest Advantage: Richer user interface.
Biggest Disadvantage: Must be installed on each client machine.
Biggest Disadvantage: Must be installed on each client machine.
Web-based and application clients have their own distinct benefits and drawbacks that must be taken into consideration regarding the needs and requirements of the solution being deployed (e.g., CRM, ECMS, ERP, etc.).
While these architectures are usually kept distinct, there is another model that has not been much utilized, but which presents some obvious advantages in a mix of these capabilities, both internal to the enterprise and in its external-facing modalities. These are application-specific runtimes that can be fairly limited additional extension profiles to existing core markup mime typed plug-ins to augment UIs that travel with the application from the Web tier to the Web-based client, where the functionality is optionally added to the client's Web browser for the length of runtime required by the application to take the processing load off the server onto the client or that can be maintained as an addition to the browser's plug-ins.
This model is characterized by specialized viewers that have not found their way into markup standards for Web services as yet, such as Macromedia Flash MX which has added forms management to its feature set along with Adobe SVG Viewer for Lifecycle forms manager. Heretofore, this model has been widely dropped in favor of server-based processing, where the implementation of increased capacity is more predictable and, therefore, more economically feasible than in the client.
However, consider the recent announcement of an Outlook standalone subset available by subscription. This is an attempt by Microsoft to see if such a modularization will fit its evolving software-by-subscription service strategy. If Redmond is looking into this, others will, too. Despite the fact that the aforementioned display technologies are not now modularized to take advantage of this model, it seems likely that, as seen in the Microsoft experiment cited above, the modularization of software-by-subscription or in special-purpose, short-lived extensions that travel with their application, modularization seems inevitable.
The monolithic single-vendor solution model seems doomed in the face of open-source software based on open, public standards. Open-source developers already have their offerings aligned with this modularized model, by default largely since OSS does not lend itself to monolithic, deliberately non-interoperable proprietary systems, and with its availability and the advantages to the business world of eliminating single-vendor locked-in dependence, this prediction of the demise of these unwieldy, bloated leviathans certainly looks like the handwriting on the wall in this arena. Regardless, there is currently an excess amount of processing power going unused on the client side, and load-balancing considerations, as we move into an era of greater processing asset utilization (grids) will increasingly require moving the processing load onto the client, especially if this capacity is kept to small and optionally short-lived profiles. Also, there is a good chance that more modular architectures will find favor in a more mix-and-match set of software functionalities as the post-Y2K IT environment presents the necessity of adapting to a necessarily heterogeneous systems.
J2EE Server Machine (Web Tier and Business Tier)
In basic terms, an application server is the middleware that acts as the medium for a company's front-end applications through its back-end business systems. It must be able to extract core data and present it to a variety of clients (e.g., desktops, smart cards, Web browsers, etc.). Application servers provide developers with the capability to build and deploy Web application logic with data access through APIs. Leading cost-type J2EE application server offerings include BEA WebLogic 8.1, IBM WebSphere V6, Oracle Application Server 10g and Sun Java System Application Server. In addition, there are a number of open-source J2EE application servers currently available that include Apache Jakarta Tomcat, JBoss and Jonas. The following are the core components and other key supporting server-side technologies that comprise the J2EE server machine (Web tier and business tier).
Web Tier
J2EE Web components are either pages using JSP technology (JSP pages) or servlets.
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JSP: Java server pages (JSP) are text-based documents that execute as servlets. A JSP page contains two types of text that include:
· Static Template Data: May be expressed in any text-based format (e.g., HTML, WML, XML, etc.).
· JSP Elements: Determine how a page constructs dynamic content.
Servlets: Allow users to run Java code on the server and send HTML pages to a browser. Java servlet technology enables developers to define HTTP-specific servlet classes. As a result, a servlet class extends the capabilities of servers, which host applications that are accessed by way of a request-response programming model.
Business Tier
Business code, which is logic that solves the requirements or needs of a business entity (e.g., banking, brokerage, insurance, etc.) is handled by Enterprise JavaBeans (EJB) running on the business tier. EJB may be viewed server component architecture, which conform to the Sun EJB component model. They can be used to create a business object and related content may be sent using Java server pages (JSPs). Furthermore, an EJB can receive data from a client program, process it (if required) and send it to the EIS tier for storage or retrieve data from storage, process it (if required), and send it back to the client program. There are three types on EJBs that include session beans, entity beans and message-driven beans, and brief descriptions of each follow:
· Session Bean:A session bean implements a conversation between a client and the server side. Session beans execute a particular business task on behalf of a single client during a single session.
· Entity Bean:An entity bean represents a business object in a persistent storage mechanism. Examples of business objects include customers, orders and products. In the J2EE SDK, the persistent storage mechanism is a relational database. Typically, each entity bean has an underlying table in a relational database, and each instance of the bean corresponds to a row in that table.
· Message Driven Bean:A message-driven bean is an enterprise bean that allows J2EE applications to process messages asynchronously. It acts as a JMS message listener, which is similar to an event listener except that it receives messages instead of events.
One of main benefits of entity beans is that developers do not have to write SQL code or use the JDBC API directly to perform database access operations because the EJB container handles this task.
Database Machine (EIS Tier)
Enterprise information systems (EIS) provide the information infrastructure that is vital to the business processes of an enterprise. The EIS tier handles software and includes enterprise infrastructure systems such as ERP, mainframe transactions processing, database systems and other related legacy systems. For example, J2EE application components may require access to EIS for database connectivity. The database plays a critical role in the storing and retrieving of information.
A database is a collection of data that is organized so its contents may be accessed, managed and updated. The four main types of databases include:
· Distributed - Can be dispersed or replicated among different points in a network.
· Object Oriented - Is congruent with data defined in object classes and subclasses.
· Relational - A tabular design in which data is defined so that it can be organized and accessed.
· Object Relational - A combination of object and relational concepts where objects are mapped to relational databases, often used to persist EJB.
At this time, relational databases are the most prevalent type of offering. Leading relational database vendors include IBM, Microsoft, Oracle and Sybase. These offerings support a wide range of solutions that include business intelligence, collaboration, multimedia and transactions processing. The database foundation for most businesses and organizations deploying Web services and SOAs will most likely be based on a two-tier architecture that is comprised of agency data marts and a central data warehouse. This type database architecture provides four primary benefits that include 1) high-speed access, 2) the ability to expand functionality both on the data mart and/or
the central data warehouse levels without reengineering the core architectural topology, 3) improved security, 4) a 360-degree perspective. The key components of the two-tier architecture are:
Data Mart. The data mart acts as the information focal point regarding the activities of a specific entity (e.g., local office, regional official, foreign office, etc.). It employs a modular architecture that is comprised of individual data silos that are directly coupled and synchronized with the entities software solutions (e.g., CRM, ECMS, ERP, etc.). A data silo methodology allows for faster access times because a query is only performed against a specific section of the data mart and does not have to search the entire data mart for the targeted information. Security is greatly improved because data silos house only information on specific types of solutions, so access can be implemented on a finer level of granularity. The information held in the data mart, and or data marts may then be sent to the central data warehouse on a scheduled basis chosen by the business or organization.
The Central Data Warehouse. The central data warehouse acts as the main repository and focal point for all data mart information. Each data mart is directly coupled and synchronized with the central data warehouse. The information housed in the central data warehouse provides the authorized user with a 360-degree perspective of the entire workings of the enterprise. For example, this holistic view enables the business or organizations to better leverage business intelligence tools (BI) to look for hidden trends and other previously unknown information within the data.
The chosen database foundation should leverage important open-standards such as extensible markup language (XML) for internal as well as external applications; hence, the need to create the proper infrastructure to support this essential technology. The ability to store and retrieve XML documents in their native format will be of paramount importance to businesses and organizations deploying Web services and SOAs.
Over the near term, the database landscape and the J2EE architecture that supports and relies upon it are changing rapidly. As the expanding parameters, which are blurring the differences, of what constitutes a thick or thin, Web-based or application client, so also in the realm of data; the only certain demand in the marketplace is for flexibility, adaptability and quick responses.
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In a recent article, we wrote on the topic of integrated development environments (IDE), we discovered that in the midst of a burgeoning of application server choices there has been an unexpected development of a relatively simplified set of platforms that are organized along lines so similar as to be nearly identical. NetBeans looks like Eclipse without the XML emphasis. This is also true of development environments for building OWL-based ontological resources, such as Protégé and applications such as inference engines to build semantically viable knowledge bases out of data collections. The fact is that this makes increasing modularization almost inevitable.
The advent of object and object-relational databases will only accelerate this process as business learns how to optimize the functionalities used most, especially through SOA components, which are likely to be housed in object or object-relational database repositories. The essence of building a competitive advantage in the near term is going to be building the most effective market-response systems, and the key to that will lie in organizing, accessing data with a BI toolset that quickly transforms data into useful information for timely or critical decision making.
Example 1: Application Client Directly Accessing EJBs Running on the Business Tier
Example 2: Application CLient Using an Open HTTP Connection to Establish Communication with a Servlet Running in th Web Tier
J2EE Development Tools
An integrated development environment or IDE is a programming environment developed to produce reasonably standard applications within a specific programming language or platform such as C++, Java, Java++, C#, etc., on Windows, Linux and Macintosh operating systems. It enables developers to more easily and consistently create applications that are meant to satisfy specific needs and or requirements. This is facilitated because, as much as possible, IDEs organize application-specific coding into modules or units automatically within an overall governing structure called a "project" as opposed to requiring a programmer to organize the myriad code files and resources, such as DLLs, and build programs manually. These applications share a common structure, with their various resources and directories organized into more or less standard patterns. They are considered integrated because the source code components are packaged in one unit for delivery to the end user. This means that the end user only needs to click on a setup or installer icon to install the software. These end products can be tailored for specific versions of hardware platforms and operating systems meant to run these applications. IDEs have become far more sophisticated during the last three years and provide rich functionality across many languages and technologies.
Leading Java IDE offerings include: Borland Software Platform for J2EE, IBM WebSphere Studio V5.1.2, Oracle JDeveloper 10g, Sun Studio Enterprise and Sybase PowerBuilder 10. There is also the ubiquitous, now open-sourced Eclipse 3.0 platform that IBM has converted to pure XML and can output Java, and Sun's contribution to the open source community, the NetBeans IDE, which, while not currently devoted to pure XML, can be used with Eclipse to reverse engineer into XML.
The Challenges
High-end cost-type J2EE application servers support a number of core enterprise requirements, which include superior availability, reliability, scalability and security. In addition, they provide a wide-range of features and functions that support the needs of large-scale environments. Typically, high-end J2EE application servers from BEA, IBM, Oracle, Sun and Sybase range in price from $10,000 to $20,000 per-processor. Careful assessment is required because price is not the greatest differentiator regarding these types of middleware offerings. J2EE certification and open-standards support should be viewed as the two most important core elements. These factors go a long way in determining the features and functions provided by a specific application server. For example, the Java API for XML-based RPC (JAX-RPC) released as part of Sun's of J2EE 1.4 is used to build Web applications and Web services, incorporating XML-based RPC functionality according to the simple object access protocol (SOAP) 1.1 specification. While JAX-RPC is most often associated with building Web applications on the Java platform, it may also be used for Web services interoperability across heterogeneous platforms and languages. For that reason, JAX-RPC can be considered a key technology for Web services integration. As a result, business and organizations currently face two main challenges in developing and deploying traditional and Web services application that include 1) application server capabilities, 2) development tool capabilities. What follows are brief summaries of these two main challenges.
Java 2 Platform, Enterprise Edition (J2EE) Overview
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