Welcome!

Java IoT Authors: Elizabeth White, Yeshim Deniz, Tim Hinds, Douglas Lyon, Stackify Blog

Related Topics: Java IoT

Java IoT: Article

XML DTD for EJB Deployment Descriptors

XML DTD for EJB Deployment Descriptors

To those of you familiar with Enterprise JavaBeans (EJB), deployment descriptors are nothing new. Essentially, a deployment descriptor's purpose is to collect declarative information that can be modified during deployment of an enterprise bean. Deployment descriptors are a key element in the component-based development capabilities of EJB. They allow users to modify, link and deploy EJB in a graphical environment rather than having to perform low-level code changes to reuse a component. The latest public draft of EJB specification 1.1 includes sections on the XML DTD for deployment descriptors, an important step toward enterprise bean portability between EJB servers.

In the spirit of JDJ's focus on XML this month, I'll cover some important pieces of the newly released XML DTD for deployment descriptors in EJB specification 1.1 (section 16.6). As this is being written I have yet to find a production EJB server that supports the DTD (if you know of one, please let me know!); however, I'll include a "best shot" example descriptor using the DTD so you get a feel for the format of its metadata. The example is based on the Intergalactic Ticket System's TicketEntityBean from September's EJB Home column (JDJ Vol. 4, issue 8). For reference see the online source code at the JDJ Web site.

A Look Inside the EJB's XML DTD
A deployment descriptor contains two kinds of metadata (data about data) for an enterprise bean:

  • Structural information
  • Application assembly information

    Structural information describes specific characteristics of an enterprise bean such as whether it is an entity or session bean, and any external dependencies it might have. This information must be included in an ejb-jar file by its producer. Structural information about an enterprise bean is entered by the bean provider, and it's advisable not to modify this information during ejb-jar assembly or deployment. Table 1 lists common structural information about an enterprise bean that you might include in a deployment descriptor.

    Application assembly information is the responsibility of the application assembler. It describes how an enterprise bean in an ejb-jar file is assembled into a coarse-grained deployment unit. This information isn't mandatory, and it may be modified at deployment time. However, be aware that an enterprise bean's behavior may be affected by these changes. Table 2 lists common application assembly information you might encounter in a deployment descriptor.

    The EJB specification describes the responsibilities of roles during the life cycle of an enterprise bean's development and deployment. The roles of bean provider and application assembler are separate, and they are assigned different responsibilities regarding the creation/modification of a deployment descriptor. There will be overlap in the responsibilities of each role, however, resulting in an application assembler's possibly modifying structural information about an enterprise bean. I played each role in creating the example descriptor.

    TicketEntityBean XML Deployment Descriptor
    The EJB XML DTD (enough with the acronyms!) defines how to describe both session and entity beans. Some element tags, like env-entry ­ a description of a bean environment property ­ pertain to both bean types. Others are specifically for session or entity beans only. The TicketEntityBean XML descriptor example clarifies common entity bean elements for you. Listing 1 contains the complete source code of this XML descriptor.

    As indicated earlier, the DTD contains structural information about an enterprise bean and may contain assembly information as well. I'll begin analyzing the structural information about the TicketEntityBean deployment descriptor and finish with the assembly information.

    First, notice the top line of the ejb-jar descriptor in the TicketEntityBean descriptor. A well-formed, valid deployment descriptor must refer to the DTD with the statement:

    Sun Microsystems has plans to deliver an ejb-jar file verifier that will check for malformed XML as described in EJB specification 1.1, section 16.6. A verifier will provide bean providers and application assemblers the ability to validate their work, ensuring correct DTD semantics are upheld.

    Next, I continue the XML descriptor with the ejb-jar element.

    <ejb-jar>Š</ejb-jar>

    This element is the root of an EJB deployment descriptor, which may contain multiple enterprise beans. This month's example contains only one enterprise bean. The ejb-jar element may contain optional descriptions of the ejb-jar, its icon files, display name and an assembly-descriptor section, but it must include at least one enterprise bean element.

    The enterprise bean element contains one or more declared enterprise beans: session or entity. The XML descriptor will not be valid if this element is empty.

    <enterprise-beans>Š</enterprise-beans>

    Within this section I enter the structural information about my TicketEntityBean.

    TicketEntityBean's Structural Information
    The entity element in my example contains the structural information that is the bean provider's responsibility to enter.

    <entity>Š</entity>

    The entity element has mandatory and optional entries to allow the bean provider to add detail to the bean as needed.

    Mandatory Entity Elements
    Mandatory elements are the ejb-name, home, remote, ejb-class, persistence-type, prim-key-class and reentrant fields.

    For all but the ejb-name element, I have simply copied the values from my previous deployment descriptor file from the September column into these elements as necessary. Thus you can see that the example's home element contains the fully qualified name of the entity bean's home interface class. Similarly, the remote and ejb-class hold the fully qualified class names of the remote and entity bean, respectively.

    <ejb-name>TicketEntityBean</ejb-name>
    <home>jdj.ticketing.containermanaged.TicketEntityHome</home>
    <remote>jdj.ticketing.containermanaged.TicketEntity</remote>
    <ejb-class> jdj.ticketing.containermanaged.TicketEntityBean </ejb-class>

    Note: ejb-name is simply a logical name for the enterprise bean. It is not the JNDI that will be assigned by the deployer at a later time. Also, ejb-name must be unique for a given ejb-jar file.

    Because TicketEntityBean is container-managed, my descriptor's persistence-type is "Container," and like the home and remote elements, I have entered the prim-key-class in fully qualified form.

    <persistence-type>Container</persistence-type>
    <prim-key-class>jdj.ticketing.containermanaged.TicketEntityPK</prim-key-class>

    The last mandatory entry in the entity element is whether or not the bean is reentrant. I have listed my TicketEntityBean as False.

    <reentrant>False</reentrant>

    Optional Entity Elements
    The entity element can optionally include a description, display name and icon files. Additional optional fields may be contingent on factors such as whether the bean is container-managed or bean-managed. These include cmp-field (container-manager field), prim-key-field, env-entry (a bean environment property), ejb-ref (references to other ejbs in the ejb-jar file), security-role-ref and resource-ref (reference to external resources). Because the TicketEntityBean is container-managed, I've included some of these elements in my descriptor.

    This is an example of an optional environment property where the entity bean has declared an idleTimeoutSeconds environment property with a value of 5.

    <env_entry>
    <env_entry-name>idleTimeoutSeconds</env_entry-name>
    <env_entry-type>String</env_entry-type>
    <env_entry-value>5</env_entry-value>
    </env_entry>
    more env-entries possibleŠ

    Following is an example of a few of the container-managed fields declared for the TicketEntityBean:

    <cmp-field><field-name>arrivalCity</field-name></cmp-field>
    <cmp-field><field-name>departDt</field-name></cmp-field>
    more cmp-fields possibleŠ

    Application Assembly Information
    Table 2 describes numerous elements that an application assembler can include in the descriptor. All are optional; thus the assembly descriptor may be left out of the ejb-jar file.

    The assembly-descriptor element ­

    <assembly-descriptor>Š</assembly-descriptor>

    ­ can optionally contain information about security roles, method permissions and an enterprise bean's transaction semantics with its container. I have opted to have no role-based security on my TicketEntityBean, nor any special method permissions based on role. However, another ticket agency reusing this entity bean may decide to place a security restriction on the bean, allowing only TicketAgent roles to access it. In this case an entry would be made by the application assembler to include the security role element:

    <security-role>Š</security-role>

    Likewise, they would want to include which methods are restricted to this new security role in the form of the following tag:

    <method-permissions>Š</method-permissions>

    I don't have security information to worry about; however, I do want to describe how my entity bean behaves within the context of a transaction. To do so I have to include an element, container-transaction. The full assembly-descriptor element is listed below.

    <assembly-descriptor>
    <container-transaction>
    <method>
    <ejb-name>TicketEntityBean</ejb-name>
    <method-name>*</method-name>
    </method>
    <trans-attribute>Required</trans-attribute>
    </container-transaction>
    </assembly-descriptor>

    In this example I list the entity bean in question (i.e., ejb-name), which methods are managed by the container (i.e., method-name) and exactly how they are managed (i.e., trans-attribute). For my purposes I am dealing with the TicketEntityBean, in which all methods signified by an asterisk (*) are required (Required) to operate within a transaction context.

    The assembly-descriptor adds character to your enterprise beans that is not or cannot be determined by the bean provider. As security or transaction context needs evolve, the assembly-descriptor enhances EJB's component-model capabilities by allowing modification of bean properties without code changes. Summary

    With the addition of a DTD for deployment descriptors in the EJB specification 1.1, Sun Microsystems is stepping in the right direction toward an end goal of interoperability for enterprise beans among EJB vendors' products. A standard allowing EJB developers and deployers to speak a common language will only increase the efficiency of EJB application development.

    As with the first draft of any spec, there are holes in the DTD that still need to be filled. For example, there is no description of how container-managed fields map into their persistent storage, and at the time of this writing sections 16.4 and 16.5, deployer's responsibilities and container provider's responsibilities, haven't been specified. When these sections are detailed, an element to describe a bean's JNDI name, for instance, will become self-evident (no pun intended!). In the next column I'll cover other portability issues beyond XML, with regards to the EJB specification.

  • More Stories By Jason Westra

    Jason Westra is the CTO of Verge Technologies Group, Inc. (www.vergecorp.com). Verge is a Boulder, CO based firm specializing in eBusiness solutions with Enterprise JavaBeans.

    Comments (0)

    Share your thoughts on this story.

    Add your comment
    You must be signed in to add a comment. Sign-in | Register

    In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


    @ThingsExpo Stories
    BnkToTheFuture.com is the largest online investment platform for investing in FinTech, Bitcoin and Blockchain companies. We believe the future of finance looks very different from the past and we aim to invest and provide trading opportunities for qualifying investors that want to build a portfolio in the sector in compliance with international financial regulations.
    A strange thing is happening along the way to the Internet of Things, namely far too many devices to work with and manage. It has become clear that we'll need much higher efficiency user experiences that can allow us to more easily and scalably work with the thousands of devices that will soon be in each of our lives. Enter the conversational interface revolution, combining bots we can literally talk with, gesture to, and even direct with our thoughts, with embedded artificial intelligence, whic...
    Imagine if you will, a retail floor so densely packed with sensors that they can pick up the movements of insects scurrying across a store aisle. Or a component of a piece of factory equipment so well-instrumented that its digital twin provides resolution down to the micrometer.
    In his keynote at 18th Cloud Expo, Andrew Keys, Co-Founder of ConsenSys Enterprise, provided an overview of the evolution of the Internet and the Database and the future of their combination – the Blockchain. Andrew Keys is Co-Founder of ConsenSys Enterprise. He comes to ConsenSys Enterprise with capital markets, technology and entrepreneurial experience. Previously, he worked for UBS investment bank in equities analysis. Later, he was responsible for the creation and distribution of life settle...
    Product connectivity goes hand and hand these days with increased use of personal data. New IoT devices are becoming more personalized than ever before. In his session at 22nd Cloud Expo | DXWorld Expo, Nicolas Fierro, CEO of MIMIR Blockchain Solutions, will discuss how in order to protect your data and privacy, IoT applications need to embrace Blockchain technology for a new level of product security never before seen - or needed.
    Leading companies, from the Global Fortune 500 to the smallest companies, are adopting hybrid cloud as the path to business advantage. Hybrid cloud depends on cloud services and on-premises infrastructure working in unison. Successful implementations require new levels of data mobility, enabled by an automated and seamless flow across on-premises and cloud resources. In his general session at 21st Cloud Expo, Greg Tevis, an IBM Storage Software Technical Strategist and Customer Solution Architec...
    Nordstrom is transforming the way that they do business and the cloud is the key to enabling speed and hyper personalized customer experiences. In his session at 21st Cloud Expo, Ken Schow, VP of Engineering at Nordstrom, discussed some of the key learnings and common pitfalls of large enterprises moving to the cloud. This includes strategies around choosing a cloud provider(s), architecture, and lessons learned. In addition, he covered some of the best practices for structured team migration an...
    No hype cycles or predictions of a gazillion things here. IoT is here. You get it. You know your business and have great ideas for a business transformation strategy. What comes next? Time to make it happen. In his session at @ThingsExpo, Jay Mason, an Associate Partner of Analytics, IoT & Cybersecurity at M&S Consulting, presented a step-by-step plan to develop your technology implementation strategy. He also discussed the evaluation of communication standards and IoT messaging protocols, data...
    Coca-Cola’s Google powered digital signage system lays the groundwork for a more valuable connection between Coke and its customers. Digital signs pair software with high-resolution displays so that a message can be changed instantly based on what the operator wants to communicate or sell. In their Day 3 Keynote at 21st Cloud Expo, Greg Chambers, Global Group Director, Digital Innovation, Coca-Cola, and Vidya Nagarajan, a Senior Product Manager at Google, discussed how from store operations and ...
    In his session at 21st Cloud Expo, Raju Shreewastava, founder of Big Data Trunk, provided a fun and simple way to introduce Machine Leaning to anyone and everyone. He solved a machine learning problem and demonstrated an easy way to be able to do machine learning without even coding. Raju Shreewastava is the founder of Big Data Trunk (www.BigDataTrunk.com), a Big Data Training and consulting firm with offices in the United States. He previously led the data warehouse/business intelligence and B...
    "IBM is really all in on blockchain. We take a look at sort of the history of blockchain ledger technologies. It started out with bitcoin, Ethereum, and IBM evaluated these particular blockchain technologies and found they were anonymous and permissionless and that many companies were looking for permissioned blockchain," stated René Bostic, Technical VP of the IBM Cloud Unit in North America, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Conventi...
    When shopping for a new data processing platform for IoT solutions, many development teams want to be able to test-drive options before making a choice. Yet when evaluating an IoT solution, it’s simply not feasible to do so at scale with physical devices. Building a sensor simulator is the next best choice; however, generating a realistic simulation at very high TPS with ease of configurability is a formidable challenge. When dealing with multiple application or transport protocols, you would be...
    Smart cities have the potential to change our lives at so many levels for citizens: less pollution, reduced parking obstacles, better health, education and more energy savings. Real-time data streaming and the Internet of Things (IoT) possess the power to turn this vision into a reality. However, most organizations today are building their data infrastructure to focus solely on addressing immediate business needs vs. a platform capable of quickly adapting emerging technologies to address future ...
    We are given a desktop platform with Java 8 or Java 9 installed and seek to find a way to deploy high-performance Java applications that use Java 3D and/or Jogl without having to run an installer. We are subject to the constraint that the applications be signed and deployed so that they can be run in a trusted environment (i.e., outside of the sandbox). Further, we seek to do this in a way that does not depend on bundling a JRE with our applications, as this makes downloads and installations rat...
    Widespread fragmentation is stalling the growth of the IIoT and making it difficult for partners to work together. The number of software platforms, apps, hardware and connectivity standards is creating paralysis among businesses that are afraid of being locked into a solution. EdgeX Foundry is unifying the community around a common IoT edge framework and an ecosystem of interoperable components.
    DX World EXPO, LLC, a Lighthouse Point, Florida-based startup trade show producer and the creator of "DXWorldEXPO® - Digital Transformation Conference & Expo" has announced its executive management team. The team is headed by Levent Selamoglu, who has been named CEO. "Now is the time for a truly global DX event, to bring together the leading minds from the technology world in a conversation about Digital Transformation," he said in making the announcement.
    In this strange new world where more and more power is drawn from business technology, companies are effectively straddling two paths on the road to innovation and transformation into digital enterprises. The first path is the heritage trail – with “legacy” technology forming the background. Here, extant technologies are transformed by core IT teams to provide more API-driven approaches. Legacy systems can restrict companies that are transitioning into digital enterprises. To truly become a lead...
    Digital Transformation (DX) is not a "one-size-fits all" strategy. Each organization needs to develop its own unique, long-term DX plan. It must do so by realizing that we now live in a data-driven age, and that technologies such as Cloud Computing, Big Data, the IoT, Cognitive Computing, and Blockchain are only tools. In her general session at 21st Cloud Expo, Rebecca Wanta explained how the strategy must focus on DX and include a commitment from top management to create great IT jobs, monitor ...
    "Cloud Academy is an enterprise training platform for the cloud, specifically public clouds. We offer guided learning experiences on AWS, Azure, Google Cloud and all the surrounding methodologies and technologies that you need to know and your teams need to know in order to leverage the full benefits of the cloud," explained Alex Brower, VP of Marketing at Cloud Academy, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clar...
    The IoT Will Grow: In what might be the most obvious prediction of the decade, the IoT will continue to expand next year, with more and more devices coming online every single day. What isn’t so obvious about this prediction: where that growth will occur. The retail, healthcare, and industrial/supply chain industries will likely see the greatest growth. Forrester Research has predicted the IoT will become “the backbone” of customer value as it continues to grow. It is no surprise that retail is ...