Java IoT Authors: Elizabeth White, Liz McMillan, Yeshim Deniz, Pat Romanski, William Schmarzo

Related Topics: Java IoT

Java IoT: Article

UniqueID Generator: A Pattern for Primary Key Generation

UniqueID Generator: A Pattern for Primary Key Generation

Several patterns exist for generating primary keys for your EJB application. This month I'll provide a pattern for generating PKs that's scalable, generic, and portable.

My format for defining the pattern will follow the catalogued layout presented in the Gang of Four book, Design Patterns: Elements of Reusable Object-Oriented Software.

UniqueID Generator

Generate unique IDs for persistent objects in an EJB application

Also Known As:
PID (Persistent ID) Factory
GUID (Globally UniqueID) Manager

Enterprise JavaBeans is a server-side component model that targets the specific business domain of online transaction processing (OLTP) applications. OLTP applications generally have the need to store information persistently. The data records or objects for each transaction require unique identifiers to allow them to be stored and retrieved accurately. Thus there's a need to generate unique identifiers for the data involved in an EJB transaction processing system.

For the purposes of this pattern, I'm assuming a relational database is used as the data store rather than an object database, which would provide its own ID generator. A relational database table typically has a primary key column that's indexed to prevent duplicate IDs, which would lead to data integrity problems. Thus each row stored in the table is uniquely identifiable. For instance, in EJB the return value from the call to myHome.findByPrimaryKey is a single entity bean, not multiple entities!

There are numerous ways to generate unique IDs in a Java application. Let's review some approaches before discussing the UniqueID generator pattern presented in this article.

An easy way to generate unique IDs is to utilize the System.currentTimeMillis() method to get the current time in milliseconds and use it as your ID. Although it's an easy way to start creating applications, this approach has implications across high-volume applications. A high-volume OLTP application may perform several calls to System.currentTimeMillis() at the same time, resulting in the generation of duplicate IDs. Thus the generator must perform some sort of synchronization on ID requests. Typically, this is done with a wrapper object that uses the synchronized modifier to queue threads accessing it.

Next, you ask, "What about synchronization across multiple JVMs?" Certainly a clustered-server, multi-JVM architecture will be the norm for an enterprise application, but a clustered application poses two problems for this approach toward generating unique IDs:

  1. The system time on each machine may be different. Thus, in a multi-JVM architecture, calls to System.currentTimeMillis() can lead to duplicate values.
  2. The Java synchronize operator doesn't work across multiple JVMs, so even if the system times were equal, simultaneous calls to different machines could still result in duplicate IDs.

EntityBean Key Generator
This approach uses an entity bean to select the next value from a relational database table, which holds the latest value for unique ID generation. An entity bean can encapsulate the SQL, which it executes in a generic fashion by loading in a bean environment property containing a SQL string for each type of database. For instance, in Oracle the dual table should automatically return a sequence value. The SQL statement might look something like this:

"select mysequence.nextval from dual"

Oracle sequences are a proprietary feature and increment the value automatically for the caller by a specified increment count. Other databases that don't have this feature must increment a next ID field and select it in one call. Stored procedures are a common cure for the need to execute multiple database operations within a single request. To get the same ID generation capabilities from Microsoft SQL Server, a stored procedure could be called that both returns a value and increments it for the next caller. Since the stored procedure performs its work inside a transaction in one database request, it eliminates a "window" of opportunity when simultaneous calls for another ID get the same row and attempt to update the value.

Thus our entity bean key generator executes SQL, which it retrieved generically from its bean environment property and executed on the database. However, there are some drawbacks to this approach:

  • Each call to get another ID is a remote method invocation, which can create unwanted chatter depending on where the entity bean is deployed in your system.
  • Some might argue that entity beans are for business entities rather than utilitarian functionality like generating IDs for business entities.
  • Few application servers provide synchronized caching across a cluster. Thus the ability to cache a set of IDs, improving ID generation by preventing database operations, is negated when the application is clustered.

A more scalable approach to ID generation that provides both local caching and guaranteed unique IDs is a singleton object that hands out IDs from its local cache (see Figure 1). Each time the cache of the singleton object is depleted, it gets a set of IDs representing the next available IDs for the application. The singleton fetches IDs from a stateless session bean that accesses the database in a portable manner, allowing it to interact with any database.

Use UniqueID Generator:

  1. To return a unique identifier for object and/or database row identity
  2. To cache sets of IDs across multiple JVMs for scalable ID generation
  3. To abstract database implementations from the core ID generation classes


  • Singleton: Acts as the wrapper of the UniqueIDEJB and caches sets of unique IDs to prevent chatty remote invocations and database operations
  • UniqueIDEJB: Component made up of UniqueID (remote interface) and UniqueIDHome (home interface); performs generic SQL to fetch a set of IDs from the database and return them to the singleton client


  • Singleton: Calls UniqueIDEJB component to fetch a set of IDs; set is cached locally and a new set is fetched when the maximum is surpassed

The UniqueID generator has several key benefits and some limitations:

  1. Limited remote method invocations and database operations: The UniqueID generator's singleton object caches a set of IDs that are depleted before another request is made to the UniqueIDEJB. This limits the number of remote method invocations on the EJB and the number of hits the database must handle to generate new IDs.
  2. Guaranteed UniqueIDs: The UniqueID generator pattern guarantees unique identifiers for your objects/data across an n-tiered solution. If a set of IDs is requested from multiple JVMs at the same time, the transaction isolation of the UniqueIDEJB and/or database layer will automatically queue multiple requests to ensure that only one singleton's request for an ID set is processed at a time.
  3. Portable across EJB servers: The pattern represents a component that's portable across EJB servers. It's a session bean, and session beans have been mandatory in the specification since its inception, whereas any EJB server still not up to the 1.1 version of the specification wouldn't be able to utilize an entity bean-based pattern.

  1. Portable across database servers: The implementation of the pattern really determines its portability, but the pattern itself allows for database-specific SQL to be loaded generically from the EJB's environment so that no code changes are required to deploy it against disparate databases.
  2. Singleton knows nothing about the "incrementBy" value: The singleton object knows nothing about how many IDs are returned in a set. This is controlled at the UniqueIDEJB level by an environment property. To change the incrementBy value, simply redeploy the EJB with a hot-deploy mechanism to avoid downtime and the increment will be changed to the new value without repercussions on the rest of the application.
  3. ID gaps: Gaps in IDs will occur with this solution. For example, if a set of 50 IDs is retrieved and the server crashes midway, 25 IDs would be lost. My recommendation is to increment only by one until ready for production, then set the UniqueIDEJB's incrementBy environment property to be sufficient for your application's load. This prevents wasting IDs in development and test.
  4. Support for other data types: The structure section's class diagram shows a long data type used for IDs, yet this could be any data type your application requires. However, the UniqueID generator pattern would have to be extended to account for different ID data types in a single application. For instance, if your application mixed doubles, strings, longs, and ints as keys, the singleton would have to be extended.

Consider the following issues when implementing a generic, portable UniqueID generator pattern:

  • Determining incrementBy for your application: The amount of IDs contained in each ID set (and subsequently cached in the JVM) should be determined based on the number of users attempting "insert" transactions per JVM. Thus, if your incrementBy is 50 on a single J2EE server, set it to approximately 25 if you cluster two servers. Also, set incrementBy to a low number, even 1, for development and testing. As with any tunable parameter, metrics gathered from stress testing your application should ultimately drive your settings.
  • Ensure portability across EJB servers: When communicating from the UniqueIDEJB to the database, don't use proprietary logic to obtain a connection from a connection pool. Use data sources looked up through JNDI instead.
  • Ensuring portability across databases: There are a few ways to ensure that your code to fetch a set of IDs is portable. One way is to store the SQL that will be executed in the EJB's environment. The SQL is set in the deployment descriptor, which allows it to be modified during deployment rather than having to modify the codebase. Another option is to use data access objects (DAOs) to contain the database-specific SQL code. Last, your UniqueIDEJB component couldn't take advantage of database-specific sequence generators. Your component's implementation should create the table at runtime if it doesn't exist already. This approach isn't recommended, but it's an alternative nonetheless.

  • Generating different IDs for different tables (classes): To generate a different ID for different tables, each class in the pattern would have to change its interface to take a "sequence" parameter, which indicates which class you want to get the next ID for and is forwarded throughout the pattern to the JDBC call against the database.
  • Generating IDs shouldn't rely on a business transaction outcome: The UniqueIDEJB should create its own new transaction when getting an ID set. Incrementing the database to the "next ID value" shouldn't rely on whether or not the business transaction currently executing in your application succeeds or fails.
  • Business transactions rely on generated ID success: An error fetching an ID set from the UniqueIDEJB will cause a business transaction to fail. Don't mix different approaches to generating unique IDs when one fails. For instance, let's say your application uses the System.currentTimeMillis() approach to key generation if the first approach, calling UniqueIDEJB, fails. This provides an extra layer of fault tolerance to your application, but you could encounter duplicate IDs! If your database counter is near the number generated by the System.currentTimeMillis(), you'll have problems.

Sample Code
The code in Listing 1 shows how to implement the singleton to cache the ID set, fetch a new set, and handle failures when calling the UniqueIDEJB.

This month I provided an EJB pattern to a common problem in the OLTP world, generating unique IDs. While there are variations of the pattern, the UniqueID generator overcomes many scalability and flexibility issues where other patterns fall short, such as local ID caching, limiting remote method invocations, and portability. I hope this pattern is helpful for your EJB engagement. For other EJB patterns see www.theServerSide.com. And let me know if you're interested in JDJ featuring more patterns in the future.

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
As IoT continues to increase momentum, so does the associated risk. Secure Device Lifecycle Management (DLM) is ranked as one of the most important technology areas of IoT. Driving this trend is the realization that secure support for IoT devices provides companies the ability to deliver high-quality, reliable, secure offerings faster, create new revenue streams, and reduce support costs, all while building a competitive advantage in their markets. In this session, we will use customer use cases...
Business professionals no longer wonder if they'll migrate to the cloud; it's now a matter of when. The cloud environment has proved to be a major force in transitioning to an agile business model that enables quick decisions and fast implementation that solidify customer relationships. And when the cloud is combined with the power of cognitive computing, it drives innovation and transformation that achieves astounding competitive advantage.
Digital Transformation: Preparing Cloud & IoT Security for the Age of Artificial Intelligence. As automation and artificial intelligence (AI) power solution development and delivery, many businesses need to build backend cloud capabilities. Well-poised organizations, marketing smart devices with AI and BlockChain capabilities prepare to refine compliance and regulatory capabilities in 2018. Volumes of health, financial, technical and privacy data, along with tightening compliance requirements by...
DevOpsSummit New York 2018, colocated with CloudEXPO | DXWorldEXPO New York 2018 will be held November 11-13, 2018, in New York City. Digital Transformation (DX) is a major focus with the introduction of DXWorldEXPO within the program. Successful transformation requires a laser focus on being data-driven and on using all the tools available that enable transformation if they plan to survive over the long term. A total of 88% of Fortune 500 companies from a generation ago are now out of bus...
With 10 simultaneous tracks, keynotes, general sessions and targeted breakout classes, @CloudEXPO and DXWorldEXPO are two of the most important technology events of the year. Since its launch over eight years ago, @CloudEXPO and DXWorldEXPO have presented a rock star faculty as well as showcased hundreds of sponsors and exhibitors! In this blog post, we provide 7 tips on how, as part of our world-class faculty, you can deliver one of the most popular sessions at our events. But before reading...
DXWordEXPO New York 2018, colocated with CloudEXPO New York 2018 will be held November 11-13, 2018, in New York City and will bring together Cloud Computing, FinTech and Blockchain, Digital Transformation, Big Data, Internet of Things, DevOps, AI, Machine Learning and WebRTC to one location.
DXWorldEXPO LLC announced today that ICOHOLDER named "Media Sponsor" of Miami Blockchain Event by FinTechEXPO. ICOHOLDER give you detailed information and help the community to invest in the trusty projects. Miami Blockchain Event by FinTechEXPO has opened its Call for Papers. The two-day event will present 20 top Blockchain experts. All speaking inquiries which covers the following information can be submitted by email to [email protected] Miami Blockchain Event by FinTechEXPO also offers s...
DXWorldEXPO | CloudEXPO are the world's most influential, independent events where Cloud Computing was coined and where technology buyers and vendors meet to experience and discuss the big picture of Digital Transformation and all of the strategies, tactics, and tools they need to realize their goals. Sponsors of DXWorldEXPO | CloudEXPO benefit from unmatched branding, profile building and lead generation opportunities.
Dion Hinchcliffe is an internationally recognized digital expert, bestselling book author, frequent keynote speaker, analyst, futurist, and transformation expert based in Washington, DC. He is currently Chief Strategy Officer at the industry-leading digital strategy and online community solutions firm, 7Summits.
Digital Transformation and Disruption, Amazon Style - What You Can Learn. Chris Kocher is a co-founder of Grey Heron, a management and strategic marketing consulting firm. He has 25+ years in both strategic and hands-on operating experience helping executives and investors build revenues and shareholder value. He has consulted with over 130 companies on innovating with new business models, product strategies and monetization. Chris has held management positions at HP and Symantec in addition to ...
Cloud-enabled transformation has evolved from cost saving measure to business innovation strategy -- one that combines the cloud with cognitive capabilities to drive market disruption. Learn how you can achieve the insight and agility you need to gain a competitive advantage. Industry-acclaimed CTO and cloud expert, Shankar Kalyana presents. Only the most exceptional IBMers are appointed with the rare distinction of IBM Fellow, the highest technical honor in the company. Shankar has also receive...
Enterprises have taken advantage of IoT to achieve important revenue and cost advantages. What is less apparent is how incumbent enterprises operating at scale have, following success with IoT, built analytic, operations management and software development capabilities - ranging from autonomous vehicles to manageable robotics installations. They have embraced these capabilities as if they were Silicon Valley startups.
Poor data quality and analytics drive down business value. In fact, Gartner estimated that the average financial impact of poor data quality on organizations is $9.7 million per year. But bad data is much more than a cost center. By eroding trust in information, analytics and the business decisions based on these, it is a serious impediment to digital transformation.
The standardization of container runtimes and images has sparked the creation of an almost overwhelming number of new open source projects that build on and otherwise work with these specifications. Of course, there's Kubernetes, which orchestrates and manages collections of containers. It was one of the first and best-known examples of projects that make containers truly useful for production use. However, more recently, the container ecosystem has truly exploded. A service mesh like Istio addr...
Predicting the future has never been more challenging - not because of the lack of data but because of the flood of ungoverned and risk laden information. Microsoft states that 2.5 exabytes of data are created every day. Expectations and reliance on data are being pushed to the limits, as demands around hybrid options continue to grow.
The best way to leverage your Cloud Expo presence as a sponsor and exhibitor is to plan your news announcements around our events. The press covering Cloud Expo and @ThingsExpo will have access to these releases and will amplify your news announcements. More than two dozen Cloud companies either set deals at our shows or have announced their mergers and acquisitions at Cloud Expo. Product announcements during our show provide your company with the most reach through our targeted audiences.
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 ...
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 settlement products to hedge funds and investment banks. After, he co-founded a revenue cycle management company where he learned about Bitcoin and eventually Ethereal. Andrew's role at ConsenSys Enterprise is a mul...
DXWorldEXPO LLC announced today that "Miami Blockchain Event by FinTechEXPO" has announced that its Call for Papers is now open. The two-day event will present 20 top Blockchain experts. All speaking inquiries which covers the following information can be submitted by email to [email protected] Financial enterprises in New York City, London, Singapore, and other world financial capitals are embracing a new generation of smart, automated FinTech that eliminates many cumbersome, slow, and expe...
Cloud Expo | DXWorld Expo have announced the conference tracks for Cloud Expo 2018. Cloud Expo will be held June 5-7, 2018, at the Javits Center in New York City, and November 6-8, 2018, at the Santa Clara Convention Center, Santa Clara, CA. Digital Transformation (DX) is a major focus with the introduction of DX Expo within the program. Successful transformation requires a laser focus on being data-driven and on using all the tools available that enable transformation if they plan to survive ov...