Weblogic Authors: Yeshim Deniz, Elizabeth White, Michael Meiner, Michael Bushong, Avi Rosenthal

Related Topics: Weblogic

Weblogic: Article

The Promise of Entity Beans

The Promise of Entity Beans

Working as a BEA consultant, I've helped customers successfully design and deploy applications on various versions of the WebLogic Server (WLS). BEA has been supporting container-managed persistence (CMP) entity beans since EJB 1.0, and a few of our customers have used them. Unfortunately, some used them without understanding the ramifications; others heard about performance constraints and completely excluded entity beans from their architecture/design choices.

It was difficult to come up with reasons to use CMP entity beans when chief architects asked, "When should I consider using CMP entity beans at all?" The nirvana of entity beans lies in two things: caching and object-relational mapping. Both were done poorly in the earlier implementations, but EJB 2.0 came to the rescue. WLS 7.0's add-on features to the EJB 2.0 specification bridge the gap in performance between using entity beans and using stateless session beans with DAO and JDBC - in some cases even performing faster than the latter. When using JDBC, developers are strongly advised to use container-managed transactions.

Problems with Earlier Versions
Several customers who used entity beans in the past had to redesign and use JDBC because their systems were too slow to meet service-level agreements. That slowness was due to some of the following problems:

  • No caching: Each transaction went to the database to load the entity bean. One of the promises customers look for in using entity beans is caching, and none was available for regular entity beans in a clustered environment.
  • Single-table support (O-R mapping too simplistic): Customers were also looking for object-relational mapping to be done by the entity bean, but the mapping provided by the container was too simplistic.
  • Single instance of the entity bean per virtual machine (VM): Because WebLogic 5.1 and below only supported exclusive locking, all the calls to the entity bean were serialized, causing bottlenecks even for read-only beans.
  • Exclusive locking: Deadlocks were highly likely when some beans used transactions and some did not.
  • Single setX call: This caused the entire entity bean to be written to the database. Before the EJB 2.0 specification, the container didn't have any hooks for determining what changed and what didn't. This meant that on an ejbStore, all the attributes were updated.
  • Loading: Loading the entity bean caused all data members to be loaded in memory, even if only a couple were needed.
  • No dynamic queries: EJB had to be redeployed to write a new query.
  • Queries: Queries can instantiate large numbers of entity beans, consuming memory and degrading performance.

    WLS 7.0 Features
    WLS 7.0 implements the EJB 2.0 specification, providing for richer object-relational mapping. EJB 2.0 also provides the container with a lot more flexibility for doing optimized reads and writes to the database. The following features elucidate the richness and flexibility developers have in designing entity beans in WLS 7.0.

  • Container-managed relationships: Entity beans can have relationships with other beans; these relationships can be either bidirectional or unidirectional. WLS supports three types of relationship mappings managed by WebLogic CMP: one-to-one, one-to-many, and many-to-many.
  • Multiple table mapping to an entity bean: Multiple table support allows an implementer of EJB 2.0 CMP beans to map a single EJB to multiple DBMS tables within a single database.
  • Tuned writes with EJB 2.0: Instead of writing all the fields to the database when ejbStore is called, only the updated fields are written to the database.
  • Tuned reads using field groups: On an ejbLoad the container, instead of loading all the fields of the entity bean, loads only fields in the field-group.
  • Caching of relationships: This feature increases entity bean performance by loading related beans into the cache in a single join query instead of multiple queries.
  • Entity beans can return ResultSets: WLS supports ejbSelect() queries that return the results of multicolumn queries in the form of a java.sql.ResultSet.
  • Application-wide cache for heterogeneous entity beans: Instead of a separate cache for each entity bean, this feature enables multiple entity beans within an EAR to share a single runtime cache.
  • Dynamic queries: The EJB 2.0 specification forces users to hard-code queries in the deployment descriptor. With dynamic queries, new queries can be constructed and executed programmatically without redeploying the beans.
  • Read-mostly design pattern: In the real world, most applications are 90% read and 10% update. An entity bean can be written to model the data and can be deployed as both a read-only entity bean and a regular entity bean. With this approach, users who want to read data talk to the read-only entity bean, and users who want to update data talk to the regular entity bean. When an update occurs, the container invalidates all the read-only entity beans, forcing the container to call ejbLoad the next time the data is accessed.

    Other useful features include automatic primary key generation, cascade delete support, EJB QL support, ejbSelect methods, and the concurrency strategies described below.

    Concurrency Strategies
    A concurrency strategy defines how many instances of an entity bean are created, who does the locking to maintain transactional integrity, and the access pattern of the data modeled in the entity bean. The right concurrency strategy can make a tremendous difference in the performance of your entity beans.

  • Exclusive: The container creates only one instance of an entity bean per VM, and all calls to the entity bean are serialized as the container locks the entity bean on use (for both read and write). This is never recommended.
  • Database: The container defers locking to the database, and each transaction gets its own copy of the entity bean. ejbLoad and ejbStore are called at the beginning and end of the transaction respectively.
  • Read-only entity beans: Neither the database nor the container holds any locks, and each transaction gets its own copy of the entity bean. A configurable parameter called <read-timeout-seconds> controls when ejbLoad is called on the entity bean. ejbStore is never called on the entity bean. Clients can still call create, remove, and update operations on the entity beans. The creation and removal will be successful, but the updates won't modify the database because ejbStore isn't called. It's the programmer's responsibility to not call CUD (create,update,delete) methods on read-only entity beans. Read-only entity beans are a perfect solution to the "distributed cache" problem.
  • Optimistic entity beans: The container defers locking to the database, but locks aren't held during the transaction. The basic idea is that the container checks for modified data before committing and rolls back if someone else has modified it. This is useful if you want higher consistency than TX_READ_COMMITTED but don't want to go as high as TX_SERIALIZABLE. Use it if you can live with reading stale data for a short time but want complete transactional integrity for updates. There are four options for checking optimistic conflicts: 1.   Check columns that were read 2.   Check columns that were modified 3.   Check timestamp column 4.   Check a version column

    Options 3 and 4 aren't recommended because the schema of the table needs to be changed to incorporate this concurrency strategy. Also, with the optimistic concurrency strategy, you can configure whether you want caching between transactions to be true or false. With caching between transactions set to false, ejbLoad will be called at the beginning of each transaction.

    With CMP, there will always be additional processing due to the integration of the EJB container and a layer of container-generated code-handling transactions, security, pooling, life-cycle management, failover, caching, and relationships. CMP (by design or by spec) has to do internal operations, (ejbLoad, ejbStore, ejbActivate, ejbPassivate) as opposed to JDBC logic manually programmed by developers. The benefits of the container infrastructure are optimized, generated database access; accelerated development; and simplified code maintenance.

    On the benchmarks I've seen, unless the data is cached, [stateless session bean + DAO (doing JDBC)] has performed 30-50% faster than the entity bean implementation.

    When to Use What
    Entity beans shouldn't be used as a substitute for writing JDBC. Use entity beans if your object-relational model isn't overly complex (involving numerous joins, etc.) and flexibility and code maintenance are more important than raw speed for your project.

    Use JDBC for simplistic, atomic-blind updates; to integrate with stored procedures and triggers; and to handle large ResultSets.

    WebLogic add-ons such as the read-mostly design pattern and optimistic caching with cache-between-transactions set to true are two design choices that make entity beans an attractive option. Both are BEA-proprietary, and both are specified in the WebLogic-specific deployment descriptor. No code changes are needed when migrating to another J2EE-compliant application server. Use optimistic caching concurrency strategy if it's OK for the application to read stale data for a short period of time.

    Use the read-mostly design pattern for the use case in which you read most of the time and update less frequently. This design pattern also has the shortcoming that the readers can read stale data. In case some of the readers should not read stale data at all, they can be made to read from the read-write bean.

    Read-only entity beans for CMP entity beans are mentioned in the features deferred to future releases of the EJB specification. Use read-only entity beans to implement a distributed cache that can be refreshed periodically.

    Most real-world applications do far more reads than writes. Implementing the read-mostly pattern will provide the best of both worlds. It provides easy development and flexible deployment, along with excellent performance characteristics for accessing data and paying extra overhead only when data is being modified. Optimistic concurrency with cache-between-transactions set to true can be faster than JDBC. Writing optimized SQL is hard for regular Java programmers, so don't ignore entity beans - evaluate and determine whether they're a good fit.

    Entity Beans Examples
    Examples are provided in subdirectories of BEA-HOME/samples/server/src/ejb20.

  • For an example that demonstrates the relationships, look at the BEA-HOME/samples/server/src/ejb20/relationships/bands directory.
  • For an example that demonstrates multiple table mapping, look at the BEA-HOME/samples/server/src/ejb20/multitable directory.
  • To use the database concurrency option specify <concurrency-strategy>Database</concurrency-strategy> in the weblogic-ejb-jar.xml. weblogic-ejb-jar.xml To use the read-only concurrency option, specify <concurrency-strategy>Read-Only</concurrency-strategy> in the weblogic-ejb-jar.xml.
  • To use the optimistic concurrency with cache-between-transactions and check on Modified option specify <concurrency strategy>Optimistic</concurrency-strategy> <cache-between-transactions>True</cache-between-transactions> in the weblogic-ejb-jar.xml and specify <verify-columns>Modified</verify-columns> in the weblogic-cmp-rdbms-jar.xml.
  • To implement the "read-mostly" design pattern register the bean implementation as two EJBs, one as read-only and the other as Read-Write, and add the <invalidate>ejb-name</invalidate> where ejbname is the read-only entity bean name in the weblogic-ejb-jar.xml.


  • http://edocs.bea.com/wls/docs70/ejb/index.html
  • http://java.sun.com/products/ejb/docs.html
  • More Stories By Vijay Mandava

    Vijay Mandava joined BEA as a technical manager in the Professional Services organization in 1999. He now works as a principal systems engineer in the Systems Engineering organization. Vijay is a Sun certified Java programmer and a BEA certified Weblogic Server developer.

    Comments (1) View Comments

    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.

    Most Recent Comments
    N. Bharadwaj 09/18/02 03:26:00 AM EDT

    This was an excellent article. Thanks to you, some of the important doubts I had on entity beans are cleared.

    When to use entity beans, weblogic 7.0 addons for EJB 2.0 provide a good understanding.
    "Most real-world applications do far more reads than writes" is a terrific point.
    "Use read-only entity beans to implement a distributed cache that can be refreshed periodically" is a great idea.
    Thanks Vijay Mandava. Your article is appreciated.

    @ThingsExpo Stories
    Michael Maximilien, better known as max or Dr. Max, is a computer scientist with IBM. At IBM Research Triangle Park, he was a principal engineer for the worldwide industry point-of-sale standard: JavaPOS. At IBM Research, some highlights include pioneering research on semantic Web services, mashups, and cloud computing, and platform-as-a-service. He joined the IBM Cloud Labs in 2014 and works closely with Pivotal Inc., to help make the Cloud Found the best PaaS.
    Everything run by electricity will eventually be connected to the Internet. Get ahead of the Internet of Things revolution. In his session at @ThingsExpo, Akvelon expert and IoT industry leader Sergey Grebnov provided an educational dive into the world of managing your home, workplace and all the devices they contain with the power of machine-based AI and intelligent Bot services for a completely streamlined experience.
    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...
    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.
    Personalization has long been the holy grail of marketing. Simply stated, communicate the most relevant offer to the right person and you will increase sales. To achieve this, you must understand the individual. Consequently, digital marketers developed many ways to gather and leverage customer information to deliver targeted experiences. In his session at @ThingsExpo, Lou Casal, Founder and Principal Consultant at Practicala, discussed how the Internet of Things (IoT) has accelerated our abilit...
    In his session at Cloud Expo, Alan Winters, U.S. Head of Business Development at MobiDev, presented a success story of an entrepreneur who has both suffered through and benefited from offshore development across multiple businesses: The smart choice, or how to select the right offshore development partner Warning signs, or how to minimize chances of making the wrong choice Collaboration, or how to establish the most effective work processes Budget control, or how to maximize project result...
    To get the most out of their data, successful companies are not focusing on queries and data lakes, they are actively integrating analytics into their operations with a data-first application development approach. Real-time adjustments to improve revenues, reduce costs, or mitigate risk rely on applications that minimize latency on a variety of data sources. In his session at @BigDataExpo, Jack Norris, Senior Vice President, Data and Applications at MapR Technologies, reviewed best practices to ...
    Data is the fuel that drives the machine learning algorithmic engines and ultimately provides the business value. In his session at Cloud Expo, Ed Featherston, a director and senior enterprise architect at Collaborative Consulting, discussed the key considerations around quality, volume, timeliness, and pedigree that must be dealt with in order to properly fuel that engine.
    "Akvelon is a software development company and we also provide consultancy services to folks who are looking to scale or accelerate their engineering roadmaps," explained Jeremiah Mothersell, Marketing Manager at Akvelon, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
    In his keynote at 19th Cloud Expo, Sheng Liang, co-founder and CEO of Rancher Labs, discussed the technological advances and new business opportunities created by the rapid adoption of containers. With the success of Amazon Web Services (AWS) and various open source technologies used to build private clouds, cloud computing has become an essential component of IT strategy. However, users continue to face challenges in implementing clouds, as older technologies evolve and newer ones like Docker c...
    Two weeks ago (November 3-5), I attended the Cloud Expo Silicon Valley as a speaker, where I presented on the security and privacy due diligence requirements for cloud solutions. Cloud security is a topical issue for every CIO, CISO, and technology buyer. Decision-makers are always looking for insights on how to mitigate the security risks of implementing and using cloud solutions. Based on the presentation topics covered at the conference, as well as the general discussions heard between sessio...
    To Really Work for Enterprises, MultiCloud Adoption Requires Far Better and Inclusive Cloud Monitoring and Cost Management … But How? Overwhelmingly, even as enterprises have adopted cloud computing and are expanding to multi-cloud computing, IT leaders remain concerned about how to monitor, manage and control costs across hybrid and multi-cloud deployments. It’s clear that traditional IT monitoring and management approaches, designed after all for on-premises data centers, are falling short in ...
    Organizations planning enterprise data center consolidation and modernization projects are faced with a challenging, costly reality. Requirements to deploy modern, cloud-native applications simultaneously with traditional client/server applications are almost impossible to achieve with hardware-centric enterprise infrastructure. Compute and network infrastructure are fast moving down a software-defined path, but storage has been a laggard. Until now.
    DXWorldEXPO LLC announced today that the upcoming DXWorldEXPO | CloudEXPO New York event will feature 10 companies from Poland to participate at the "Poland Digital Transformation Pavilion" on November 12-13, 2018.
    Digital Transformation is much more than a buzzword. The radical shift to digital mechanisms for almost every process is evident across all industries and verticals. This is often especially true in financial services, where the legacy environment is many times unable to keep up with the rapidly shifting demands of the consumer. The constant pressure to provide complete, omnichannel delivery of customer-facing solutions to meet both regulatory and customer demands is putting enormous pressure on...
    The best way to leverage your CloudEXPO | DXWorldEXPO presence as a sponsor and exhibitor is to plan your news announcements around our events. The press covering CloudEXPO | DXWorldEXPO 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 CloudEXPO. Product announcements during our show provide your company with the most reach through our targeted audienc...
    In an era of historic innovation fueled by unprecedented access to data and technology, the low cost and risk of entering new markets has leveled the playing field for business. Today, any ambitious innovator can easily introduce a new application or product that can reinvent business models and transform the client experience. In their Day 2 Keynote at 19th Cloud Expo, Mercer Rowe, IBM Vice President of Strategic Alliances, and Raejeanne Skillern, Intel Vice President of Data Center Group and ...
    More and more brands have jumped on the IoT bandwagon. We have an excess of wearables – activity trackers, smartwatches, smart glasses and sneakers, and more that track seemingly endless datapoints. However, most consumers have no idea what “IoT” means. Creating more wearables that track data shouldn't be the aim of brands; delivering meaningful, tangible relevance to their users should be. We're in a period in which the IoT pendulum is still swinging. Initially, it swung toward "smart for smart...
    @DevOpsSummit at Cloud Expo, taking place November 12-13 in New York City, NY, is co-located with 22nd international CloudEXPO | first international DXWorldEXPO and will feature technical sessions from a rock star conference faculty and the leading industry players in the world.
    DXWorldEXPO LLC announced today that All in Mobile, a mobile app development company from Poland, will exhibit at the 22nd International CloudEXPO | DXWorldEXPO. All In Mobile is a mobile app development company from Poland. Since 2014, they maintain passion for developing mobile applications for enterprises and startups worldwide.