Welcome!

Java IoT Authors: Liz McMillan, Pat Romanski, Yeshim Deniz, Elizabeth White, Paul Simmons

Related Topics: Java IoT, Microservices Expo

Java IoT: Article

Moving to SOA in J2EE 1.4

How to take an existing J2EE 1.3 bean and convert it into a Web service endpoint with almost no changes to its business interfac

This past year the J2EE 1.4 specification enjoyed increased adoption by the industry, with most major application server vendors having released their J2EE 1.4 products and more and more enterprises upgrading their application servers and production applications to comply with it.

Apart from merely upgrading, there's a natural desire to leverage the primary focus of J2EE 1.4 - its support for service oriented architectures and Web services - and make it benefit the business by exposing the business logic of J2EE applications in a way that makes them portably accessible from the various heterogeneous environments that are around today.

Here at Compuware (the company I work for) we chose to make the ability to generate J2EE 1.4 applications one of the top requirements of the upcoming version of our OptimalJ product, an MDA-based development product that enables you to generate (from user-defined models) complex, standards-compliant J2EE 1.3 and J2EE 1.4 applications that run on JBoss, WebSphere, and WebLogic. To do this, we were faced with the formidable task of ensuring that the user-modeled enterprise beans or Stateless Session Beans (SLSBs) that used to be translated into EJB 2.0 code can now be translated into EJB 2.1 Beans with Web Service endpoints with a minimum of changes to the signatures of their business methods. The same was accomplished for Java components running in the Web container.

Essentially what we learned is how to take an existing J2EE 1.3 bean (a SLSB or a Java component running in the Web container) and convert it into a Web Service endpoint with almost no changes to its business interface by craftily applying Java-to-WSDL/XML mapping to its business interface.

What makes this difficult is that when a bean is exposed and accessed as a Web Service endpoint, parameter passing is subject to SOAP serialization rules, which are far more restrictive than RMI-IIOP serialization semantics.

What we did was stress the ASs' compliance to J2EE 1.4 to its limits and gained firsthand knowledge of what works and what doesn't. We found numerous problems in the application services that we targeted - JBoss 4.0.x and WebSphere 6.0.x, which we addressed in cooperation with the respective vendors. In this article I will share the valuable knowledge that we learned on this project, show portable solutions, and draw attention to common pitfalls.

Service Endpoints in J2EE 1.4
Web Service endpoint is a term used in J2EE to describe Web Service components deployed in a J2EE container. A service endpoint can be implemented using a stateless session bean, in which case it runs in the EJB container, or as a Java class that is registered as a servlet, in which case it runs in the Web container and is termed a JAX-RPC endpoint.

Associated with each service endpoint is its service endpoint interface (SEI for brevity). Given that the Web Service endpoint is implemented by a J2EE component, it's sometimes called a service implementation bean.

Conceptually and visually the SEI is very similar to the remote component interface of Enterprise JavaBeans. It too extends java.rmi.Remote, its methods must declare java.rmi.RemoteException in their throws clauses, and looking at the code of a SEI and a remote component interface alone is often impossible to tell the two apart. This similarity is delusive since, in the case of the SEI, parameter and return value passing is subject to the restrictive SOAP serialization rules, while for the remote component interface the more liberal Java serialization semantics apply (let alone communication via local component interfaces where no extra restrictions apply).

SOAP serialization rules only permit argument and return values of the following types:

  1. The primitive Java types (with the exception of char) and their wrapper counterparts
  2. The standard JDK classes java.lang.String, java.util.Date, java.util.Calendar, java.math.BigInteger, java.math.BigDecimal, javax.xml.namespace.QName, and java.net.URI
  3. JavaBeans with default constructors whose properties and public fields types are, in turn, allowed SOAP serialization types
  4. Java arrays whose underlying types are, in turn, permitted SOAP serialization types. An important special case is that arrays of type Object aren't supported because java.lang.Object is not enumerated as a supported type. Even though not explicitly mentioned in the specification, multidimensional arrays also pose problems and should be avoided to achieve compliancy with the WS-I Basic Profile.
And that's all - no Java collections, even if a JavaBean class implements java.io.Serializable, it doesn't imply its eligibility for SOAP serialization! Even though there's a concept of custom serializers/deserializers for Web Service endpoints, such serializers aren't portable across Web Services for J2EE providers and, as a result, aren't supported in J2EE 1.4. Yet, despite the apparent restrictions, we found out that in many situations it's still possible to devise portable ways of exposing your business interfaces as SEIs without changing them much.

An SEI can coexist with the remote/local component interfaces of a SLSB or the business interface of a Web component in which case it may have a different number of business methods than the accompanying component interface(s). Like its remote/local counterparts, a SEI can feature overloaded methods that should be mapped to wsdl:operations with distinct names (more on that can be found in the Pullout on WS-I Basic Profile). We observed that JBoss didn't support overloaded methods in SEIs prior to version 4.0.4. (See http://jira.jboss.com/jira/browse/JBWS-463.)

Another important difference between the remote or local component interface and the SEI is that the latter must be accompanied by a WSDL definition that provides a canonical description of its Web Service endpoint that can be published to third parties (which may not necessarily be using a Java environment).

This essentially brings in an additional dimension because the SEI's WSDL definition influences how method invocations are serialized into XML. One way to influence the serialization of method invocations is the binding that the WSDL definition has assigned to the SEI. J2EE 1.4 supports two portable bindings - document-literal and rpc-literal, whose details can be found in [1, 2, and 3]. Thus in J2EE 1.4 a Web Service endpoint is fully described by the pair { SEI, WSDL } and the same SEI accompanied by different WSDL definitions leads to different XML messages on the wire.

The fact that a J2EE Web service endpoint is defined by the { SEI, WSDL } pair entails two different ways of developing one:

  • Start from a SEI. The rules of this approach are defined in the Java-to-XML/WSDL mapping whose definition can be found in the JAX-RPC 1.1 specification.
  • Start from a WSDL definition. This development approach is governed by the WSDL/XML-to-Java mapping.
The two mappings aren't symmetrical. Moreover each allows variations. That is, the transformation SEI1 -> WSDL -> SEI2 need not imply that SEI1 = SEI2. When dealing with an existing stateless session bean or existing business logic component running in the Web container, it is of course the Java-to-XML/WSDL mapping that's applicable. This mapping is also prevalent in new projects and the rest of the article will concentrate on it. (The WSDL/XML-to-Java mapping is typically turned to only when one needs to develop a Web Service endpoint that conforms to the interface and binding information provided by a given WSDL document.)

Java-to-XML/WSDL Mapping
When using the development approach based on the Java-to-XML/WSDL mapping, what you do first is define the SEI for the component you want to expose as a Web Service. You typically do so by copying the signatures of an existing component's business methods from its remote component interface (for EJBs) or business interface (for components running in the Web container). Sometimes you may have to change the signature slightly and I will explain later when that is necessary.

When mapping Java types to XML Schema definitions all non-standard types are regarded as JavaBeans. An essential and little considered aspect of this mapping is that only public non-final non-transient fields and read/write properties as defined by the java.beans.Introspector class are taken into account. Java exceptions are treated slightly differently; in their case read properties are also counted in. Each read property must be accompanied by a corresponding parameter in the constructor; otherwise it wouldn't be possible to assign the property a value. We found out that some application servers (e.g., JBoss 4.0.x - cf. http://jira.jboss.com/jira/browse/JBAS-2139) have problems with read-only properties in exceptions when a property's type is an array.

The fact that 1) public non-final fields are very uncommon and their use is discouraged and that 2) properties are queried for by using java.beans.Introspector means that we can accompany "problematic" Java types - that in themselves don't qualify for SOAP serialization rules - with BeanInfo counterparts that present explicit information of what the properties of a given Java type are. Listing 1 offers an example of a "problematic" Java type that was used as a superclass for all application exceptions in our project.

The problem with this class is that it features two properties that don't qualify for SOAP serialization - cause of type Throwable and values of type Object[]. No matter how you map this class to an XML Schema complex type (even if you exclude the problematic properties from the complex type's content model), you're bound to run into problems during your application's execution. Listing 2 shows an accompanying BeanInfo class that makes AlturaException a legitimate type for SOAP serialization.

As you can see the BeanInfo class simply excluded the cause property from the serialized state. It also redirected the values property to a new getter and setter - getStringValues and setStringValues (the setter is required to cater to those ASs that don't yet adequately support read-only properties of array types in exceptions). The new getter and setter are shown below:

/** Returns a String representation of this object's arguments. */
public String[] getStringValues() {
   return getValues() == null
       || getValues().getClass() != String[].class
     ? null : (String[]) getValues();
}
public void setStringValues(String values[]) {
   args = values;
}

When dealing with abstract Java classes, some application servers (e.g., WebSphere 6.0.x) require that they be mapped to abstract complex types, which is a sensible requirement that should be followed not only for portability but also to support polymorphism in the SEI methods.

With our changes to the serialized state of AlturaException, we can now portably map it to an XML Schema complex type:

<xsd:complexType name="AlturaException" abstract="true">
   <xsd:sequence>
     <xsd:element name="key" type="xsd:string"/>
     <xsd:element name="values" type="xsd:string" nillable="true"
     minOccurs="0" maxOccurs="unbounded"/>
   </xsd:sequence>
</xsd:complexType>

More Stories By Andrei Iltchenko

Andrei Iltchenko is a development lead at Compuware Corporation where he works on the MDA product OptimalJ and is responsible for the business logic area of OptimalJ-generated J2EE applications. He is also a Sun certified Java developer for Java Web Services, a Sun Certified Business Component Developer, a Sun Certified Developer, and a Sun Certified Programmer.

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
SYS-CON Belgium News Desk 02/17/06 07:11:44 PM EST

This past year the J2EE 1.4 specification enjoyed increased adoption by the industry, with most major application server vendors having released their J2EE 1.4 products and more and more enterprises upgrading their application servers and production applications to comply with it.

@ThingsExpo Stories
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...
JETRO showcased Japan Digital Transformation Pavilion at SYS-CON's 21st International Cloud Expo® at the Santa Clara Convention Center in Santa Clara, CA. The Japan External Trade Organization (JETRO) is a non-profit organization that provides business support services to companies expanding to Japan. With the support of JETRO's dedicated staff, clients can incorporate their business; receive visa, immigration, and HR support; find dedicated office space; identify local government subsidies; get...
DXWorldEXPO LLC announced today that ICC-USA, a computer systems integrator and server manufacturing company focused on developing products and product appliances, will exhibit at the 22nd International CloudEXPO | DXWorldEXPO. DXWordEXPO New York 2018, colocated with CloudEXPO New York 2018 will be held November 11-13, 2018, in New York City. ICC is a computer systems integrator and server manufacturing company focused on developing products and product appliances to meet a wide range of ...
@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 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.
22nd International Cloud Expo, taking place June 5-7, 2018, at the Javits Center in New York City, NY, and co-located with the 1st DXWorld Expo will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud ...
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...
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.
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...
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.
In his Opening Keynote at 21st Cloud Expo, John Considine, General Manager of IBM Cloud Infrastructure, led attendees through the exciting evolution of the cloud. He looked at this major disruption from the perspective of technology, business models, and what this means for enterprises of all sizes. John Considine is General Manager of Cloud Infrastructure Services at IBM. In that role he is responsible for leading IBM’s public cloud infrastructure including strategy, development, and offering m...
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.
We are seeing a major migration of enterprises applications to the cloud. As cloud and business use of real time applications accelerate, legacy networks are no longer able to architecturally support cloud adoption and deliver the performance and security required by highly distributed enterprises. These outdated solutions have become more costly and complicated to implement, install, manage, and maintain.SD-WAN offers unlimited capabilities for accessing the benefits of the cloud and Internet. ...
Headquartered in Plainsboro, NJ, Synametrics Technologies has provided IT professionals and computer systems developers since 1997. Based on the success of their initial product offerings (WinSQL and DeltaCopy), the company continues to create and hone innovative products that help its customers get more from their computer applications, databases and infrastructure. To date, over one million users around the world have chosen Synametrics solutions to help power their accelerated business or per...
Founded in 2000, Chetu Inc. is a global provider of customized software development solutions and IT staff augmentation services for software technology providers. By providing clients with unparalleled niche technology expertise and industry experience, Chetu has become the premiere long-term, back-end software development partner for start-ups, SMBs, and Fortune 500 companies. Chetu is headquartered in Plantation, Florida, with thirteen offices throughout the U.S. and abroad.
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.
Bill Schmarzo, author of "Big Data: Understanding How Data Powers Big Business" and "Big Data MBA: Driving Business Strategies with Data Science," is responsible for setting the strategy and defining the Big Data service offerings and capabilities for EMC Global Services Big Data Practice. As the CTO for the Big Data Practice, he is responsible for working with organizations to help them identify where and how to start their big data journeys. He's written several white papers, is an avid blogge...
I think DevOps is now a rambunctious teenager - it's starting to get a mind of its own, wanting to get its own things but it still needs some adult supervision," explained Thomas Hooker, VP of marketing at CollabNet, in this SYS-CON.tv interview at DevOps Summit at 20th Cloud Expo, held June 6-8, 2017, at the Javits Center in New York City, NY.
"MobiDev is a software development company and we do complex, custom software development for everybody from entrepreneurs to large enterprises," explained Alan Winters, U.S. Head of Business Development at MobiDev, 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.