Welcome!

Java IoT Authors: APM Blog, Liz McMillan, Elizabeth White, Simon Hill, Stackify Blog

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
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 ...
"There's plenty of bandwidth out there but it's never in the right place. So what Cedexis does is uses data to work out the best pathways to get data from the origin to the person who wants to get it," explained Simon Jones, Evangelist and Head of Marketing at Cedexis, 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 session at 21st Cloud Expo, Carl J. Levine, Senior Technical Evangelist for NS1, will objectively discuss how DNS is used to solve Digital Transformation challenges in large SaaS applications, CDNs, AdTech platforms, and other demanding use cases. Carl J. Levine is the Senior Technical Evangelist for NS1. A veteran of the Internet Infrastructure space, he has over a decade of experience with startups, networking protocols and Internet infrastructure, combined with the unique ability to it...
SYS-CON Events announced today that CrowdReviews.com has been named “Media Sponsor” of SYS-CON's 22nd International Cloud Expo, which will take place on June 5–7, 2018, at the Javits Center in New York City, NY. CrowdReviews.com is a transparent online platform for determining which products and services are the best based on the opinion of the crowd. The crowd consists of Internet users that have experienced products and services first-hand and have an interest in letting other potential buye...
"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.
SYS-CON Events announced today that Telecom Reseller has been named “Media Sponsor” of SYS-CON's 22nd International Cloud Expo, which will take place on June 5-7, 2018, at the Javits Center in New York, NY. Telecom Reseller reports on Unified Communications, UCaaS, BPaaS for enterprise and SMBs. They report extensively on both customer premises based solutions such as IP-PBX as well as cloud based and hosted platforms.
WebRTC is great technology to build your own communication tools. It will be even more exciting experience it with advanced devices, such as a 360 Camera, 360 microphone, and a depth sensor camera. In his session at @ThingsExpo, Masashi Ganeko, a manager at INFOCOM Corporation, introduced two experimental projects from his team and what they learned from them. "Shotoku Tamago" uses the robot audition software HARK to track speakers in 360 video of a remote party. "Virtual Teleport" uses a multip...
Gemini is Yahoo’s native and search advertising platform. To ensure the quality of a complex distributed system that spans multiple products and components and across various desktop websites and mobile app and web experiences – both Yahoo owned and operated and third-party syndication (supply), with complex interaction with more than a billion users and numerous advertisers globally (demand) – it becomes imperative to automate a set of end-to-end tests 24x7 to detect bugs and regression. In th...
"Space Monkey by Vivent Smart Home is a product that is a distributed cloud-based edge storage network. Vivent Smart Home, our parent company, is a smart home provider that places a lot of hard drives across homes in North America," explained JT Olds, Director of Engineering, and Brandon Crowfeather, Product Manager, at Vivint Smart Home, in this SYS-CON.tv interview at @ThingsExpo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
"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...
"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...
It is of utmost importance for the future success of WebRTC to ensure that interoperability is operational between web browsers and any WebRTC-compliant client. To be guaranteed as operational and effective, interoperability must be tested extensively by establishing WebRTC data and media connections between different web browsers running on different devices and operating systems. In his session at WebRTC Summit at @ThingsExpo, Dr. Alex Gouaillard, CEO and Founder of CoSMo Software, presented ...
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...
SYS-CON Events announced today that Evatronix will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Evatronix SA offers comprehensive solutions in the design and implementation of electronic systems, in CAD / CAM deployment, and also is a designer and manufacturer of advanced 3D scanners for professional applications.
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...
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 ...
An increasing number of companies are creating products that combine data with analytical capabilities. Running interactive queries on Big Data requires complex architectures to store and query data effectively, typically involving data streams, an choosing efficient file format/database and multiple independent systems that are tied together through custom-engineered pipelines. In his session at @BigDataExpo at @ThingsExpo, Tomer Levi, a senior software engineer at Intel’s Advanced Analytics gr...
When talking IoT we often focus on the devices, the sensors, the hardware itself. The new smart appliances, the new smart or self-driving cars (which are amalgamations of many ‘things’). When we are looking at the world of IoT, we should take a step back, look at the big picture. What value are these devices providing? IoT is not about the devices, it’s about the data consumed and generated. The devices are tools, mechanisms, conduits. In his session at Internet of Things at Cloud Expo | DXWor...
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.
SYS-CON Events announced today that Synametrics Technologies will exhibit at SYS-CON's 22nd International Cloud Expo®, which will take place on June 5-7, 2018, at the Javits Center in New York, NY. Synametrics Technologies is a privately held company based in Plainsboro, New Jersey that has been providing solutions for the developer community since 1997. Based on the success of its initial product offerings such as WinSQL, Xeams, SynaMan and Syncrify, Synametrics continues to create and hone inn...