Microservices Expo Authors: Jason Bloomberg, Karthick Viswanathan, Elizabeth White, Mehdi Daoudi, Pat Romanski

Related Topics: Microservices Expo

Microservices Expo: Article

Wireless Web Serviceswith J2ME Part IISOAP or XML-RPC? The answer depends on your needs

Wireless Web Serviceswith J2ME Part IISOAP or XML-RPC? The answer depends on your needs

Last month in Part I (WSJ Vol. 2 Issue 1) we discussed J2ME and accessing Web services from wireless devices using the XML-RPC protocol. In this article, we will consider SOAP as a vehicle for accessing Web services from wireless devices, comparing and contrast-ing it with XML-RPC. Our sample application will again be a J2ME midlet, however, we will use EnhydraME's kSOAP rather than kXML-RPC to provide the protocol's implementation.

Overview of SOAP
The Simple Object Access Protocol is, according to the 1.1 specification, "a lightweight protocol for exchange of information in a decentralized, distributed environment." The protocol is entirely based on XML, vendor-neutral, and one of the cornerstone technologies in the Web services revolution. It is quite similar to XML-RPC, but we will examine that more closely in the next section.

SOAP was originally conceived and developed at Microsoft between 1998 and 1999. SOAP did not, however, gain widespread attention until DevelopMentor, IBM, Lotus, and Microsoft submitted the SOAP 1.1 version to the W3C on April 26, 2000. With both IBM and Microsoft behind it, the industry began to give SOAP some serious consideration. As of this writing, the SOAP 1.2 specification is being drafted by the W3C's XML Protocol Working Group. The latest draft of the 1.2 spec can be found at www.w3.org/TR/soap12/.

When examining SOAP, it is important to identify the three main components of any SOAP message: the SOAP envelope, rules for encoding data, and a request/response interaction mechanism. The SOAP messaging architecture can be compared to a postal system (see Figure 1). A document is enclosed in an envelope and that envelope is transmitted via the transport mechanism, the mail system in our analogy, or HTTP across a network in the case of SOAP. With the mail, a zip code identifies the locale an envelope should be delivered to; with SOAP, HTTP header data provides such routing information. At this point, the analogy breaks down. Whereas the "last mile service" provided by a postal carrier is directed by the street address on the envelope, it is information encoded in the body of the XML document itself that ultimately directs the SOAP request to the specific service on the server.

Although SOAP and XML-RPC have similar roots (XML-RPC is based on a subset of the original SOAP spec that was developed at Microsoft in the late 1990s), they are very different animals. Both XML-RPC and SOAP are XML-based protocols for communication and data exchange, so when should one be chosen over the other? We'll take a look at their strengths and weaknesses, and then evaluate these two protocols from a business perspective.

XML-RPC is an extremely lightweight mechanism for invoking XML-based services. It is a clean, simple protocol that provides the minimum overhead necessary to invoke remote services and exchange data in a platform-, language-, and vendor-neutral manner. It defines six simple data types and two complex types. The result is that XML-RPC is a highly-efficient lightweight protocol. Messages are simple to construct, simple to parse, simple to debug, and are easily human-readable. XML-RPC requires a minimal amount of active memory for processing, building, and parsing messages, and produces a thin message body to be exchanged between client and server.

In contrast, SOAP is a fatter protocol (although generally considered lightweight). In exchange for some additional overhead, SOAP provides namespace awareness, a sophisticated data-typing mechanism, and a flexible messaging paradigm. The W3C's XML Namespaces specification is leveraged to provide namespace awareness, and the XML Schema specification provides the data-typing mechanism. As such, SOAP supports over 40 standard data types and provides the capabilities to define custom simple and complex data types. This provides a tremendous degree of flexibility in terms of describing robust data structures with intricate relationships with other data contained in the message body.

The SOAP architecture also introduces a flexible messaging architecture, supporting a variety of messaging paradigms, including unidirectional, bidirectional, multicast (publish-subscribe), and sequentialmessaging (multiple parties chained together in a particular order). One aspect that facilitates these paradigms is the ability of a SOAP message to include a header section. This allows security, transaction, and routing information to be exchanged between multiple parties. For example, a client can send a SOAP request with an intended destination, but also declare in the SOAP envelope's headers that a particular party should receive the message, process the pertinent header information, and then pass the message on to the next party in the chain (or the intended recipient if no other parties have been declared). One final distinction is that SOAP supports asynchronous messaging, while XML-RPC requires a synchronous communication between the two parties in an exchange.

With all of these differences between the two protocols, executives, project managers, and wireless architects alike are wondering - "How do I make a choice between SOAP and XML-RPC for a particular wireless project or system?" Well, even if you weren't wondering that, we're going to tell you anyway.

In a nutshell, XML-RPC provides a fast, compact protocol for exchanging data and invoking services in a neutral, standardized way. If application size, memory, and bandwidth are your top priorities, then XML-RPC is the way to go. On the other hand, if your application requires a robust data-typing mechanism, extensive security or transaction support, or a flexible messaging architecture, then SOAP is your answer. Also, SOAP is more mainstream than XML-RPC, so if your application needs to access a variety of services that you have no control over, SOAP may be a better match from an interoperability perspective. To break it down into more detail, Table 1 that outlines the business justifications for using each protocol.

Wireless SOAP Example
In our previous article we developed a sample application using kXML-RPC (http://kxmlr pc.enhydra.org), an open-source implementation of the XML-RPC protocol for micro devices maintained by Enhydra. kSOAP (http://ksoap.enhydra.org) is another Enhydra Micro Edition project, providing SOAP support for mobile devices. We will create a MIDP interface with the kSOAP libraries underneath to activate a SOAP-based Web service located on a remote HTTP server.

For our application, we will be using three classes from the kSOAP library to handle the marshalling and unmarshalling of data via SOAP:

  • HttpTransport: A convenient API that enables SOAP calls via HTTP using the J2ME Generic Connection Framework
  • ClassMap: Provides namespace support and a two-way mapping between namespace-qualified XML names and Java classes
  • SoapObject: A generic object used to represent any SOAP object within the body of a SOAP request or response. SOAP objects can also be nested
Rather than creating both the client and the service we are accessing, we will simply access an existing service. Xmet hods.com provides a Web service registry for publicly available Web services. We will be invoking a service provided by Cape Clear that gathers and disseminates airport weather information on behalf of a client. The details regarding that service can be located at: www.xmethods.com/detail.html?id=129, and the source code for this midlet (Airport Weather.java) can be downloaded from the kSOAP Web site at http://ksoap.enhydra.org/software/downloads/index.html.

In creating our sample SOAP midlet (AirportWeather.java), the process is identical to the one we used in Part 1. This time, the packages and names have been changed to protect the innocent. We will import, extend, and use classes from the kSOAP library rather than the kXML-RPC library.

The first step, obviously, is to import the necessary packages and declare the MIDP components that will be used in the application. After this, we define the midlet's constructor, initializing all the UI components, and add them to the display as necessary. With that complete, we need to fill in the three other lifecycle methods. In the startApp() method, we simply bring the MIDP display into action. Since we don't use any shared resources, the pauseApp() method is blank. Finally, the destroyApp() method releases the local resources that we have allocated for our midlet.

As with Part 1, all the action takes place in the commandAction() method. This method is called anytime the user performs a command event (pressing a key, selecting an item from a list, etc.). The Command and Displayable objects are then queried to determine which component has actually been activated/ deactivated, and the appropriate actions are performed. When our midlet is launched, it displays a list of popular international airports for which weather information can be retrieved (see Figure 2). It also displays an exit button to allow the user to exit the midlet.

Upon selecting an airport, a list of weather information services for that airport is displayed (see Figure 3). A back button is also displayed to allow the user to return to the airport menu. The user then selects the weather information service he or she is interested in and the midlet sends a SOAP request to the server to collect the desired information. A SOAP response is returned, parsed by the midlet, and the result is displayed on the screen. So how does all of that work? See Listing 1 for the command Action() method.

The outer level of the commandAct ion() method checks to see what component has been activated. We'll look at each of these four events individually, beginning with the airport menu:

if ( dis == airportMenu && com == List.SELECT_COMMAND ) {
currentAirport = airportMenu.getSelectedIndex();
servicesMenu.setTitle( airports[ currentAirport ] + " weather" );
display.setCurrent( servicesMenu ); //display the list of services

When an airport is selected, we set the currentAirport variable, set the title for the services menu to reflect the selected airport, and display the services menu.

Next we'll look at the services menu. There are seven possible weather services that can be retrieved: wind conditions, temperature, pressure, humidity, sky conditions, visibility, and a complete summary containing the six individual pieces of information:

else if ( dis == servicesMenu && com == List.SELECT_COMMAND ) {
String result = null;
int choice = servicesMenu.getSelectedIndex();

The first thing to do is to declare a String variable to store the result of the service call that will be made. Next, determine which service has been selected and store the index value in an integer variable and perform a switch on that variable. The switch statement can be seen in Listing 2. The first case retrieves a summary and the other cases retrieve individual weather items. After the switch statement, the results are displayed on the screen via an Alert object.

Within each case statement in the switch block, the callSer vice() method is used to handle the exchange of SOAP messages. See Listing 3).

Four essential things take place in this method. An HttpTran sport object is created, a PrefixMap namespace is created for the SOAP envelope, a SoapObject is created to represent the request, and the request object is sent via the HttpTransport class's call() method.

The next else/if block checks to see if the back command has been selected, in which case the list of airports is displayed:

else if ( com == backCommand ) {
display.setCurrent( airportMenu );

Finally, the exit command is checked to allow the application to be exited:

else if ( com == exitCommand ) {
destroyApp( true );

That's all there is to it. Download the source code to get the details for the interface and then you are ready to build the midlet interface, compile the code and access this weather service from a J2ME phone using SOAP!

Web services are sweeping the industry and changing the face of business. Mobile computing and wireless access to information at any time, from anywhere, is an increasingly popular idea. The combination of the two is explosive! In these two articles, we've explored XML-RPC and SOAP as protocols for accessing Web services from wireless devices. XML-RPC provides a highly-efficient, extremely lightweight mechanism for invoking Web services that is ideal for mobile and embedded devices. SOAP provides a slightly heavier protocol with increased functionality and flexibility. Between these two, an appropriate protocol will likely be found for any wireless project.

More Stories By Kyle Gabhart

Kyle Gabhart is a subject matter expert specializing in strategic planning and tactical delivery of enterprise technology solutions, blending EA, BPM, SOA, Cloud Computing, and other emerging technologies. Kyle currently serves as a director for Web Age Solutions, a premier provider of technology education and mentoring. Since 2001 he has contributed extensively to the IT community as an author, speaker, consultant, and open source contributor.

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.

@MicroservicesExpo Stories
Many organizations are now looking to DevOps maturity models to gauge their DevOps adoption and compare their maturity to their peers. However, as enterprise organizations rush to adopt DevOps, moving past experimentation to embrace it at scale, they are in danger of falling into the trap that they have fallen into time and time again. Unfortunately, we've seen this movie before, and we know how it ends: badly.
These days, APIs have become an integral part of the digital transformation journey for all enterprises. Every digital innovation story is connected to APIs . But have you ever pondered over to know what are the source of these APIs? Let me explain - APIs sources can be varied, internal or external, solving different purposes, but mostly categorized into the following two categories. Data lakes is a term used to represent disconnected but relevant data that are used by various business units wit...
There is a huge demand for responsive, real-time mobile and web experiences, but current architectural patterns do not easily accommodate applications that respond to events in real time. Common solutions using message queues or HTTP long-polling quickly lead to resiliency, scalability and development velocity challenges. In his session at 21st Cloud Expo, Ryland Degnan, a Senior Software Engineer on the Netflix Edge Platform team, will discuss how by leveraging a reactive stream-based protocol,...
Today most companies are adopting or evaluating container technology - Docker in particular - to speed up application deployment, drive down cost, ease management and make application delivery more flexible overall. As with most new architectures, this dream takes significant work to become a reality. Even when you do get your application componentized enough and packaged properly, there are still challenges for DevOps teams to making the shift to continuous delivery and achieving that reducti...
21st International Cloud Expo, taking place October 31 - November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA, 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 strategy. Me...
Enterprises are moving to the cloud faster than most of us in security expected. CIOs are going from 0 to 100 in cloud adoption and leaving security teams in the dust. Once cloud is part of an enterprise stack, it’s unclear who has responsibility for the protection of applications, services, and data. When cloud breaches occur, whether active compromise or a publicly accessible database, the blame must fall on both service providers and users. In his session at 21st Cloud Expo, Ben Johnson, C...
Many organizations adopt DevOps to reduce cycle times and deliver software faster; some take on DevOps to drive higher quality and better end-user experience; others look to DevOps for a clearer line-of-sight to customers to drive better business impacts. In truth, these three foundations go together. In this power panel at @DevOpsSummit 21st Cloud Expo, moderated by DevOps Conference Co-Chair Andi Mann, industry experts will discuss how leading organizations build application success from all...
‘Trend’ is a pretty common business term, but its definition tends to vary by industry. In performance monitoring, trend, or trend shift, is a key metric that is used to indicate change. Change is inevitable. Today’s websites must frequently update and change to keep up with competition and attract new users, but such changes can have a negative impact on the user experience if not managed properly. The dynamic nature of the Internet makes it necessary to constantly monitor different metrics. O...
The last two years has seen discussions about cloud computing evolve from the public / private / hybrid split to the reality that most enterprises will be creating a complex, multi-cloud strategy. Companies are wary of committing all of their resources to a single cloud, and instead are choosing to spread the risk – and the benefits – of cloud computing across multiple providers and internal infrastructures, as they follow their business needs. Will this approach be successful? How large is the ...
Agile has finally jumped the technology shark, expanding outside the software world. Enterprises are now increasingly adopting Agile practices across their organizations in order to successfully navigate the disruptive waters that threaten to drown them. In our quest for establishing change as a core competency in our organizations, this business-centric notion of Agile is an essential component of Agile Digital Transformation. In the years since the publication of the Agile Manifesto, the conn...
You know you need the cloud, but you’re hesitant to simply dump everything at Amazon since you know that not all workloads are suitable for cloud. You know that you want the kind of ease of use and scalability that you get with public cloud, but your applications are architected in a way that makes the public cloud a non-starter. You’re looking at private cloud solutions based on hyperconverged infrastructure, but you’re concerned with the limits inherent in those technologies.
The nature of the technology business is forward-thinking. It focuses on the future and what’s coming next. Innovations and creativity in our world of software development strive to improve the status quo and increase customer satisfaction through speed and increased connectivity. Yet, while it's exciting to see enterprises embrace new ways of thinking and advance their processes with cutting edge technology, it rarely happens rapidly or even simultaneously across all industries.
Most of the time there is a lot of work involved to move to the cloud, and most of that isn't really related to AWS or Azure or Google Cloud. Before we talk about public cloud vendors and DevOps tools, there are usually several technical and non-technical challenges that are connected to it and that every company needs to solve to move to the cloud. In his session at 21st Cloud Expo, Stefano Bellasio, CEO and founder of Cloud Academy Inc., will discuss what the tools, disciplines, and cultural...
With the rise of DevOps, containers are at the brink of becoming a pervasive technology in Enterprise IT to accelerate application delivery for the business. When it comes to adopting containers in the enterprise, security is the highest adoption barrier. Is your organization ready to address the security risks with containers for your DevOps environment? In his session at @DevOpsSummit at 21st Cloud Expo, Chris Van Tuin, Chief Technologist, NA West at Red Hat, will discuss: The top security r...
"NetApp's vision is how we help organizations manage data - delivering the right data in the right place, in the right time, to the people who need it, and doing it agnostic to what the platform is," explained Josh Atwell, Developer Advocate for NetApp, in this SYS-CON.tv interview at 20th Cloud Expo, held June 6-8, 2017, at the Javits Center in New York City, NY.
The “Digital Era” is forcing us to engage with new methods to build, operate and maintain applications. This transformation also implies an evolution to more and more intelligent applications to better engage with the customers, while creating significant market differentiators. In both cases, the cloud has become a key enabler to embrace this digital revolution. So, moving to the cloud is no longer the question; the new questions are HOW and WHEN. To make this equation even more complex, most ...
One of the biggest challenges with adopting a DevOps mentality is: new applications are easily adapted to cloud-native, microservice-based, or containerized architectures - they can be built for them - but old applications need complex refactoring. On the other hand, these new technologies can require relearning or adapting new, oftentimes more complex, methodologies and tools to be ready for production. In his general session at @DevOpsSummit at 20th Cloud Expo, Chris Brown, Solutions Marketi...
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...
Today companies are looking to achieve cloud-first digital agility to reduce time-to-market, optimize utilization of resources, and rapidly deliver disruptive business solutions. However, leveraging the benefits of cloud deployments can be complicated for companies with extensive legacy computing environments. In his session at 21st Cloud Expo, Craig Sproule, founder and CEO of Metavine, will outline the challenges enterprises face in migrating legacy solutions to the cloud. He will also prese...
DevOps at Cloud Expo – being held October 31 - November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA – announces that its Call for Papers is open. Born out of proven success in agile development, cloud computing, and process automation, DevOps is a macro trend you cannot afford to miss. From showcase success stories from early adopters and web-scale businesses, DevOps is expanding to organizations of all sizes, including the world's largest enterprises – and delivering real r...