Javaâ„¢ 2 Platform, Micro Edition (J2MEâ„¢) Web Services Java 2 Platform, Micro Edition (J2ME) Web Services White Paper Javaâ„¢ 2 Platform, Micro Edition (J2MEâ„¢) Web Services On the Web sun.com A Technical White Paper July 2004 Javaâ„¢ 2 Platform, Micro Edition(J2MEâ„¢) Web Services

Chapter 3 An Overview of Web Services To fulfill the promise of Web services requires cooperation. Companies like Sun Microsystems and others work closely with bodies such as the World Wide Web Consortium (W3C) and the Java Community Process SM (JCP SM ) program to develop new standards and protocols. Many difficult technical problems — such as connectivity, discovery, data description, and security — must be solved. For example, what does it take for a client developer in California to find and use a remote Web service developed by a programmer in the Czech Republic? For this to happen, solutions to three different but interrelated problems must be in place: 1. How must an application be written and deployed so that it is accessible to clients on the network? 2. How does a client developer, who wants to use a certain type of Web service, find that service? 3. Once a service is located, how does a client developer access its functionality? The solution to these problems provides a context for understanding the field of Web services. Web Services Solutions The first problem described — writing and deploying accessible applications — is best addressed by using the tools and techniques of the Java programming language. The compact nature of Java technology code, the inherent security of the Java Virtual Machine, and the standardized deployment methodologies of the Java 2 Platform, Enterprise Edition (J2EEâ„¢ platform) make the Java language particularly well-suited for Web services development and deployment. The second problem — finding a remote service — is handled through the use of a network registry . A registry is a centralized location where developers post information about a service so that other developers can use it. Although there is more than one network registry available, the most widely used is the Universal Description, Discovery, and Integration (UDDI) registry. The third problem — connecting with and using a network service — lies at the heart of the Web services paradigm. To address this requires a number of well-defined steps, and makes use of the following standard protocols: • eXtensible Markup Language (XML) : A portable document markup language used extensively in the Web services paradigm. It provides a transportable means of describing system and configuration information that can be passed between applications. Both SOAP and WSDL files are written using XML P5 An Overview of Web Services Sun Microsystems, Inc. Figure 1. Steps in the Web Services Paradigm Scope of This Paper For the purpose of describing the J2ME Web Services Specification, further discussion of steps 1, 2, 3, 4, and 5 in Figure 1 are largely outside the scope of this paper. For more information on writing and deploying Java applications, visit java.sun.com. There are also a number of excellent books available that provide information on using the UDDI registry as well as the details of the SOAP, WSDL, XML, and RPC protocols. The Web Services Client Model As described in “Using Web Services, ” once a client developer has obtained the WSDL file for a remote Web service, it becomes possible for the client to make calls to that service. Note – The following steps expand on the actions described in Figure 1, Step 7. The following is a typical interaction between a Web services client and a remote Web service (as illustrated in Figure 2): 1. A local application makes a procedure call to a local client component that has been developed using the WSDL file obtained from a remote Web service. 2. The local client component sets up an HTTP communication channel with the remote Web service, using the service endpoint defined in the WSDL file. A procedure call is sent to the remote service over the HTTP connection, using SOAP and RPC….. P7 The J2ME Web Services Specification Sun Microsystems, Inc. Chapter 4 The J2ME Web Services Specification The J2ME Web Services Specification is specifically designed to facilitate development of small, fast, and robust Java platform applications in the wireless marketplace. The J2ME Web Services Specification provides two XML- based optional packages that can be used to develop Java Web services for small, reduced-memory, handheld devices such as cell phones, PDAs, and pagers. These packages are: •Java API for XML Processing (JAXP) •Java API for XML-based RPC (JAX-RPC) The J2ME Client Platform The J2ME platform is a set of standard Java APIs defined through the Java Community Process (JCP). It provides a flexible user interface, robust security, and built-in network protocols. The J2ME platform can be tailored for a specific class of device by matching it with a specific configuration and profile, and can be extended for a specific market by adding additional optional packages. The J2ME Web Services Specification supports the following: • Connected Limited Device Configuration (CLDC), v1.x . CLDC is designed for small devices with 16-bit or 32-bit CPUs and 128 KB to 512 KB of memory. • Mobile Information Device Profile (MIDP), v1.x and 2.x . MIDP is specifically designed for cell phones and entry- level PDAs, and provides the user interface, network connectivity, local data storage, and application management needed by these devices.

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