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Web Services Interoperability

Web Services Interoperability

Web services has been promising to solve several business problems, including those of integration and interoperability. While Web services standards like SOAP, WSDL, and UDDI help to facilitate it, they don't really ensure it.

In the past, application-to-application integration and business-to-business integration were not easy due to the various platforms involved or different software used. With the advent of Web services and related standards, it all looks very simple. Web services standards have been widely adopted by several vendors, who provide their own implementation for these standards and tools to develop and deploy Web services.

With the evolution of these standards, multiple versions and multiple implementations of Web services coexist among the applications. Loose definitions in standards may be interpreted in different ways. For example, SOAPAction, defined in the SOAP 1.1 specification, may be interpreted as the intended target for the message or the name of the target service. Vendors provide tools to generate services and clients from WSDL; WSDLs are generated by tools and applications to describe Web service. All these result in Web service interoperability issues.

In order to keep Web services interoperable, we need to ensure that various vendor implementations are interoperable, the tools that are used do not affect the integrity of the Web services, and standards are strictly followed and implemented.

Several industry efforts like SOAP builders and the Web Service Interoperability Organization (WS-I) were started to address these issues. BEA has been actively participating in these efforts to make sure that BEA's Web services are interoperable. This article provides an introduction to Web services interoperability efforts and shows how some of these tests can be easily implemented and performed using WebLogic server tools and WebLogic Workshop. I also list some useful resources.

SOAPBuilders
SOAPBuilders was created to promote interoperability as the SOAP specification evolves. The test labs provide test suites that can be used by SOAP implementations to test interoperability. SOAPBuilders defines four rounds of interoperability tests. The first three rounds are already available; the fourth was expected to be finalized in October 2002.

Round 1
This round defines echo tests for String, StringArray, Integer, IntegerArray, Float, FloatArray, Struct, StructArray, Void, Base64, and Date. In the echo tests, the data types sent by the client are simply echoed back by the server. While this may sound very simple, it tests several aspects of implementation including serialization, deserialization, encoding, conformance to standards, support for data types, etc. The Round 1 SOAP interoperability tests specification can be found at www.xmethods.net/soapbuilders/proposal.html. The WSDL can be found at www.xmethods.net/tmodels/InteropTest.wsdl.

Round 2
SOAPBuilders Round 2 defines the specifications for echo tests using SOAP 1.1 and Section 5 encoding. Round 2 has been classified into three test suites: base, Group B, and echo Header. Table 1 summarizes the test suite, URLs for proposal, and WSDL.

Round 3
This round proposed overall testing strategy to make sure that SOAP/WSDL tools can generate WSDL docs for given scenarios correctly, consume WSDL docs generated by others, and consume and reuse given WSDL docs. The focus of this round was to demonstrate WSDL interoperability between SOAP-based Web service toolkits.

Round 3 is split into groups D, E, and F. Group D targets the classic RPC development model. Tests are defined by a given WSDL definition that is used to generate both servers and clients.

Group E targets ensuring coverage of mainstream WSDL features. These tests rely on a server-centric development model, ensuring that clients can consume WSDL generated by servers and matching certain criteria.

Group F tests are defined in terms of WSDL documents to test the ability of a toolkit to generate and execute client code based on given WSDL without error. More information on round 3 can be found at www.whitemesa.com/r3/interop3.html.

Round 4
This round is divided into groups G, H and I. Group G focuses on testing the ability to send and receive attachments using SwA (SOAP messages with Attachments) and DIME (Direct Internet Message Encapsulation). WSDL documents for RPC style and Document/literal style test cases can be found at www.whitemesa.com/r4/interop4.html.

Group H addresses fault message processing and Group I focuses on WSDL/XSD testing.

SOAPBuilders Forum
A Yahoo group, http://groups.yahoo.com/group/soapbuilders, has been created to facilitate communication about interoperability issues. This group is a forum for builders of SOAP implementations to discuss cross-implementation interoperability issues, SOAP spec interpretations, etc.

WS-I
WS-I is an open industry organization chartered to promote Web services interoperability across platforms, operating systems, and programming languages. The organization works across the industry and standards organizations to respond to customer needs by providing guidance, best practices, and resources for developing Web services solutions.

While SOAPBuilders focuses on testing tool interoperability, WS-I focuses on providing the Web service implementer or developer with a set of tools and implementation guidance to ensure that the services they build can interoperate and conform to the current Web service standards. Whereas testing materials from other organizations tend to focus on a particular specification, WS-I-created test tools will address interoperability at a level above that of specification-by-specification and help determine the overall conformance of a given Web service to a profile or set of specifications that may come from various sources.

WS-I.org has 3 primary goals:

  • Provide implementation guidance and education to help customers with Web services adoption.
  • Promote consistent and reliable interoperability among Web services across platforms, applications, and programming languages.
  • Articulate and promote a common industry vision for Web services interoperability to ease customer decision making, grow industry adoption of Web services and ensure the continued evolution of Web services technologies.

    WebLogic Web Services Interoperability
    You can easily implement and test the interoperability tests using the tools provided by WebLogic Server 7.0. WebLogic Server provides plenty of powerful tools and utilities to develop and test Web services and Web services clients. This section shows you how to use WebLogic tools like WebLogic Workshop and clientgen ant task to effectively implement and perform the tests. While this article does not attempt to show how to implement all the test suites, it explains some nice features of WebLogic utilities that can be used to easily develop and test these services.

    Creating Echo Web Service
    To implement a test from the given WSDL, WebLogic workshop offers a feature to generate JWS file from WSDL. Once the JWS file is generated, it can be edited to complete the implementation. For example, to implement the round 2 base test using Workshop, follow the steps listed below:

  • Copy the WSDL file from SOAP Builders Web site
  • Create a new text file in workshop with .wsdl extension, paste the WSDL file into it.
  • Edit the service end point information in the WSDL file. If the <service> section is not already present, add it. Enter appropriate service name, port name, and location. For example:

    <service name="InteropTest">
    <port name="InteropTestPort" binding="tns:InteropTestSoapBinding">
    <soap:address location="http://localhost:7001/interop/InteropTest.jws"/>
    </port>
    </service>

  • Save the file, right click on it in the project tree and choose "Generate JWS from WSDL".
  • Workshop generates the Web service as shown in Figure 1.
  • Go to the source view tab and complete the methods. In our case, to implement the echo test, just type "return <input argument>;" for all the methods except echoVoid().
  • When the service is run from Workshop, it displays the test form as shown in Figure 2. It may show that the operation is not supported over HTTP-GET. If you want to test the service using the test form, you will have to disassociate the WSDL in the JWS file and set form-get and form-post to "true" for each method in the property editor.
  • The Web service can be tested using clients generated externally but still the logs can be viewed using the test form. Writing client programs is explained later in this article.

    Creating clients
    As explained earlier, SOAPBuilders' round 3 defines tests that ensure interoperability between generated clients, prebuilt server and generated servers. Client proxies can be generated using clientgen ant task or WebLogic workshop. This section discusses how to generate and code clients using each of these methods.

    Generating client proxy using clientgen
    Clientgen ant task can be used to generate the client proxy to test the InteropTest Web service we just created. Following is an excerpt from the build.xml file (source code for this article may be found at www.sys-con.com/weblogic/sourcec.cfm):

    <target name="build" depends="check">
    <mkdir dir="${build}"/>
    <clientgen wsdl="http://localhost:7001/interop/InteropTest.jws?WSDL"
    serviceName="InteropTest"
    autotype="True"
    overwrite="False"
    useServerTypes="False"
    packageName="com.bea.interoptest"
    clientJar="${build}"/>
    </target>

    When the ant task runs, it creates the client proxies for the Web service specified by the WSDL URL in the build directory under the package specified by packageName. This could point to a local Web service or a remote service on the Internet. It should be noted that the client proxy can be generated for Web services implemented on other vendor platforms too. The serviceName parameter is the name of the service defined in the WSDL.

    Proxy Wrapper
    The following listing shows the proxy wrapper that invokes the client proxy to call the Web service.

    private InteropTestPortType service;
    // Constructor
    public ProxyWrapper() {
    try {
    service = new InteropTest_Impl().getInteropTestPortType();
    } catch(Exception e) { /*Process Exception here*/ }
    }
    // echoString
    public String echoString(String input) {
    try {
    return service.echoString(input);
    } catch (Exception e) { /* Process Exception here*/ }
    }

    Clientgen generates several classes, two of which are important for us. One class is derived from the service name; the other is derived from the port name specified in the WSDL. You can also verify the class names by checking the package directory specified in the build.xml file. This proxy wrapper nicely encapsulates the client proxy access details and may be used by a test driver like jUnit test case to invoke the service. The following listing shows a sample jUnit test case using the proxy wrapper:

    import junit.framework.TestCase;
    ......
    public class InteropTest extends TestCase {
    .......
    public void testEchoString() throws Exception {
    ProxyWrapper soapInterop = new ProxyWrapper();
    String input = "Foo";
    assertEquals("Failed on echo String", input,soapInterop.echoString(input));
    }
    ........
    }

    Creating Client Using Workshop
    One of the nice features of WebLogic Workshop is the service control. To create a client for a Web service, follow these steps:

  • Create a Web service, InteropClient.jws from the WSDL as explained in the "Create Echo Web Service" section
  • Add a service control and input the WSDL URL and variable name for the Web service. The design view looks like Figure 3.
  • In the method definitions, proxy the requests to the service control. For example:

    /**
    * @jws:operation
    * @jws:protocol soap-style="rpc"
    */
    public java.lang.String echoString (java.lang.String inputString)
    {
    return interopServer.echoString(inputString);
    }

  • If you want to test using the test form, accept String for echoByte and echoByteArray and pass String.getBytes() to the service control
  • Accept elements of the structure as input and populate the structure in the code for echoStruct and echoStructArray as structures can not be entered directly.
  • Figure 4 shows the Test form for the InteropClient service.

    Interoperability with other vendors
    www.whitemesa.net lists several live end points for several vendors to test various rounds of the interoperability test. Clients can be generated using one of the methods described in the previous section and interoperability test may be performed.

    BEA Interoperability Server
    BEA maintains an interoperability server and test implementations in an effort to support Web services interoperability. This server is available at http://Webservice.bea.com:7001/index.html for SOAP 1.1.

    SOAP 1.2 versions of these tests are available at http://webservice.bea.com:9001. WSDLs for various interoperability tests may be obtained from this server. This Web site also has browser clients to perform the tests.

    Resources

  • SOAP Builders interop Web site: www.whitemesa.com/interop.htm
  • SOAP Builders Web site: www.whitemesa.net
  • SOAP Builders interoperability lab: www.xmethods.net/ilab
  • BEA dev2dev Web services page: http://dev2dev.bea.com/managed_content/ direct/webservice/index.html
  • BEA interoperability test server for SOAP 1.1: http://webservice.bea.com:7001/index.html
  • BEA interoperability test server for SOAP 1.2: http://webservice.bea.com:9001/index.html
  • Chappell, David A. and Jewell, Tyler (2002). Java Web Services. O'Reilly & Associates.
  • SOAP Builders forum http://groups.yahoo.com/group/soapbuilders
  • More Stories By Anbarasu Krishnaswamy

    Anbarasu Krishnaswamy has over 15 years of IT industry experience, nine of which were with BEA. In his current role as the Enterprise Architect Lead, he leads the enterprise architecture and SOA practices for the central region professional services at BEA. As a SOA practitioner, he has helped several customers with SOA transformation and implementation. His experience also includes design and development of Java/J2EE applications, client/server computing, Web development, and enterprise application integration (EAI). Anbarasu holds a MBA from NIU and an MS in computer science and engineering.

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