11 Web Services Tags

General Web Services Overview

Web services are sets of procedures, or actions, that can be invoked by a client over the Internet, regardless of the computing platform. Web services consist of loosely coupled components over a distributed computing environment following a widely adopted set of standards such as SOAP, WSDL, and UDDI (all discussed later in this chapter). As an example, there might be a "World Cup Soccer" service that consists of actions to get scores, schedules, and standings.

A Web service must have the following features:

• It must be able to describe itself, such as its functionality and its input and output attributes. A Web service describes itself through an XML-style WSDL document. See "Overview of Web Services Description Language Key Elements".

• It must make itself generally available so that client applications can access it. The standard way to do this is to be listed in a Universal Description, Discovery, and Integration (UDDI) directory. Public UDDI directories are available to aggregate groups of businesses or users (or perhaps to anyone on the Internet), while private UDDI directories are available only within a particular business or group.

• A client application must be able to invoke it through a standard protocol once the application has found and examined it. A leading protocol for Web services is Simple Object Access Protocol (SOAP). With SOAP, the Web service is behind a SOAP server at the server end and the client application goes through a SOAP server at the client end. Data exchanges are "SOAP-enveloped" and can gain access through firewalls. This SOAP exchange is conceptually similar to a Remote Method Invocation (RMI) exchange, except that RMI exchanges cannot go through firewalls. See "Overview of SOAP and Related Features" below for a brief overview of SOAP.

• Once invoked, it must return a response to provide requested results to the client application. This is performed through the same standard protocol, such as SOAP.

For more information about Web services, particularly OracleAS Web Services, you can refer to the Oracle Application Server Web Services Developer's Guide.

For related specifications, refer to the following Web sites for the W3C SOAP specification, W3C WSDL specification, and UDDI specification, respectively:

http://www.w3.org/TR/SOAP

http://www.w3.org/TR/wsdl

http://www.uddi.org/specification.html

Overview of SOAP and Related Features

This section offers a brief overview of SOAP. See the W3C Simple Object Access Protocol (SOAP) 1.1 specification for details.

SOAP is a lightweight, XML-based protocol for exchanging typed and structured data over the Internet or other distributed environments. Among other features, SOAP supports remote procedure call (RPC) and message-oriented data exchanges.

In a message-oriented implementation, data is exchanged through a modular packaging and encoding model. A message is a WSDL component that specifies input data parts and output data parts associated with an operation. See "Overview of Web Service Messages and XML Schema Definitions" for more information.

RPC is an alternative to sockets, with the communication interface being at the level of procedure calls. It is as though you are calling a local procedure, but arguments of the call are actually packaged and sent to a remote target. The RPC mechanism uses a request/response methodology, where an end-point receives a procedure-oriented message and sends back a corresponding response.

Using SOAP with RPC is independent of the protocol binding. Where HTTP is the protocol binding, HTTP requests correspond to RPC calls, and HTTP responses correspond to RPC responses.

Key aspects of SOAP include the following.

• SOAP envelope construct: The envelope encloses a SOAP header and SOAP body and indicates what is in a message, whether it is required, and who should process it.

• SOAP encoding rules: Encoding rules define serialization mechanisms for the exchange of instances of the datatypes used in an application.

• SOAP RPC representation: The RPC representation specifies a convention for representing RPC calls and responses.

Overview of Web Services Description Language Key Elements

A Web service is described using the XML-based Web Services Description Language in a WSDL (.wsdl) document.

Following are some key WSDL terms.

• Operation: An operation is a particular action performed by a service, such as any of the "get scores", "get schedules", and "get standings" examples for a World Cup service.

• Message: A message is an abstract definition that specifies the data that is being input and output for an operation.

• Port type: A port type is an abstract definition of the operations supported by a service.

• Binding: A binding is a protocol and data format specification for one or more operations supported by a service. A binding mechanism maps the generic or abstract definition of a Web service to a concrete implementation, including data encoding, message protocol, and communication protocol.

• Port: A port is a single end-point, a combination of a binding and a network address. Essentially, a port is the concrete manifestation of the capabilities described by a port type. In a SOAP-based implementation, a port is a SOAP location.

  To be more precise than previously, a Web service is really a collection of related ports, or end-points, not just a collection of abstract actions or operations.

The WSDL specification outlines the general structure of a WSDL document, which includes the following key elements. Refer to the W3C Web Services Description Language (WSDL) 1.1 specification for complete information.

• A <types> element , through one or more <schema> subelements, contains descriptions of the data that is exchanged in messages used by the operations of the service.

• A <message> element provides an abstract definition of data being sent as input or output for an operation.

• A <portType> element, through one or more <operation> subelements, contains abstract definitions of the operations of the Web service. An <operation> element specifies the message that is used for input and the message that is used for output for the operation.

• A <binding> element, also through <operation> subelements, binds each operation to the particular protocol and data formats to be used.

• A <service> element defines the ports, or end-points, of the Web service. Within the <service> element is one or more <port> subelements, where each <port> element ties a binding to an address to define the end-point.

Overview of Web Service Messages and XML Schema Definitions

Messages define parameters used by the operations, or methods, of a Web service. A message is a typed definition of the data being communicated, consisting of one or more parts. Each part corresponds to a logical entity, such as a "Purchase Order" part and an "Invoice" part. For each part, there are type specifications for the associated data items.

In a SOAP-based implementation, such as for OracleAS Web Services, the datatypes used by a message are defined through the XML Schema Definition (XSD) language, which supports predefined simple types as well as user-defined complex types.

With an implementation that uses XSD, the syntax for defining a message is as follows:

   <message name="nmtoken">
      <part name="nmtoken" [type="qname"] [element="qname"] />
   </message>

In this syntax, the element attribute refers to where an XSD complex type is defined using XSD syntax, the type attribute indicates an XSD simple type, "nmtoken" indicates a standard XML name token, and "qname" indicates a standard XML qualified name. There can be zero or more messages, and zero or more parts for each message.

For a SOAP encoding style of encoded, only simple types are allowed, so the element attribute is not used. For an encoding style of literal, you can have simple types or complex types, so a <part> element can use either the type attribute or the element attribute, but not both.

Here is an example of a message definition, from "Example: WSDL Definition", which follows shortly:

   <message name="GetLastTradePriceInput">
      <part name="body" element="xsd1:TradePriceRequest"/>
   </message>

GetLastTradePriceInput is the name of the message, which is an input message (as the name implies). In this case, the element attribute refers to a namespace where a complex type, TradePriceRequest, is defined. Here is an example of such a definition (also part of "Example: WSDL Definition" below):

   <element name="TradePriceRequest">
      <complexType>
         <all>
             <element name="tickerSymbol" type="string"/>
             <element name="companyName" type="string"/>
         </all>
      </complexType>
   </element>

An XML schema primer is available from W3C at the following location:

http://www.w3.org/TR/xmlschema-0/

Web Service Example

This example shows the WSDL definition of a Web service, illustrating the input and output messages embedded in an HTTP request and HTTP response, respectively.

<?xml version="1.0"?>
<definitions name="StockQuote"

targetNamespace="http://example.com/stockquote.wsdl"
          xmlns:tns="http://example.com/stockquote.wsdl"
          xmlns:xsd1="http://example.com/stockquote.xsd"
          xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/"
          xmlns="http://schemas.xmlsoap.org/wsdl/">

   <types>
      <schema targetNamespace="http://example.com/stockquote.xsd"
              xmlns="http://www.w3.org/2000/10/XMLSchema">
         <element name="TradePriceRequest">
            <complexType>
               <all>
                  <element name="tickerSymbol" type="string"/>
               </all>
            </complexType>
         </element>
         <element name="TradePrice">
            <complexType>
               <all>
                  <element name="price" type="float"/>
               </all>
            </complexType>
         </element>
      </schema>
   </types>

   <message name="GetLastTradePriceInput">
      <part name="body" element="xsd1:TradePriceRequest"/>
   </message>

   <message name="GetLastTradePriceOutput">
      <part name="body" element="xsd1:TradePrice"/>
   </message>

   <portType name="StockQuotePortType">
      <operation name="GetLastTradePrice">
         <input message="tns:GetLastTradePriceInput"/>
         <output message="tns:GetLastTradePriceOutput"/>
      </operation>
   </portType>

   <binding name="StockQuoteSoapBinding" type="tns:StockQuotePortType">
      <soap:binding style="document" 
                    transport="http://schemas.xmlsoap.org/soap/http"/>
      <operation name="GetLastTradePrice">
         <soap:operation soapAction="http://example.com/GetLastTradePrice"/>
            <input>
               <soap:body use="literal"/>
            </input>
            <output>
               <soap:body use="literal"/>
            </output>
      </operation>
   </binding>

   <service name="StockQuoteService">
      <documentation>My first service</documentation>
         <port name="StockQuotePort" binding="tns:StockQuoteBinding">
            <soap:address location="http://example.com/stockquote"/>
          </port>
   </service>

</definitions>

POST /StockQuote HTTP/1.1
Host: www.stockquoteserver.com
Content-Type: text/xml; charset="utf-8"
Content-Length: nnnn
SOAPAction: "SOAP_URI"

   <soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
      <soapenv:Body>
         <m:GetLastTradePrice xmlns:m="xmlns_URI">
            <m:tickerSymbol>DIS</m:tickerSymbol>
         </m:GetLastTradePrice>
      </soapenv:Body>
   </soapenv:Envelope>

HTTP/1.1 200 OK
Content-Type: text/xml; charset="utf-8"
Content-Length: nnnn

   <soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
      <soapenv:Body>
         <m:GetLastTradePriceResponse xmlns:m="Some_URI">
            <m:price>34.5</m:price>
         </m:GetLastTradePriceResponse>
      </soapenv:Body>
   </soapenv:Envelope>

Overview of OracleAS Web Services and the Tag Library Implementation

The Web services tag library provided with OC4J enables developers to conveniently create JSP pages for Web service client applications. The implementation uses a SOAP-based mechanism. A client application would access the WSDL document, then use the WSDL information to access the operations of a Web service.

The tag library also uses the Oracle implementation of the dynamic invocation API, described in the Oracle Application Server Web Services Developer's Guide. When a client application acquires a WSDL document at runtime, the dynamic invocation API is the vehicle for invoking any SOAP operation described in the WSDL document. The tag handler uses the API when sending a SOAP request that invokes a Web service and when handling the SOAP response.

The Oracle dynamic invocation API consists of classes and interfaces in the oracle.j2ee.ws.client and oracle.j2ee.ws.client.wsdl packages.

The oracle.j2ee.ws.client package includes the following.

• WebServiceProxyFactory: Given a WSDL document (through a Java input stream that contains the document or through the URL of the document), a WebServiceProxyFactory instance can use the name of a service and the name of one of its ports, as specified in the WSDL document, to create a WebServiceProxy instance (an instance of a class that implements the WebServiceProxy interface).

• WebServiceProxy: Use this interface in representing a service defined in a WSDL document. Each WebServiceProxy instance is based on the location of the WSDL document and, optionally, on additional qualifiers that identify which service and port should be used. A WebServiceProxy class exposes methods to determine the WSDL port type, including the syntax and signatures of all operations exposed by the WSDL document, and to invoke the defined operations.

• WebServiceMethod: Use this interface in invoking a Web service method, or operation.

The oracle.j2ee.ws.client.wsdl package includes the following.

• Operation: This interface represents a WSDL operation.

• Message: This interface represents a message used in the input or output of an operation.

• Part: This interface represents a message part.

• Input: This interface represents an input message.

• Output: This interface represents an output message.

  
  

  Note: The dynamic invocation API is packaged in dsv2.jar in the ORACLE_HOME/lib directory. Also note that the SOAP implementation requires soap.jar in the ORACLE_HOME/soap directory.

  
  

Overview of Functionality of Web Services Tags

This section provides an overview of the OC4J Web services tag library and its functionality. The tag library includes support for the following:

• Binding to a Web service

• Using a Web service operation through SOAP requests and SOAP responses

• Defining input and output message parts

• Mapping SOAP/XML datatypes to Java types

• Setting custom properties for use by the client application

The tag library supports invoking operations defined in WSDL documents that use the W3C XML schema version whose namespace is the following:

http://www.w3.org/2001/XMLSchema

The Web services tag library includes the webservice tag, optionally with nested map and property tags, and the invoke tag, optionally with nested part tags. They are used as follows.

• webservice: Use this tag to create a Web service proxy. The tag requires the URL of a WSDL document and then uses one of the following combinations:

  • A binding and SOAP location, useful for a WSDL document identified in a UDDI registry

  • A service name and port, provided through tag attributes or through the first service and its first port from the WSDL document

• map: The Web service proxy uses this tag, if specified, to add an entry to the SOAP mapping registry, which is a registry that maps local SOAP/XML types to Java types. Any number of map tags can be nested within a webservice tag, one tag for each desired type mapping.

• property: Optionally, use this tag to define any of several supported custom properties for use by the Web service client application. Each property tag must be nested within the webservice tag; the property will have the same scope as the parent Web service.

• invoke: Use this tag to invoke an operation of the Web service. An invoke tag accesses a Web service proxy either by being nested within a webservice tag, or through a scripting variable.

• part: If an operation has input message parts, use part tags, nested within an invoke tag, to define the message parts. Use one part tag for each part.

  
  

  Notes: The tag library does not support the use of <import> elements within WSDL documents to import other WSDL documents. Custom bindings, including custom HTTP bindings or custom MIME bindings, are not supported. Because the OC4J Web services tag library implementation is based on the OracleAS Web Services implementation, any additional limitations of OracleAS Web Services also apply to the tag library.

  
  

Web Services Tag Descriptions

The following sections supply detailed descriptions of the OC4J Web services tags, a standards-compliant JavaServer Pages tag library implementation, including syntax documentation:

• Web Services webservice Tag

• Web Services map Tag

• Web Services property Tag

• Web Services invoke Tag

• Web Services part Tag

Note the following requirements for the Web services tag library:

• The Web services tag library is included in the ojsputil.jar file. This file is provided with OC4J, in the "well-known" tag library directory. Verify that this file is installed and in your classpath.

• The tag library descriptor, wstaglib.tld, must be available to the application, and any JSP page using the library must have an appropriate taglib directive. In an Oracle Application Server installation, the TLD is in ojsputil.jar. The uri value for wstaglib.tld is the following:

  http://xmlns.oracle.com/j2ee/jsp/tld/ojsp/wstaglib.tld
  
  

You can refer to the Oracle Application Server Containers for J2EE Support for JavaServer Pages Developer's Guide for information about taglib directives, the well-known tag library directory, TLD files, and the meaning of uri values.

For an example that uses the tags described in this section, see "Web Services Tag Examples".

<ws:webservice wsdlUrl = "WSDL_URL_of_Web_service"
             [ id = "variable_name_for_Web_service_proxy" ]
             [ scope = "page" | "request" | "session" | "application" ]
             [ binding = "SOAP_binding_information" ]
             [ soapLocation = "SOAP_endpoint_URL" ]
             [ service = "service_name_in_WSDL" ]
             [ port = "port_name_for_service" ] >

...body / nested tags...

</ws:webservice>

<ws:map localName = "local_name_of_SOAPXML_type"
        namespaceUri = "URI_of_namespace_for_SOAPXML_type"
        javaType = "Java_type_to_map"
        encodingStyle = "URL_of_SOAP_encoding_style"
        java2xmlClassName = "Java_to_XML_serializer"
        xml2javaClassName = "XML_to_Java_deserializer" />

<ws:property name="http.proxyHost" | "http.proxyPort" | "javax.net.ssl.KeyStore"
             value = "property_value" />

<ws:invoke id = "variable_name_for_output_result"
           operation = "operation_to_invoke"
         [ webservice = "variable_name_of_Web_service_proxy" ]
         [ inputMsgName = "name_of_input_message" ]
         [ outputMsgName = "name_of_output_message" ] 
         [ xmlToWriter = "true" | "false" ]
         [ toXMLObjName = "objectname" ] >

...body / nested tags...

</ws:invoke>

<ws:part name = "part_name"
       [ value = "part_value" ] >

...optional body, with request element, for document-style...

</ws:part>

Web Services Tag Examples

This section provides a template for use of the Web services tag library, a sample JSP page to invoke an RPC-style Web service, and a sample page to invoke a document-style Web service.

<HTML>
<HEAD>
<TITLE>Title</TITLE>
</HEAD>
<BODY>
<H2>This is sample HTML text.</H2>
<%@ taglib uri="http://xmlns.oracle.com/j2ee/jsp/tld/ojsp/wstaglibrary.tld"
           prefix="ws" %>
<ws:webservice id="myws" 
               wsdlUrl="wsdlurl" 
               {
                  binding="" soapLocation="" | service="" port=""
               }
               {
                  scope="page | request | session | application"
               }
                >
   <ws:property name="property" value="string"/>

   <ws:map encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"
           localname="SOAPStruct"
           namespaceUri="http://soapinterop.org/xsd"
           javaType="MySoapStructBean"
           java2xmlClassName="org.apache.soap.encoding.soapenc.BeanSerializer"
           xml2javaClassName="org.apache.soap.encoding.soapenc.BeanSerializer"
    />

</ws:webservice>

<ws:invoke id="result" webservice="myws" operation="add" inputMsgName=""
           outputMsgName=""> 
   <ws:part name="part_name" value="{string | <%= expression %>}"/>
</ws:invoke>

<% =result %>
</BODY>
</HTML>

<%@ page contentType="text/html"%>
<%@ taglib uri="http://xmlns.oracle.com/j2ee/jsp/tld/ojsp/wstaglib.tld"
           prefix="ws" %>
<HTML>
<HEAD>
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; ">
</HEAD>
<BODY>
<%
 String itemID = request.getParameter("itemID");
%>
<ws:webservice id="ebay" 
    wsdlUrl="http://www.xmethods.net/sd/2001/EBayWatcherService.wsdl"
    binding="eBayWatcherBinding"
    soapLocation="http://services.xmethods.net:80/soap/servlet/rpcrouter"
    scope="page">
  <ws:property name="http.proxyHost" value="www-proxy.us.oracle.com"/>
  <ws:property name="http.proxyPort" value="80"/>
</ws:webservice>
<ws:invoke id="price" webservice="ebay" operation="getCurrentPrice">
  <ws:part name="auction_id" value="<%=itemID%>"/>
</ws:invoke>
<B>
Action price for eBay Item # <%=itemID%> is :
</B>
<P>
$<%= price%> 
@ 
<%= new java.util.Date()%>
</P>
</BODY>
</HTML>

<%@ page contentType="text/xml;"%>
<%@ page  import= oracle.xml.parser.v2.XMLElement;"%>
<%@ taglib uri="http://xmlns.oracle.com/j2ee/jsp/tld/ojsp/wstaglib.tld"
           prefix="ws" %>
<%@ taglib uri="http://xmlns.oracle.com/j2ee/jsp/tld/ojsp/xml.tld"
           prefix="xml" %>
<ws:webservice id="bookService" 
        wsdlUrl="http://hosting.msugs.ch/cheeso9/books/books.asmx?WSDL"
        binding="LookyBookServiceSoap"
        soapLocation ="http://hosting.msugs.ch/cheeso9/books/books.asmx"
        scope="session">
</ws:webservice>
<ws:invoke id="bookResult"
        operation="GetInfo"
        webservice="bookService">
    <ws:part name="parameters">
        <GetInfo xmlns="http://dinoch.dyndns.org/webservices/">
          <ISBN>SomeISBNNumber</ISBN>
        </GetInfo>
    </ws:part>
</ws:invoke>
<% 
    XMLNode resultNode = (XMLNode) bookResult;
    resultNode.Error! Bookmark not defined.(new java.io.PrintWriter(out));
%>
</BODY>
</HTML>