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Oracle Application Server Containers for J2EE JSP Tag Libraries and Utilities Reference
10g (9.0.4)
Part Number B10319-01
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11
Web Services Tags

Oracle furnishes a tag library with OC4J that enables developers to create JSP pages for use as client programs for Web services. This chapter describes the tag library and consists of the following sections:

This chapter is written with the assumption that you are already familiar with Web services, Simple Object Access Protocol (SOAP), and the Web Services Description Language (WSDL); however, some overview is provided here. There are also references to additional documents, including related specifications from the World Wide Web Consortium (W3C).

The OC4J Web services tag library is based on Oracle Application Server Web Services. See the Oracle Application Server Web Services Developer's Guide for information.

Overview of Web Services

The following sections provide a quick overview of Web services concepts:

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:

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:

http://www.w3.org/TR/SOAP (W3C SOAP specification)

http://www.w3.org/TR/wsdl (W3C WSDL specification)

http://www.uddi.org/specification.html (UDDI specification)

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.

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.

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.

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.

Example: WSDL Definition

The W3C Web Services Description Language (WSDL) 1.1 specification provides the following example of a WSDL document that defines a stock quote service taking a ticker symbol as input and returns the current stock price as output. Note this uses a SOAP encoding style of literal, so complex types are allowed (and used). 

<?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>

This WSDL definition first specifies the GetLastTradePriceInput and GetLastTradePriceOutput input and output messages, then ties them to the operation GetLastTradePrice, then defines a binding and a port for that operation.

Notes:

  • This example has all aspects of the Web service definition, including the XML schema definitions for data exchanges, in the same document. Alternatively, stockquote.xsd, for example, could be a separate XSD document instead of a namespace within this document. The W3C WSDL specification illustrates this. Be aware, however, that the OC4J Web services tag library does not support WSDL documents that use <import> elements to import other WSDL documents.

  • The example uses a document-style binding. The OC4J 9.0.4 implementation of the Web services tag library supports RPC-style and document-style bindings. In the document-style case, the output response object is an XML document of type XMLElement. In the RPC-style case, the output object might be of any type.

Example: SOAP Messages Embedded in HTTP Request and Response

Corresponding to the Web service defined in the preceding example, this section shows what the messages would look like, with the soap-enveloped input message embedded in an HTTP request, and the soap-enveloped output message embedded in an HTTP response. These examples are also from the W3C Web Services Description Language (WSDL) 1.1 specification.

Here is a request: 

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>

In this example, xmlns_URI is a URI value used to identify the namespace where the GetLastTradePrice operation and its messages are defined, such as the WSDL document in the preceding "Example: WSDL Definition". This is also where tickerSymbol is defined. The request is for a stock quote for Walt Disney Company. SOAP_URI is the URI for the SOAP action HTTP header for the HTTP binding of SOAP.

And here is the response: 

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>

By convention, the response for an operation Xxxx is called XxxxResponse. Some_URI is a URI value used to identify the namespace where the GetLastTradePriceResponse operation is defined.

OC4J Web Services Tags

The following sections provide an overview and details of the Web services tag library, as well as an overview of OracleAS Web Services, upon which the tag library implementation is based.

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.

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

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:

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:

Notes:

As of Oracle Application Server 10g (9.0.4):

  • 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:

Note the following requirements for the Web services tag library:

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".

Notes:

  • The prefix "ws:" is used in the tag syntax here. This is by convention, but is not required. You can specify any desired prefix in the taglib directive.

  • See "Tag Syntax Symbology and Notes" for general information about tag syntax conventions in this manual.

Web Services webservice Tag

Use this tag to create a Web service proxy, an instance of a class that implements the oracle.j2ee.ws.client.WebServiceProxy interface. The tag requires the URL of a WSDL document and uses a binding and SOAP location or a service name and port, as follows:

  1. First, if tag attributes provide a binding and SOAP location, the tag handler uses them in creating the proxy. Tag attributes for service name and port are ignored in this case.

  2. If no binding and SOAP location are provided, the tag handler uses a service name and port, as follows:

    1. If a service name and port are provided through tag attributes, then the tag handler uses them in creating the proxy.

    2. If no service name and port are provided, the tag handler uses the first service in the WSDL document and the first port listed for that service.

Using a binding and SOAP location is particularly useful for a Web service whose WSDL document is accessed through a UDDI registry. In that case, the binding and location can be determined through UDDI queries and supplied to the tag through request-time expressions.

After the Web service proxy is created, it will use any nested map tags to add entries to the SOAP mapping registry. See the next section, "Web Services map Tag".

Syntax

<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>

Note:

The scope attribute cannot take request-time expressions.

Attributes

Web Services map Tag

For interoperability, a mapping mechanism is necessary to map WSDL-defined SOAP/XML datatypes to the Java types used in JSP pages of a Java client application. This is possible through the OracleAS Web Services SOAP mapping registry.

You can have any number of map tags nested within a webservice tag, to have the Web service proxy add entries to the registry. Use one map tag for each desired type mapping.

The registry is an instance of the XMLJavaMappingRegistry class of the org.apache.soap.util.xml package. A WebServiceProxy instance has a getXMLMappingRegistry() method to access the registry.

The map tag includes attributes to specify the encoding style, serializer, deserializer, and namespace URI to facilitate the type mapping. The Web services tag library supports custom serializers and deserializers, if you want to create your own.

Important:

When using a map tag, you must nest it within a webservice tag.

Syntax

<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" />
Attributes

Web Services property Tag

You can optionally use this tag to specify a name/value pair that defines any of several supported custom properties for use by the Web service client application. For example, you could use property tags to specify an HTTP proxy host and proxy port if a proxy is required for access through a network firewall. The following properties are supported:

Important:

When using a property tag, you must nest it within a webservice tag. The property will have the same scope as the parent Web service.

Syntax

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

Web Services invoke Tag

Use this tag to invoke an operation of the Web service. The tag handler will call the remote Web service operation by passing an input message in a SOAP request, then will wait for the SOAP response. You must specify the operation, as well as an object ID for the object that will contain the returned response. The tag handler uses the operation name to find the operation in the WSDL document.

The invoke tag gains access to a Web service proxy in one of two ways:

In a situation where there are overloaded operations (two operations of the same name using different I/O messages), the invoke tag has attributes to specify the input and output message names for the desired operation. In this case, for RPC-style bindings, the specified input and output message names are used to form the RPC signature of the operation. Otherwise, the RPC signature is the default according to the WSDL document.

If the output message has multiple parts, then the returned result is an array of message parts (all within a single SOAP response).

Beginning with the OC4J 9.0.4 implementation, the invoke tag can act as an XML producer, supporting explicit passing of an XML output object through the toXMLObjName attribute. This is useful if the invoke tag is nested inside other kinds of tags such as Web Object Cache tags or the XML transform tag. Also note that an XML output object can be written to the JspWriter object of the JSP page for output directly to the user's browser. This is enabled through the xmlToWriter attribute.

Notes:

  • Waiting for the SOAP response is a blocking function.

  • The scope of the output result object, identified by the id attribute, is the same as the scope of the proxy object defined in the webservice tag for the Web service. For an invoke tag nested within a webservice tag, this scope is from the webservice start-tag to the webservice end-tag. However, the id object can still be accessed outside the webservice tag through use of the findAttribute() method of the JSP page context object.

Syntax

<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>
Attributes

Web Services part Tag

Use this tag, nested within an invoke tag, if the operation being performed requires input message part values, using one part tag for each input part.

How to specify the part value might depend on whether you are using an RPC-style or document-style Web service. For RPC-style, you must use the value attribute. For document-style, you have the option of passing the value through an XML request element in the tag body.

Note:

If you use both a tag body and the value attribute, the tag body is ignored.

Syntax

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

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

</ws:part>
Attributes

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.

Web Services Example: Usage Template

<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>

Web Services Example: Sample JSP Page for RPC-Style Web Service

<%@ 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>

Web Services Example: Sample JSP Page for Document-Style Web Service

<%@ 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>

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