39.2. Using XML in a Service Provider

Abstract

The Provider interface is a low-level JAX-WS API that allows you to implement a service provider that works directly with messages as raw XML. The messages are not packaged into JAXB objects before being passed to an object that implements the Provider interface.

39.2.1. Messaging Modes

Overview

Objects that implement the Provider interface have two messaging modes:
The messaging mode you specify determines the level of messaging detail that is passed to your implementation.

Message mode

When using message mode, a Provider implementation works with complete messages. A complete message includes any binding specific headers and wrappers. For example, a Provider implementation that uses a SOAP binding receives requests as fully specified SOAP message. Any response returned from the implementation must be a fully specified SOAP message.
To specify that a Provider implementation uses message mode by provide the value java.xml.ws.Service.Mode.MESSAGE as the value to the javax.xml.ws.ServiceMode annotation, as shown in Example 39.9, “Specifying that a Provider Implementation Uses Message Mode”.

Example 39.9. Specifying that a Provider Implementation Uses Message Mode

@WebServiceProvider
@ServiceMode(value=Service.Mode.MESSAGE)
public class stockQuoteProvider implements Provider<SOAPMessage>
{
  ...
}

Payload mode

In payload mode a Provider implementation works with only the payload of a message. For example, a Provider implementation working in payload mode works only with the body of a SOAP message. The binding layer processes any binding level wrappers and headers.
Tip
When working with a binding that does not use special wrappers, such as the Apache CXF XML binding, payload mode and message mode provide the same results.
To specify that a Provider implementation uses payload mode by provide the value java.xml.ws.Service.Mode.PAYLOAD as the value to the javax.xml.ws.ServiceMode annotation, as shown in Example 39.10, “Specifying that a Provider Implementation Uses Payload Mode”.

Example 39.10. Specifying that a Provider Implementation Uses Payload Mode

@WebServiceProvider
@ServiceMode(value=Service.Mode.PAYLOAD)
public class stockQuoteProvider implements Provider<DOMSource>
{
  ...
}
Tip
If you do not provide a value for the @ServiceMode annotation, the Provider implementation uses payload mode.

39.2.2. Data Types

Overview

Because they are low-level objects, Provider implementations cannot use the same JAXB generated types as the higher level consumer APIs. Provider implementations work with the following types of objects:

Using Source objects

A Provider implementation can accept and return objects that are derived from the javax.xml.transform.Source interface. Source objects are low level objects that hold XML documents. Each Source implementation provides methods that access the stored XML documents and manipulate its contents. The following objects implement the Source interface:
DOMSource
Holds XML messages as a Document Object Model(DOM) tree. The XML message is stored as a set of Node objects that are accessed using the getNode() method. Nodes can be either updated or added to the DOM tree using the setNode() method.
SAXSource
Holds XML messages as a Simple API for XML (SAX) object. SAX objects contain an InputSource object that holds the raw data and an XMLReader object that parses the raw data.
StreamSource
Holds XML messages as a data stream. The data stream can be manipulated the same as any other data stream.
If you create your Provider object so that it uses generic Source objects, Apache CXF returns the messages as SAXSource objects.
This behavior can be changed using the endpoint's source-preferred-format property. See Part IV, “Configuring Web Service Endpoints” for information about configuring the Apache CXF runtime.
Important
When using Source objects the developer is responsible for ensuring that all required binding specific wrappers are added to the message. For example, when interacting with a service expecting SOAP messages, the developer must ensure that the required SOAP envelope is added to the outgoing request and that the SOAP envelope's contents are correct.

Using SOAPMessage objects

Provider implementations can use javax.xml.soap.SOAPMessage objects when the following conditions are true:
  • The Provider implementation is using the SOAP binding
  • The Provider implementation is using message mode
A SOAPMessage object holds a SOAP message. They contain one SOAPPart object and zero or more AttachmentPart objects. The SOAPPart object contains the SOAP specific portions of the SOAP message including the SOAP envelope, any SOAP headers, and the SOAP message body. The AttachmentPart objects contain binary data that is passed as an attachment.

Using DataSource objects

Provider implementations can use objects that implement the javax.activation.DataSource interface when the following conditions are true:
  • The implementation is using the HTTP binding
  • The implementation is using message mode
DataSource objects provide a mechanism for working with MIME typed data from a variety of sources, including URLs, files, and byte arrays.

39.2.3. Implementing a Provider Object

Overview

The Provider interface is relatively easy to implement. It only has one method, invoke(), that must be implemented. In addition it has three simple requirements:
  • An implementation must have the @WebServiceProvider annotation.
  • An implementation must have a default public constructor.
  • An implementation must implement a typed version of the Provider interface.
    In other words, you cannot implement a Provider<T> interface. You must implement a version of the interface that uses a concrete data type as listed in Section 39.2.2, “Data Types”. For example, you can implement an instance of a Provider<SAXSource>.
The complexity of implementing the Provider interface is in the logic handling the request messages and building the proper responses.

Working with messages

Unlike the higher-level SEI based service implementations, Provider implementations receive requests as raw XML data, and must send responses as raw XML data. This requires that the developer has intimate knowledge of the messages used by the service being implemented. These details can typically be found in the WSDL document describing the service.
WS-I Basic Profile provides guidelines about the messages used by services, including:
  • The root element of a request is based in the value of the name attribute of the wsdl:operation element that corresponds to the operation that is invoked.
    Warning
    If the service uses doc/literal bare messages, the root element of the request is based on the value of name attribute of the wsdl:part element referred to by the wsdl:operation element.
  • The root element of all messages is namespace qualified.
  • If the service uses rpc/literal messages, the top-level elements in the messages are not namespace qualified.
    Important
    The children of top-level elements might be namespace qualified, but to be certain you will must check their schema definitions.
  • If the service uses rpc/literal messages, none of the top-level elements can be null.
  • If the service uses doc/literal messages, then the schema definition of the message determines if any of the elements are namespace qualified.

The @WebServiceProvider annotation

To be recognized by JAX-WS as a service implementation, a Provider implementation must be decorated with the @WebServiceProvider annotation.
Table 39.2, “@WebServiceProvider Properties” describes the properties that can be set for the @WebServiceProvider annotation.

Table 39.2. @WebServiceProvider Properties

PropertyDescription
portNameSpecifies the value of the name attribute of the wsdl:port element that defines the service's endpoint.
serviceNameSpecifies the value of the name attribute of the wsdl:service element that contains the service's endpoint.
targetNamespaceSpecifies the targetname space of the service's WSDL definition.
wsdlLocationSpecifies the URI for the WSDL document defining the service.
All of these properties are optional, and are empty by default. If you leave them empty, Apache CXF creates values using information from the implementation class.

Implementing the invoke() method

The Provider interface has only one method, invoke(), that must be implemented. The invoke() method receives the incoming request packaged into the type of object declared by the type of Provider interface being implemented, and returns the response message packaged into the same type of object. For example, an implementation of a Provider<SOAPMessage> interface receives the request as a SOAPMessage object and returns the response as a SOAPMessage object.
The messaging mode used by the Provider implementation determines the amount of binding specific information the request and the response messages contain. Implementations using message mode receive all of the binding specific wrappers and headers along with the request. They must also add all of the binding specific wrappers and headers to the response message. Implementations using payload mode only receive the body of the request. The XML document returned by an implementation using payload mode is placed into the body of the request message.

Examples

Example 39.11, “Provider<SOAPMessage> Implementation” shows a Provider implementation that works with SOAPMessage objects in message mode.

Example 39.11. Provider<SOAPMessage> Implementation

import javax.xml.ws.Provider;
import javax.xml.ws.Service;
import javax.xml.ws.ServiceMode;
import javax.xml.ws.WebServiceProvider;

1@WebServiceProvider(portName="stockQuoteReporterPort"
                    serviceName="stockQuoteReporter")
2@ServiceMode(value="Service.Mode.MESSAGE")
public class  stockQuoteReporterProvider implements Provider<SOAPMessage>
{
3public stockQuoteReporterProvider()
  {
  }

4public SOAPMessage invoke(SOAPMessage request)
  {
5  SOAPBody requestBody = request.getSOAPBody();
6  if(requestBody.getElementName.getLocalName.equals("getStockPrice"))
    {
7    MessageFactory mf = MessageFactory.newInstance();
      SOAPFactory sf = SOAPFactory.newInstance();

8    SOAPMessage response = mf.createMessage();
      SOAPBody respBody = response.getSOAPBody();
      Name bodyName = sf.createName("getStockPriceResponse");
      respBody.addBodyElement(bodyName);
      SOAPElement respContent = respBody.addChildElement("price");
      respContent.setValue("123.00");
      response.saveChanges();
9    return response;
    }
    ...
  }
}
1
Specifies that the following class implements a Provider object that implements the service whose wsdl:service element is named stockQuoteReporter, and whose wsdl:port element is named stockQuoteReporterPort.
2
Specifies that this Provider implementation uses message mode.
3
Provides the required default public constructor.
4
Provides an implementation of the invoke() method that takes a SOAPMessage object and returns a SOAPMessage object.
5
Extracts the request message from the body of the incoming SOAP message.
6
Checks the root element of the request message to determine how to process the request.
7
Creates the factories required for building the response.
8
Builds the SOAP message for the response.
9
Returns the response as a SOAPMessage object.
Example 39.12, “Provider<DOMSource> Implementation” shows an example of a Provider implementation using DOMSource objects in payload mode.

Example 39.12. Provider<DOMSource> Implementation

import javax.xml.ws.Provider;
import javax.xml.ws.Service;
import javax.xml.ws.ServiceMode;
import javax.xml.ws.WebServiceProvider;

1@WebServiceProvider(portName="stockQuoteReporterPort" serviceName="stockQuoteReporter")
2@ServiceMode(value="Service.Mode.PAYLOAD")
public class  stockQuoteReporterProvider implements Provider<DOMSource>
3public stockQuoteReporterProvider()
  {
  }

4public DOMSource invoke(DOMSource request)
  {
    DOMSource response = new DOMSource();
    ...
    return response;
  }
}
1
Specifies that the class implements a Provider object that implements the service whose wsdl:service element is named stockQuoteReporter, and whose wsdl:port element is named stockQuoteReporterPort.
2
Specifies that this Provider implementation uses payload mode.
3
Provides the required default public constructor.
4
Provides an implementation of the invoke() method that takes a DOMSource object and returns a DOMSource object.