Chapter 6. Using Spring Web Services on the Client

6.1. Introduction


Spring-WS provides a client-side Web service API that allows for consistent, XML-driven access to Web services. It also allows for use of marshallers and unmarshallers.

The package org.springframework.ws.client.core provides the core functionality for using the client-side access API. It contains template classes that simplifies the use of Web services, much like the JdbcTemplate does for JDBC. The design principle common to Spring template classes is to provide helper methods to perform common operations and for more sophisticated usage, delegate the essence of the processing task to user implemented callback interfaces. The Web service template follows the same design. The classes offer various convenience methods for the sending and receiving of XML messages, marshalling objects to XML before sending, and allows for multiple transports,

6.2. Using the client-side API

6.2.1. WebServiceTemplate

The WebServiceTemplate is the core class for client-side Web service access in Spring-WS. It contains methods for sending Source objects, and receiving response messages as either Source or Result. Additionally, it can marshal objects to XML before sending them across a transport, and unmarshal the response XML into an object again.

6.2.1.1. Transports

The WebServiceTemplate requires a reference to a MessageSender. The message sender is responsible for sending the XML message across a transport layer.

There are two implementations of the MessageSender interface for sending messages via HTTP. The simplest implementation is the HttpUrlConnectionMessageSender, which uses the facilities provided by Java SE itself. The alternative is the CommonsHttpMessageSender, which uses the Jakarta Commons HttpClient. Use the latter if you need more advanced and easy-to-use functionality. Both HTTP message senders require an URL to be set using the url property.

6.2.1.2. Message factories

In addition to a message sender, the WebServiceTemplate requires a Web service message factory. As explained in Section 4.1.3, “Message Factories”, there are two message factories for SOAP: SaajSoapMessageFactory and AxiomSoapMessageFactory. If no message factory is specified, Spring-WS will use the SaajSoapMessageFactory by default.

6.2.2. Sending and receiving a WebServiceMessage

The WebServiceTemplate contains many convenience methods to send and receive web service messages. There are methods that take and return Source and those that return a Result. Additionally, there are methods which marshal and unmarshal objects to XML. Here is an example that sends a simple XML message to a Web service.

import java.io.IOException;
import java.io.StringReader;
import javax.xml.transform.stream.StreamResult;
import javax.xml.transform.stream.StreamSource;

import org.springframework.ws.WebServiceMessageFactory;
import org.springframework.ws.client.core.WebServiceTemplate;
import org.springframework.ws.transport.WebServiceMessageSender;

public class WebServiceClient {

    private static final String MESSAGE = "<message xmlns=\"http://tempuri.org\">Hello World</message>";
    private WebServiceTemplate webServiceTemplate = new WebServiceTemplate();

    public void setMessageFactory(WebServiceMessageFactory messageFactory) {
        webServiceTemplate.setMessageFactory(messageFactory);
    }

    public void setMessageSender(WebServiceMessageSender messageSender) {
        webServiceTemplate.setMessageSender(messageSender);
    }

    public void simpleSendAndReceive() throws IOException {
        StreamSource source = new StreamSource(new StringReader(MESSAGE));
        StreamResult result = new StreamResult(System.out);
        webServiceTemplate.sendAndReceive(source, result);
    }

}

Here is the corresponding configuration:

<beans xmlns="http://www.springframework.org/schema/beans">

    <bean id="webServiceClient" class="WebServiceClient">
        <property name="messageSender">
            <bean class="org.springframework.ws.transport.http.HttpUrlConnectionMessageSender">
                <property name="url" value="http://localhost:8080/WebService"/>
            </bean>
        </property>
    </bean>

</beans>

This example uses the template to send a hello world message to the web service located at http://localhost:8080/WebService, and writes the result to the console. The WebServiceTemplate is injected with the message sender. A zero argument constructor and messageFactory / messageSender bean properties are provided and can be used for constructing the instance (using a BeanFactory or plain Java code). Alternatively, consider deriving from Spring-WS's WebServiceGatewaySupport convenience base class, which provides pre-built bean properties for configuration.

6.2.3. Marshalling, sending, receiving, and unmarshalling

In order to facilitate the sending of plain Java objects, the WebServiceTemplate has a send methods that take an object as an argument for a message's data content. The method marshalSendAndReceive in WebServiceTemplate delegates the conversion of the request object to XML to a Marshaller, and the conversion of the response XML to an object to an Unmarshaller. For more information about marshalling and unmarshaller, refer to Chapter 8, Marshalling XML using O/X Mappers. By using the marshallers, you and your application code can focus on the business object that is being sent or received and not be concerned with the details of how it is represented as XML. In order to use the marshalling functionality, you have to set a marshaller and unmarshaller with the marshaller/unmarshaller properties of the WebServiceTemplate.

6.2.4. WebServiceMessageCallback

To accommodate the setting of a SOAP headers, and other settings on the message, the WebServiceMessageCallback interface gives you access to the message after it has been created, but before it is sent. The example below demonstrates how to set the SOAP Action header on a message that is created by marshalling an object.

public void marshalWithSoapActionHeader(MyObject o) {
    webServiceTemplate.marshalSendAndReceive(o, new WebServiceMessageCallback() {
        public void doInMessage(WebServiceMessage message) {
            ((SoapMessage)message).setSoapAction("http://tempuri.org/Action");
        }
    });
}