Service References
The JAX-RPC examples in the preceding section, "A JAX-RPC Client," all required manual configuration of the WSDL URL and knowledge of the XML nature of the web services in question. This can be a configuration nightmare, but if your code is a J2EE component, there is another option. J2EE components can declare service references and look up JAXRPC Service objects in JNDI without needing to hard-code any web service references in the code.
To show how this works, let's first look at a session bean that needs to make a call to the hello web service:
rt java.rmi.RemoteException;
import javax.xml.rpc.Service;
import javax.xml.rpc.ServiceException;
import org.jboss.chap12.hello.Hello;
public class ExampleBean
implements SessionBean
{
public String doWork()
{
try {
Context ctx = new InitialContext();
Service service = (Service) ctx.lookup("java:comp/env/services/hello");
Hello hello = (Hello) service.getPort(Hello.class);
return hello.hello("example bean");
} catch (NamingException e) {
throw new EJBException(e);
} catch (ServiceException e) {
throw new EJBException(e);
} catch (RemoteException e) {
throw new EJBException(e);
}
}
public void ejbCreate() {};
public void ejbRemove() {};
public void ejbActivate() {}
public void ejbPassivate() {}
public void setSessionContext(SessionContext ctx) {}
}
ExampleBean invokes the hello web service in its doWork method. The dynamic proxy invocation method is used here, but any of the JAX-RPC supported invocation methods are fine. The interesting point here is that the bean has obtained the service reference from a JNDI lookup in its ENC. Web service references are declared using a service-ref element inside an ejb-jar.xml file, as shown in Figure 12.3.
The following elements are supported by the service-ref:
service-ref-name This is the JNDI name the service object is bound under in the bean's ENC. It is relative to java:comp/env/. service-interface This is the name of the JAX-RPC service interface the client uses. Normally this is javax.xml.rpc.Service, but it's possible to provide your own service class. wsdl-file This is the location of the WSDL file. The WSDL file should be under META-INF/wsdl. jaxrpc-mapping-file This is the location of the JAX-RPC mapping file. service-qname This element specifies the name of the service in the web services file. It is only mandatory if the WSDL file defines multiple services. The value must be a QName, which means it needs to be a namespace qualified value, such as ns:ServiceName, where ns is an XML namespace valid at the scope of the service-qname element. port-component-ref This element provides the mapping between a service endpoint interface and a port in a web service. handler This allows the specification of handlers, which act like filters or interceptors on the current request.
The following service-ref declares a reference to the hello web service for the Example session bean:
<session>
<ejb-name>Example</ejb-name>
<home>org.jboss.chap12.example.ExampleHome</home>
<remote>org.jboss.chap12.example.Example</remote>
<ejb-class>org.jboss.chap12.example.ExampleBean</ejb-class>
<session-type>Stateless</session-type>
<transaction-type>Container</transaction-type>
<service-ref>
<service-ref-name>services/hello</service-ref-name>
<service-interface>javax.xml.rpc.Service</service-interface>
<wsdl-file>META-INF/wsdl/hello.wsdl</wsdl-file>
<jaxrpc-mapping-file>META-INF/mapping.xml</jaxrpc-mapping-file>
<service-qname xmlns:hello="http://hello.chap12.jboss.org">hello:HelloService<
 /service-qname>
</service-ref>
</session>
This instructs the EJB deployer to make a Service object available for the bean in JNDI under the name java:comp/env/services/hello, which talks to the hello web service. The session bean can then invoke normal web services' operations on the service.
Because most of the web services' configuration options are completely standard, there's little need to go into great depths here. However, JBoss does provide several additional web services' configuration options through the service-ref element in the jboss.xml deployment descriptor. The content model for the service-ref element is shown in Figure 12.4.
The configurable elements are
service-ref-name This element should match the service-ref-name in the ejb-jar.xml file being configured. port-component-ref The port-component-ref element provides additional information for a specific port. This includes properties that should be associated with the JAX-RPC stub for the port. wsdl-override This provides an alternate location for the WSDL file. The value can be any valid URL. This can be used in coordination with the wsdl-publish-location to get the final WSDL file for a locally published web service. It could also be the URL of a remotely published WSDL you don't want duplicated in the deployment file. call-property This sets properties on the JAX-RPC stub.
Because the WSDL file generated by wscompile doesn't contain the SOAP address of your web service, use the WSDL override feature to dynamically download the correct WSDL file from the server. Although this might not be the best technique to use in a production application, it does illustrate the WSDL override functionality very well.
The following jboss.xml file links the published URL for the hello-servlet version of the hello web service:
<!DOCTYPE jboss PUBLIC
"-//JBoss//DTD JBOSS 4.0//EN"
"http://www.jboss.org/j2ee/dtd/jboss_4_0.dtd">
<jboss>
<enterprise-beans>
<session>
<ejb-name>Example</ejb-name>
<service-ref>
<service-ref-name>services/hello</service-ref-name>
<wsdl-override>http://localhost:8080/hello-servlet/Hello?wsdl </wsdl-override>
</service-ref>
</session>
</enterprise-beans>
</jboss>
This example can be run as shown below:
[examples]$ ant -Dchap=chap12 -Dex=2 run-example
...
run-example3:
[echo] Waiting for 5 seconds for deploy...
[copy] Copying 1 file to /tmp/jboss-4.0.1/server/default/deploy
[echo] Waiting for 5 seconds for deploy...
[java] output:Hello example bean!
The service-ref element is not limited to the ejb-jar.xml file. It's available to any J2EE component. A service reference can be placed in the web.xml file for use by web tier components or in the application-client.xml file for use by J2EE client applications.
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