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About Gilbert Lopez

Gilbert Lopez is an application developer and systems integration developer with experience building business solutions for large and medium-sized companies. He has worked on many Java EE projects. His roles have included lead developer, systems analyst, business analyst and consultant. Gilbert graduated from California State University in Los Angeles with a Bachelor of Science degree in Business.

Jax-Ws vs Jax-Rpc: Comparison and Differences

In this article, we will compare the JAX-WS and JAX-RPC programming APIs with respect to the Java programming model.

Note: This article is for academic purposes only. JAX-RPC is obsolete and its use is discouraged for any new Java development projects.

1. Introduction

The Web Services Architecture evolved in part to address interoperability between disparate and heterogeneous systems. SOAP (Simple Object Access Protocol) was designed to be an agnostic message format for exchanging messages. WSDL (Web Service Description Language) was developed to describe web services and how to access them. JAX-RPC (Java API for XML-based Remote Procedure Call) was subsequently introduced to specify how to write Java web services components for disparate systems using SOAP and WSDL.

JAX-RPC is based on the RPC programming model for invoking operations of a web service. The RPC programming model invokes stubs located on the client to call methods on a remote server.

JAX-WS is the successor to JAX-RPC. JAX-WS provides support for message-oriented web services. This model allows service requests to be sent asynchronously. Additionally, JAX-WS provides support for the more recent versions of the following specifications: SOAP, WSDL, WS-I BP (Basic Profile), and SAAJ (SOAP with Attachments API for Java).

2. Comparison and Differences

Let’s take a look at some other differences between these two APIs as they pertain to the Java programming model.

2.1 Java 5

Java 5 introduced new features to the Java API, such as annotations, generics, and executors. JAX-WS relies on many of these features and requires the Java 5 compile and runtime components. This union is a boon to developers as it simplifies the development process. For example, annotations can be used to expose endpoints and clients as web service components within the code itself instead of using XML descriptor files, WSDL files, and data mapping XML files, which can be tedious to work with. By including annotations within the Java classes, you encapsulate the metadata with the source files.

Also, mapping tools used for top-down or WSDL-first Java development (such as the WSDL2Java tool) will generate Java classes with annotations.

Here is an example of how to define a Service Endpoint Interface (SEI) as a web service using an annotation:

HelloWorld.java

import javax.jws.WebService;

@WebService
public interface HelloWorld {

	public String sayHello(String name);
}

There are two things to note here:

  1. The @WebService annotation communicates to the JAX-WS runtime to expose all public methods on this bean as web service operations.
  2. JAX-WS does not require the SEI to extend java.rmi.Remote, as is the case with JAX-RPC, since it does not use the RPC programming model.

You can fine-tune the web service by adding additional annotations on individual methods and parameters. Here are some common annotations used.

Note: These annotations are part of the javax.jws package.

AnnotationDescription
@WebMethodUsed to indicate that this method is a web service operation.  Typically used when specific public methods in the class should be exposed as web service operations.
@WebParamUsed to map the name of the parameter to the element in the WSDL file.
@WebResultUsed to map the name of the result response to the element in the WSDL file.

Here is an example of how these annotations are used:

Other Web Service Annotations Example

  @WebMethod()
  @WebResult(name="NumberOutput")
  public int echoNumber(
      @WebParam(name="NumberInput")
      int input)
  {
    System.out.println("echoNumber '" + input + "' back to you.");
    return input;
  }

The JAX-RPC programming model was based on the older 1.4 version of Java.

2.2 Asynchronous Invocation of Web Services

When invoking a web service synchronously, the client must wait for the response before resuming its work. When invoking a web service asynchronously, the client can work on other tasks while it waits for the response.

JAX-WS supports both the callback and polling methods of invoking a web service asynchronously. When using the callback method, the client provides a callback handler to accept and process the response.

When using the polling method, a client issues a request and receives a response object, which is polled intermittently to check if the server has responded. When the server responds, the actual response is acquired.

Here is an example of a Service Endpoint Interface with methods for both synchronous and asynchronous requests:

ChangeMessage.java

import java.util.concurrent.Future;

import javax.jws.WebService;
import javax.xml.ws.AsyncHandler;
import javax.xml.ws.Response;;

@WebService
public interface ChangeMessage {

    // sync operation
    public String changeMessage(String message);
    
    // async operation with callback
    public Future changeMessageAsync(String message, AsyncHandler asyncHandler);

    // async operation with polling
    public Response changeMessageAsync(String message);
}

Asynchronous method names are suffixed with “Async” as this is the naming convention.  The AsyncHandler callback handler is provided by the caller and is responsible for handling the response when using the callback method.  The method returns a Future that represents the pending result of the task.  The Future interface exposes methods to test for completion of a task and to retrieve the result of the task.

The client receives an object of type javax.xml.ws.Response when using the polling method,. The Response object is polled to determine when the operation is complete and to get the actual result, as described earlier.

JAX-RPC does not support asynchronous invocation of a web service.

2.3 Java-XML Data Binding

SOAP-based web services use XML to exchange request and response messages. This requires an architecture for converting Java objects to XML and the reverse. JAXB (Java Architecture for XML Binding) was developed for this purpose.

JAX-RPC uses its own data mapping model. This is because the JAXB specification had not been finalized when when the first version of JAX-RPC was completed. The JAX-RPC data mapping model lacks support for some XML schemas.

JAX-WS uses JAXB for data binding. JAXB provides mapping for virtually all schemas.

You can use JAXB annotations on your Java bean and JAX-WS will convert it and its properties to XML elements at runtime when sending the SOAP message.

Person.java

import javax.xml.bind.annotation.*;

@XmlRootElement(name = "person")
@XmlType(propOrder = {"id","name"})
public class Person {


    @XmlElement(name = "id", required = true)
    int ID;
    @XmlElement(name = "name", required = true)
    String Name;

    // accessors and mutators
}

Sample SOAP Request

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" >
   <soapenv:Header/>
   <soapenv:Body>
      <addPerson>
        <person>
           <id>0</id>
           <name>This Person</name>
        </person>
      </addPerson>
   </soapenv:Body>
</soapenv:Envelope>

The following table describes the JAXB annotations used in the code example above.

AnnotationDescription
@XmlRootElement(name = “preferredName”)Defines the root element for an XML tree
@XmlType(propOrder = { “field2”, “field1”,.. })Used to define the order in which the fields are written in the XML file
@XmlElement(name = “newName”)Define the XML element name to use for this property. This is only used if the “newName”is different than the JavaBean name

2.4 SOAP Message Attachments and MTOM

JAX-RPC uses the SOAP with Attachments (Sw/A) model for exchanging binary data and uses the SAAJ specification. The SAAJ specification includes the javax.xml.soap package and provides the API for creating and populating a SOAP message. The following example shows how to create and populate a SOAP message using SAAJ:

SAAJ Example

 
    // Create a message.  This example works with the SOAPPart.
    SOAPMessage request = mf.createMessage();
    SOAPPart part = request.getSOAPPart();

    // Obtain the SOAPEnvelope and header and body elements.
    SOAPEnvelope env = part.getEnvelope();
    SOAPHeader header = env.getHeader();
    SOAPBody body = env.getBody();

    // Construct the message payload.
    SOAPElement operation = body.addChildElement("sayHello",
     "http://com/javacodegeeks/example/helloworld/");
    SOAPElement value = operation.addChildElement("name");
    value.addTextNode("Java Code Geeks");

While JAX-WS also supports Sw/A, it adds support for Message Transmission Optimization Mechanism (MTOM). MTOM is a web service standard for optimizing the transfer of binary data in a SOAP message. The standard specifies the message format for packaging base64Binary data (such as an image file or PDF file).

For example, you can add the following annotation to the SEI implementation to indicate that the web service should use MTOM optimization:

FileServiceImpl.java

// This example is for SOAP version 1.2.
@BindingType(value = SOAPBinding.SOAP12HTTP_MTOM_BINDING)
@WebService
public class FileServiceImpl {
...
}

Here is an example on how to enable MTOM on the web service client:

MTOM Client Example

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import javax.activation.DataHandler;
import javax.xml.ws.BindingProvider;
import javax.xml.ws.soap.SOAPBinding;

public class AttachmentClient {

	static FileAttachmentService service;
	static FileAttachment port;
	
	public static void main(String[] args) {
		
		service = new FileAttachmentService();
		port = service.getFileAttachmentPort();
		
		BindingProvider bp = (BindingProvider)port;
		SOAPBinding binding = (SOAPBinding)bp.getBinding();
		
		//Enable MTOM..
		binding.setMTOMEnabled(true);

		DataHandler downloadfile = port.downloadFile();
		
		try (InputStream input = downloadfile.getInputStream();
				OutputStream output = new FileOutputStream(
						new File("/Users/gilbertlopez/uploaded/testingfile.jpg"));) {
			
			byte[] b = new byte[100000];
			int bytesRead = 0;
			while ((bytesRead = input.read(b)) != -1) {
				output.write(b, 0, bytesRead);
			}
			
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
			System.exit(-1);
		}

		System.exit(0);
	}

}

These are the steps for enabling MTOM on the web service client:

  1. Instantiate a BindingProvider from the web service port.
  2. Instantiate a SOAPBinding from the BindingProvider.
  3. Set the MTOM enabled property of the SOAPBinding to true .

JAX-WS leverages JAXB, which provides APIs for marshalling and unmarshalling both Sw/A and MTOM attachments.

JAX-RPC does not provide MTOM support.

2.5 Dynamic Clients

Both JAX-RPC and JAX-WS hide the details of mapping Java method invocations to the underlying SOAP messages. Both use a dynamic invocation interface (DII) to call operations on the web service.

JAX-RPC clients use javax.xml.rpc.Call for this purpose. Here is an example:

JAX-RPC Dynamic Client Example

    // Create the dynamic invocation object from this service.
    Call call = service.createCall();
    call.setTargetEndpointAddress(
            "http://localhost:8080/HelloWorldService/services/port");

    // Build the message.
    QName operationName = new QName(
            "urn:helloWorld/example/javacodegeeks/com",
            "sayHello");
    call.setOperationName(operationName);
    call.addParameter(
            "name",             // parameter name
            XMLType.XSD_STRING, // parameter XML type QName
            String.class,       // parameter Java type class
            ParameterMode.IN);  // parameter mode
    call.setReturnType(XMLType.XSD_STRING);

    // Invoke the operation.
    Object[] actualArgs = {"Java Code Geeks"};
    String response = (String) call.invoke(actualArgs);

With JAX-RPC, the Call object is configured to invoke a specific operation from the WSDL.

In some cases, working at the XML message level is preferred. JAX-WS allows this capability by providing the javax.xml.ws.Dispatch interface. In JAX-WS’s messaging model, the Dispatch object is not concerned about the operation being invoked and is only sending XML data. Here is an example:

JAX-WS Dynamic Client Example

    
    // Create a service and add at least one port to it.
    Service service = Service.create(serviceName);
    service.addPort(portName, SOAPBinding.SOAP11HTTP_BINDING, "http://localhost:8080/HelloWorldService/services/port");    
    // Create a Dispatch instance from a service.
    Dispatch dispatch = service.createDispatch(portName,
    SOAPMessage.class, Service.Mode.MESSAGE);

    // Create SOAPMessage request. 
    // compose a request message
    MessageFactory mf = MessageFactory.newInstance(SOAPConstants.SOAP_1_1_PROTOCOL);

    // Create a message.  This example works with the SOAPPART.
    SOAPMessage request = mf.createMessage();
    SOAPPart part = request.getSOAPPart();

    // Obtain the SOAPEnvelope and header and body elements.
    SOAPEnvelope env = part.getEnvelope();
    SOAPHeader header = env.getHeader();
    SOAPBody body = env.getBody();

    // Construct the message payload.
    SOAPElement operation = body.addChildElement("sayHello",
     "http://com/javacodegeeks/example/helloworld/");
    SOAPElement value = operation.addChildElement("name");
    value.addTextNode("Java Code Geeks");
    request.saveChanges();

    // Invoke the service endpoint. 
    SOAPMessage response = dispatch.invoke(request);

The javax.xml.ws.Service object acts as a factory for creating:

  • Proxies for a target service endpoint.
  • Instances of Dispatch for dynamic message-oriented invocation of a remote operation.

There are several methods available to create a Dispatch client. In the example above, it is created by calling the createDispatch method with the following parameters:

  • endpointReference – The EndpointReference for the target service endpoint that will be invoked by the returned Dispatch object.
  • type – The class of object used for messages or message payloads. Implementations are required to support javax.xml.transform.Source and javax.xml.soap.SOAPMessage.
  • mode – Controls whether the created dispatch instance is message or payload oriented, i.e. whether the client will work with complete messages or message payloads. The Mode must be MESSAGE when the type is SOAPMessage.

The dispatch client is an XML messaging oriented client. Data is sent in either PAYLOAD or MESSAGE mode. When using the PAYLOAD mode, the dispatch client is responsible for providing the contents of the SOAP body only and JAX-WS adds the SOAP envelope and header. When using the MESSAGE mode, the dispatch client is responsible for providing the entire SOAP envelope including the SOAP header and body. This example uses the MESSAGE mode since the “type” parameter is SOAPMessage.

As you can see, the difference between the two is that JAX-RPC follows the RPC model, while JAX-WS follows a messaging model.

3. Conclusion

Although JAX-RPC is still supported by some application server vendors, it does not provide support for the latest web services specifications and standards and is, for all intents and purposes, obsolete. For that reason, JAX-WS should be used when developing SOAP-based web services.

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m m
m m
1 year ago

Thanks for the great article. I know its bee a while, but hoping I can get some clarification…We are in the process of a tech refresh and are planning to move our JAX-RPC webservices from websphere 8.5 to weblogic 12.2.x( company preferences) . This is going to be a interim solution with the webservices being replaced eventually, so prefer to keep the effort low for both us the service providers & consuming clients. If we do upgrade the webservices to JAX-WS, will it be transparent to the JAX-RPC clients?Or do the JAX-RPC based clients need to make any code/configuration changes… Read more »