Developing a Consumer with CXF

Generating the Stub Code

The starting point for developing a service consumer (or client) in CXF is a WSDL contract, complete with port type, binding, and service definitions. You can then use the wsdl2java utility to generate the Java stub code from the WSDL contract. The stub code provides the supporting code that is required to invoke operations on the remote service.
For CXF clients, the wsdl2java utility can generate the following kinds of code:

  • Stub code - supporting files for implementing a CXF client.
  • Client starting point code - sample client code that connects to the remote service and invokes every operation on the remote service.
  • Ant build file - a build.xml file intended for use with the ant build utility. It has targets for building and for running the sample client application.

Basic HelloWorld WSDL contract

The below shows the HelloWorld WSDL contract. This contract defines a single port type, Greeter, with a SOAP binding, Greeter_SOAPBinding, and a service, SOAPService, which has a single port, SoapPort.

HelloWorld WSDL Contract

The Greeter port type defines the following WSDL operations:

  • sayHi - has a single output parameter, of xsd:string.
  • greetMe - has an input parameter, of xsd:string, and an output parameter, of xsd:string.
  • greetMeOneWay - has a single input parameter, of xsd:string. Because this operation has no output parameters, CXF can optimize this call to be a oneway invocation (that is, the client does not wait for a response from the server).
  • pingMe - has no input parameters and no output parameters, but it can raise a fault exception.

This WSDL also defines a binding, Greeter_SOAPBinding, for the SOAP protocol. In practice, the binding is normally generated
automatically - for example, by running either of the CXF wsdl2soap or wsdl2xml utilities. Likewise, the SOAPService service can be generated automatically by running the CXF wsdl2service utility.

Generating the stub code

After defining the WSDL contract, you can generate client code using the CXF wsdl2java utility. Enter the following command at a command-line prompt:

wsdl2java -ant -client -d ClientDir hello_world.wsdl

Where ClientDir is the location of a directory where you would like to put the generated files and
hello_world.wsdl is a file containing the contract shown in the WSDL above. The -ant option generates an ant build.xml file, for use with the ant build utility. The -client option generates starting point code for a client main() method.

The preceding wsdl2java command generates the following Java packages:

  • org.apache.hello_world_soap_http
    This package name is generated from the http://apache.org/hello_world_soap_http target namespace. All of the WSDL entities defined in this target namespace (for example, the Greeter port type and the SOAPService service) map to Java classes in the corresponding Java package.
  • org.apache.hello_world_soap_http.types
    This package name is generated from the http://apache.org/hello_world_soap_http/types target namespace. All of the XML types defined in this target namespace (that is, everything defined in the wsdl:types element of the HelloWorld contract) map to Java classes in the corresponding Java package.

The stub files generated by the wsdl2java command fall into the following categories:

  • Classes representing WSDL entities (in the org.apache.hello_world_soap_http package) - the following classes are generated to represent WSDL entities:
    • Greeter is a Java interface that represents the Greeter WSDL port type. In JAX-WS terminology, this Java interface is a service endpoint interface.
    • SOAPService is a Java class that represents the SOAPService WSDL service element.
    • PingMeFault is a Java exception class (extending java.lang.Exception) that represents the pingMeFault WSDL fault element.
  • Classes representing XML types (in the org.apache.hello_world_soap_http.types package) - in the HelloWorld example, the only generated types are the various wrappers for the request and reply messages. Some of these data types are useful for the
    asynchronous invocation model.

Implementing a CXF Client

This section describes how to write the code for a simple Java client, based on the WSDL contract above. To implement the client, you need to use the following stub classes:

  • Service class (that is, SOAPService).
  • Service endpoint interface (that is, Greeter).

Generated service class

The below shows the typical outline for a generated service class, ServiceName, which extends the javax.xml.ws.Service base class.

Outline of a Generated Service Class

The ServiceName class defines the following methods:

  • Constructor methods - the following forms of constructor are defined:
    • ServiceName(URL wsdlLocation, QName serviceName) constructs a service object based on the data in the serviceName service in the WSDL contract that is obtainable from wsdlLocation.
    • ServiceName() is the default constructor, which constructs a service object based on the service name and WSDL contract that were provided at the time the stub code was generated (for example, when running the CXF wsdl2java command). Using this constructor presupposes that the WSDL contract remains available at its original location.
  • get_PortName_() methods - for every PortName port defined on the ServiceName service, CXF generates a corresponding get_PortName_() method in Java. Therefore, a wsdl:service element that defines multiple ports will generate a service class with multiple get_PortName_() methods.

Service endpoint interface

For every port type defined in the original WSDL contract, you can generate a corresponding service endpoint interface in Java. A service endpoint interface is the Java mapping of a WSDL port type. Each operation defined in the original WSDL port type maps to a corresponding method in the service endpoint interface. The operation's parameters are mapped as follows:

  1. The input parameters are mapped to method arguments.
  2. The first output parameter is mapped to a return value.
  3. If there is more than one output parameter, the second and subsequent output parameters map to method arguments (moreover, the values of these arguments must be passed using Holder types).

For example, the below shows the Greeter service endpoint interface, which is generated from the Greeter port type defined in #Example1. For simplicity, #Example3 omits the standard JAXB and JAX-WS annotations.

The Greeter Service Endpoint Interface

Client main function

Here is Java code that implements the HelloWorld client. In summary, the client connects to the SoapPort port on the SOAPService service and then proceeds to invoke each of the operations supported by the Greeter port type.

Client Implementation Code

The Client.main() function proceeds as follows:

  1. The CXF runtime is implicitly initialized - that is, provided the CXF runtime classes are loaded. Hence, there is no need to call a special function in order to initialize CXF.
  2. The client expects a single string argument that gives the location of the WSDL contract for HelloWorld. The WSDL location is stored in wsdlURL.
  3. A new port object (which enables you to access the remote server endpoint) is created in two steps, as shown in the following code fragment:
    To create a new port object, you first create a service object (passing in the WSDL location and service name) and then call the appropriate get PortName () method to obtain an instance of the particular port you need. In this case, the SOAPService service supports only the SoapPort port, which is of Greeter type.
  4. The client proceeds to call each of the methods supported by the Greeter service endpoint interface.
  5. In the case of the pingMe() operation, the example code shows how to catch the PingMeFault fault exception.

Setting Connection Properties with Contexts

You can use JAX-WS contexts to customize the properties of a client proxy. In particular, contexts can be used to modify connection properties and to send data in protocol headers. For example, you could use contexts to add a SOAP header, either to a request message or to a response message. The following types of context are supported on the client side:

  • Request context - on the client side, the request context enables you to set properties that affect outbound messages. Request context properties are applied to a specific port instance and, once set, the properties affect every subsequent operation invocation made on the port, until such time as a property is explicitly cleared. For example, you might use a request context property to set a connection timeout or to initialize data for sending in a header.
  • Response context - on the client side, you can access the response context to read the property values set by the inbound message from the last operation invocation. Response context properties are reset after every operation invocation. For example, you might access a response context property to read header information received from the last inbound message.

Setting a request context

To set a particular request context property, ContextPropertyName, to the value, PropertyValue, use the code shown here:

Setting a Request Context Property on the Client Side

You have to cast the port object to javax.xml.ws.BindingProvider in order to access the request context. The request context itself is of type, java.util.Map<String, Object>, which is a hash map that has keys of String and values of arbitrary type. Use java.util.Map.put() to create a new entry in the hash map.

Reading a response context

To retrieve a particular response context property, ContextPropertyName, use the code shown here:

Reading a Response Context Property on the Client Side

The response context is of type, java.util.Map<String, Object>, which is a hash map that has keys of type String and values of an arbitrary type. Use java.util.Map.get() to access an entry in the hash map of response context properties.

Supported contexts

CXF supports the following context properties:

Context Property Name

Context Property Type

org.apache.cxf.ws.addressing.JAXWSAConstants.CLIENT_ADDRESSING_PROPERTIES

org.apache.cxf.ws.addressing.AddressingProperties

Asynchronous Invocation Model

In addition to the usual synchronous mode of invocation, CXF also supports two forms of asynchronous invocation, as follows:

  • Polling approach - in this case, to invoke the remote operation, you call a special method that has no output parameters, but returns a javax.xml.ws.Response instance. The Response object (which inherits from the javax.util.concurrency.Future interface) can be polled to check whether or not a response message has arrived.
  • Callback approach - in this case, to invoke the remote operation, you call another special method that takes a reference to a callback object (of javax.xml.ws.AsyncHandler type) as one of its parameters. Whenever the response message arrives at the client, the CXF runtime calls back on the AsyncHandler object to give it the contents of the response message.

Both of these asynchronous invocation approaches are described here and illustrated by code examples.

Contract for asynchronous example

The following example shows the WSDL contract that is used for the asynchronous example. The contract defines a single port type, GreeterAsync, which contains a single operation, greetMeSometime.

HelloWorld WSDL Contract for Asynchronous Example

Generating the asynchronous stub code

The asynchronous style of invocation requires extra stub code (for example, dedicated asychronous methods defined on the service endpoint interface). This special stub code is not generated by default, however. To switch on the asynchronous feature and generate the requisite stub code, you must use the mapping customization feature from the WSDL 2.0 specification.

Customization enables you to modify the way the wsdl2java utility generates stub code. In particular, it enables you to modify the WSDL-to-Java mapping and to switch on certain features. Here, customization is used to switch on the asynchronous invocation feature. Customizations are specified using a binding declaration, which you define using a jaxws:bindings tag (where the jaxws prefix is tied to the http://java.sun.com/xml/ns/jaxws namespace). There are two alternative ways of specifying a binding declaration:

  • External binding declaration - the jaxws:bindings element is defined in a file separately from the WSDL contract. You specify the location of the binding declaration file to the wsdl2java utility when you generate the stub code.
  • Embedded binding declaration - you can also embed the jaxws:bindings element directly in a WSDL contract, treating it as a WSDL extension. In this case, the settings in jaxws:bindings apply only to the immediate parent element.

This section considers only the first approach, the external binding declaration. The template for a binding declaration file that switches on asynchronous invocations is shown next:

Template for an Asynchronous Binding Declaration

Where AffectedWSDLContract specifies the URL of the WSDL contract that is affected by this binding declaration. The AffectedNode is an XPath value that specifies which node (or nodes) from the WSDL contract are affected by this binding declaration. You can set AffectedNode to wsdl:definitions, if you want the entire WSDL contract to be affected. The {jaxws:enableAsyncMapping}} element is set to true to enable the asynchronous invocation feature.

For example, if you want to generate asynchronous methods only for the GreeterAsync port type, you could specify <bindings node="wsdl:definitions/wsdl:portType@name='GreeterAsync'"> in the preceding binding declaration.

Assuming that the binding declaration is stored in a file, async_binding.xml, you can generate the requisite stub files with asynchronous support by entering the following wsdl2java command:

wsdl2java -ant -client -d ClientDir -b async_binding.xml hello_world.wsdl

When you run the wsdl2java command, you specify the location of the binding declaration file using the -b option. After generating the stub code in this way, the GreeterAsync service endpoint interface (in the file GreeterAsync.java) is defined as shown below:

Service Endpoint Interface with Methods for Asynchronous Invocations

In addition to the usual synchronous method, greetMeSometime(), two asynchronous methods are also generated for the greetMeSometime operation, as follows:

  • greetMeSometimeAsync() method with Future<?> return type and an extra javax.xml.ws.AsyncHandler parameter - call this method for the callback approach to asynchronous invocation.
  • greetMeSometimeAsync() method with Response<GreetMeSometimeResponse> return type - call this method for the polling approach to asynchronous invocation.

The details of the callback approach and the polling approach are discussed in the following subsections.

Implementing an asynchronous client with the polling approach

The below sample illustrates the polling approach to making an asynchronous operation call. Using this approach, the client invokes the
operation by calling the special Java method, _OperationName_Async(), that returns a javax.xml.ws.Response<T> object, where T is the type of the operation's response message. The Response<T> object can be polled at a later stage to check whether the operation's response message has arrived.

Polling Approach for an Asynchronous Operation Call

The greetMeSometimeAsync() method invokes the greetMeSometimes operation, transmitting the input parameters to the remote service and returning a reference to a javax.xml.ws.Response<GreetMeSometimeResponse> object. The Response class is defined by extending the standard java.util.concurrency.Future<T> interface, which is specifically designed for polling the outcome of work performed by a concurrent thread. There are essentially two basic approaches to polling using the Response object:

  • Non-blocking polling - before attempting to get the result, check whether the response has arrived by calling the non-blocking
    Response<T>.isDone() method. For example:
  • Blocking polling - call Response<T>.get() right away and block until the response arrives (optionally specifying a timeout). For example, to poll for a response, with a 60 second timeout:

Implementing an asynchronous client with the callback approach

An alternative approach to making an asynchronous operation invocation is to implement a callback class, by deriving from the
javax.xml.ws.AsyncHandler interface. This callback class must implement a handleResponse() method, which is called by the CXF runtime to notify the client that the response has arrived. The following shows an outline of the AsyncHandler interface that you need to implement.

The javax.xml.ws.AsyncHandler Interface

In this example, a callback class, TestAsyncHandler, is defined as shown below.

The TestAsyncHandler Callback Class

The implementation of handleResponse() shown in #Example11 simply gets the response data and stores it in a member variable, reply. The extra getResponse() method is just a convenience method that extracts the sole output parameter (that is, responseType) from the response.

#Example12 illustrates the callback approach to making an asynchronous operation call. Using this approach, the client invokes the operation by calling the special Java method, _OperationName_Async(), that returns a java.util.concurrency.Future<?> object and takes an extra parameter of AsyncHandler<T>.

Callback Approach for an Asynchronous Operation Call

The Future<?> object returned by greetMeSometimeAsync() can be used only to test whether or not a response has arrived yet - for example, by calling response.isDone(). The value of the response is only made available to the callback object, testAsyncHandler.