Invoking a WSDL-based web service through the WSIF API

The Web Services Invocation Framework (WSIF) provides a Java API for invoking web services, independent of the format of the service, or the transport protocol through which it is invoked.

WSIF includes an EJB provider for EJB invocation that uses the Remote Method Invocation over Internet Inter-ORB Protocol (RMI-IIOP). However, for EJB(IIOP)-based web service invocation, invoke RMI-IIOP Web services using JAX-RPC instead.

Ensure that the application uses only one thread to call WSIF.

The WSIF API supports the invocation of Web Services Description Language (WSDL)-defined web services. WSIF is intended for use in both WSIF clients and web service intermediaries.

The WSIF API is driven by the abstract service description in WSDL; it is completely independent of the binding used. This independence makes the API more natural to work with because it uses WSDL terms to refer to message parts, operations, and other items.

The WSIF API was designed for the WSDL usage model:

1. Select a port that supports the port type needed.

2. Invoke the operation by providing the necessary abstract input message consisting of the required parts, without worrying about how the message is mapped to a specific binding protocol.

Other web service APIs, for example SOAP APIs, are not designed on WSDL, but for a specific binding protocol with its associated syntax; for example, target URIs and encoding styles.

The main WSIF API interfaces are described in the following procedure.

Apache no longer supports WSIF.

Tasks

• Create a message for sending to a port through the WSIFMessage interface.

  In WSDL, a message describes the abstract type of the input or output to an operation. The corresponding WSIF class is WSIFMessage, which represents in memory the input or output of an operation. The WSIFMessage interface separates the representation of the data from the abstract type defined by WSDL.

  A WSIFMessage class is a container for a set of named parts. WSIFMessage classes can be sent between Java Virtual Machines (JVMs).

  1. Choose whether to represent the WSIF message at run time as a Java class or as XML.

     There are two natural ways to represent a WSDL message in a runtime environment:

     • The generated Java class, based on a WSDL to Java mapping such as that provided by a JAX-RPC.

     • The XML representation of the data, for example using SOAP Encoding.

     Each option offers benefits in different scenarios. The Java class is the natural approach when WSIF is used in a standard Java client. However, in other scenarios where WSIF is used in an intermediary, it might be more efficient to keep a WSDL message in the SOAP encoded format. The style used to define messages must be consistent within the message, so all the parts in one message must be consistent. A string - getRepresentationStyle() - always returns null. This indicates that parts on this WSIFMessage class are represented as Java objects.

  2. Get and set the parts of the WSIF message.

     You add parts to a WSIFMessage class with the setObjectPart or setTypePart methods. Each part is named. Part names within a message are unique. If we set a part more than once, the last setting is the one used.

     You retrieve parts by name from a WSIFMessage class with the getObjectPart or getTypePart methods. If the named part does not exist, the method returns a WSIFException error.

     Use Iterators to retrieve parts from the message through the getParts() and getPartNames() methods.

     The order in which we set the parts is not important, but the message implementation might be more efficient if the parts are set in the parameter order specified by WSDL.

     WSIFMessage classes are cloneable and serializable. If the parts set are not cloneable, the implementation can try to clone them using serialization. If the parts are not serializable either, then a CloneNotSupportedException exception is thrown if cloning is attempted.

  3. Set the WSIF message name.

     In addition to the containing parts, a WSIFMessage class also has a message name. This is required for operation overloading, which is supported by WSDL and WSIF.

  For more information about the WSIFMessage interface (/wsi/org/apache/wsif/WSIFMessage.html) see the generated API documentation supplied with WSIF.

• Find a port factory or service through the WSIFService interface and the WSIFServiceFactory class.

  The WSIFService interface is a port factory that models and supports the WSDL approach in which a service is available on one or more ports. The factory hides the implementation of the port. WSIF supports dynamic ports that are based on a particular protocol and transport and configured using the WSDL at run time. For example, the dynamic SOAP port can invoke any SOAP service based on the WSDL description of that service, so we can hide and modify the set of available ports at run time.

  To find a service from a WSDL document at a web address, or from a code-generated code base, use the WSIFServiceFactory class.

• Invoke an operation through the WSIFPort interface and the WSIFOperation interface.

  A WSIFPort interface handles the details of invoking an operation. The port provides access to the implementation of the service.

  A WSDL document can provide many different WSDL bindings, and these bindings can drive multiple ports. The client can choose a port, the service stub can choose a port, or WSIF can choose a default port.

  The port offers an interface to retrieve an Operation object. A WSIFOperation interface offers the ability to run the given operation.

  If the port is serialized and deserialized at a later time, WSIF ensures that the client provides the correct information to the server to identify the instance. If the server instance is no longer available, the server must decide whether to create a fault or provide a new instance. That behavior can depend on the type of service. For example, for an enterprise bean, the WSIFPort interface stores the EJB Home and uses it to select the bean before each invocation. The client is responsible for serializing or maintaining the port instance if it requires instance support. The client must create a new operation and messages for each invocation.

Subtopics

• WSIFService interface
  The WSIFService interface can generate an instance of the WSIFOperation interface to use for a particular invocation of a service operation.
• WSIFServiceFactory class
  To find a service from a Web Services Description Language (WSDL) document at a web address, or from a code-generated code base, we can use the WSIFServiceFactory class.
• WSIFPort interface
  The port implements a factory method for the WSIFOperation interface.
• WSIFOperation interface
  We use the WSIFOperation interface to invoke a service, based on a particular binding.

Related:

Web Services Invocation Framework (WSIF)