Structure
In WSDL, a binding defines how to map between the abstract PortType and a real service format and protocol. For example, the SOAP binding defines the encoding style, the SOAPAction header, the namespace of the body (the targetURI), and so forth.
WSDL allows multiple implementations for a Web service and multiple ports that share the same PortType. In other words, WSDL allows the same interface to have bindings to services such as SOAP and IIOP.
WSIF provides an API to allow the same client code to access any available binding. Since the client code can be written to the PortType, the choice of which port and binding it uses can be determined by deployment, configuration settings, or code
The WSIF uses providers to support these multiple WSDL bindings. A provider is a piece of code that supports a WSDL extension and allows invocation of the service through that particular implementation. WSIF providers use the J2SE JAR service provider specification, making them discoverable at runtime.
Clients can utilize new implementations and delegate the choice of port to the infrastructure and runtime, which allows the implementation to be chosen on the basis of quality of service characteristics or business policy.
Description
WSIF enables developers to interact with abstract representations of Web services through their WSDL descriptions instead of working directly with the Simple Object Access Protocol (SOAP) APIs, which is the usual programming model. With WSIF, developers can work with the same programming model regardless of how the Web service is implemented and accessed.
WSIF allows stubless or completely dynamic invocation of a Web service, based upon examination of the metadata about the service at runtime. It also allows updated implementations of a binding to be plugged into WSIF at runtime, allowing the calling service to defer choosing a binding until runtime.
It is closely based on WSDL enabling it to invoke any service that can be described in the language.
If a complicated enterprise software system consists of various pieces of software, developed over a period of decades—EJBs, legacy apps accessed using Java's connector architecture, SOAP services hosted on external servers, old code accessed through messaging middleware—it is necessary to write software applications that use all these pieces to do useful things, where differences in protocols and mobility of software conflict with each other.
If the software is moved to a different server, the code breaks. The SOAP libraries used change—for example, when transitioning from using Apache SOAP to Apache Axis, as it employs a now-deprecated SOAP API. Something that was previously accessible as an EJB is now available through messaging middleware via JMS—again, the code that uses the software must be fixed, or if one has an EJB which is offered as a SOAP service to external clients. Using SOAP results in a performance penalty compared to accessing the EJB directly.
WSIF resolves these issues by enabling WSDL to serve as a normalized description of disparate software and allowing users to access this software without depending on a specific protocol or location. The separation of the API from the actual protocol also means there is flexibility—protocols, location, etc. can be switched without having to recompile client code. If an externally available SOAP service becomes available as an EJB, users can use RMI/IIOP by changing the service description (the WSDL), without making any modification in applications that use the service. WSDL's extensibility, its capability to offer multiple bindings for the same service, deciding on a binding at runtime, etc. can be exploited.
Differences between WSIF and Axis
Axis is an implementation of SOAP. It includes on the server-side infrastructure for deploying web service implementations and then routing SOAP messages between clients and those implementations. It also implements the JAX-RPC specification for invoking SOAP services.
WSIF is similar to the client piece of Axis, in that it is used for invoking services. However, WSIF's API is WSDL-driven and protocol independent; it allows protocol-specific code ("providers") to be plugged in. For invoking SOAP services, WSIF is packaged with an Axis provider, that uses Axis APIs (i.e. JAX-RPC) to do the invocation. So WSIF operates at a more abstract level than Axis.
In distributed computing, a remote procedure call (RPC) is when a computer program causes a procedure (subroutine) to execute in a different address space, which is written as if it were a normal (local) procedure call, without the programmer explicitly writing the details for the remote interaction. That is, the programmer writes essentially the same code whether the subroutine is local to the executing program, or remote. This is a form of client–server interaction, typically implemented via a request–response message passing system. In the object-oriented programming paradigm, RPCs are represented by remote method invocation (RMI). The RPC model implies a level of location transparency, namely that calling procedures are largely the same whether they are local or remote, but usually, they are not identical, so local calls can be distinguished from remote calls. Remote calls are usually orders of magnitude slower and less reliable than local calls, so distinguishing them is important.
SOAP is a messaging protocol specification for exchanging structured information in the implementation of web services in computer networks. It uses XML Information Set for its message format, and relies on application layer protocols, most often Hypertext Transfer Protocol (HTTP), although some legacy systems communicate over Simple Mail Transfer Protocol (SMTP), for message negotiation and transmission.
Jakarta Enterprise Beans is one of several Java APIs for modular construction of enterprise software. EJB is a server-side software component that encapsulates business logic of an application. An EJB web container provides a runtime environment for web related software components, including computer security, Java servlet lifecycle management, transaction processing, and other web services. The EJB specification is a subset of the Java EE specification.
The Common Object Request Broker Architecture (CORBA) is a standard defined by the Object Management Group (OMG) designed to facilitate the communication of systems that are deployed on diverse platforms. CORBA enables collaboration between systems on different operating systems, programming languages, and computing hardware. CORBA uses an object-oriented model although the systems that use the CORBA do not have to be object-oriented. CORBA is an example of the distributed object paradigm.
A web service (WS) is either:
Message-oriented middleware (MOM) is software or hardware infrastructure supporting sending and receiving messages between distributed systems. MOM allows application modules to be distributed over heterogeneous platforms and reduces the complexity of developing applications that span multiple operating systems and network protocols. The middleware creates a distributed communications layer that insulates the application developer from the details of the various operating systems and network interfaces. APIs that extend across diverse platforms and networks are typically provided by MOM.
Apache XML is a category of projects at the Apache Software Foundation that focus on XML-related projects.
Web Services Discovery provides access to software systems over the Internet using standard protocols. In the most basic scenario there is a Web Service Provider that publishes a service and a Web Service Consumer that uses this service. Web Service Discovery is the process of finding suitable web services for a given task.
Apache Axis is an open-source, XML based Web service framework. It consists of a Java and a C++ implementation of the SOAP server, and various utilities and APIs for generating and deploying Web service applications. Using Apache Axis, developers can create interoperable, distributed computing applications. Axis development takes place under the auspices of the Apache Software Foundation.
Jakarta XML RPC allows a Jakarta EE application to invoke a Java-based web service with a known description while still being consistent with its WSDL description. JAX-RPC is one of the Java XML programming APIs. It can be seen as Java RMIs over web services. JAX-RPC 2.0 was renamed JAX-WS 2.0. JAX-RPC 1 is deprecated with Java EE 6. The JAX-RPC service utilizes W3C standards like WSDL . The core API classes are located in the Java package javax.xml.rpc.
JSON-RPC is a remote procedure call (RPC) protocol encoded in JSON. It is similar to the XML-RPC protocol, defining only a few data types and commands. JSON-RPC allows for notifications and for multiple calls to be sent to the server which may be answered asynchronously.
XML Interface for Network Services (XINS) is an open-source technology for definition and implementation of internet applications, which enforces a specification-oriented approach.
The Windows Communication Foundation (WCF), previously known as Indigo, is a free and open-source runtime and a set of APIs in the .NET Framework for building connected, service-oriented applications.
The Spring Framework is an application framework and inversion of control container for the Java platform. The framework's core features can be used by any Java application, but there are extensions for building web applications on top of the Java EE platform. The framework does not impose any specific programming model.. The framework has become popular in the Java community as an addition to the Enterprise JavaBeans (EJB) model. The Spring Framework is free and open source software.
The Jakarta XML Web Services is a Jakarta EE API for creating web services, particularly SOAP services. JAX-WS is one of the Java XML programming APIs.
Apache Axis2 is a web service engine. It is a redesign and re-write of the widely used Apache Axis SOAP stack. Implementations of Axis2 are available in Java and C.
Apache CXF is an open source software project developing a Web services framework. It originated as the combination of Celtix developed by IONA Technologies and XFire developed by a team hosted at the now defunct host CodeHaus in 2006. These two projects were combined at the Apache Software Foundation. The name "CXF" was derived by combining "Celtix" and "XFire".
The Web Services Description Language is an XML-based interface description language that is used for describing the functionality offered by a web service. The acronym is also used for any specific WSDL description of a web service, which provides a machine-readable description of how the service can be called, what parameters it expects, and what data structures it returns. Therefore, its purpose is roughly similar to that of a type signature in a programming language.
Spring Roo is an open-source software tool that uses convention-over-configuration principles to provide rapid application development of Java-based enterprise software. The resulting applications use common Java technologies such as Spring Framework, Java Persistence API, Thymeleaf, Apache Maven and AspectJ. Spring Roo is a member of the Spring portfolio of projects.
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