XML Web Service: adapting legacy applications
Since the beginnings of e-commerce, many applications have been developed to support the growing demand of online shopping systems. Many of the systems use proprietary implementations, often because of the lack of open standards at the time of development. However, the business processes these earlier-generation proprietary applications support will continue to be necessary in the future. This can be credited to the significant investments that have been made into these e-business applications. In order to enable legacy applications to participate in dynamic e-business, we need to apply Web service technologies which will allow the services to be defined so as to hide some of the complexity of the legacy application interface. Web services are the next stage of evolution for e-business. They view everything as a service that can be dynamically discovered and orchestrated, using messaging on the network. Enterprises can dynamically sell their services to others by publishing their Web services. The Web services architecture
(WSA) is an ideal technology to incorporate enterprise legacy applications into this new area. The conceptual
architecture to access legacy applications via SOAP (XML
WebService) covers the three components of a Web service: service provider, service
request, and service broker.
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Objective: to realize an Adapter for accessing a legacy application via SOAP. The Web service
Adapter has to be developed for each service to enable them for services
access. It is typically a Java application program that connects to the
backend server. This connection can be any communication link supported by
the backend server. SOAP
request is issued as a HTTP POST request. Using HTTP has the advantage
that it can pass the normally available firewalls on Web servers. In above example the legacy application is a Java Servlet-based application for the exchange of information (XML data) about tourist sector. This application is not described. The following description explains the main components in detail: the Web Service Adapter and the WSDL Service Description. Then, to verify the architecture described earlier, a sample implementation of the Service Requestor will be developed. The Soap Router component is built-in into various implementations of the SOAP protocol for different platforms (I use Apache SOAP Toolkit 2.2). The Info-Service allows Service Requestor to get last-minute information about hotels located in Italy:
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Investment in application development is always an issue for the enterprise. As an open standard networked world begins to dominate the IT world, the preservation of these investments is likely to change. Today many enterprises are trying to change their legacy applications into component-oriented systems. A new option to facilitate this change can be the use of Web services technology. Elementary services from legacy applications can be wrapped as Web services and orchestrated to higher value services.
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