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Web services development
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Web Services Development |
| Web Services today are frequently just
Application Programming Interfaces
(API) or
Web Application Programming Interfaces
(WAPIs) that can be accessed over an Internet, and executed on a remote system hosting
the requested services. Web services provide a standard way to implement a business
function that can be invoked remotely. They support interoperability by separating the
mechanisms of access from the implementation. For this reason, Web services are the de
facto standard for implementing an SOA that requires a loose coupling between a
requester and a provider. The
development tools
industry quickly jumped onto the web services bandwagon and provided mechanisms for
developing web services. These mechanisms can now be formalized into a set of development
patterns for web services. Each of these patterns has advantages and disadvantages that
determine which pattern should be used in a given situation. |
Bottom-up approach |
The advantages of the bottom-up approach are:
- It is a quick way to expose legacy implementations as web services.
- It requires little or no knowledge of
Web Services Description Language(WSDL)
or
Extensible Markup Language(XML)
because the WSDL document is generated by the tools.
- It has excellent tools support. In fact the sophisticated tools do all the work to
create a deployable, executable web service implementation on the provider side and all
the work to allow a request to access the implementation on the requester side.
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Top-down approach |
The advantages of the top-down approach are:
- It supports the use of existing standards-based XSD types.
- When new schema types are developed for the current service, they can be easily reused
for other services by simply importing the newly developed XSD into the other services.
- It allows for parallel and independent development of client-side and server-side.
- Incremental changes to the service are best managed by changing the
WSDL
itself. Since the
WSDL
is the common interface (or contract) for both the client-side and server-side, these
changes can be easily managed so they don't affect interoperability with existing
requesters or providers.
- The tools will use the name-spaces defined in the
WSDL
to determine the package names of the generated
JavaBeans(or DTOs).
Most of the tools support name-space to package name
mappings. The advantage with starting from Web Services Description Language is that both
the client-side and server-side can use different package name mappings without affecting
the access of the service.
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Round-trip approach |
| The primary advantage of the approach is that you can use it to circumvent tooling problems
or to compensate for insufficient knowledge of
web services tools and
technologies.
This approach allows customization of an existing schema and web service via code changes
rather than schema changes. You can also use it if the tooling does not support implementation
of the service in the desired form, such as an
Enterprise JavaBean(EJB).
The bottom-up pattern is the best approach for exposing existing function as a web service.
The top-down pattern offers the most flexibility and reusability, and is rapidly approaching
the status of a
best practice
when developing new web services. The round-trip pattern can be used as an aide when
one of the better methods cannot be used. |
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