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todays most popular web services apis - jax-rpc and jaxm - support two very different programming models for invocation of web services, one synchronous, one asynchronous. if users need both models in a single application, they are forced to use two sets of very different apis. this article, the first of a two-part series, describes an architecture and programming model - the web services invocation framework (wsif) - that provides a single set of apis that supports both models.
jax-rpc, which is currently part of j2ee and consequently is a mandatory implementation for all j2ee application services vendors, defines and uses an xml-based remote procedure call mechanism. jax-rpc is a very powerful, easy-to-use api for rpc-style web services communications. the relative simplicity of the rpc model, which is very similar to the method invocation of the local java class, explains its widespread popularity. nearly all web services tool vendors provide out-of-the-box support for these apis, allowing for automatic generation of jax-rpc stub- and proxy-based service implementation (either java class or ejb). incorporation of the decorating filters pattern allows for a very powerful mechanism for extending the jax-rpc programming model and support for additional emerging web services standards.
the drawback of using jax-rpc, according to some experts, is that it usually leads to the creation of brittle applications. remote procedures are strongly typed and possess a static signature that defines fixed parameters and return values. if there are any changes in the procedure signature, all dependent clients must be modified to reflect these changes. in addition, rpc by definition is a synchronous programming model, so a caller cannot continue execution until the procedure has returned. although asynchronous invocations are occasionally supported or can be simulated, most jax-rpc procedures are synchronous, and therefore not responsive to changing network conditions. this leads many experts to believe that rpc-style invocations are not applicable to building ev... 下一页