A single web-application communicating with different 3-party systems and gathering responses

[Jignesh Gohel]

My apologies in case this topic does not belong to this forum.I am need of suggestions regarding what all Java technologies or API are available/can be used to handle the below mentioned scenarios.

Following are the applications involved in a proposed system:

MainWebApplication - a web application
ExternalApplication_A - an external application
ExternalApplication_B - an external application
ExternalApplication_C - an external application

MainWebApplication will send request to each of the ExternalApplication(s) (and the request needs to be in the ExternalApplication's desired format) and gather the responses obtained from each of the ExternalApplication(s) and render to the user.

For e.g. ExternalApplication_A exposes an XML API to communicate with it and requires a XML request from MainApplication and will send back a XML response to the MainApplication.Also a constraint is there that ExternalApplication can or cannot be a web-service.

Thanks.