如何在ubuntu12上设置系统范围的代理，以便我们可以在代码中调用webservice

I am new to ubuntu, now i use eclipse 3.7 on ubuntu 12; In the code i need to call a webservice, but my work environment works behind a proxy, i need to find a way to set system-wide proxy.I am new to ubuntu, now i use eclipse 3.7 on ub