单个请求Web服务的设计模式

I plan to create a webservice (in Tomcat) that works with a certain file on the system and make some system calls. The challenge am having is to make sure only 1 request can be processed at a given time and the previous request needs to be pre-empted. I currently have a singleton class that works on the request. And requesting threads somehow wait until the running thread is done. But what is the general design pattern for such problems?I plan to create a webservice (in Tomcat) that