In Memory Buffer to store data in java

I have a requirement to store data coming from UI into some place that can be processed later. Writing in DB or file is not an option because these will take time. I need this operation to be asynchronous so that the person does not have to wait for the data to be processed. JMS is an option but the Queue might get overloaded because the calls are thousands in number. Is there a way I can write it into a temporary Map or something that can be used later. It need not be synchronized