i've looked everywhere , unable find information on how create java listener listens information website , reads information.
i want listener running in background time.
it woudl website control, have website send data when user checks out , want know how listen data in background without being in intervals.
it isn't possible implement listener website, because websites not publish updates listeners can listen for. http protocol has no notion of polling, notifications, or publish-subscribe. why search engines have crawl internet.
what can write web crawler polls site(s) you're interested in every often, , when site updates have crawler notify listeners.
going how design crawler beyond can cover in answer, programmers se has couple of relevant questions:
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