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How do I ensure each http request for jsp is within one jsessionid ?

Just insert a http cookie manager. It will automatically handle the session for all the request within the threadgroup treating it like one sessionan HTTP Cookie Manager. This keeps track of all cookies for each thread within the thread group. Without http cookie manager, each request is a new session as no session state is cookies are kept. jsessionid is only shown for the very first request, subsequent request will not see the jsessionid. to use a variable in jmeter is ${name of variable}.

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