Feeling

stackoverflow有類似的問題：
http://stackoverflow.com/questions/2608763/why-does-first-call-to-java-io-file-createtempfilestring-string-file-take-5-se

有人提到是因為用戶屬于guest group的原因：
As noted as a comment on one of the answers below, I noticed this time is actually spent in the first invocation of SecureRandom.nextLong(). Also, I found that this behavior only occurs when a user has the "Guest" group associated with them. I can execute this test with a user and have it run in less than 100ms and then re-execute the same test with the same user account after just adding that user to the "Guests" group (without removing any other group associations from the user had in the previous run).

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@小明
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