Why does jackson use the thread-unsafe date class SimpleDateFormat?

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I have encountered a problem. When my program is deserializing, the thread is stuck in the Blocked state. Moreover, the current thread holds a lock, causing a large number of my threads to fall into the BLOCKED state. I don't know why the culprit thread is stuck in BLOCKED state. It already holds the lock but has no competing locks, and it enters the BLOCKED state through the deserialization operation in the synchronization code block. At this point, it is doing the deserialization process of the date string. I guess it's too slow, why use this thread-unsafe SimpleDateFormat class?I'm not sure if my analysis is right, I can provide the stack! The culprit thread above is : http-nio2-9797-exec-57
20230522_103001.txt