java - Should I declare Jackson's ObjectMapper as a static field? - Stack Overflow

java - Should I declare Jackson's ObjectMapper as a static field? - Stack Overflow

Although ObjectMapper is thread safe, I would strongly discourage from declaring it as a static variable, especially in multithreaded application. Not even because it is a bad practice, but because you are running a heavy risk of deadlocking. I am telling it from my own experience. I created an application with 4 identical threads that were getting and processing JSON data from web services. My application was frequently stalling on the following command, according to the thread dump:

Map aPage = mapper.readValue(reader, Map.class);

Beside that, performance was not good. When I replaced static variable with the instance based variable, stalling disappeared and performance quadrupled. I.e. 2.4 millions JSON documents were processed in 40min.56sec., instead of 2.5 hours previously.

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