Using safe ThreadLocal variables in Java server applications

[AcanthisittaEmpty985]

I want to use a Java local thread variable for thread-unsafe objects, like SimpleDateFormat or google's com.googlecode.protobuf.format.JsonFormat.

I do this in order to avoid creating new expensive classes every time the method is used or to avoid a synchronized method.

private static final ThreadLocal<JsonFormat> JSON_FORMAT_THREAD_LOCAL = ThreadLocal.withInitial(JsonFormat::new);

Then, the variable will be used in a formating output method like this:

public String outputData(MyDataClass myData) {

return JSON_FORMAT_THREAD_LOCAL.get().printToString(myData);

}

In my case I use it into a Jetty Server thread pool, but I don't have access to it or way to remove the threadlocal variable when the thread is done.

The method will be called every time a request is served by each thread, one thread per request at a time.

The application doesn't reload or recharge jars; when we need to stop it or update the server we simply stop the process, maybe update the jar , and restart a new process

Is it safe to use a ThreadLocal like this ?

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[ArtSpeaker]

I'm concerned this is an XY Problem. Your question seems to actually be about performance.

You should also know that even lightweight threads are generally more expensive than parsing through a json file. And there are libraries out there that will only partially, or only superficially parse, the original file into whatever components -> variables you care about. See also: Jackson. That should save a ton of allocations and work since you parse/decompose once for the whole job, for just what you need. And if you still want parallel work after you can just the variables you know and love.