Are Spring Controllers Thread-Safe

Question

I came upon this Controller example, and am wondering if it is thread-safe? I am wondering specifically about the gson instance variable.

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import com.google.gson.Gson;
import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@Controller
public class TestController {

    private final Gson gson = new Gson();

    @RequestMapping(value = "/test", method = RequestMethod.GET)
    public void test(HttpServletResponse res, HttpServletRequest req) throws IOException {
        HashMap<String, String> hm = new HashMap();
        res.getWriter().print(gson.toJson(results));
        res.getWriter().close();
    }
}

Answer 1

To answer the question in the title, "Are Spring Controllers Thread-Safe", Spring Controllers are singletons, therefore they SHOULD be implemented in a thread safe manner but it's up to you to ensure that your implementation is ACTUALLY thread safe.

In the code you post you should be fine since as others have pointed out, GSON is thread safe.