Why is Spring MVC json serialization 10x slower than calling jackson manually?

The only idea that I have is that Spring's default ObjectMapper is configured a bit differently than the one you use in your benchmark. Like the comments mention, you'd probably see a bit of overhead if you let Spring handle the mapping automatically but it shouldn't have more than a few percent's worth of impact.

To be sure that the comparison is fair, add this bean definition to your configuration:

@Bean@PrimaryObjectMapper objectMapper() {    return new ObjectMapper(new JsonFactory());}

and replace ObjectMapper mapper = new ObjectMapper(new JsonFactory()); with an autowired field:

@AutowiredObjectMapper mapper;

and see if the benchmarks return the same value.

EDIT

I wanted to verify this for myselt so I wrote a JMeter plan and executed each endpoint exactly 5kk times, with a 1-minute warm-up period. The results were as expected, no major differences between the approaches:

Label,# Samples,Average,Min,Max,Std. Dev.,Error %,Throughput,KB/sec,Avg. BytesAuto Request,5000000,2,0,108,5.88,0.00%,15577.3,3088.08,203.0Manual Request,5000000,2,0,149,5.99,0.00%,15660.2,2813.94,184.0

The important thing to note is the throughput difference - auto's 15577.3 vs. manual's 15660.2.

Here's my JMeter test plan, if you'd like to test it yourself, I was running on port 8081. If I find the time, I'll try another benchmarking framework, perhaps Gatling.