Category Archives: REST API

  • 3

Java REST API Benchmark: Tomcat vs Jetty vs Grizzly vs Undertow, Round 3

Too many things have changed since round 2

From Apache Bench to Gatling

The ApacheBench software I initially used for round 1 and round 2 is very good to get started with.
But there are better tools that allow to have more detailed reports and insight into the load test.
Another strong reason was that ApacheBench only support HTTP/1.0. The lack of support for HTTP/1.1 may have a negative impact on performance.
Switching to Gatling gave me more flexibility and also allowed to generate pretty graphs and more detailed statistics.
This will also allow anybody with Java installed to be able to run the tests without having to install any additional software.

HTTP Headers

One of the issues pointed out by Stuart in his comment is that the response header for each container was different.
Most importantly, Grizzly was sending the least header i.e Grizzly was transmitting less data than the other 3 containers and this certainly has an impact on performance and response time.
To address this, changes have been made so that every single container is returning the very same response header.
Since Grizzly by default would not allow to add the Server  HTTP header to the response, I had to implement a filter to allow for that header to be added to every response.

Now, all containers have the very same header which looks like this:


On the other hand, with Gatling, I was also setting request headers like:


Running the load test from a remote host

Another issue mentioned by Stuart is that ideally we want the HTTP containers being tested and the load generator to be on separate servers.
This has been addressed too.
This leads us to 2 machines in the very same Local Area Network.

HTTP containers are running on:


Gatling the load generator is runnig on


Proper warm-up

In round 1 and round 2, I was warming up the HTTP containers with a single HTTP GET request.
As suggested by Stuart, I am now doing a full 10 minute warm-up before running the real load test for 15 minutes.

Running the tests

–  One need to first start the HTTP server . This can be done by following the commands on the GitHub REST-API project page

–  Run Gatling: Please see the Gitub Gatling Page


The results

Compared to previous rounds, this one has shown unexpected results

The through output:

As show on the graph, Grizzly has shown the best through output, followed by Undertow.
More detail about the bench


Throughoutput for a 15min run with 10min warmup and 128 concurrent users for 32 worker threads


The response time

Here, we have Undertow leading in term of response time for 99% of requests.

99% of Response time in ms for 128 concurrent users for a 15minute run


95% of Response time in ms for 128 concurrent users for a 15minute run

95% of Response time in ms for 128 concurrent users for a 15minute run

– When we consider 95% of responses, Undertow and Grizzly both have same 6ms response time


75% of Response time in ms for 128 concurrent users for a 15minute run

75% of Response time in ms for 128 concurrent users for a 15minute run

– When we consider 75% of response, Undertow and grizzly both have the same 4ms response time

Undertow and Grizzly have very similar performance here.

For more detail, please see the links in the resource section

Note that Grizzly remains a very interesting beast.
For instance the detailed response time of grizzly is depicted on the following graph:
grizzly-response-time-in-round-03Despite the 10 minute warm-up, the response time was still high during the first 6 minutes of the load test, then response time suddenly dropped down from above 100ms to under 30ms and remained lower… Just as if Grizzly has an internal cache.
No other container has shown such a behaviour.



The changes such as

– same request and response headers (Yes, size does matter here… all containers need to be returning the very same header size),
– HTTP/1.1
– proper warm-up phase, and
– running load test from remote host

have shown totally different results from what we got in round 1 and round 2.

As shown in previous tests, Grizzly seems to perform best but here, we have learnt that Undertow can come very close.

Given that Undertow is a fully blown Servlet Container with support for the latest Servlet spec, JSP, JSF etc, it is an excellent choice for complex web applications.


More detail about the load test reports can be found at





  • 3

Java REST API Benchmark: Tomcat vs Jetty vs Grizzly vs Undertow, Round 2

This is a follow-up to the initial REST/JAX-RS benchmark comparing Tomcat, Jetty, Grizzly and Undertow.

In the previous round where default server configuration was used, the race was led by Grizzly, followed by Jetty, Undertow and finally Tomcat.

In this round, I have set the maximum worker thread pool size to 250 for all 4 containers.

To make this happen, I had to do some code changes for Jetty as well as Grizzly as this was not possible in the original benchmark.

This allowed me to start the container with the thread pool size as a command line parameter.

For more detail about running the tests yourself, please have a look at the github link in the resources section.

Note that here, the test have been run only for 128 concurrent users as from the previous round, the number of concurrent users did not make a big impact

System information


Note that here, we have more free ram than in the previous round as I have shut down all running applications.

I also restarted the machine before every single test run




Through output for 10 million request, 128 concurrent users, 250 server worker thread

As shown on the graph above, as fas as tough output is concerned, again, Grizzly is far ahead leading the race, followed by Jetty.

Undertow came third very close to Jetty. Then Tomcat came last.






Response time for 10 million requests, 128 concurrent users, 250 server worker thread

The Response time graph above shows Grizzly ahead in the game, followed by Jetty, Undertow and Tomcat last


I expected Undertow to be the fastest of all. But somehow, this did not happen

The result of this round 2 is very similar to what we have seen in round 1: Grizzly is the fastest container when it comes to serving JAX-RS requests.


Source code and detailed benchmark results are available at









  • 5

Java REST API Benchmark: Tomcat vs Jetty vs Grizzly vs Undertow

This is early 2016 and over and over again the question arises as to what Java web container to use, especially with the rise of micro-services where containers are  being embedded into the application.

Recently, we have been facing the very same question. Should we go with:

  1. Jetty, well known for its performance, speed and stability?
  2. Grizzly, which is embedded by default into Jersey?
  3. Tomcat, the de-facto standard web container?
  4. Undertow, the new kid in the block, prised for it’s simplicity, modularity and performance?

Our use case is mainly about delivering Java REST APIs using JAX-RS.
Since we were already using Spring, we were also looking into leverage frameworks such as Spring Boot.

Spring boot out of the box supports Tomcat, Jetty and Undertow.

This post discusses about which web container to use when it comes to delivering fast, reliable and highly available JAX-RS REST API.

For this article, Jersey is being used as the implementation.
We are comparing 4 of the most popular containers:

  1. Tomcat(8.0.30),
  2. Jetty(9.2.14),
  3. Grizzly(2.22.1) and
  4. Undertow(1.3.10.FINAL).

The implemented API is returning a very simple constant Json response …. no extra processing involved.

The code has been kept deliberately very simple. The very same API code is executed on all containers.

For more detail about the code, please look at the link in the resource section.
We ran the load test using ApacheBench with concurrency level=1, 4, 16, 64 and 128
the results in term of fastest or slowest container does not change no matter the concurrency level
so, here, I am publishing only concurrent users=1 and concurrent users=128

System Specification

This benchmark has been executed on my laptop:



Concurrent number of Users = 1


Response Time for 10 million requests for 1 concurrent user


Through-output for 10 million requests for 1 concurrent user


from the 2 graphs above, Grizzly is leading the benchmark followed by Jetty, followed by Undertow. Tomcat remains the last in this benchmark

Concurrent number of Users = 128



Response Time for 10 million requests and 128 concurrent users


Through-output for 10 millions requests and 128 concurrent users

Note that Grizzly is still leading here and that concurrency level =128 did not change anything to which server is best or worst.

Note that we have also tested for concurrency level =4, 16 and  64 and the final result is pretty much the same


For this benchmark, a very simple Jersey REST API implementation is being used.

Grizzly seems to give us the very best through-output and response time no matter the concurrency level.

in this test, I have been using the default web container settings.
And as we all know, no one put a container into production with its default settings.

in the next blog post, I will change the server configuration and rerun the very same tests


The source code is available on GitHub