Spring is bloated
Over the years, Spring seemed to be the replacement of JEE servers with IoC container and light weight servlet container as its foundation. Especially recently, Spring Boot brings in an easy development model and increases developer productivity dramatically.
However, there are two issues or limitations in Spring applications.
Spring is bloated and it becomes too heavy
When Spring was out, it was only a small core with IoC contain and it was fast and easy to use. Now, I cannot even count how many Spring Components available today. In order to complete with JEE, Spring basically implemented all replacements of JEE and these are heavy components.
Most Spring applications are based on old servlet API and it is slow.
Another issue with Spring is due to the foundation of servlet container which was designed over ten years ago without multi-core, NIO etc in consideration. There is a little improvement in Servlet 3.1 but it wasn’t right due to backward compatible requirement.
I did a performance test between Spring Boot and My own Light Java Framework and Spring Boot is 44 times slower. The performance test code and result can be found here
The test result for Spring Boot was based on the embedded tomcat server and later on I have switched to Undertow servlet container for Spring Boot. The Undertow Servlet container is faster but still over 20-30 times slower then Light Java Framework which is built on top of Undertow core http server.
The 20-30 times difference between the two is due to Servlet overhead and Spring Boot overhead and it is very significant.
After I published the peformance test results, one of the Spring developers pointed me to a new approach to build Spring Boot application with Netty. The performance is getting better but still very slow compare with Light Java.
Memory Footprint
During these test, I observed that Spring Boot with embedded servlet container uses at least 5 times more memory. This is a big different in cloud computer as memory is very expensive.
Conclusion
Given above reasons, there is no way that Spring Boot can be used as a light weight platform for microservices. It is too heavy and two slow. And if you compare the codebase on both Spring Boot and Light Java, you can see Light Java code is small and easy to understand without any annotations.