This project shows how to build "micro" applications with Spring and Spring Boot - the smallest, functional units, with the fewest dependencies and fastest start times

Building the Apps

Build the jar:

$ ./mvnw clean install

Run it

$ java -jar target/micro-0.0.1-SNAPSHOT.jar
...
2018-05-23 10:03:41.776 [main] INFO  com.example.demo.DemoApplication - Started DemoApplication in 1.885 seconds (JVM running for 3.769)
...

The default app is relatively full-bodied - it uses Spring Boot and auto-configuration.

You can run the smaller apps using command line flags:

$ java -jar target/micro-0.0.1-SNAPSHOT.jar --thin.main=com.example.mini.MiniApplication
...
May 23, 2018 10:05:41 AM reactor.util.Loggers$Slf4JLogger info
INFO: Started HttpServer on /127.0.0.1:8080

The main class could be one of

Main	Description
com.example.demo.DemoApplication	(The default). Spring Boot with Webflux and full autoconfiguration
com.example.boot.BootApplication	Spring Boot with Webflux and RouterFunction but no autoconfiguration
com.example.func.BuncApplication	Spring Boot with Webflux and RouterFunction using manual functional bean registration
com.example.mini.MiniApplication	Raw Spring, no autoconfiguration, but using @Configuration and RouterFunction
com.example.micro.MicroApplication	Raw Spring with no @Configuration

The thin.profile could be empty (the default) for just spring-boot-starter-webflux dependencies, or you can try jack for a more "normal" set of dependencies, e.g. with hibernate-validator, jackson, and logback. Other choices add more dependencies (e.g. actr for spring-boot-starter-actuator). You will need the "jack" profile to use actuators, so --thin.profile=actr,jack.

The apps are already systematically benchmarked here with regular JVMs: https://github.com/dsyer/spring-boot-startup-bench/blob/master/flux/README.adoc. The point of this project is just to extract them out of the JMH benchmarks, and make them easily executable as standalone apps. In the benchmarks, the "jack" profile is the default, and "jlog" is the faster reduced set of dependencies.

Benchmarks

class        method  sample  beans   classes  heap    memory  median  mean  range
MainBenchmark  main  empt  24.000   3230.000  5.103  38.769  0.546  0.555  0.018
MainBenchmark  main  jlog  80.000   3598.000  6.141  43.006  0.667  0.679  0.019
MainBenchmark  main  demo  93.000   4365.000  8.024  49.564  0.766  0.773  0.011
MainBenchmark  main  actr  174.000  5172.000  8.538  54.216  0.902  0.911  0.020
MainBenchmark  main  jdbc  131.000  5261.000  9.174  55.252  0.883  0.902  0.031
MainBenchmark  main  actj  214.000  5510.000  9.007  56.571  0.995  1.021  0.065

class         method  sample  beans  classes  heap  memory  median  mean  range
MiniBenchmark  boot   jlog  28.000  3336.000  7.082  41.949  0.588  0.597  0.014
MiniBenchmark  boot   demo  28.000  4012.000  6.508  45.566  0.703  0.710  0.011
MiniBenchmark  first  jlog  2.000   2176.000  6.556  38.574  0.416  0.418  0.004
MiniBenchmark  first  demo  2.000   2913.000  5.647  42.091  0.515  0.523  0.008
MiniBenchmark  micro  jlog  2.000   2176.000  4.608  32.886  0.336  0.345  0.013
MiniBenchmark  micro  demo  2.000   2913.000  7.318  40.454  0.438  0.451  0.016
MiniBenchmark  mini   jlog  27.000  3059.000  5.487  38.953  0.534  0.545  0.018
MiniBenchmark  mini   demo  27.000  3732.000  5.969  43.726  0.631  0.636  0.007

Building a Native Image

All the apps are compilable to a native binary image using the Graal tools once you have Andy’s Spring Boot Graal Feature library - just clone it and mvn install it.

Download GraalVM and install it (add the bin dir to you path and set the JAVA_HOME to point to GraalVM). You can also use sdkman to download it. You will need GraalVM 19.0.

Compute the classpath using the graal profile so that we can work around some limitations of the Graal Features library:

$ CP=`java -jar target/micro-0.0.1-SNAPSHOT.jar --thin.classpath --thin.profile=graal`

Then build an image:

$ native-image -Dio.netty.noUnsafe=true --no-server -H:Name=target/micro -H:+ReportExceptionStackTraces --no-fallback --allow-incomplete-classpath --report-unsupported-elements-at-runtime -cp target/classes:$CP:${HOME}/.m2/repository/org/springframework/spring-boot-graal-feature/0.5.0.BUILD-SNAPSHOT/spring-boot-graal-feature-0.5.0.BUILD-SNAPSHOT.jar com.example.micro.MicroApplication

Then run it:

$ ./target/micro
Started HttpServer: 2ms

Excellent!

You can do the same with all the applications in this project, including DemoApplication (full Spring Boot):

$ native-image -Dio.netty.noUnsafe=true --no-server -H:Name=target/demo -H:+ReportExceptionStackTraces --no-fallback --allow-incomplete-classpath --report-unsupported-elements-at-runtime -cp target/classes:$CP:${HOME}/.m2/repository/org/springframework/spring-boot-graal-feature/0.5.0.BUILD-SNAPSHOT/spring-boot-graal-feature-0.5.0.BUILD-SNAPSHOT.jar com.example.demo.DemoApplication
$ ./target/demo

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::

Aug 07, 2018 11:25:13 AM org.springframework.boot.StartupInfoLogger logStarting
INFO: Starting application on tower with PID 11253 (started by dsyer in /home/dsyer/dev/demo/workspace/micro)
Aug 07, 2018 11:25:13 AM org.springframework.boot.SpringApplication logStartupProfileInfo
INFO: No active profile set, falling back to default profiles: default
Aug 07, 2018 11:25:13 AM org.springframework.boot.web.embedded.netty.NettyWebServer start
INFO: Netty started on port(s): 8080
Aug 07, 2018 11:25:13 AM org.springframework.boot.StartupInfoLogger logStarted
INFO: Started application in 0.036 seconds (JVM running for 0.04)
Benchmark app started
Started HttpServer: 40ms

Note that whenever @Configuration is used, including in meta annotations like @SpringBootApplication, it must have the proxyBeanMethods = false flag set. CGLib is not friendly with GraalVM native images.