Add JMH benchmark infrastructure

Prior to this commit, the Spring Framework test suite would rely only on
"Performance" tests associated with a specific CI build. As outlined in
gh-24830, the way they're built and executed is not working well
anymore.

This commit introduces a new JMH benchmark infrastructure in the build.
The goal here is not to run those benchmarks as part of a CI build, but
rather provide a proper infrastructure for writing and locally running
micro-benchmarks when working on specific optimizations.

This commit adds and configures a Gradle JMH plugin to allow for JMH
benchmark classes in Spring Framework modules (in `src/jmh/java` of each
`spring-*` module). It's also relaxing the checkstyle rules for JMH
classes, especially around Javadoc rules: this code is not meant to
have Javadocs.

Finally, this commit links to a new Wiki page on the project GitHub
repository documenting the infrastructure and helping contributors to
run and design benchmarks.

See gh-24830

README.md

@@ -17,6 +17,10 @@ For access to artifacts or a distribution zip, see the [Spring Framework Artifac
 The Spring Framework maintains reference documentation ([published](https://docs.spring.io/spring-framework/docs/current/spring-framework-reference/) and [source](src/docs/asciidoc)), Github [wiki pages](https://github.com/spring-projects/spring-framework/wiki), and an
 [API reference](https://docs.spring.io/spring-framework/docs/current/javadoc-api/). There are also [guides and tutorials](https://spring.io/guides) across Spring projects.
 
+## Micro-Benchmarks
+
+See the [Micro-Benchmarks](https://github.com/spring-projects/spring-framework/wiki/Micro-Benchmarks) Wiki page.
+
 ## Build from Source
 
 See the [Build from Source](https://github.com/spring-projects/spring-framework/wiki/Build-from-Source) Wiki page and the [CONTRIBUTING.md](CONTRIBUTING.md) file.

build.gradle

@@ -7,6 +7,7 @@ plugins {
 	id 'de.undercouch.download' version '4.0.4'
 	id "io.freefair.aspectj" version '5.0.0' apply false
 	id "com.github.ben-manes.versions" version '0.28.0'
+	id "me.champeau.gradle.jmh" version "0.5.0" apply false
 }
 
 ext {

gradle/spring-module.gradle

@@ -1,7 +1,17 @@
 apply plugin: 'org.springframework.build.compile'
 apply plugin: 'org.springframework.build.optional-dependencies'
+apply plugin: 'me.champeau.gradle.jmh'
 apply from: "$rootDir/gradle/publications.gradle"
 
+dependencies {
+	jmh 'org.openjdk.jmh:jmh-core:1.23'
+	jmh 'org.openjdk.jmh:jmh-generator-annprocess:1.23'
+	jmh 'net.sf.jopt-simple:jopt-simple:4.6'
+}
+jmh {
+	duplicateClassesStrategy = DuplicatesStrategy.EXCLUDE
+}
+
 jar {
 	manifest.attributes["Implementation-Title"] = project.name
 	manifest.attributes["Implementation-Version"] = project.version

src/checkstyle/checkstyle-suppressions.xml

@@ -7,6 +7,9 @@
 	<suppress files="[\\/]src[\\/](test|testFixtures)[\\/]java[\\/]org[\\/]springframework[\\/].+(Tests|Suite)" checks="IllegalImport" id="bannedJUnitJupiterImports" />
 	<suppress files="[\\/]src[\\/](test|testFixtures)[\\/]java[\\/]" checks="SpringJUnit5" message="should not be public" />
 
+	<!-- JMH benchmarks -->
+	<suppress files="[\\/]src[\\/]jmh[\\/]java[\\/]org[\\/]springframework[\\/]" checks="JavadocVariable|JavadocStyle" />
+
 	<!-- spring-beans -->
 	<suppress files="TypeMismatchException" checks="MutableException"/>
 	<suppress files="BeanCreationException" checks="MutableException"/>