KAFKA-10787 Add import ordering checkstyle rule and configure an automatic formatter (#16097)

Reviewers: Chia-Ping Tsai <chia7712@gmail.com>

README.md

@@ -227,11 +227,16 @@ There are two code quality analysis tools that we regularly run, spotbugs and ch
 Checkstyle enforces a consistent coding style in Kafka.
 You can run checkstyle using:
 
-    ./gradlew checkstyleMain checkstyleTest
+    ./gradlew checkstyleMain checkstyleTest spotlessCheck
 
 The checkstyle warnings will be found in `reports/checkstyle/reports/main.html` and `reports/checkstyle/reports/test.html` files in the
 subproject build directories. They are also printed to the console. The build will fail if Checkstyle fails.
 
+#### Spotless ####
+The import order is a part of static check. please call `spotlessApply` to optimize the imports of Java codes before filing pull request :
+
+    ./gradlew spotlessApply
+
 #### Spotbugs ####
 Spotbugs uses static analysis to look for bugs in the code.
 You can run spotbugs using:

build.gradle

@@ -47,7 +47,9 @@ plugins {
   // Updating the shadow plugin version to 8.1.1 causes issue with signing and publishing the shadowed
   // artifacts - see https://github.com/johnrengelman/shadow/issues/901
   id 'com.github.johnrengelman.shadow' version '8.1.0' apply false
-  id 'com.diffplug.spotless' version '6.14.0' apply false // 6.14.1 and newer require Java 11 at compile time, so we can't upgrade until AK 4.0
+  //  the minimum required JRE of 6.14.0+ is 11
+  //  refer:https://github.com/diffplug/spotless/tree/main/plugin-gradle#requirements
+  id 'com.diffplug.spotless' version "6.13.0" apply false
 }
 
 ext {
@@ -198,6 +200,9 @@ def determineCommitId() {
   }
 }
 
+def spotlessApplyModules = ['']
+
+
 apply from: file('wrapper.gradle')
 
 if (repo != null) {
@@ -793,6 +798,16 @@ subprojects {
     skipProjects = [ ":jmh-benchmarks", ":trogdor" ]
     skipConfigurations = [ "zinc" ]
   }
+
+  if (project.name in spotlessApplyModules) {
+    apply plugin: 'com.diffplug.spotless'
+    spotless {
+      java {
+        importOrder('kafka', 'org.apache.kafka', 'com', 'net', 'org', 'java', 'javax', '', '\\#')
+        removeUnusedImports()
+      }
+    }
+  }
 }
 
 gradle.taskGraph.whenReady { taskGraph ->

checkstyle/checkstyle.xml

@@ -82,6 +82,8 @@
       <property name="file" value="${config_loc}/${importControlFile}"/>
     </module>
 
+    <!--   don't define any import order here! Import order check/format is addressed by spotless.-->
+
     <!-- whitespace -->
     <module name="GenericWhitespace"/>
     <module name="NoWhitespaceBefore"/>