[java][okhttp] Add spotless maven, gradle plugin (#10785)

* add spotless maven plugin

* add spotless gradle plug-in

* add spotless version

samples/client/petstore/java/okhttp-gson-dynamicOperations/build.gradle

@@ -1,6 +1,7 @@
 apply plugin: 'idea'
 apply plugin: 'eclipse'
 apply plugin: 'java'
+apply plugin: 'com.diffplug.spotless'
 
 group = 'org.openapitools'
 version = '1.0.0'
@@ -12,6 +13,7 @@ buildscript {
     dependencies {
         classpath 'com.android.tools.build:gradle:2.3.+'
         classpath 'com.github.dcendents:android-maven-gradle-plugin:1.5'
+        classpath 'com.diffplug.spotless:spotless-plugin-gradle:5.17.1'
     }
 }
 
@@ -123,3 +125,27 @@ dependencies {
 javadoc {
     options.tags = [ "http.response.details:a:Http Response Details" ]
 }
+
+// Use spotless plugin to automatically format code, remove unused import, etc
+// To apply changes directly to the file, run `gradlew spotlessApply`
+// Ref: https://github.com/diffplug/spotless/tree/main/plugin-gradle
+spotless {
+    format 'misc', {
+        // define the files (e.g. '*.gradle', '*.md') to apply `misc` to
+        target '.gitignore'
+
+        // define the steps to apply to those files
+        trimTrailingWhitespace()
+        indentWithSpaces() // Takes an integer argument if you don't like 4
+        endWithNewline()
+    }
+    java {
+        // don't need to set target, it is inferred from java
+
+        // apply a specific flavor of google-java-format
+        googleJavaFormat('1.8').aosp().reflowLongStrings()
+
+        removeUnusedImports()
+        importOrder()
+    }
+}

samples/client/petstore/java/okhttp-gson-dynamicOperations/pom.xml

@@ -179,6 +179,48 @@
                     </execution>
                 </executions>
             </plugin>
+            <!-- Use spotless plugin to automatically format code, remove unused import, etc
+                 To apply changes directly to the file, run `mvn spotless:apply`
+                 Ref: https://github.com/diffplug/spotless/tree/main/plugin-maven
+            -->
+            <plugin>
+              <groupId>com.diffplug.spotless</groupId>
+              <artifactId>spotless-maven-plugin</artifactId>
+              <version>${spotless.version}</version>
+              <configuration>
+                <formats>
+                  <!-- you can define as many formats as you want, each is independent -->
+                  <format>
+                    <!-- define the files to apply to -->
+                    <includes>
+                      <include>.gitignore</include>
+                    </includes>
+                    <!-- define the steps to apply to those files -->
+                    <trimTrailingWhitespace/>
+                    <endWithNewline/>
+                    <indent>
+                      <tabs>true</tabs>
+                      <spacesPerTab>4</spacesPerTab>
+                    </indent>
+                  </format>
+                </formats>
+                <!-- define a language-specific format -->
+                <java>
+                  <!-- no need to specify files, inferred automatically, but you can if you want -->
+
+                  <!-- apply a specific flavor of google-java-format and reflow long strings -->
+                  <googleJavaFormat>
+                    <version>1.8</version>
+                    <style>AOSP</style>
+                    <reflowLongStrings>true</reflowLongStrings>
+                  </googleJavaFormat>
+
+                  <removeUnusedImports/>
+                  <importOrder/>
+
+                </java>
+              </configuration>
+            </plugin>
         </plugins>
     </build>
 
@@ -297,5 +339,6 @@
         <jakarta-annotation-version>1.3.5</jakarta-annotation-version>
         <junit-version>4.13.2</junit-version>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <spotless.version>2.17.3</spotless.version>
     </properties>
 </project>