apply google java format

app/src/main/java/org/astraea/App.java

@@ -4,11 +4,11 @@
 package org.astraea;
 
 public class App {
-    public String getGreeting() {
-        return "Hello World!";
-    }
+  public String getGreeting() {
+    return "Hello World!";
+  }
 
-    public static void main(String[] args) {
-        System.out.println(new App().getGreeting());
-    }
+  public static void main(String[] args) {
+    System.out.println(new App().getGreeting());
+  }
 }

app/src/test/java/org/astraea/AppTest.java

@@ -3,12 +3,14 @@
  */
 package org.astraea;
 
-import org.junit.jupiter.api.Test;
 import static org.junit.jupiter.api.Assertions.*;
 
+import org.junit.jupiter.api.Test;
+
 class AppTest {
-    @Test void appHasAGreeting() {
-        App classUnderTest = new App();
-        assertNotNull(classUnderTest.getGreeting(), "app should have a greeting");
-    }
+  @Test
+  void appHasAGreeting() {
+    App classUnderTest = new App();
+    assertNotNull(classUnderTest.getGreeting(), "app should have a greeting");
+  }
 }

build.gradle

@@ -0,0 +1,20 @@
+/*
+ * This file was generated by the Gradle 'init' task.
+ *
+ * This generated file contains a sample Java application project to get you started.
+ * For more details take a look at the 'Building Java & JVM projects' chapter in the Gradle
+ * User Manual available at https://docs.gradle.org/7.2/userguide/building_java_projects.html
+ */
+
+plugins {
+    id "com.diffplug.spotless" version "5.14.3"
+}
+
+spotless {
+    java {
+        importOrder()
+        removeUnusedImports()
+        target '**/java/**/*.java'
+        googleJavaFormat()
+    }
+}