Turned on checkstyle

pom.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<project xmlns="http://maven.apache.org/POM/4.0.0"
-	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+		 xmlns="http://maven.apache.org/POM/4.0.0"
+		 xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
 	<modelVersion>4.0.0</modelVersion>
 
 	<artifactId>spring-cloud-function-parent</artifactId>
@@ -13,7 +13,7 @@
 		<groupId>org.springframework.cloud</groupId>
 		<artifactId>spring-cloud-build</artifactId>
 		<version>2.1.3.BUILD-SNAPSHOT</version>
-		<relativePath />
+		<relativePath/>
 	</parent>
 
 	<properties>
@@ -23,6 +23,9 @@
 		<spring-cloud-task.version>2.1.0.RELEASE</spring-cloud-task.version>
 		<wrapper.version>1.0.15.RELEASE</wrapper.version>
 		<docs.main>spring-cloud-function</docs.main>
+		<maven-checkstyle-plugin.failsOnError>true</maven-checkstyle-plugin.failsOnError>
+		<maven-checkstyle-plugin.failsOnViolation>true
+		</maven-checkstyle-plugin.failsOnViolation>
 	</properties>
 
 	<dependencyManagement>
@@ -91,6 +94,14 @@
 					</execution>
 				</executions>
 			</plugin>
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-checkstyle-plugin</artifactId>
+			</plugin>
+			<plugin>
+				<groupId>io.spring.javaformat</groupId>
+				<artifactId>spring-javaformat-maven-plugin</artifactId>
+			</plugin>
 		</plugins>
 		<pluginManagement>
 			<plugins>
@@ -99,7 +110,8 @@
 					<inherited>false</inherited>
 					<configuration>
 						<aggregate>true</aggregate>
-						<excludePackageNames>com.example,functions,example</excludePackageNames>
+						<excludePackageNames>com.example,functions,example
+						</excludePackageNames>
 					</configuration>
 					<executions>
 						<execution>
@@ -216,6 +228,15 @@
 		</pluginRepository>
 	</pluginRepositories>
 
+	<reporting>
+		<plugins>
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-checkstyle-plugin</artifactId>
+			</plugin>
+		</plugins>
+	</reporting>
+
 	<profiles>
 		<profile>
 			<id>java11+</id>