Update SparkJava samples

Signed-off-by: Guillaume Lours <guillaume.lours@docker.com>

sparkjava/sparkjava/Dockerfile

@@ -1,10 +1,14 @@
-FROM maven:3.5-jdk-8-alpine AS build
-COPY pom.xml .
-RUN mvn --batch-mode dependency:resolve
-COPY src/ src
+FROM maven:3.6.3-jdk-11 AS build
+WORKDIR /workdir/server
+COPY pom.xml /workdir/server/pom.xml
+RUN mvn dependency:go-offline
+
+COPY src /workdir/server/src
+
 RUN mvn --batch-mode clean compile assembly:single
 
-FROM openjdk:8-jre-alpine3.7
+FROM openjdk:11-jre-slim
+ARG DEPENDENCY=/workdir/server/target
 EXPOSE 8080
-COPY --from=build target/app.jar /app.jar
+COPY --from=build ${DEPENDENCY}/app.jar /app.jar
 CMD java -jar /app.jar

sparkjava/sparkjava/pom.xml

@@ -40,7 +40,7 @@
         <dependency>
             <groupId>com.sparkjava</groupId>
             <artifactId>spark-core</artifactId>
-            <version>2.5</version>
+            <version>2.8.0</version>
         </dependency>
 
     </dependencies>

sparkjava/sparkjava/src/main/java/App.java

@@ -4,6 +4,6 @@ public class App {
     public static void main(String[] args) {
         port(8080);
 
-        get("/", (req, res) -> "Hello world");
+        get("/", (req, res) -> "Hello from Docker!");
     }
 }