add sparkjava application sample

Signed-off-by: Anca Iordache <anca.iordache@docker.com>

samples/sparkjava/docker-compose.yaml

@@ -0,0 +1,6 @@
+version: "3.7"
+services:
+  sparkjava:
+    build: sparkjava
+    ports:
+    - 80:8080

samples/sparkjava/sparkjava/Dockerfile

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+FROM maven:3.5-jdk-8-alpine AS build
+COPY pom.xml .
+RUN mvn --batch-mode dependency:resolve
+COPY src/ src
+RUN mvn --batch-mode clean compile assembly:single
+
+FROM openjdk:8-jre-alpine3.7
+EXPOSE 8080
+COPY --from=build target/app.jar /app.jar
+CMD java -jar /app.jar

samples/sparkjava/sparkjava/pom.xml

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+<?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">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>com.company</groupId>
+    <artifactId>project</artifactId>
+    <version>1.0-SNAPSHOT</version>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <configuration>
+                    <source>8</source>
+                    <target>8</target>
+                </configuration>
+            </plugin>
+            <plugin>
+                <artifactId>maven-assembly-plugin</artifactId>
+                <configuration>
+                    <archive>
+                        <manifest>
+                            <mainClass>App</mainClass>
+                        </manifest>
+                    </archive>
+                    <descriptorRefs>
+                        <descriptorRef>jar-with-dependencies</descriptorRef>
+                    </descriptorRefs>
+                    <finalName>app</finalName>
+                    <appendAssemblyId>false</appendAssemblyId>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <dependencies>
+        <dependency>
+            <groupId>com.sparkjava</groupId>
+            <artifactId>spark-core</artifactId>
+            <version>2.5</version>
+        </dependency>
+
+    </dependencies>
+
+</project>

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

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+import static spark.Spark.*;
+
+public class App {
+    public static void main(String[] args) {
+        port(8080);
+
+        get("/", (req, res) -> "Hello world");
+    }
+}