add sparkjava-mysql application sample

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

samples/sparkjava-mysql/backend/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-mysql/backend/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>
+
+        <dependency>
+            <groupId>mysql</groupId>
+            <artifactId>mysql-connector-java</artifactId>
+            <version>8.0.11</version>
+        </dependency>
+        <dependency>
+            <groupId>com.google.code.gson</groupId>
+            <artifactId>gson</artifactId>
+            <version>2.8.4</version>
+        </dependency>
+
+    </dependencies>
+
+</project>

samples/sparkjava-mysql/backend/src/main/java/App.java

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+import com.google.gson.Gson;
+import com.mysql.cj.jdbc.exceptions.CommunicationsException;
+
+import static spark.Spark.*;
+
+import java.nio.file.Files;
+import java.nio.file.Paths;
+import java.sql.*;
+import java.util.ArrayList;
+import java.util.List;
+
+public class App {
+
+    public static void main(String[] args) throws Exception {
+        Class.forName("com.mysql.cj.jdbc.Driver");
+
+        prepare();
+
+        port(8080);
+
+        get("/", (req, res) -> new Gson().toJson(titles()));
+    }
+
+    private static List<String> titles() {
+        try (Connection conn = connect()) {
+            List<String> titles = new ArrayList<>();
+            try (Statement stmt = conn.createStatement()) {
+                try (ResultSet rs = stmt.executeQuery("SELECT title FROM blog")) {
+                    while (rs.next()) {
+                        titles.add(rs.getString("title"));
+                    }
+                }
+            }
+            return titles;
+        } catch (Exception ex) {
+            return new ArrayList<>();
+        }
+    }
+
+    public static void prepare() throws Exception {
+        try (Connection conn = connect()) {
+            recreateTable(conn);
+            insertData(conn);
+        }
+    }
+
+    private static void insertData(Connection conn) throws SQLException {
+        for (int i = 0; i < 5; i++) {
+            try (PreparedStatement stmt = conn.prepareStatement("INSERT INTO blog (title) VALUES (?);")) {
+                stmt.setString(1, "Blog post #" + i);
+                stmt.execute();
+            }
+        }
+    }
+
+    private static void recreateTable(Connection conn) throws SQLException {
+        try (Statement stmt = conn.createStatement()) {
+            stmt.execute("DROP TABLE IF EXISTS blog");
+            stmt.execute("CREATE TABLE IF NOT EXISTS blog (id int NOT NULL AUTO_INCREMENT, title varchar(255), PRIMARY KEY (id))");
+        }
+    }
+
+
+    private static Connection connect() throws Exception {
+        for (int i = 0; i < 60; i++) {
+            try {
+                return DriverManager.getConnection("jdbc:mysql://db/example?useSSL=false", "root", Files.lines(Paths.get("/run/secrets/db-password")).findFirst().get());
+            } catch (CommunicationsException ex) {
+                Thread.sleep(1000L);
+                continue;
+            } catch (Exception ex) {
+                throw ex;
+            }
+        }
+        throw new RuntimeException("Unable to connect to MySQL");
+    }
+}
+

samples/sparkjava-mysql/db/password.txt

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+db-vp2lf

samples/sparkjava-mysql/docker-compose.yaml

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+version: "3.7"
+services:
+  backend:
+    build: backend
+    image: docker.io/docker/back
+    ports:
+    - 80:8080
+    secrets:
+    - db-password
+  db:
+    environment:
+      MYSQL_DATABASE: example
+      MYSQL_ROOT_PASSWORD_FILE: /run/secrets/db-password
+    image: mysql:5.7
+    restart: always
+    secrets:
+    - db-password
+    volumes:
+    - db-data:/var/lib/mysql
+volumes:
+  db-data: {}
+secrets:
+  db-password:
+    file: db/password.txt