Add "singleton container" example

examples/singleton-container/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">
+    <parent>
+        <artifactId>testcontainers-java-examples</artifactId>
+        <groupId>org.testcontainers.examples</groupId>
+        <version>NOVERSION</version>
+    </parent>
+    <modelVersion>4.0.0</modelVersion>
+
+    <artifactId>singleton-container</artifactId>
+
+	<dependencies>
+		<dependency>
+			<groupId>redis.clients</groupId>
+			<artifactId>jedis</artifactId>
+			<version>3.0.1</version>
+		</dependency>
+		<dependency>
+			<groupId>com.google.code.gson</groupId>
+			<artifactId>gson</artifactId>
+			<version>2.8.5</version>
+		</dependency>
+		<dependency>
+			<groupId>com.google.guava</groupId>
+			<artifactId>guava</artifactId>
+			<version>23.0</version>
+		</dependency>
+		<dependency>
+			<groupId>org.slf4j</groupId>
+			<artifactId>slf4j-api</artifactId>
+			<version>1.7.25</version>
+			<scope>provided</scope>
+		</dependency>
+		<dependency>
+			<groupId>ch.qos.logback</groupId>
+			<artifactId>logback-classic</artifactId>
+			<version>1.2.3</version>
+			<scope>test</scope>
+		</dependency>
+	</dependencies>
+</project>

examples/singleton-container/src/main/java/com/example/cache/Cache.java

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+package com.example.cache;
+
+import java.util.Optional;
+
+public interface Cache {
+
+	void put(String key, Object value);
+
+	<T> Optional<T> get(String key, Class<T> expectedClass);
+}

examples/singleton-container/src/main/java/com/example/cache/RedisBackedCache.java

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+package com.example.cache;
+
+import com.google.gson.Gson;
+import redis.clients.jedis.Jedis;
+
+import java.util.Optional;
+
+public class RedisBackedCache implements Cache {
+
+	private final Jedis jedis;
+	private final String cacheName;
+	private final Gson gson;
+
+	public RedisBackedCache(Jedis jedis, String cacheName) {
+		this.jedis = jedis;
+		this.cacheName = cacheName;
+		this.gson = new Gson();
+	}
+
+	public void put(String key, Object value) {
+		String jsonValue = gson.toJson(value);
+		this.jedis.hset(this.cacheName, key, jsonValue);
+	}
+
+	public <T> Optional<T> get(String key, Class<T> expectedClass) {
+		String foundJson = this.jedis.hget(this.cacheName, key);
+
+		if (foundJson == null) {
+			return Optional.empty();
+		}
+
+		return Optional.of(gson.fromJson(foundJson, expectedClass));
+	}
+}

examples/singleton-container/src/test/java/com/example/AbstractIntegrationTest.java

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+package com.example;
+
+import org.testcontainers.containers.GenericContainer;
+
+public abstract class AbstractIntegrationTest {
+
+	public static final GenericContainer redis = new GenericContainer("redis:3.0.6")
+                                            .withExposedPorts(6379);
+
+	static {
+		redis.start();
+	}
+}

examples/singleton-container/src/test/java/com/example/BarConcreteTestClass.java

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+package com.example;
+
+import com.example.cache.Cache;
+import com.example.cache.RedisBackedCache;
+import org.junit.Before;
+import org.junit.Test;
+import redis.clients.jedis.Jedis;
+
+import java.util.Optional;
+
+import static org.rnorth.visibleassertions.VisibleAssertions.assertEquals;
+import static org.rnorth.visibleassertions.VisibleAssertions.assertTrue;
+
+public class BarConcreteTestClass extends AbstractIntegrationTest {
+
+	private Cache cache;
+
+	@Before
+	public void setUp() {
+		Jedis jedis = new Jedis(redis.getContainerIpAddress(), redis.getMappedPort(6379));
+
+		cache = new RedisBackedCache(jedis, "bar");
+	}
+
+	@Test
+	public void testInsertValue() {
+		cache.put("bar", "BAR");
+		Optional<String> foundObject = cache.get("bar", String.class);
+
+		assertTrue("When inserting an object into the cache, it can be retrieved", foundObject.isPresent());
+		assertEquals("When accessing the value of a retrieved object, the value must be the same", "BAR", foundObject.get());
+	}
+
+}

examples/singleton-container/src/test/java/com/example/FooConcreteTestClass.java

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+package com.example;
+
+import com.example.cache.Cache;
+import com.example.cache.RedisBackedCache;
+import org.junit.Before;
+import org.junit.Test;
+import redis.clients.jedis.Jedis;
+
+import java.util.Optional;
+
+import static org.rnorth.visibleassertions.VisibleAssertions.assertEquals;
+import static org.rnorth.visibleassertions.VisibleAssertions.assertTrue;
+
+public class FooConcreteTestClass extends AbstractIntegrationTest {
+
+    private Cache cache;
+
+    @Before
+    public void setUp() throws Exception {
+        Jedis jedis = new Jedis(redis.getContainerIpAddress(), redis.getMappedPort(6379));
+
+        cache = new RedisBackedCache(jedis, "foo");
+    }
+
+	@Test
+	public void testInsertValue() {
+		cache.put("foo", "FOO");
+		Optional<String> foundObject = cache.get("foo", String.class);
+
+		assertTrue("When inserting an object into the cache, it can be retrieved", foundObject.isPresent());
+		assertEquals("When accessing the value of a retrieved object, the value must be the same", "FOO", foundObject.get());
+	}
+}