Implemented Registry pattern (#1543)

* #1310 Implemented registry pattern

* fixed parent pom version

* added empty line in registry.urm.puml

Co-authored-by: Subhrodip Mohanta <subhrodipmohanta@gmail.com>

registry/src/main/java/com/iluwatar/registry/App.java

@@ -0,0 +1,27 @@
+package com.iluwatar.registry;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class App {
+
+  private static final Logger LOGGER = LoggerFactory.getLogger(App.class);
+
+  /**
+   * Program entry point.
+   *
+   * @param args command line args
+   */
+  public static void main(String[] args) {
+    CustomerRegistry customerRegistry = CustomerRegistry.getInstance();
+    var john = new Customer("1", "John");
+    customerRegistry.addCustomer(john);
+
+    var julia = new Customer("2", "Julia");
+    customerRegistry.addCustomer(julia);
+
+    LOGGER.info("John {}", customerRegistry.getCustomer("1"));
+    LOGGER.info("Julia {}", customerRegistry.getCustomer("2"));
+  }
+
+}

registry/src/main/java/com/iluwatar/registry/Customer.java

@@ -0,0 +1,28 @@
+package com.iluwatar.registry;
+
+public class Customer {
+
+  private final String id;
+  private final String name;
+
+  public Customer(String id, String name) {
+    this.id = id;
+    this.name = name;
+  }
+
+  public String getId() {
+    return id;
+  }
+
+  public String getName() {
+    return name;
+  }
+
+  @Override
+  public String toString() {
+    return "Customer{"
+        + "id='" + id + '\''
+        + ", name='" + name + '\''
+        + '}';
+  }
+}

registry/src/main/java/com/iluwatar/registry/CustomerRegistry.java

@@ -0,0 +1,28 @@
+package com.iluwatar.registry;
+
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+public final class CustomerRegistry {
+
+  private static final CustomerRegistry instance = new CustomerRegistry();
+
+  public static CustomerRegistry getInstance() {
+    return instance;
+  }
+
+  private final Map<String, Customer> customerMap;
+
+  private CustomerRegistry() {
+    customerMap = new ConcurrentHashMap<>();
+  }
+
+  public Customer addCustomer(Customer customer) {
+    return customerMap.put(customer.getId(), customer);
+  }
+
+  public Customer getCustomer(String id) {
+    return customerMap.get(id);
+  }
+
+}

registry/src/test/java/com/iluwatar/registry/CustomerRegistryTest.java

@@ -0,0 +1,44 @@
+package com.iluwatar.registry;
+
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
+
+public class CustomerRegistryTest {
+
+  private static CustomerRegistry customerRegistry;
+
+  @BeforeAll
+  public static void setUp() {
+    customerRegistry = CustomerRegistry.getInstance();
+  }
+
+  @Test
+  public void shouldBeAbleToAddAndQueryCustomerObjectFromRegistry() {
+    Customer john = new Customer("1", "john");
+    Customer julia = new Customer("2", "julia");
+
+    customerRegistry.addCustomer(john);
+    customerRegistry.addCustomer(julia);
+
+    Customer customerWithId1 = customerRegistry.getCustomer("1");
+    assertNotNull(customerWithId1);
+    assertEquals("1", customerWithId1.getId());
+    assertEquals("john", customerWithId1.getName());
+
+    Customer customerWithId2 = customerRegistry.getCustomer("2");
+    assertNotNull(customerWithId2);
+    assertEquals("2", customerWithId2.getId());
+    assertEquals("julia", customerWithId2.getName());
+  }
+
+  @Test
+  public void shouldReturnNullWhenQueriedCustomerIsNotInRegistry() {
+    Customer customerWithId5 = customerRegistry.getCustomer("5");
+    assertNull(customerWithId5);
+  }
+
+}