Incorporated review changes - 1) Created sql file for central schema 2)

Changed getById return type to Optional

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

@@ -73,15 +73,14 @@ public class App {
   private static void deleteSchema(DataSource dataSource) throws SQLException {
     try (Connection connection = dataSource.getConnection();
         Statement statement = connection.createStatement()) {
-      statement.execute("DROP TABLE CUSTOMERS");
+      statement.execute(CustomerSchemaSql.DELETE_SCHEMA_SQL);
     }
   }
 
   private static void createSchema(DataSource dataSource) throws SQLException {
     try (Connection connection = dataSource.getConnection();
         Statement statement = connection.createStatement()) {
-      statement.execute("CREATE TABLE CUSTOMERS (ID NUMBER, FNAME VARCHAR(100), "
+      statement.execute(CustomerSchemaSql.CREATE_SCHEMA_SQL);
-          + "LNAME VARCHAR(100))");
     }
   }
 

dao/src/main/java/com/iluwatar/dao/CustomerDao.java

@@ -23,6 +23,7 @@
 
 package com.iluwatar.dao;
 
+import java.util.Optional;
 import java.util.stream.Stream;
 
 /**
@@ -51,10 +52,11 @@ public interface CustomerDao {
   
   /**
    * @param id unique identifier of the customer.
-   * @return customer with unique identifier <code>id</code> if found, null otherwise.
+   * @return an optional with customer if a customer with unique identifier <code>id</code>
+   *     exists, empty optional otherwise.
    * @throws Exception if any error occurs.
    */
-  Customer getById(int id) throws Exception;
+  Optional<Customer> getById(int id) throws Exception;
 
   /**
    * @param customer the customer to be added.

dao/src/main/java/com/iluwatar/dao/CustomerSchemaSql.java

@@ -0,0 +1,9 @@
+package com.iluwatar.dao;
+
+public interface CustomerSchemaSql {
+
+  String CREATE_SCHEMA_SQL = "CREATE TABLE CUSTOMERS (ID NUMBER, FNAME VARCHAR(100), " 
+      + "LNAME VARCHAR(100))";
+  
+  String DELETE_SCHEMA_SQL = "DROP TABLE CUSTOMERS";
+}

dao/src/main/java/com/iluwatar/dao/DbCustomerDao.java

@@ -27,6 +27,7 @@ import java.sql.Connection;
 import java.sql.PreparedStatement;
 import java.sql.ResultSet;
 import java.sql.SQLException;
+import java.util.Optional;
 import java.util.Spliterator;
 import java.util.Spliterators;
 import java.util.function.Consumer;
@@ -109,7 +110,7 @@ public class DbCustomerDao implements CustomerDao {
    * {@inheritDoc}
    */
   @Override
-  public Customer getById(int id) throws Exception {
+  public Optional<Customer> getById(int id) throws Exception {
     try (Connection connection = getConnection();
         PreparedStatement statement = 
             connection.prepareStatement("SELECT * FROM CUSTOMERS WHERE ID = ?")) {
@@ -117,9 +118,9 @@ public class DbCustomerDao implements CustomerDao {
       statement.setInt(1, id);
       ResultSet resultSet = statement.executeQuery();
       if (resultSet.next()) {
-        return createCustomer(resultSet);
+        return Optional.of(createCustomer(resultSet));
       } else {
-        return null;
+        return Optional.empty();
       }
     } catch (SQLException ex) {
       throw new Exception(ex.getMessage(), ex);
@@ -131,7 +132,7 @@ public class DbCustomerDao implements CustomerDao {
    */
   @Override
   public boolean add(Customer customer) throws Exception {
-    if (getById(customer.getId()) != null) {
+    if (getById(customer.getId()).isPresent()) {
       return false;
     }
 

dao/src/main/java/com/iluwatar/dao/InMemoryCustomerDao.java

@@ -25,6 +25,7 @@ package com.iluwatar.dao;
 
 import java.util.HashMap;
 import java.util.Map;
+import java.util.Optional;
 import java.util.stream.Stream;
 
 /**
@@ -46,13 +47,13 @@ public class InMemoryCustomerDao implements CustomerDao {
   }
 
   @Override
-  public Customer getById(final int id) {
+  public Optional<Customer> getById(final int id) {
-    return idToCustomer.get(id);
+    return Optional.ofNullable(idToCustomer.get(id));
   }
 
   @Override
   public boolean add(final Customer customer) {
-    if (getById(customer.getId()) != null) {
+    if (getById(customer.getId()).isPresent()) {
       return false;
     }
     

dao/src/test/java/com/iluwatar/dao/DbCustomerDaoTest.java

@@ -46,8 +46,7 @@ public class DbCustomerDaoTest {
   public void createSchema() throws SQLException {
     try (Connection connection = DriverManager.getConnection(DB_URL);
         Statement statement = connection.createStatement()) {
-      statement.execute("CREATE TABLE CUSTOMERS (ID NUMBER, FNAME VARCHAR(100),"
+      statement.execute(CustomerSchemaSql.CREATE_SCHEMA_SQL);
-          + " LNAME VARCHAR(100))");
     }
   }
 
@@ -85,7 +84,7 @@ public class DbCustomerDaoTest {
         assertTrue(result);
 
         assertCustomerCountIs(2);
-        assertEquals(nonExistingCustomer, dao.getById(nonExistingCustomer.getId()));
+        assertEquals(nonExistingCustomer, dao.getById(nonExistingCustomer.getId()).get());
       }
 
       @Test
@@ -106,12 +105,12 @@ public class DbCustomerDaoTest {
         boolean result = dao.update(customer);
 
         assertFalse(result);
-        assertNull(dao.getById(nonExistingId));
+        assertFalse(dao.getById(nonExistingId).isPresent());
       }
 
       @Test
-      public void retrieveShouldReturnNull() throws Exception {
+      public void retrieveShouldReturnNoCustomer() throws Exception {
-        assertNull(dao.getById(getNonExistingCustomerId()));
+        assertFalse(dao.getById(getNonExistingCustomerId()).isPresent());
       }
     }
 
@@ -130,7 +129,7 @@ public class DbCustomerDaoTest {
 
         assertFalse(result);
         assertCustomerCountIs(1);
-        assertEquals(existingCustomer, dao.getById(existingCustomer.getId()));
+        assertEquals(existingCustomer, dao.getById(existingCustomer.getId()).get());
       }
 
       @Test
@@ -139,7 +138,7 @@ public class DbCustomerDaoTest {
 
         assertTrue(result);
         assertCustomerCountIs(0);
-        assertNull(dao.getById(existingCustomer.getId()));
+        assertFalse(dao.getById(existingCustomer.getId()).isPresent());
       }
 
       @Test
@@ -151,7 +150,7 @@ public class DbCustomerDaoTest {
 
         assertTrue(result);
 
-        final Customer cust = dao.getById(existingCustomer.getId());
+        final Customer cust = dao.getById(existingCustomer.getId()).get();
         assertEquals(newFirstname, cust.getFirstName());
         assertEquals(newLastname, cust.getLastName());
       }
@@ -207,12 +206,12 @@ public class DbCustomerDaoTest {
     }
     
     @Test
-    public void retrievingACustomerByIdReturnsNull() throws Exception {
+    public void retrievingACustomerByIdFailsWithExceptionAsFeedbackToClient() throws Exception {
       dao.getById(existingCustomer.getId());
     }
     
     @Test
-    public void retrievingAllCustomersReturnsAnEmptyStream() throws Exception {
+    public void retrievingAllCustomersFailsWithExceptionAsFeedbackToClient() throws Exception {
       dao.getAll();
     }
 
@@ -226,7 +225,7 @@ public class DbCustomerDaoTest {
   public void deleteSchema() throws SQLException {
     try (Connection connection = DriverManager.getConnection(DB_URL);
         Statement statement = connection.createStatement()) {
-      statement.execute("DROP TABLE CUSTOMERS");
+      statement.execute(CustomerSchemaSql.DELETE_SCHEMA_SQL);
     }
   }
 

dao/src/test/java/com/iluwatar/dao/InMemoryCustomerDaoTest.java

@@ -29,6 +29,7 @@ import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assume.assumeTrue;
 
+import java.util.Optional;
 import java.util.stream.Stream;
 
 import org.junit.Before;
@@ -49,7 +50,7 @@ public class InMemoryCustomerDaoTest {
   @Before
   public void setUp() {
     dao = new InMemoryCustomerDao();
-    dao.add(CUSTOMER);
+    assertTrue(dao.add(CUSTOMER));
   }
 
   /**
@@ -69,7 +70,7 @@ public class InMemoryCustomerDaoTest {
       assertTrue(result);
 
       assertCustomerCountIs(2);
-      assertEquals(nonExistingCustomer, dao.getById(nonExistingCustomer.getId()));
+      assertEquals(nonExistingCustomer, dao.getById(nonExistingCustomer.getId()).get());
     }
 
     @Test
@@ -90,12 +91,12 @@ public class InMemoryCustomerDaoTest {
       boolean result = dao.update(customer);
 
       assertFalse(result);
-      assertNull(dao.getById(nonExistingId));
+      assertFalse(dao.getById(nonExistingId).isPresent());
     }
 
     @Test
-    public void retrieveShouldReturnNull() throws Exception {
+    public void retrieveShouldReturnNoCustomer() throws Exception {
-      assertNull(dao.getById(getNonExistingCustomerId()));
+      assertFalse(dao.getById(getNonExistingCustomerId()).isPresent());
     }
   }
 
@@ -111,7 +112,7 @@ public class InMemoryCustomerDaoTest {
 
       assertFalse(result);
       assertCustomerCountIs(1);
-      assertEquals(CUSTOMER, dao.getById(CUSTOMER.getId()));
+      assertEquals(CUSTOMER, dao.getById(CUSTOMER.getId()).get());
     }
 
     @Test
@@ -120,7 +121,7 @@ public class InMemoryCustomerDaoTest {
 
       assertTrue(result);
       assertCustomerCountIs(0);
-      assertNull(dao.getById(CUSTOMER.getId()));
+      assertFalse(dao.getById(CUSTOMER.getId()).isPresent());
     }
 
     @Test
@@ -132,10 +133,18 @@ public class InMemoryCustomerDaoTest {
 
       assertTrue(result);
 
-      final Customer cust = dao.getById(CUSTOMER.getId());
+      final Customer cust = dao.getById(CUSTOMER.getId()).get();
       assertEquals(newFirstname, cust.getFirstName());
       assertEquals(newLastname, cust.getLastName());
     }
+    
+    @Test
+    public void retriveShouldReturnTheCustomer() {
+      Optional<Customer> optionalCustomer = dao.getById(CUSTOMER.getId());
+      
+      assertTrue(optionalCustomer.isPresent());
+      assertEquals(CUSTOMER, optionalCustomer.get());
+    }
   }
 
   /**