implemented and added test cases for DB dao. Added dependency of Hierarchical junit runner in parent pom

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

@@ -1,38 +1,130 @@
 package com.iluwatar.dao;
 
+import java.sql.Connection;
+import java.sql.DriverManager;
+import java.sql.PreparedStatement;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.util.Spliterator;
+import java.util.Spliterators;
+import java.util.function.Consumer;
 import java.util.stream.Stream;
+import java.util.stream.StreamSupport;
 
 public class DBCustomerDao implements CustomerDao {
 
-  @Override
-  public Stream<Customer> getAll() {
-    // TODO Auto-generated method stub
-    return null;
+  private String dbUrl;
+
+  public DBCustomerDao(String dbUrl) {
+    this.dbUrl = dbUrl;
   }
 
+  @Override
+  public Stream<Customer> getAll() {
+    
+    Connection connection;
+    try {
+      connection = getConnection();
+      PreparedStatement statement = connection.prepareStatement("SELECT * FROM CUSTOMERS");
+      ResultSet resultSet = statement.executeQuery();
+      return StreamSupport.stream(new Spliterators.AbstractSpliterator<Customer>(Long.MAX_VALUE, Spliterator.ORDERED) {
+        
+        @Override
+        public boolean tryAdvance(Consumer<? super Customer> action) {
+          try {
+            if (!resultSet.next()) {
+              return false;
+            }
+            action.accept(createCustomer(resultSet));
+            return true;
+          } catch (SQLException e) {
+            e.printStackTrace();
+            return false;
+          }
+          
+        }}, false).onClose(() -> mutedClose(connection));
+    } catch (SQLException e) {
+      e.printStackTrace();
+      return null;
+    }
+  }
+  
+  private void mutedClose(Connection connection) {
+    try {
+      connection.close();
+    } catch (SQLException e) {
+      e.printStackTrace();
+    }
+  }
+
+  private Customer createCustomer(ResultSet resultSet) throws SQLException {
+    return new Customer(resultSet.getInt("ID"), 
+        resultSet.getString("FNAME"), 
+        resultSet.getString("LNAME"));
+  }
+  
   @Override
   public Customer getById(int id) {
-    // TODO Auto-generated method stub
+    try (Connection connection = getConnection();
+        PreparedStatement statement = connection.prepareStatement("SELECT * FROM CUSTOMERS WHERE ID = ?")) {
+        statement.setInt(1, id);
+        ResultSet resultSet = statement.executeQuery();
+        if (resultSet.next()) {
+          return createCustomer(resultSet);
+        }
+    } catch (SQLException ex) {
+      ex.printStackTrace();
+    }
     return null;
   }
 
   @Override
   public boolean add(Customer customer) {
-    // TODO Auto-generated method stub
-    return false;
+    if (getById(customer.getId()) != null) {
+      return false;
+    }
+    
+    try (Connection connection = getConnection();
+        PreparedStatement statement = connection.prepareStatement("INSERT INTO CUSTOMERS VALUES (?,?,?)")) {
+      statement.setInt(1, customer.getId());
+      statement.setString(2, customer.getFirstName());
+      statement.setString(3, customer.getLastName());
+      statement.execute();
+      return true;
+    } catch (SQLException ex) {
+      ex.printStackTrace();
+      return false;
+    }
   }
 
   @Override
   public boolean update(Customer customer) {
-    // TODO Auto-generated method stub
-    return false;
+    try (Connection connection = getConnection();
+        PreparedStatement statement = connection.prepareStatement("UPDATE CUSTOMERS SET FNAME = ?, LNAME = ? WHERE ID = ?")) {
+      statement.setString(1, customer.getFirstName());
+      statement.setString(2, customer.getLastName());
+      statement.setInt(3, customer.getId());
+      return statement.executeUpdate() > 0;
+    } catch (SQLException ex) {
+      ex.printStackTrace();
+      return false;
+    }
   }
 
   @Override
   public boolean delete(Customer customer) {
-    // TODO Auto-generated method stub
-    return false;
+    try (Connection connection = getConnection();
+        PreparedStatement statement = connection.prepareStatement("DELETE FROM CUSTOMERS WHERE ID = ?")) {
+      statement.setInt(1, customer.getId());
+      return statement.executeUpdate() > 0;
+    } catch (SQLException ex) {
+      ex.printStackTrace();
+      return false;
+    }
   }
 
+  private Connection getConnection() throws SQLException {
+    return DriverManager.getConnection(dbUrl);
+  }
 
 }