As getAll method returns a Stream, we cannot close the involved

resources (Connection, Statement and resultSet) until the stream is
closed by the consumer. So try-with-resources is not an option as per
sonarqube’s recommendation. But it is still recommended to close
statement and result set. When connection pool used, connection is not
closed when close() called. It is just returned to the pool.

Using //NOSONAR to avoid false blocker issue.

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

@@ -65,8 +65,8 @@ public Stream<Customer> getAll() throws Exception {
     Connection connection;
     try {
       connection = getConnection();
-      PreparedStatement statement = connection.prepareStatement("SELECT * FROM CUSTOMERS");
-      ResultSet resultSet = statement.executeQuery();
+      PreparedStatement statement = connection.prepareStatement("SELECT * FROM CUSTOMERS");  //NOSONAR
+      ResultSet resultSet = statement.executeQuery(); //NOSONAR
       return StreamSupport.stream(new Spliterators.AbstractSpliterator<Customer>(Long.MAX_VALUE, 
           Spliterator.ORDERED) {
 
@@ -82,7 +82,7 @@ public boolean tryAdvance(Consumer<? super Customer> action) {
             throw new RuntimeException(e);
           }
         }
-      }, false).onClose(() -> mutedClose(connection));
+      }, false).onClose(() -> mutedClose(connection, statement, resultSet));
     } catch (SQLException e) {
       throw new Exception(e.getMessage(), e);
     }
@@ -92,8 +92,10 @@ private Connection getConnection() throws SQLException {
     return dataSource.getConnection();
   }
 
-  private void mutedClose(Connection connection) {
+  private void mutedClose(Connection connection, PreparedStatement statement, ResultSet resultSet) {
     try {
+      resultSet.close();
+      statement.close();
       connection.close();
     } catch (SQLException e) {
       e.printStackTrace();