Demo :: Using Template Method Pattern

AbstractCSVReader.java

public abstract class AbstractCSVReader<T> {

	public List<T> getAll(File file) throws Exception {
		List<T> returnData = new ArrayList<>();
		try (BufferedReader reader = new BufferedReader(new FileReader(file))) {
			String line = reader.readLine();
			while (line != null && !"".equals(line.trim())) {
				String[] tokens = line.split("\\s*,\\s*");
				T data = unmarshall(tokens);
				returnData.add(data);
				line = reader.readLine();
			}
		}
		return returnData;
	}

	public abstract T unmarshall(String[] tokens);

}

CustomerCSVReader.java

public class CustomerCSVReader {

	public List<Customer> getAll(File customersFile) throws Exception {
		List<Customer> customers = new ArrayList<Customer>();
		try (BufferedReader reader = new BufferedReader(new FileReader(customersFile))) {
			String line = reader.readLine();
			while (line != null && !line.trim().equals("")) {
				String[] tokens = line.split("\\s*,\\s*");
				Customer customer = new Customer(Integer.parseInt(tokens[0]), tokens[1], tokens[2]);
				customers.add(customer);
				line = reader.readLine();
			}
		}
		return customers;
	}
}

CustomerCSVReader2.java

public class CustomerCSVReader {

	public List<Customer> getAll(File file) throws Exception {
		List<Customer> returnData = new ArrayList<Customer>();
		try (BufferedReader reader = new BufferedReader(new FileReader(file))) {
			String line = reader.readLine();
			while (line != null && !"".equals(line.trim())) {
				String[] tokens = line.split("\\s*,\\s*");
				Customer customer = unmarshall(tokens);
				returnData.add(customer);
				line = reader.readLine();
			}
		}
		return returnData;
	}
	
	private Customer unmarshall(String[] tokens) {
		Customer customer = new Customer(Integer.parseInt(tokens[0]), tokens[1], tokens[2]);
		return customer;
	}

}

CustomerCSVReader3.java

public class CustomerCSVReader extends AbstractCSVReader<Customer> {
	
	@Override
	public Customer unmarshall(String[] tokens) {
		Customer customer = new Customer(Integer.parseInt(tokens[0]), tokens[1], tokens[2]);
		return customer;
	}

}

ProductCSVReader.java

public class ProductCSVReader {

	public List<Product> getAll(File customersFile) throws Exception {
		List<Product> products = new ArrayList<Product>();
		try (BufferedReader reader = new BufferedReader(new FileReader(customersFile))) {
			String line = reader.readLine();
			while (line != null && !line.trim().equals("")) {
				String[] tokens = line.split("\\s*,\\s*");
				Product product = new Product(Integer.parseInt(tokens[0]), tokens[1], Double.parseDouble(tokens[2]));
				products.add(product);
				line = reader.readLine();
			}
		}
		return products;
	}
}

ProductCSVReader3.java

public class ProductCSVReader extends AbstractCSVReader<Product> {

	@Override
	public Product unmarshall(String[] tokens) {
		Product product = new Product(Integer.parseInt(tokens[0]), tokens[1], Double.parseDouble(tokens[2]));
		return product;
	}
}