Description

Lab 04

In this lab, you will:
• Experience, through your own alterations, how to implement ‘separation of concerns’ with regard to a software architecture.
• This will occur through an alteration of the code, specifically separating certain aspects of a controller class, which are them moved into a Repository, implementing the Repository pattern.
• Finally, building on the notion of software architecture you will be guided to implement a Data Access Object pattern to help abstract the data persistence seen in the code, and in previous examples.

… which will result in the following learning outcomes:
• An appreciation of the practical steps required to implement architectural changes.
• A practical appreciation of the following concept from the lecture:
o “Separation of concerns: a design principle which encourages the development of software units that focus on single aspects of the overall program functionality, and overlap with each other as little as possible…….”

Table of Contents
1.1 Preliminary 3
1.2 Exercise 1 3
1.3 Exercise 2 4
1.4 Exercise 3 5
1.5 Exercise 4 6

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1.7 Task ……………………………………………………………………….. Error! Bookmark not defined. 1.7.1 Subtask ……………………………………………………………………. Error! Bookmark not defined.

Figure 1: Lab4_CustomerProjectsAppLab4Starter ………………………………………………………….. 3

1.1 Preliminary

• Download the lab 4 zip file <Lab4_CustomerProjectsAppStarter.zip> from GCULearn and unzip

• Open the Lab4_CustomerProjectsAppStarter project in NetBeans:

Figure 1: Lab4_CustomerProjectsAppStarter

1.2 Exercise 1
a. Open the Customer class, in the model folder, and note the attributes:
customerId, customerName, and customerProjects. Constructor, getter and setter methods are defined as well as add, and remove project methods and the overridden method toString().

b. Now open the customers.txt file and note the format. Ensure you understand how this might be loaded into a collection using the ideas in labs 2 & 3.
1,”Martin”,2,”MLGProj1″,”MLGProj2″
2,”Lynn”,1,”LPKProj1″
3,”Ciara”,3,”CODProj1″,”CODProj2″,”CODProj3″

Open the controller class: a constructor method requests a file name from the user and passes the filename into a load method. Ensure you understand the load() private method:
public ArrayList<Customer> load(String filename) { ArrayList<Customer> repository = new ArrayList<>();

try (BufferedReader br = new BufferedReader(
new FileReader(filename))) {
String[] temp;
String line = br.readLine(); while(line!=null){ temp=line.split(Character.toString(DELIMITER));
int customerId = Integer.parseInt(temp[0]); String customerName = stripQuotes(temp[1]); Customer customer =
new Customer(customerId, customerName); int noProjects = Integer.parseInt(temp[2]); for (int i=0; i<noProjects; i++) {
String project = stripQuotes(temp[i+3]); customer.addProjectToCustomer(project);
}
repository.add(customer); line = br.readLine();
}
br.close();
} catch (IOException ex) { … } return repository;
}

c. Run the CustomerProjectsApp class and test that the customer projects can be successfully loaded and displayed. Add and remove projects from a specified customer and store them back to a text file. Ensure you can reload the file correctly.
1.3 Exercise 2
We are now going to modify the architecture of the app to implement a repository pattern to manage the customers collection.
a. Open the CustomerProjectsController class and amend the model definition from an ArrayList<Customer> to a Repository:

private final Repository repository;

Add the import for the Repository class, adjust the lines which create the
Repository object and remove the load(), store() & stripQuotes() methods – this functionality is now implemented in the Repository class.

b. View the Repository class in the repositories folder and ensure you understand its attributes and methods.

c. Amend the addProjectToCustomer() and removeProjectFromCustomer() methods by replacing the for loop with the commented statement:

//requiredCustomer = repository.getItem(customerId); for (Customer customer:this.repository) { if (customer.getCustomerId() == customerId) requiredCustomer = customer;
}

d. Adjust the Finish menu option to call the store() method of the repository object.

e. Run the CustomerProjectsApp class and test that the customer projects can be successfully loaded and displayed. Add and remove projects from a specified customer and store them back to a text file. Ensure you can reload the file correctly.

f. Modify the Repository class to utilise a LinkedList implementation rather than an ArrayList implementation. Make the changes required to the
Repository class and then run the CustomerProjectsApp as before.
1.4 Exercise 3
We are now going to abstract the code which handles persistence i.e. File I-O from the controller class to allow it to focus on the functionality of the app. This approach uses a Data Access Object (DAO) pattern with dedicated classes for File I-O of model objects.
a. Create a daos folder within the project and an interface, DAOInterface, to specify the methods a DAO object must have i.e. load() and store(). The interface cannot be instantiated but defines methods signatures, including parameters, which an implementation must implement.

public interface DAOInterface {
public Repository load(String filename);

public void store(String filename, Repository repository);
}

Note the load() method expects a filename, as String, and returns a Repository object; while the store() method expects the String filename and a Repository object to persist.

b. As we cannot instantiate an interface object, and, anyway, it doesn’t actually contain code to implement the load() and store() methods, we need to have implementation classes.

Initially, we will focus on a text file implementation. Create a DAOTextImpl class in the daos folder to implement the load() and store() methods using delimited text files.

public class DAOTextImpl implements DAOInterface {

static final char DELIMITER=’,’;

@Override
public Repository load(String filename) { …

Move the load and store code from the Repository class and make any changes required.

c. Adjust the Repository constructor and store() methods to create a dao object and execute its load() and store() methods respectively:
DAOTextImpl dao = new DAOTextImpl();
this.items = dao.load(filename).getItems();

and:
DAOTextImpl dao = new DAOTextImpl(); dao.store(filename, this);

d. Run the CustomerProjectsApp as before.
1.5 Exercise 4
a. Create a class to implement the DAOInterface using object files.

b. Run the CustomerProjectsApp as before.