Let’s get to know the files we have in the project that we fetched during the Setup task. The logic is implemented to authenticate users. This is done by checking the username and password they entered against a data source. Application has functionality to perform authentication both when the user is offline (using LocalStorage.java which gets username and password data from a local file) and online (using NetworkStorage.java which fetches this information from a site on the cloud)

• App.java - contains logic to check if username and password matches

  • loginOffline(username, password) - use locally saved (file based) data to authenticate user

  • loginOnline(username, password) - use data saved on cloud to authenticate user

  • main() - serves as the frontend (for now) where users will input username and password data

• LocalStorage.java - performs storage operations and fetches login data from UnameToPass.txt file saved locally

  • getPassword(username) - fetches password for a particular username

  • getUsernameToPasswordMapping() - fetches all username to password mappings from the UnameToPass.txt file

• NetworkStorage.java - similar functionality as LocalStorage.java, but fetches data over the Internet. (We’ll look at this in the later milestones)

The main() method of the App class is calling its loginOffline(username, password) method with parameters Dhoni and dhoni**Password. The methods provided by the LocalStorage class is used to fetch the password corresponding to a username. The loginOffline() method checks if the passwords match and returns a message to the user accordingly

LocalStorage localStorage = new LocalStorage();

public String loginOffline(String username, String inputPassword) {

    String expectedPassword = localStorage.getPassword(username);

    if (expectedPassword.equals(inputPassword)) {

        return "Login successful";

    } else {

        return "Invalid password!";

    }

}

public static void main(String[] args) {

    App app = new App();

    System.out.println(app.loginOffline("Dhoni", "dhoniPassword"));

}

The UnameToPass.txt file contains the username-password mapping which the LocalStorage class utilizes. Check it, does username, Dhoni map to password, dhoni**Password? Try compiling and running the App.java file.

We see an error!

Let’s understand the error printed out. It’s trying to tell us there are a couple of exceptions, FileNotFoundException and IOException, which are not caught. We must either catch them or declare the methods to throw these exceptions. The lines causing the error are in the LocalStorage.java file. This file also gets compiled when compiling App.java as it’s used within it.

You’ll see VS code underlining the exact lines where the compilation error occurs, in red. Hover over these and you’ll find that the class/method declaration has an extra throws keyword followed by one of the exceptions we saw earlier. To resolve the compilation error, you’d remember from the error seen earlier that the options were

1. Catch the error OR

2. Declare exceptions to be thrown.

As you’d have guessed, throws keyword is used to say that a class/method can throw an exception. This leaves the responsibility of dealing with the exception (FileNotFoundException ) to the method that uses the FileReader class. Here, the getUsernameToPasswordMapping() method has to deal with it.

So, the getUsernameToPasswordMapping() method has two options.

• Throw the exception using throws so that the exception needs to be handled by any other function calls getUsernameToPasswordMapping()

• Catch the exception and handle it.

Let’s explore both the methods one by one.

TODO: Modify getUsernameToPasswordMapping() to handle the exceptions by throwing both the exceptions. Compile the App.java file again. Does it show errors at lines in getUsernameToPasswordMapping() like before or in a different method?

public Map<String, String> getUsernameToPasswordMapping() throws FileNotFoundException, IOException {

Similarly, you’ll see the same issue for the getPassword() method as it’s using the getUsernameToPasswordMapping() method.

TODO: Modify getPassword() to throw the exceptions it needs to handle like we did with getUsernameToPasswordMapping().