GET Token - JAVA

public class Program{
  public static void main(String[] args){
    
    // Set local variables
    String username = "username";
    String password = "password";
    String getTokenUri = "https://fim.api.ENV.fleetmatics.com/token";

    // Pass variables to create a new TokenGenerator object    
    TokenGenerator token = new TokenGenerator(username, password, getTokenUri);
    
    // Display auth string    	
    System.out.println(token.GetAuthString());
  }
}

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import javax.net.ssl.HttpsURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Base64;
import java.util.Date;
import java.util.Calendar;

  public class TokenGenerator{
    
    private String _authString; 
    
    private Date _expiredDateTime;
    
    private String _username;
    
    private String _password;
      
    private String _getTokenUri;
      	  
    // Public property that returns the token string. The logic contained
    // evaluates if the token is expired when it is accessed. If expired, 
    // a new token is automatically populated, and new token string returned	
    public String GetAuthString(){
      Date now = new Date();
      if(now.after(_expiredDateTime)){
        this._authString = GetToken();
      }
      return this._authString; 
    }  

    // Constructor that takes username, password, and enpoint for the Token API	
    public TokenGenerator(String username, String password, String getTokenUri){
      _username = username;
      _password = password;
      _getTokenUri = getTokenUri;
      _authString = GetToken();
    }
    
    private String GetToken(){
      String authString = "";
      try
      {         
        // Get authentication, Base64 encoded, string	  
        String basicAuth = BuildBasicAuth(_username, _password);
        
        URL url = new URL(_getTokenUri);                                       // Construct a url with the earlier supplied GetToken URI
        HttpsURLConnection conn = (HttpsURLConnection) url.openConnection();   // Open a new Https connection for transmission
        conn.setRequestMethod("GET");                                          // Set request type to GET
        conn.setRequestProperty("Authorization", basicAuth);                   // Pass in auth string into Authorization header
        conn.setRequestProperty("Accept", "text/plain");                       // Denote type of response expected
        conn.setDoOutput(false);                                               // Do not send request body

        // Execute request, read response. If we do not receive a 200 OK, throw exception		
        if (conn.getResponseCode() != HttpsURLConnection.HTTP_OK) {
          throw new RuntimeException("Failed : HTTP error code : " + conn.getResponseCode());
        }

        // Reads text from a character-input stream
        BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream()));
                    
        this.SetExpiredDateTime();             // Set expiration date of token (expires after 20 minutes)
        authString = br.readLine();            // Read the buffer into the authString variable, not including any line-termination characters
        
        conn.disconnect();                     // Close HttpsURLConnection
                
      } catch (MalformedURLException e) {      // Required Exception
        e.printStackTrace(); 
      } catch (IOException e) {                // Required Exception
        e.printStackTrace(); 
      }
      return authString;
    }

    // Supply username and password to build a Base64 encoded authentication string
    private static String BuildBasicAuth(String username, String password) {
      String userCredentials = username + ":" + password;                                   // Prepare user credentials for encoding 
      return "Basic " + Base64.getEncoder().encodeToString(userCredentials.getBytes());     // Base64 encode the user credentials and append to "Basic " and return 
    }
    
    // Set the newly acquired token's expiration date and time
    private void SetExpiredDateTime(){
      Calendar now = Calendar.getInstance();      // Get current date time 
      now.add(Calendar.MINUTE, 20);               // Add twenty minutes (token is invalid after this time frame) 
      this._expiredDateTime = now.getTime();      // set expired date time to a date representing the time value plus twenty minutes.
    }    
}