public class PropertiesEmail {

String host = "imap.gmail.com";
String user = "userEmail";
String password = "password";
int port = 993;

public Properties setServerProperties(){
    Properties properties = new Properties();
    properties.put("mail.imap.host", host);
    properties.put("mail.imap.port", port);
    properties.put("mail.imap.starttls.enable", "true");
    properties.put("mail.store.protocol", "imaps");
    return properties;
}

}

import javax.mail.*;
import javax.mail.search.FlagTerm;
import java.util.Properties;

public class CheckUnreadEmail {

public static void checkUnreadEmail(){

    try{

        //Create object email properties
        PropertiesEmail propertiesEmail = new PropertiesEmail();

        //Set email server properties
        Properties props = propertiesEmail.setServerProperties();

        Session session = Session.getDefaultInstance(props);

        Store store = session.getStore();

        store.connect(propertiesEmail.host, propertiesEmail.user, propertiesEmail.password);

        //Create the folder object and open it
        Folder folder = store.getFolder("INBOX");
        folder.open(Folder.READ_WRITE);

        //Total unread messages
        System.out.println("Total messages: " + folder.getMessageCount());
        System.out.println("Unread messages: " + folder.getUnreadMessageCount());


        //Create variable for search unread message
        FlagTerm flag = new FlagTerm(new Flags(Flags.Flag.SEEN), false);

        //Retrieve all messages
        //Message [] messages = folder.getMessages();

        //Retrieve unread messages from the folder INBOX
        Message [] unreadMessage = folder.search(flag);

        for (int i = 0, n = unreadMessage.length; i < n; i++){
            Message message = unreadMessage[i];
            System.out.println("--------------");
            System.out.println("Subject: " + message.getSubject());
        }

        //folder.setFlags(unreadMessage, new Flags(Flags.Flag.SEEN), true);

        //close the store and folder objects
        folder.close(false);
        store.close();

    }catch(Exception e){
        e.printStackTrace();
    }

}

}