hello/java/samples/properties/swing2/PersonStore.java

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 */
package propertiesswing2;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.HashSet;
import java.util.Set;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 *
 * @author denis
 */
public class PersonStore {
    private static Set<User> persons = new HashSet<>();
    private static PersonStore personStore;
    private File file;
    
    private PersonStore(){
        file = new File("persons.txt");
        if(!file.exists()) try {
            file.createNewFile();
        } catch (IOException ex) {
            ex.printStackTrace();
        }else readStore();
    }
    
    public static PersonStore getPersonStore(){
        if (personStore == null) personStore = new PersonStore();
        return personStore;
    }
    
    public void addUser(User user){
        persons.add(user);
        saveStore();
    }
    
    public HashSet<User> getPersons(){
        return new HashSet<>(persons);
    }
    
    private void readStore(){
        if(file==null || !file.canRead()) return;
        try (ObjectInputStream ois = new ObjectInputStream(new FileInputStream(file))) {
            Object result = ois.readObject();
            persons = result!=null ? (HashSet<User>)result : new HashSet<>();
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
    
    private void saveStore(){
        if(file==null || !file.canRead()) return;
        try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(file))) {
            oos.writeObject(persons);
        } catch (FileNotFoundException ex) {
            ex.printStackTrace();
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }
}