Làm sao để đọc và ghi(ghi nhiều lần) arraylist vào file trong java?

Đây là code mình viết như không đọc đk dữ liệu nhập kể từ lần thứ 2 trở đi

Class Function

/*
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package ObjectIO;

import ListObjectIO.ObRead;
import ListObjectIO.ObWirte;
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.ObjectOutput;
import java.io.ObjectOutputStream;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.Scanner;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 *
 * @author Tien Nguyen
 */
public class Function {

    public Function() {
        ArrayList<Studental = new ArrayList();
        boolean a = false;
        Student a1 = new Student(555, "nnnnnnnnnnnnnnnn", "mmmmmmmmmmmmmmmmm", 5, 10);
        Student a2 = new Student(555, "dddddddddddddd", "cccccccccccccccccccccccccccc", 5, 10);
        Student a3 = new Student(555, "wwwwwwwwwwwwwwwwwwwwwwwwwww", "aaaaaaaaaaaâ", 5, 10);
        al.add(a1);
        al.add(a2);
        al.add(a3);
        ObWrite(al, false);
    }

    public void Input() {
        ArrayList<Studental = new ArrayList();
        Scanner s = new Scanner(System.in);
        System.out.println("=========== Them moi sinh vien =============");
        System.out.print("Nhap ID: ");
        int id = s.nextInt();
        s = new Scanner(System.in);
        System.out.println("Nhap ten: ");
        String name = s.nextLine();
        System.out.println("Nhap Lop: ");
        String classs = s.nextLine();
        System.out.println("Nhap diem 1: ");
        int mark1 = s.nextInt();
        System.out.println("Nhap diem 1: ");
        int mark2 = s.nextInt();
        Student st = new Student(id, name, classs, mark1, mark2);
        al.add(st);

        ObWrite(al, true);
        //a = true;
    }

    public void ObWrite(ArrayList st, boolean append) {
        String path = "src\ObjectIO\Student.dat";
        File file = new File(path);

        OutputStream outputStream;
        try {
            ObjectOutputStream ois;
            if (append) {
                outputStream = new FileOutputStream(file, append);
                ois = new ObjectOutputStream(outputStream) {
                    @Override
                    protected void writeStreamHeader() throws IOException {

                    }
                };
            } else {
                outputStream = new FileOutputStream(file);
                ois = new ObjectOutputStream(outputStream);
            }
            ois.writeObject(st);
            ois.flush();
            ois.close();
            outputStream.flush();
            outputStream.close();
        } catch (IOException ex) {
            Logger.getLogger(Function.class.getName()).log(Level.SEVERE, null, ex);
        }

    }

    public static ArrayList<StudentreadAppend() {
        String path = "src\ObjectIO\Student.dat";
        File f = new File(path);
        ArrayList<Studentres = new ArrayList<>();
        ArrayList<Studentres2 = new ArrayList<>();
        ObjectInputStream obin = null;
        try {
            FileInputStream in = new FileInputStream(f);
            obin = new ObjectInputStream(in);

            res = (ArrayList<Student>) obin.readObject();

            res2 = (ArrayList<Student>) obin.readObject();
            System.out.println("ab <-----------------------------------------------");
            for (int i = 0; i < res2.size(); i++) {
                System.out.println(i + " " + res2.get(i).getId() + "	" + res2.get(i).getName() + "	" + res2.get(i).getClasss() + "	" + res2.get(i).getMark1() + "	" + res2.get(i).getMark2());

            }
        } catch (Exception ex) {
        } finally {
            if (obin != null) {
                try {
                    obin.close();
                    System.out.println("---------------- Error -------------");
                } catch (IOException ex) {
                    Logger.getLogger(ObRead.class.getName()).log(Level.SEVERE, null, ex);
                }
            }
        }
        return res;

    }

    public void ShowStudent(ArrayList<Studentst) {
        System.out.println("NO  StudentID	StudentName	Class   	Mark	Mark");
        for (int i = 0; i < st.size(); i++) {
            System.out.println(i + " " + st.get(i).getId() + "	" + st.get(i).getName() + "	" + st.get(i).getClasss() + "	" + st.get(i).getMark1() + "	" + st.get(i).getMark2());

        }
    }
}

Class Student

/*
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package ObjectIO;

import java.io.Serializable;

/**
 *
 * @author Tien Nguyen
 */
public class Student implements Serializable{
private int id;
private String name;
private String classs;
private int mark1;
private int mark2;

public Student(int id, String name, String classs, int mark1, int mark2) {
    this.id = id;
    this.name = name;
    this.classs = classs;
    this.mark1 = mark1;
    this.mark2 = mark2;
}

public Student() {
}

public int getId() {
    return id;
}

public void setId(int id) {
    this.id = id;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public String getClasss() {
    return classs;
}

public void setClasss(String classs) {
    this.classs = classs;
}

public int getMark1() {
    return mark1;
}

public void setMark1(int mark1) {
    this.mark1 = mark1;
}

public int getMark2() {
    return mark2;
}

public void setMark2(int mark2) {
    this.mark2 = mark2;
}


}

Class main

/*
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 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package ObjectIO;

import java.util.ArrayList;
import java.util.Scanner;

/**
 *
 * @author Tien Nguyen
 */
public class Run {

public static void main(String[] args) {
    Function f = new Function();
    ArrayList<Studentsl = null;
    while (true) {
        System.out.println("1. Them moi sinh vien");
        System.out.println("2. Xem danh sach sinh vien");
        Scanner s = new Scanner(System.in);
        System.out.print("#chon: ");
        int choice = s.nextInt();

        switch (choice) {
            case 1:
                f.Input();
                break;
            case 2:
                sl = f.readAppend();
                f.ShowStudent(sl);
                break;
        }
    }
}
}