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.io.Serializable;
import java.util.HashMap;
import java.util.Map;

public class Test {
    public static void main(String args[]) {
        writer();//自己可以注释掉代码试试
        reader();
    }
    public static void writer(){
        Map<Integer,Student> students=new HashMap<Integer,Student>();
        students.put(1, new Student("A"));
        students.put(2, new Student("B"));
        File stuInfo = new File("stuInfo.txt");
        ObjectOutputStream oos = null;
        try {
            oos = new ObjectOutputStream( new FileOutputStream(stuInfo));
            oos.writeObject(students);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }finally{
            try {
                oos.flush();
                oos.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
    public static void reader(){
        Map<Integer,Student> students= null;
        File stuInfo = new File("stuInfo.txt");
        ObjectInputStream ois = null;
        try {
            ois = new ObjectInputStream(new FileInputStream(stuInfo));
            Object o = ois.readObject();
            students = (Map<Integer,Student>)o;
            
            System.out.println(students);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }finally{
            try {
                ois.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
    
}
class Student implements Serializable{
    Student(String name){
        this.name = name;
    }
    private String name;
    
    @Override
    public String toString(){
        
        return "Student name:"+name;
    }
}

------解决方案--------------------
你真狠。。。看看你的构造函数：
Test(File stuinfo){
 this.stuinfo=stuinfo;
 try {
 oos = new ObjectOutputStream(new FileOutputStream(stuinfo));

直接就用把FileOutputStream这个文件的内容清空了。。。