如何将一个Java对象序列化到文件里

import junit.framework.TestCase;

import java.io.*;
import java.util.ArrayList;
import java.util.List;

/**
 * Created by y_str on 2017/11/9 0009.
 */
public class ObjectToFile extends TestCase {
    public void test(){
        List<Object> list = new ArrayList<Object>();
        UserObj user = new UserObj();
        user.setAge(20);
        user.setUserId(1000L);
        user.setUserName("测试");
        list.add(user);
        list.add(user);
        try {
            ObjectOutputStream ous = new ObjectOutputStream(new FileOutputStream("test.txt"));
            ous.writeObject(user);
            ous.writeObject(list);
            ous.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        try {
            ObjectInputStream ins =  new ObjectInputStream(new FileInputStream("test.txt"));
            UserObj obj = (UserObj)ins.readObject();
            List  tempList = (List)ins.readObject();
            System.out.println(obj.toString());
            System.out.println(tempList.toString());
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}


class UserObj implements Serializable{

    private Long userId;
    private String userName;
    private Integer age;


    public Long getUserId() {
        return userId;
    }

    public void setUserId(Long userId) {
        this.userId = userId;
    }

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "UserObj{" +
                "userId=" + userId +
                ", userName='" + userName + '\'' +
                ", age=" + age +
                '}';
    }
}