我在 Java 中序列化一個 object 但在反序列化時，它的 state 與預期不符。 如何保留對象的 state？

Question

我正在嘗試在 Java 中構建一個涉及序列化和反序列化的程序。 有兩個類，Employee 和 LauncherClass。

員工.java：

import java.io.Serializable;

public class Employee implements Serializable {

    String name;
    int id;
    int age;
    double salary;

    public Employee() {
        this.name="";
        this.id=0;
        this.age=0;
        this.salary=0.0;
    }

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

    }

    public String getName() {
        return name;
    }

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

    public int getId()
    {
        return id;
    }

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

    public int getAge()
    {
        return age;
    }

    public void setSalary(double salary) {
        this.salary = salary;
    }

    public double getSalary()
    {
        return salary;
    }

    public String toString()
    {
        return id + " " + name + " " + age + " " + salary;
    }
}

LauncherClass.java：

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.Scanner;

public class LauncherClass {

    public static void main(String[] args) throws IOException, ClassNotFoundException {
        Scanner sc = new Scanner(System.in);
        Employee employee = new Employee();
        FileOutputStream fileOutputStream = new FileOutputStream("datafile");
        ObjectOutputStream objectOutputStream = new ObjectOutputStream(fileOutputStream);
        int choice;
        do {
            System.out.println("Main Menu");
            System.out.println("1.Add an Employee");
            System.out.println("2.Display All");
            System.out.println("3.Exit");
            choice = sc.nextInt();
            switch(choice)
            {
            case 1:
                System.out.print("Enter Employee ID:");
                employee.setId(sc.nextInt());
                sc.nextLine();
                System.out.print("Enter Employee Name:");
                employee.setName(sc.nextLine());
                System.out.print("Enter Employee Age:");
                employee.setAge(sc.nextInt());
                System.out.print("Enter Employee Salary:");
                employee.setSalary(sc.nextDouble());        
                objectOutputStream.writeObject(employee);

                break;
            case 2:
                System.out.println("----Report----");
                FileInputStream fileInputStream = new FileInputStream("datafile");
                ObjectInputStream objectInputStream = new ObjectInputStream(fileInputStream);
                while(fileInputStream.available()>0)
                {
                employee = (Employee)objectInputStream.readObject();
                System.out.println(employee);
                }
                System.out.println("----End of Report---");
                objectInputStream.close();
                break;
            case 3:
                System.exit(5);


            }


        } while (choice!=3);
        objectOutputStream.flush();
        objectOutputStream.close();



    }

}

我執行這個程序並添加一些員工，然后顯示 object 的數據。 到目前為止，一切正常。 但是當我退出並重新啟動程序和 select 顯示選項時，它什么也不顯示。 為什么會這樣？ 為什么object中的數據會丟失？

Answer 1

這有很多問題。

1. 您正在打開一個 ObjectOutputStream，在關閉之前您正在打開一個 ObjectInputStream。 你需要解耦你的閱讀和寫作。

2. 由於 System.exit，您的 while 循環將永遠不會讀取 Closeable 關閉/刷新調用。

3. 您需要在使用nextInt()后使用 System.out.println 因為Scanner.nextInt()不使用換行符。

4. 您需要將 Closeable 對象包裝在 try-with-resources 中。

5. 另一個用戶是正確的，你需要append，不要覆蓋。

6. 您需要在寫入后調用 ObjectOutputStream#flush 。

   public static void main(String[] args) throws IOException, ClassNotFoundException {
        Scanner sc = new Scanner(System.in);

        Employee employee = new Employee();

        int choice;

        do {
            System.out.println("Main Menu");
            System.out.println("1.Add an Employee");
            System.out.println("2.Display All");
            System.out.println("3.Exit");

            choice = sc.nextInt();

            switch (choice) {
                case 1:
                    try (FileOutputStream fileOutputStream = new FileOutputStream("datafile", true);
                         ObjectOutputStream objectOutputStream = new ObjectOutputStream(fileOutputStream)) {
                        System.out.println("Enter Employee ID:");
                        employee.setId(sc.nextInt());
                        sc.nextLine();
                        System.out.println("Enter Employee Name:");
                        employee.setName(sc.nextLine());
                        System.out.println("Enter Employee Age:");
                        employee.setAge(sc.nextInt());
                        System.out.println("Enter Employee Salary:");
                        employee.setSalary(sc.nextDouble());
                        objectOutputStream.writeObject(employee);
                        objectOutputStream.flush();
                    }
                    break;

                case 2:
                    System.out.println("----Report----");
                    try (FileInputStream fileInputStream = new FileInputStream("datafile");
                         ObjectInputStream objectInputStream = new ObjectInputStream(fileInputStream)) {
                        System.out.println("as: " + objectInputStream.available());
                        while (fileInputStream.available() > 0) {
                            employee = (Employee) objectInputStream.readObject();
                            System.out.println(employee);
                        }
                        System.out.println("----End of Report---");
                    }
                    break;

                case 3:
                    break;
            }
        } while (choice != 3);
    }