Java - 无法将对象作为文件写入目录

Question

我的程序有一个奇怪的问题.我写了一个小程序来将对象写入特定目录中的文件.

玩家级:

package readwrite;

import java.io.Serializable;

public class Player implements Serializable {

    private String name;
    private int level;

    public Player(String name, int level) {
        this.name = name;
        this.level = level;
    }

    public String getName() {
        return name;
    }

    public int getLevel() {
        return level;
    }

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

    public void setLevel(int level) {
        this.level = level;
    }

    public String toString() {
        return "Name: " + name + ", Level: " + level;
    }

    public void printInfo() {
        System.out.println(this.toString());
    }

}

PlayerReaderWriter级:

package readwrite;

import java.io.*;

public class PlayerReaderWriter {

    public static Player readPlayer(String path) {
        Player p = null;

        try {
            FileInputStream fileIn = new FileInputStream(path);
            ObjectInputStream in = new ObjectInputStream(fileIn);
            p = (Player) in.readObject();
            in.close();
            fileIn.close();
        } catch(IOException | ClassNotFoundException e) {
            e.printStackTrace();
        }

        return p;
    }

    public static void writePlayer(String path, Player p) {
        try {
            File file = new File(path);
            if (file.exists()) {
                file.delete();
                file.createNewFile();
            } else {
                file.mkdirs();
                file.createNewFile();
            }

            FileOutputStream fileOut = new FileOutputStream(path);
            ObjectOutputStream out = new ObjectOutputStream(fileOut);
            out.writeObject(p);
            out.close();
            fileOut.close();
        } catch(IOException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        Player p = new Player("Foo", 64);
        p.printInfo();
        writePlayer("players/Player.ser", p);

        Player q = readPlayer("players/Player.ser");
        q.printInfo();
    }

}

问题是:当我第一次运行程序时,当目录 "players"不存在时,我收到以下错误:

D:\Projects>java readwrite/PlayerReaderWriter
Name: Foo, Level: 64
java.io.FileNotFoundException: players\Player.ser (Access is denied)
        at java.io.FileOutputStream.open0(Native Method)
        at java.io.FileOutputStream.open(FileOutputStream.java:270)
        at java.io.FileOutputStream.<init>(FileOutputStream.java:213)
        at java.io.FileOutputStream.<init>(FileOutputStream.java:101)
        at readwrite.PlayerReaderWriter.writePlayer(PlayerReaderWriter.java:34)
        at readwrite.PlayerReaderWriter.main(PlayerReaderWriter.java:47)
java.io.FileNotFoundException: players\Player.ser (Access is deniedt)
        at java.io.FileInputStream.open0(Native Method)
        at java.io.FileInputStream.open(FileInputStream.java:195)
        at java.io.FileInputStream.<init>(FileInputStream.java:138)
        at java.io.FileInputStream.<init>(FileInputStream.java:93)
        at readwrite.PlayerReaderWriter.readPlayer(PlayerReaderWriter.java:11)
        at readwrite.PlayerReaderWriter.main(PlayerReaderWriter.java:49)
Exception in thread "main" java.lang.NullPointerException
        at readwrite.PlayerReaderWriter.main(PlayerReaderWriter.java:50)

现在程序"player" 已由程序创建,并且由于某种原因它还创建了一个名为"Player.ser" 的子目录.

当我第二次运行它时,它会工作并在"players"目录中创建一个"Player.ser" 文件.

当我只用一个名为"players"的空目录运行它时它也不起作用.

问候 :)

Answer 1

看看这段代码:

if (file.exists()) {
    file.delete();
    file.createNewFile();
} else {
    file.mkdirs();
    file.createNewFile();
}

你说如果players/Player.ser不存在,你应该把它创建为一个目录 - 然后也作为一个文件.那破了.

如果文件已经存在,则根本不需要删除该文件 - 您可以使用a FileOutputStream并让它覆盖文件,将其截断为开头,这是默认行为.

您只需要先检查目录是否存在,例如

File file = new File(path);
File parent = file.getParentFile();
// TODO: Handle parent existing, but not being a directory,
// or file existing, but being a directory...
if (!parent.exists()) {
    parent.mkdirs();
}

try (OutputStream output = new FileOutputStream(file)) {
    // ...
}

请注意try-with-resources语句,以便即使抛出异常,您的输出流也始终处于关闭状态.