java - 试图在 Android 中复制 SQLite 数据库并获取 "No such file or directory"

Question

我有一个数据库，我想将它复制到 SD 卡以进行备份，我发现了这段代码:

private void exportDB(){
    File sd = Environment.getExternalStorageDirectory();
    File data = Environment.getDataDirectory();
    FileChannel source=null;
    FileChannel destination=null;
    String currentDBPath = "/data/"+ "com.example.myapp" +"/databases/"+"mydatabase";
    String backupDBPath = "/storage/extSdCard/mydatabase";
    File currentDB = new File(data, currentDBPath);
    File backupDB = new File(sd, backupDBPath);
    try {
        source = new FileInputStream(currentDB).getChannel();
        destination = new FileOutputStream(backupDB).getChannel();
        destination.transferFrom(source, 0, source.size());
        source.close();
        destination.close();
    } catch(IOException e) {
        //e.printStackTrace();
        Toast.makeText(this, "Err:"+e, Toast.LENGTH_LONG).show();
    }
}

正如我在标题中所写，当我尝试这样做时，我得到了 No such file or directory ENOENT 错误。

显然数据库应该存储在那里。我已经尝试将路径更改为一些不同的东西，但仍然没有......我试过:

"/data/"+ "com.example.myapp" +"/"+"mydatabase.db"

和

"//data//"+ "com.example.myapp" +"//databases//"+"mydatabase"

Edit1:也试过这个但也不起作用:

String currentDBPath = this.getDatabasePath("mydatabase").toString();

等没有任何效果，我也找不到以任何方式检查路径的方法。

我基本上已经创建了数据库，向其中插入了几行，并具有一些基本功能，例如 add() 和 delete() 等。我是否遗漏了什么？我不知道我还能尝试什么。

这是 logcat 对此的评价:

01-18 11:34:46.215 10337-10337/com.example.myapp D/DBPATH: Database path is /data/data/com.example.myapp/databases/mydatabase.db

01-18 11:34:46.225 10337-10337/com.example.myapp W/System.err: java.io.FileNotFoundException: /data/data/com.example.myapp/databases/mydatabase.db: open failed: ENOENT (No such file or directory)

01-18 11:34:46.235 10337-10337/com.example.myapp W/System.err: at libcore.io.IoBridge.open(IoBridge.java:456)

01-18 11:34:46.235 10337-10337/com.example.myapp W/System.err: at java.io.FileInputStream.(FileInputStream.java:76)

01-18 11:34:46.235 10337-10337/com.example.myapp W/System.err: at com.example.myapp.TabsActivity.exportDB(TabsActivity.java:183)

01-18 11:34:46.235 10337-10337/com.example.myapp W/System.err: at com.example.myapp.TabsActivity.onOptionsItemSelected(TabsActivity.java:119)

Answer 1

如下所示，问题可能与数据库无关，而可能与外部存储有关，因为目录不存在。解决方法是创建目录。希望以下内容会起作用(对我有用):-

    try {
        source = new FileInputStream(currentDB).getChannel();
        (new File(backupDB.getParent())).mkdirs(); //<<<<<<<<<<<<<< ADDED
        destination = new FileOutputStream(backupDB).getChannel();
        //destination.transferFrom(source, 0, source.size());
        source.close();
        destination.close();
    } catch(IOException e) {
        e.printStackTrace();
        Toast.makeText(this, "Err:"+e, Toast.LENGTH_LONG).show();
    }

• 为了测试，我已经注释掉了传输。传输正常。
• 也可能存在权限问题(我的测试是在 genymotion 模拟器上进行的)。
• 刚在真机上测试过，如果不授予权限也会出现同样的错误。
• 刚刚在真实设备上测试了 Manifest 中的设置权限以及版本 > 23 的代码。复制然后工作。 :-

这可能有用 Storage permission error in Marshmallow

---

获取您的代码并根据(检查路径，查看输出)进行调整:-

java.io.FileNotFoundException: /mnt/sdcard/storage/extSdCard/mydatabase: open failed: ENOENT (No such file or directory)

private void exportDB(){
    File sd = Environment.getExternalStorageDirectory();
    File data = Environment.getDataDirectory();
    FileChannel source=null;
    FileChannel destination=null;
    String currentDBPath = "/data/"+ getPackageName() +"/databases/"+DatabaseHandler.DATABASE_NAME;
    String retreivedDBPAth = getDatabasePath(DatabaseHandler.DATABASE_NAME).getPath();
    String backupDBPath = "/storage/extSdCard/mydatabase";
    File currentDB = new File(data, currentDBPath);
    File backupDB = new File(sd, backupDBPath);
    File retrievedDB = new File(retreivedDBPAth);
    Log.d("PATHS", " CurrentDB=" +
            currentDBPath + "\n\t" + currentDB.getPath() +
            "\n\tExists=" + String.valueOf(currentDB.exists()) +
            "\nBackup=" + backupDBPath + "\n\t" + backupDB.getPath() +
            "\n\tExists=" + String.valueOf(backupDB.exists()) +
            "\nRetrieved DB=" + retreivedDBPAth + "\n\t" + retrievedDB.getPath() +
            "\n\tExists=" + String.valueOf(retrievedDB.exists())
    );
    try {
        source = new FileInputStream(currentDB).getChannel();
        destination = new FileOutputStream(backupDB).getChannel();
        //destination.transferFrom(source, 0, source.size());
        source.close();
        destination.close();
    } catch(IOException e) {
        e.printStackTrace();
        Toast.makeText(this, "Err:"+e, Toast.LENGTH_LONG).show();
    }
}

ENOENT 不是针对数据库，而是根据 的外部存储:-

01-18 11:11:32.017 2689-2689/? D/PATHS:  CurrentDB=/data/example.com.so48304909_spinner/databases/spinnerExample
                                            /data/data/example.com.so48304909_spinner/databases/spinnerExample
                                            Exists=true
                                        Backup=/storage/extSdCard/mydatabase
                                            /mnt/sdcard/storage/extSdCard/mydatabase
                                            Exists=false
                                        Retrieved DB=/data/data/example.com.so48304909_spinner/databases/spinnerExample
                                            /data/data/example.com.so48304909_spinner/databases/spinnerExample
                                            Exists=true
01-18 11:11:32.021 2689-2689/? W/System.err: java.io.FileNotFoundException: /mnt/sdcard/storage/extSdCard/mydatabase: open failed: ENOENT (No such file or directory)
01-18 11:11:32.021 2689-2689/? W/System.err:     at libcore.io.IoBridge.open(IoBridge.java:416)
01-18 11:11:32.021 2689-2689/? W/System.err:     at java.io.FileOutputStream.<init>(FileOutputStream.java:88)
01-18 11:11:32.021 2689-2689/? W/System.err:     at java.io.FileOutputStream.<init>(FileOutputStream.java:73)
01-18 11:11:32.021 2689-2689/? W/System.err:     at example.com.so48304909_spinner.MainActivity.exportDB(MainActivity.java:162)
01-18 11:11:32.021 2689-2689/? W/System.err:     at example.com.so48304909_spinner.MainActivity.onCreate(MainActivity.java:38)
01-18 11:11:32.021 2689-2689/? W/System.err:     at android.app.Activity.performCreate(Activity.java:5008)
01-18 11:11:32.021 2689-2689/? W/System.err:     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
01-18 11:11:32.021 2689-2689/? W/System.err:     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
01-18 11:11:32.021 2689-2689/? W/System.err:     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
01-18 11:11:32.021 2689-2689/? W/System.err:     at android.app.ActivityThread.access$600(ActivityThread.java:130)
01-18 11:11:32.021 2689-2689/? W/System.err:     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
01-18 11:11:32.021 2689-2689/? W/System.err:     at android.os.Handler.dispatchMessage(Handler.java:99)
01-18 11:11:32.021 2689-2689/? W/System.err:     at android.os.Looper.loop(Looper.java:137)
01-18 11:11:32.021 2689-2689/? W/System.err:     at android.app.ActivityThread.main(ActivityThread.java:4745)
01-18 11:11:32.021 2689-2689/? W/System.err:     at java.lang.reflect.Method.invokeNative(Native Method)
01-18 11:11:32.021 2689-2689/? W/System.err:     at java.lang.reflect.Method.invoke(Method.java:511)
01-18 11:11:32.021 2689-2689/? W/System.err:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
01-18 11:11:32.021 2689-2689/? W/System.err:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
01-18 11:11:32.021 2689-2689/? W/System.err:     at dalvik.system.NativeStart.main(Native Method)
01-18 11:11:32.021 2689-2689/? W/System.err: Caused by: libcore.io.ErrnoException: open failed: ENOENT (No such file or directory)
01-18 11:11:32.021 2689-2689/? W/System.err:     at libcore.io.Posix.open(Native Method)
01-18 11:11:32.021 2689-2689/? W/System.err:     at libcore.io.BlockGuardOs.open(BlockGuardOs.java:110)
01-18 11:11:32.021 2689-2689/? W/System.err:     at libcore.io.IoBridge.open(IoBridge.java:400)
01-18 11:11:32.021 2689-2689/? W/System.err:    ... 18 more