尝试在Android中复制SQLite数据库并获得“没有这样的文件或目录”-java黑洞网

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尝试在Android中复制SQLite数据库并获得“没有这样的文件或目录”

发布于2021-11-27 08:59 阅读(1115) 评论(0) 点赞(23) 收藏(5)

我有一个数据库，我想将它复制到 SD 卡以保留备份，我找到了以下代码：

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的那样，No such file or directory当我尝试这样做时，我收到了ENOENT 错误。

显然，数据库应该存储在那里。我试过改变一些不同的东西的路径，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，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。

我基本上已经对数据库所做的，插入几行到它，并有像一些基本功能add()和delete()等我失去的东西吗？我不知道我还能尝试什么。

以下是 logcat 对此的看法：

01-18 11:34:46.215 10337-10337/com.example.myapp D/DBPATH：数据库路径是/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：打开失败：ENOENT （无此文件或目录）

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

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

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

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

解决方案

如下所述，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，我已经注释掉了转移。PS 传输运行正常。
由于权限也可能存在问题（我的测试是在 genymotion 模拟器上进行的）。
刚刚在真实设备上测试过，如果没有授予权限也会出现同样的错误。
刚刚在 Manifest 以及版本 > 23 的代码中测试了真实设备设置权限。复制然后工作。:-

这可能有用Marshmallow 中的存储权限错误

获取您的代码并根据其进行调整（检查路径，请参阅输出）：-

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 不是用于数据库，而是用于外部存储，如下所示：-

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