Question

我有一个数据库，我想将其复制到SD卡以保留备份，我找到了这个代码：

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();
    }
}

正如我在标题中写的那样，当我尝试这样做时，我得到No such file or directory 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，但仍然没有...... 我试过了：

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

和

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

Edit1：也尝试了这个并且也不起作用：

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

等。什么都行不通，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，在其中插入了几行并具有一些基本功能，如add()和delete()等。我错过了什么？我不知道还能尝试什么。

以下是logcat对此的评价：

01-18 11：34：46.215 10337-10337 / com.example.myapp D / DBPATH：数据库路径为/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失败：ENOENT（没有这样的文件或目录）

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，而是可能与外部存储有关，因为目录不存在。修复是创建目录。希望以下内容可行（对我而言）： -

    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();
    }

为了进行测试，我已对传输进行了评论。 P.S。通过转移运行正常。
由于权限可能会出现问题（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，如果未授予许可，则会出现同样的错误。
刚刚在Manifest中的实际设备设置权限以及版本代码＆gt;中进行了测试23.复制然后工作。： -

这可能有用Storage permission error in Marshmallow

获取代码并根据其进行调整（检查路径，参见输出）： -

java.io.FileNotFoundException： / mnt / sdcard / storage / extSdCard / mydatabase：open failed：ENOENT（不是这样的文件或目录）

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不适用于数据库，但适用于外部存储： -

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

试图在Android中复制SQLite数据库并获取“没有这样的文件或目录”

1 个答案: