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，当我尝试去做的时候，我得到了一个
No such file or directory的错误。显然数据库应该就在那里。
我试着改变一些不同的事情，但仍然没有…
我试过：
"/data/"+ "com.example.myapp" +"/"+"mydatabase.db"
和
"//data//"+ "com.example.myapp" +"//databases//"+"mydatabase"
Edit1:也尝试过但也不起作用：
String currentDBPath = this.getDatabasePath("mydatabase").toString();
等等，没什么用，我也找不到任何方法来检查路径。
我基本上已经建立了数据库，在其中插入了几行，并且有一些基本功能，比如
add()和delete()等等。我是否遗漏了什么？我不知道还能试什么。下面是logcat要说的：
01-18 11:34:46.215 10337-10337/com.example.myapp d/db path: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 failed: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:位于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）
最佳答案
如下所述，该问题可能与数据库无关，而是与外部存储有关，并且因为目录不存在。修复方法是创建目录。希望下面的方法对我有用：-
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，我已经评论了转移。P.S.转机正常。
也可能是权限问题（我的测试是在genymotion模拟器上进行的）。
刚刚在一个真实的设备上测试过，如果不授予权限，同样的错误也会发生。
刚刚在manifest和23以上版本的代码中测试了真正的设备设置权限。复制成功。：。-
这可能有用Storage permission error in Marshmallow
获取代码并根据（检查路径，请参阅输出）调整代码：-
java.io.fileNotFoundException异常：
/mnt/sdcard/storage/extsdcard/mydatabase:打开失败：enoent（没有
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不用于数据库，而是用于符合以下条件的外部存储：
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