晚上好，我正在开发一个android应用程序，它有sqlite数据库，我需要一种方法将数据库复制到设备的外部存储，在那里我可以复制到另一个设备，这样我就可以将数据库导入到另一个设备。
例如：
假设应用程序调用“example”，则数据库位于“/data/data/com.gnd.example/databases”文件夹中，该数据库名为data.db，需要将其复制到“example/backup”文件夹中，例如“/storage/emulated/0/example/backup”。这是第一部分。
第二部分是导入，应用程序应将文件从“example/import”文件夹复制到“/data/data/com.gnd.example/databases”文件夹中。
为此，我有一个两个按钮的活动，btn_export和btn_import。
我已经依赖于以下解决方案：
导入/导出到android sqlite数据库
android上sqlite数据库的简单导出与导入
我已经把它插入了AndroidManifest
如何向用户请求权限？
我试着用一个例子中的代码复制
private void backupDatabase () throws IOException {
String inFileName = "/data/data/com.gnd.example/databases/dados.db";
File dbFile = new File (inFileName);
FileInputStream fis = new FileInputStream (dbFile);
String outFileName = Environment.getExternalStorageDirectory () + "/ example / backup / data.db";
OutputStream output = new FileOutputStream (outFileName);
byte [] buffer = new byte [1024];
int length;
while ((length = fis.read (buffer))> 0) {
output.write (buffer, 0, length);
}
output.flush ();
output.close ();
fis.close ();
}
按钮如下所示：
@Override
public void onClick (View view) {
try {
backupDatabase ();
} catch (IOException e1) {
e1.printStackTrace ();
}
});
当我按下按钮时记录：
07/01 19:35:39: Launching app
$ adb shell am start -n "com.gnd.keepkey / com.gnd.keepkey.Telephone" -a android.intent.action.MAIN -c android.intent.category.LAUNCHER
Client not ready yet..Waiting for process to come online
Waiting for process to come online
Connected to process 27724 on device motorola-moto_z2_play-0039635857
Capturing and displaying logcat messages from application. This behavior can be disabled in the "Logcat output" section of the "Debugger" settings page.
I / zygote: Do partial code cache collection, code = 20KB, data = 29KB
I / zygote: After code cache collection, code = 20KB, data = 29KB
Increasing code cache capacity to 128KB
I / zygote: Do partial code cache collection, code = 20KB, data = 47KB
I / zygote: After code cache collection, code = 20KB, data = 47KB
Increasing code cache capacity to 256KB
I / zygote: Compiler allocated 4MB to compile void android.widget.TextView. <Init> (android.content.Context, android.util.AttributeSet, int, int)
I / zygote: Full code cache collection, code = 120KB, data = 82KB
I / zygote: After code cache collection, code = 117KB, data = 62KB
I / zygote: Do partial code cache collection, code = 125KB, date = 79KB
I / zygote: After code cache collection, code = 125KB, data = 79KB
Increasing code cache capacity to 512KB
W / System.err: java.io.FileNotFoundException: /storage/emulated/0/teste/dados.db (No such file or directory)
at java.io.FileOutputStream.open0 (Native Method)
W / System.err: at java.io.FileOutputStream.open (FileOutputStream.java:287)
at java.io.FileOutputStream. <init> (FileOutputStream.java:223)
at java.io.FileOutputStream. <init> (FileOutputStream.java:110)
at com.gnd.keepkey.funcoes.Exportar_Importar.backupDatabase (Export_Importar.java:87)
at com.gnd.keepkey.funcoes.Exportar_Importar.access $ 000 (Export_Importar.java:42)
at com.gnd.keepkey.funcoes.Export_Import $ 1.onClick (Export_Import.java:69)
W / System.err: at android.view.View.performClick (View.java:6259)
at android.view.View $ PerformClick.run (View.java:24732)
at android.os.Handler.handleCallback (Handler.java:789)
at android.os.Handler.dispatchMessage (Handler.java:98)
at android.os.Looper.loop (Looper.java:164)
at android.app.ActivityThread.main (ActivityThread.java:6592)
at java.lang.reflect.Method.invoke (Native Method)
W / System.err: at com.android.internal.os.Zygote $ MethodAndArgsCaller.run (Zygote.java:240)
at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:769)
最佳答案
FieloToFunExtExchange很可能是由于目录TEST不存在，可能是由于权限。
使用：
private void backupDatabase () throws IOException {
String inFileName = "/data/data/com.gnd.example/databases/dados.db";
File dbFile = new File (inFileName);
FileInputStream fis = new FileInputStream (dbFile);
String outFileName = Environment.getExternalStorageDirectory () + "/ example / backup / data.db";
//<<<<<<<<<<< CODE ADDED >>>>>>>>>>
File os = new File(outFileName);
if (!os.getParentFile().exists()) {
os.getParentFile().mkdirs();
}
//<<<<<<<<<< END Of ADDED CODE >>>>>>>>>>
OutputStream output = new FileOutputStream(os); //<<<<<<<<<< CHANGED
byte [] buffer = new byte [1024];
int length;
while ((length = fis.read (buffer))> 0) {
output.write (buffer, 0, length);
}
output.flush ();
output.close ();
fis.close ();
}
如果目录不存在，将创建目录（假设权限是正确的）
工作示例：
以下是一个有效的应用程序
androidmanifest.xml文件
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="aso.so56843045backup">
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
注意
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>（对于早期设备）externalstoragepermissions.java外部存储权限
class ExternalStoragePermissions {
public int API_VERSION = Build.VERSION.SDK_INT;
private static final int REQUEST_EXTERNAL_STORAGE = 1;
private static String[] PERMISSIONS_STORAGE = {
//Manifest.permission.READ_EXTERNAL_STORAGE,
Manifest.permission.WRITE_EXTERNAL_STORAGE
};
public static final String THISCLASS = ExternalStoragePermissions.class.getSimpleName();
private static final String LOGTAG = "SW_ESP";
public ExternalStoragePermissions() {}
// Note call this method
public static void verifyStoragePermissions(Activity activity) {
int permission = ActivityCompat.checkSelfPermission(
activity,
Manifest.permission.WRITE_EXTERNAL_STORAGE);
if(permission != PackageManager.PERMISSION_GRANTED) {
ActivityCompat.requestPermissions(
activity,
PERMISSIONS_STORAGE,
REQUEST_EXTERNAL_STORAGE
);
}
}
}
如果未授予权限，则无法创建目录，从而导致FileNotFoundException。
dbhelper.java语言
public class DBHelper extends SQLiteOpenHelper {
public static final String DBNAME = "dados.db";
public static final int DBVERSION = 1;
public DBHelper(Context context) {
super(context, DBNAME, null, DBVERSION);
this.getWritableDatabase();
}
@Override
public void onCreate(SQLiteDatabase db) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
}
一个非常基本的空数据库（android_元数据表除外），足以检查备份。
main活动.java
public class MainActivity extends AppCompatActivity {
DBHelper mDBHlpr;
Button mBackup;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mBackup = this.findViewById(R.id.backup);
mBackup.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
mDBHlpr.close();
try {
backupDatabase();
} catch (IOException e) {
e.printStackTrace();
}
}
});
ExternalStoragePermissions.verifyStoragePermissions(this);
mDBHlpr = new DBHelper(this);
}
private void backupDatabase () throws IOException {
FileInputStream fis = new FileInputStream (this.getDatabasePath("dados.db").getPath());
String outFileName = Environment.getExternalStorageDirectory () + "/example/backup/" + String.valueOf(System.currentTimeMillis()) + "data.db";
Log.d("OSFILEPATH",outFileName);
File os = new File(outFileName);
if (!os.getParentFile().exists()) {
os.getParentFile().mkdirs();
}
OutputStream output = new FileOutputStream(os);
byte [] buffer = new byte [1024];
int length;
while ((length = fis.read (buffer))> 0) {
output.write (buffer, 0, length);
}
output.flush ();
output.close ();
fis.close ();
}
}
笔记
将为以后的设备请求安装后首次运行权限时（单击“允许”）。
备份已被命名为时间戳，因此可以存在多个备份。
数据库已关闭（这应该处理android pie+wehere默认为wal模式，关闭时应该清空（提交更改）-wal和-shm文件，从而消除备份其他文件的需要）。
结果