我正在尝试这段代码：
在我的示例中使用此代码，我总是得到FileNotFoundException，尽管在读取FileInputStream时该文件夹存在于外部存储中。
这是我的代码：
public void exportdata()
{
try
{
myInput = new FileInputStream("/data/data/com.example.hello/databases/BikeMaintenance.db");
File directory = new File("/sdcard/BikeMaintenance/Data/");
// Create the folder if it doesn't exist:
if (!directory.exists())
{
directory.mkdirs();
}
OutputStream myOutput = new FileOutputStream(directory.getPath()+"/BikeMaintenance.backup");
byte[] buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer))>0)
{
myOutput.write(buffer, 0, length);
msg="Backup Succesfull!";
Toast.makeText(MainPage.this,msg,Toast.LENGTH_SHORT).show();
}
// Close and clear the streams
myOutput.flush();
myOutput.close();
myInput.close();
}
catch (FileNotFoundException e)
{
msg="FileNotFoundException";
Toast.makeText(MainPage.this,msg,Toast.LENGTH_SHORT).show();
e.printStackTrace();
}
catch (IOException e)
{
msg="Backup Unsuccesfull!";
Toast.makeText(MainPage.this,msg,Toast.LENGTH_SHORT).show();
}
}
我哪里错了？这可能是什么原因？我为此搜索了解决方案，但未找到解决方案。
这是logcat输出：
java.io.FileNotFoundException: /data/data/com.example.hello/databases/BikeMaintenance.db: open failed: ENOENT (No such file or directory) at libcore.io.IoBridge.open(IoBridge.java:416) at java.io.FileInputStream.(FileInputStream.java:78) at java.io.FileInputStream.(FileInputStream.java:105) at com.example.hello.MainPage.exportdata(MainPage.java:625) at com.example.hello.MainPage.backup(MainPage.java:692) at com.example.hello.MainPage$1.onClick(MainPage.java:494) at com.android.internal.app.AlertController$ButtonHandler.handleMessage(AlertController.java:166) at android.os.Handler.dispatchMessage(Handler.java:99) at android.os.Looper.loop(Looper.java:137) at android.app.ActivityThread.main(ActivityThread.java:4745) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:511) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) at dalvik.system.NativeStart.main(Native Method) Caused by: libcore.io.ErrnoException: open failed: ENOENT (No such file or directory) at libcore.io.Posix.open(Native Method) at libcore.io.BlockGuardOs.open(BlockGuardOs.java:110) at libcore.io.IoBridge.open(IoBridge.java:400) ... 14 more
答案 0 :(得分：1)
您的代码看起来不错，但我认为您没有权限访问该.db文件，您可以使用DataBaseHelper类来访问您的.db文件
public class DataBaseHelper extends SQLiteOpenHelper {
private static String DB_PATH = "/data/data/com.android.electricbillgenerator/databases/";
private static String DB_NAME = "BikeMaintenance.db";
private SQLiteDatabase myDataBase;
private Context myContext;
public static final String COLUMN_ID = "_id";
public static final String COLUMN_USERNAME = "UserName";
public static final String COLUMN_PASSWORD = "Password";
public static final String TABLE_NAME = "Login";
private static final String DATABASE_NAME = "BikeMaintenance.db";
private static final int DATABASE_VERSION = 1;
// Database creation sql statement
// private static final String DATABASE_CREATE = "create table "
// + TABLE_NAME + "(" + COLUMN_ID
// + "," + COLUMN_USERNAME
// + "," + COLUMN_PASSWORD+ ");";
// private static final String DATABASE_CREATE = "create table "
// + TABLE_NAME + "(" + COLUMN_ID
// + " integer primary key autoincrement, " + COLUMN_USERNAME
// + " text not null," + COLUMN_PASSWORD+ "text not null);";
public DataBaseHelper(Context context) {
super(context, DATABASE_NAME, null, 8);
this.myContext = context;
boolean dbexist = checkDataBase();
if (dbexist) {
//System.out.println("Database exists");
openDataBase();
} else {
System.out.println("Database doesn't exist");
try {
createDataBase();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
@Override
public void onCreate(SQLiteDatabase database) {
// try {
// database.execSQL(DATABASE_CREATE);
// } catch (SQLException e) {
// // TODO Auto-generated catch block
// e.printStackTrace();
// }
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// Log.w(DataBaseHelper.class.getName(),
// "Upgrading database from version " + oldVersion + " to "
// + newVersion + ", which will destroy all old data");
// db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
// onCreate(db);
}
/**
* Creates a empty database on the system and rewrites it with your own database.
* */
public void createDataBase() throws IOException{
boolean dbExist = checkDataBase();
if(dbExist){
//do nothing - database already exist
}else{
//By calling this method and empty database will be created into the default system path
//of your application so we are gonna be able to overwrite that database with our database.
this.getReadableDatabase();
try {
copyDataBase();
} catch (IOException e) {
throw new Error("Error copying database");
}
}
}
/**
* Check if the database already exist to avoid re-copying the file each time you open the application.
* @return true if it exists, false if it doesn't
*/
private boolean checkDataBase(){
SQLiteDatabase checkDB = null;
try{
String myPath = DB_PATH + DB_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}catch(SQLiteException e){
//database does't exist yet.
}
if(checkDB != null){
checkDB.close();
}
return checkDB != null ? true : false;
}
/**
* Copies your database from your local assets-folder to the just created empty database in the
* system folder, from where it can be accessed and handled.
* This is done by transfering bytestream.
* */
private void copyDataBase() throws IOException{
//Open your local db as the input stream
InputStream myInput = myContext.getAssets().open(DB_NAME);
// Path to the just created empty db
String outFileName = DB_PATH + DB_NAME;
//Open the empty db as the output stream
OutputStream myOutput = new FileOutputStream(outFileName);
//transfer bytes from the inputfile to the outputfile
byte[] buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer))>0){
myOutput.write(buffer, 0, length);
}
//Close the streams
myOutput.flush();
myOutput.close();
myInput.close();
}
public void openDataBase() throws SQLException{
//Open the database
String myPath = DB_PATH + DB_NAME;
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}
@Override
public synchronized void close() {
if(myDataBase != null)
myDataBase.close();
super.close();
}
}
答案 1 :(得分：0)
来自Android文档
public FileInputStream (File file)
Constructs a new FileInputStream that reads from file.
Parameters
file the file from which this stream reads.
Throws
FileNotFoundException if file does not exist.
您谈到的是存在的文件夹，但错误与文件有关。仔细检查文件是否真的存在，也许用adb
$ adb shell ls /data/data/com.example.hello/databases/BikeMaintenance.db
或包含目录的权限。