我有一个数据库备份存储在驱动器的应用程序文件夹中。下面是我编写的代码。
public void startRestore(View view)
{
int EXTERNAL_WRITE_PERMISSION = ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE);
if(Build.VERSION.SDK_INT>= Build.VERSION_CODES.M)
{
if(EXTERNAL_WRITE_PERMISSION != PackageManager.PERMISSION_GRANTED)
{
if (ActivityCompat.shouldShowRequestPermissionRationale(this, Manifest.permission.WRITE_EXTERNAL_STORAGE))
{
Snackbar.make(mLayout, "Write permission is required",
Snackbar.LENGTH_INDEFINITE).setAction("OK", new View.OnClickListener() {
@Override
public void onClick(View view) {
// Request the permission
ActivityCompat.requestPermissions(BackupActivity.this,
new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},
PERMISSION_REQUEST_STORAGE);
}
}).show();
} else {
ActivityCompat.requestPermissions(this,
new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE},
PERMISSION_REQUEST_STORAGE);
}
}
}
if (backupExists())
{
Log.d("RESTORE: ", "Started restore");
final String driveFileID = sharedPreferences.getString("dbBackupDriveFileID", "");
final DriveFile driveFile = DriveId.decodeFromString(driveFileID).asDriveFile();
Log.d("RESTORE_FileID: ", driveFileID);
final Task<DriveContents> openFileTask = mDriveResourceClient.openFile(driveFile, DriveFile.MODE_READ_ONLY);
openFileTask.continueWithTask(new Continuation<DriveContents, Task<Void>>()
{
@Override
public Task<Void> then(@NonNull Task<DriveContents> task) throws Exception
{
Log.d("RESTORE: ", "open File task");
DriveContents driveContents = task.getResult();
//TODO download file an add to database
InputStream inputStream = driveContents.getInputStream();
byte[] buf = new byte[8192];
int c = 0;
String baseDir = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getAbsolutePath();
String fileName = DatabaseHelper.DATABASE_NAME;
Log.d("RESTORE: ", baseDir + "/" +fileName);
File f = new File(baseDir+File.pathSeparator+fileName);
if(f.canWrite())
{
Log.d("RESTORE: ", "File writable");
OutputStream outputStream = new FileOutputStream(f);
while ((c = inputStream.read(buf, 0, buf.length)) > 0)
{
outputStream.write(buf, 0, c);
outputStream.flush();
}
outputStream.close();
}
else
{
Log.d("RESTORE: ", "File not writable");
}
return mDriveResourceClient.discardContents(driveContents);
}
})
.addOnFailureListener(new OnFailureListener()
{
@Override
public void onFailure(@NonNull Exception e)
{
}
});
}
else
{
Toast.makeText(this, "Backup does not exists", Toast.LENGTH_SHORT).show();
}
}
在上面的代码中，控件始终达到 Log.d("RESTORE: ", "File not writable"); 。我具有清单中定义的写入权限，并且还授予了运行时权限。日志中也没有错误。
以下是备份功能供参考。
public void startBackup(View view)
{
final ProgressDialog progressDialog = new ProgressDialog(this);
final File currentDB = this.getDatabasePath(DatabaseHelper.DATABASE_NAME);
Log.d("DATABASE: ", currentDB.getAbsolutePath());
Log.d("DATABASE: ", currentDB.getName());
progressDialog.setMessage("Backing Up!!!!");
progressDialog.show();
final Task<DriveFolder> appFolderTask = mDriveResourceClient.getAppFolder();
final Task<DriveContents> createContentsTask = mDriveResourceClient.createContents();
Tasks.whenAll(appFolderTask, createContentsTask)
.continueWithTask(new Continuation<Void, Task<DriveFile>>()
{
@Override
public Task<DriveFile> then(@NonNull Task<Void> task) throws Exception
{
DriveFolder parent = appFolderTask.getResult();
DriveContents contents = createContentsTask.getResult();
InputStream inputStream = null;
try
{
inputStream = new FileInputStream(currentDB);
}
catch (FileNotFoundException e)
{
e.printStackTrace();
}
OutputStream outputStream = contents.getOutputStream();
int c = 0;
byte[] buf = new byte[8192];
if (inputStream != null)
{
while ((c = inputStream.read(buf, 0, buf.length)) > 0)
{
outputStream.write(buf, 0, c);
outputStream.flush();
}
outputStream.close();
}
else
{
Toast.makeText(BackupActivity.this, "Some error occurred", Toast.LENGTH_SHORT).show();
}
MetadataChangeSet changeSet = new MetadataChangeSet.Builder()
.setMimeType("application/x-sqlite3")
.setTitle(currentDB.getName())
.build();
return mDriveResourceClient.createFile(parent, changeSet, contents);
}
})
.addOnSuccessListener(this, new OnSuccessListener<DriveFile>() {
@Override
public void onSuccess(DriveFile driveFile)
{
progressDialog.dismiss();
String driveFileID = driveFile.getDriveId().encodeToString();
String dateTime = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss", Locale.getDefault()).format(new Date());
SharedPreferences.Editor editor = sharedPreferences.edit();
editor.putString("dbBackupDriveFileID", driveFileID);
editor.putString("lastDbBackupTime", dateTime);
editor.apply();
Log.d("DRIVE_FILE", driveFileID);
String d = getString(R.string.last_backup) + dateTime;
textView.setText(d);
Toast.makeText(BackupActivity.this, "Backup Successful. File "+driveFile.getDriveId()
.encodeToString(), Toast.LENGTH_LONG).show();
}
})
.addOnFailureListener(this, new OnFailureListener() {
@Override
public void onFailure(@NonNull Exception e)
{
progressDialog.dismiss();
Log.e("DRIVE ", "Unable to create file", e);
Toast.makeText(BackupActivity.this, "Unable to backup", Toast.LENGTH_SHORT).show();
}
});
}
我没有使用File f = new File(baseDir+File.pathSeparator+fileName);，而是将文件用法替换为FileOutputStream。修改部分恢复功能：
DriveContents driveContents = task.getResult();
//TODO download file an add to database
InputStream inputStream = driveContents.getInputStream();
byte[] buf = new byte[8192];
int c = 0;
if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED))
{
Log.d("RESTORE: ", "External DIR mounted");
String baseDir = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getAbsolutePath();
String fileName = DatabaseHelper.DATABASE_NAME;
String fileFullName = baseDir + File.separator + fileName;
Log.d("RESTORE: ", fileFullName);
FileOutputStream outputStream;
outputStream = new FileOutputStream(fileFullName, false);
while ((c = inputStream.read(buf, 0, buf.length)) > 0) {
outputStream.write(buf, 0, c);
outputStream.flush();
}
outputStream.close();
}
else
{
Log.d("RESTORE: ", "External DIR not mounted");
}
这解决了我的问题。
答案可以很简单，只需在File f = new File(baseDir+File.pathSeparator+fileName);之后和if(f.canWrite())之前立即添加f.mkdirs()。
但是，canWrite可以返回 false 的原因有很多，所以你应该检查 STATE(可能在你尝试之前canWrite
就个人而言，我使用以下相当冗长的代码：-
class StoreData {
private String directory; //Note built internally and includes subdirectory
private String subdirectory;
private String filename;
private boolean mounted;
private boolean inerror;
private boolean fileexists;
private boolean direxists;
private long errorcode;
private ArrayList<String> errorlist = new ArrayList<>();
private ArrayList<File> otherfilesindirectory = new ArrayList<>();
// Need to be aware of the API
@SuppressWarnings("unused")
public static final int API_VERSION = Build.VERSION.SDK_INT;
private static final long UNMOUNTED = 1;
private static final long FILEIOERR = 2;
private static final long READERR = 4;
private static final String NEWLINE = "rn";
/**
* Sole Constructor for a StoreData object
* Note instantiating creates but the deletes a file, assuming that
* no prior errors left the instance in an unusable state (as initially set)
* Note instantiating, if existcheck (3rd param) is true, does not create
* and delete the file, rather it checks that the file exists
* typically for reading an existing file.
*
* @param subdirectory - Sub directory in which to create file
* @param filename - the file name where actual data will be stored
* @param existcheck - whether or not to check for the existence of the file
*
* Note!! existcheck, if true, will not try to create the file
*/
public StoreData(String subdirectory, @SuppressWarnings("SameParameterValue") String filename, boolean existcheck) {
fileexists = false;
direxists = false;
mounted = false;
inerror = false;
errorcode = 0;
this.directory = "";
this.subdirectory = subdirectory;
this.filename = filename;
// External Storage must be mounted.
String chkmnt = Environment.getExternalStorageState();
if(!(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED))) {
switch (Environment.getExternalStorageState()) {
case Environment.MEDIA_SHARED : {
errorlist.add(
"Although External Storage is present." +
" It cannot be used as it's in use via USB." +
"nDisconnect the USB cable and then try again."
);
break;
}
case Environment.MEDIA_REMOVED : {
errorlist.add(
"External Storage is not present." +
"nInsert an SD Card."
);
break;
}
case Environment.MEDIA_EJECTING : {
errorlist.add(
"External Storage is being ejected." +
"nRe-insert the SD Card."
);
break;
}
case Environment.MEDIA_NOFS : {
errorlist.add(
"External Storage is blank or does not have the correct" +
" filesystem present." +
"nUse a valid SDCard."
);
break;
}
case Environment.MEDIA_BAD_REMOVAL : {
errorlist.add(
"External Storage was removed incorrectly." +
"nRe-insert the SD Card, if this fails then" +
" try restarting the device."
);
break;
}
case Environment.MEDIA_CHECKING : {
errorlist.add(
"External Storage is unavailable as it is being checked." +
"nTry again."
);
}
case Environment.MEDIA_MOUNTED_READ_ONLY : {
errorlist.add(
"External Storage is READ ONLY." +
"nInsert an SD card that is not protected."
);
}
case Environment.MEDIA_UNKNOWN : {
errorlist.add(
"External Storage state is UNKNOWN." +
"ntry a different SD Card."
);
}
case Environment.MEDIA_UNMOUNTABLE : {
errorlist.add(
"External Storage cannot be mounted." +
"nTry re-inserting the SD Card or using a different SD Card."
);
}
case Environment.MEDIA_UNMOUNTED : {
errorlist.add(
"External Storage is not mounted." +
"nTry re-inserting the SD Card or using a different SD Card."
);
}
default: {
errorlist.add(
"Undefined Error"
);
}
}
this.errorcode = UNMOUNTED;
return;
} else {
this.mounted = true;
}
// Get the required directory and specified sub directory
File dir = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS),subdirectory);
this.directory = dir.getPath();
// If existcheck is true check that the directories exist
if (existcheck && dir.exists()) {
direxists = true;
}
// If the directories do not exist try to create them and redo check
// Note! existcheck is more for file level so always try to create
// directories
else {
boolean x = dir.mkdirs();
if(dir.exists()) {
direxists = true;
}
}
if(direxists) {
refreshOtherFilesInDirectory();
}
// File level
File f = new File(directory,filename);
// Check if the file exists if requested and return if it does
if (existcheck) {
if (f.exists()) {
fileexists = true;
}
return;
}
try {
boolean x = f.createNewFile();
}
catch (IOException e) {
e.printStackTrace();
this.errorcode = FILEIOERR ;
errorlist.add(
"File Error " + e.getMessage()
);
return;
}
boolean x = f.delete();
}
@SuppressWarnings({"ConstantConditions", "UnusedReturnValue"})
public boolean refreshOtherFilesInDirectory() {
boolean rv = true;
File dir = new File(directory);
File[] dirlist = dir.listFiles();
if((dirlist.length) > 0) {
// Sort the list
Arrays.sort(dirlist, new Comparator<File>() {
@Override
public int compare(File object1, File object2) {
return object1.getName().compareTo(object2.getName());
}
});
otherfilesindirectory.clear();
for (File aDirlist : dirlist) {
if (!(aDirlist.getName().equals(this.filename))) {
otherfilesindirectory.add(aDirlist);
}
}
}
return rv;
}
/**
* writeData - Write data to the file from String Arraylist passed
* Note!! a linefeed is added to each string
* @param datatowrite - strng ArrayList holding data to write
* @return result flag
*/
@SuppressWarnings("unused")
public boolean writeData(ArrayList<String> datatowrite) {
// Check that this instance is OK
if (!this.isOK()) {
this.errorlist.add(
"nError prior to call to writeData method."
);
return false;
}
// Prepare to write
this.errorlist.clear();
File f = new File(this.directory,File.separator + this.filename);
try {
boolean x = f.createNewFile();
FileOutputStream fos = new FileOutputStream(f);
OutputStreamWriter osw = new OutputStreamWriter(fos);
for (int i = 0; i < datatowrite.size(); i++) {
osw.write(datatowrite.get(i) + NEWLINE);
}
osw.flush();
osw.close();
fos.flush();
fos.close();
this.fileexists = true;
}
catch (IOException e) {
e.printStackTrace();
this.errorcode = FILEIOERR;
errorlist.add(
"File Error " + e.getMessage()
);
return false;
}
return true;
}
/**
* readData - Populate a String ArrayList from the data in the file
* Note! Assumes linefeeds in the file separate strings of data
* @return - result flag
*/
@SuppressWarnings("unused")
public ArrayList<String> readData() {
ArrayList<String> rv = new ArrayList<>();
if(!this.isOKandExists()) {
this.errorlist.add(
"nError prior to call to readData method or the file doesn't exist."
);
this.errorcode = READERR;
return rv;
}
this.errorlist.clear();
File f = new File(this.directory,File.separator + this.filename);
try {
FileInputStream fis = new FileInputStream(f);
InputStreamReader isr = new InputStreamReader(fis);
BufferedReader br = new BufferedReader(isr);
String line;
while((line = br.readLine()) != null) {
rv.add(line);
}
}
catch (IOException e) {
e.printStackTrace();
this.errorcode = READERR;
errorlist.add(
"File Read Error" + e.getMessage()
);
return rv;
}
return rv;
}
/**
* isOK - Check if object is usable
* @return true if OK else false
*/
public boolean isOK() {
return !(errorcode != 0 || !mounted || inerror);
}
/**
* exists = Check if the file exists
* @return - Result of check
*/
@SuppressWarnings("unused")
public boolean exists() {
return this.fileexists;
}
public boolean isOKandExists() {
return this.isOK() && this.fileexists;
}
/**
* Return a string displaying the instances details
* @return string displaying object's members
*/
public String Display() {
String rv;
rv = "Directory path=" + directory + "n" +
"SubDirectory=" + subdirectory + "n" +
"Filename=" + filename + "n" +
"Mounted =" + Boolean.toString(mounted) + "n" +
"Directory Exists=" + Boolean.toString(this.direxists) + "n" +
"File Exists=" + Boolean.toString(this.fileexists) + "n" +
"In Error=" + Boolean.toString(inerror) + "n" +
"Last Error Code=" + Long.toString(errorcode);
return rv;
}
@SuppressWarnings("unused")
public String DisplayWithOtherFiles() {
String rv;
rv = this.Display() + "nOther Files in Directory (" + this.directory + ") ";
for(int i = 0; i < otherfilesindirectory.size(); i++) {
rv = rv + "nt" + otherfilesindirectory.get(i).getName();
}
return rv;
}
/**
* Retrieve generated error messages. if any
* @return sting comprised of all error messages generated
*/
@SuppressWarnings("unused")
public String getErrorMessages() {
String rv = "";
for(int i = 0; i < errorlist.size(); i++) {
rv = rv + errorlist.get(i);
}
return rv;
}
/**
* Method: getDirectory - get the backup directory as a String
* @return Directory as a String
*/
public String getDirectory() {
return this.directory;
}
/**
* Method: getFilename - get the filename of the object as a String
* @return Filename as a String
*/
@SuppressWarnings("unused")
public String getFilename() {
return this.filename;
}
/**
* Method: getSubDirectory - get the sub-directory as a string
* @return Sub-Directory as a String
*/
@SuppressWarnings("unused")
public String getSubDirectory() {
return this.subdirectory;
}
/**
* Method: getFilesInDirectory - return an ArrayList of type File
* @return List of files in the directory as an ArrayList<File>
*/
public ArrayList<File> getFilesInDirectory() {
return this.otherfilesindirectory;
}
}