Develop Reference

I can't write to the external SD card(extSdCard) in Android Studio

I have created an android app that needs to create a folder and write text files on my external SD card(extSdCard). I am using the Galaxy S4 device and have written the following codes for that. I already know the path of /mnt/.. file and have created a string for it. The android manifest.xml file uses the permission.i have checked the codes in "adb logcat" in Cmd prompt and it does not give any error but doesn't create any folder. The device has also been checked unconnected with the PC. Would appreciate if you help me. Here is the code.
String externalFilePath="/mnt/extSdCard/tmp";
Log.d(TAG, "externalFilePath is: "+externalFilePath);
File myfile = new File(externalFilePath, "Hello");

First of all make sure that you have this line inside your manifest,xml, somewhere outside application tag.
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
Then you can write a File doing this :
File sdcard = Environment.getExternalStorageDirectory();
File dir = new File(sdcard.getAbsolutePath() + "/tmp/");
// creates if doesn't exists
dir.mkdir();
// create a File
File file = new File(dir, "Example.txt");
FileOutputStream os = outStream = new FileOutputStream(file);
//this is the text that will be inside of the Example.txt
String data = "Hello world";
os.write(data.getBytes());
os.close();
Hope it helps :)

try this code to generate files under your application package
File path = getExternalFilesDir(Environment.DIRECTORY_PICTURES);
// Replace DIRECTORY_PICTURES with your needs
File file = new File(path, "Hello");
Also make sure you have added the permissions

Android RenameTo leaves empty file

Could you please help me. renameTo() leaves empty old file. So I see 2 files in file system with new name and old name. The size of old file is 0. If I delete old file after renaming it says that file does not exist while staying in file system.
An absolute path of directory is:
/storage/sdcard0/DCIM/Camera
My code:
String dir = oldpath.substring(0, oldpath.lastIndexOf("/"));
File directory = new File(dir);
File from = new File(directory, oldfilename);
File to = new File(directory, newname);
renamed = from.renameTo(to);

Try this code:
File sdcard = new File("/storage/sdcard0/DCIM/Camera");
File from = new File(sdcard, "from.txt"); // Don't forget to set the file extension.
File to = new File(sdcard, "to.txt"); // In this case, we have a '.txt' file extension.
from.renameTo(to);
You can get the sdcard directory in String type programmatically by using this code:
String sdcard = Environment.getExternalStorageDirectory().getPath();
Don't forget to add this permission in manifest:
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

RenameTo leaves an empty copy of the original file if the file is opened by another process.
For example, I wanted to rename a file after the DownloadManager finished downloading it. The DownloadManager apparently notifies the BroadcastReceivers after the download, but before closing the file. This caused the renameTo in the onReceive to leave an empty copy. To solve this problem, I had to make the BroadcastReceiver to wait half a second before renaming the file.

You must remember about two things : The file and the file extension (file type). The following is wrong way sometimes, in case of deleting and renaming file :
File file = new File (dir+"/"+myfile)
The right way is :
File file = new File (dir, myfile+".db");
For the Full Aprroach, you could look at Answer Here.

IOException: No Such File or Directory (Android)

This is my first Android app and my first attempt at writing something to file. I'm trying to capture a log according to these instructions and I'm getting the FileNotFoundExeption ENOENT (No such file or directory). That's fair enough because the directory does not exist. But then how do I create the directory? Or use another one? I don't know best practices for where to write logs to email them, nor do I know how to make a new directory for them.
This is the path I'm trying to use.
String path = Environment.getExternalStorageDirectory() + "/" + "MyFirstApp/";
String fullName = path + "mylog";
File file = new File (fullName);

The parent dir doesn't exist yet, you must create the parent first before creating the file
String path = Environment.getExternalStorageDirectory() + "/" + "MyFirstApp/";
// Create the parent path
File dir = new File(path);
if (!dir.exists()) {
dir.mkdirs();
}
String fullName = path + "mylog";
File file = new File (fullName);
Edit:
Thanks to Jonathans answer, this code sample is more correct. It uses the exists() method.
You also need the permission in your manifest:
<manifest ...>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
...
</manifest>

I'd like to add to Francesco's answer, that instead of asking if it's a directory, you could ask if it exists with dir.exists() method.
And also check that you've set the proper permissions in the Manifest file.
Hope it helps
Jonatan

Can't read the file from internal storage (file doesn't exist issue)

I have a routed device and when I do this
adb shell cat /data/misc/bluetooth/dynamic_auto_pairing.conf
it prints the content of this file.
But in my code when I write something like this, it says that the file does not exist. Well from the console I see it I know is there, but from code I can't read it. My question is what is the problem , am I missing some permission or what is the problem ? can someone provide me with some code to read the content from this file.
Thanks
File pa = new File("/data/misc/bluetooth/","dynamic_auto_pairing.conf");
//this doesn't works also
//File pa = new File("/data/misc/bluetooth","dynamic_auto_pairing.conf");
//File pa = new File("/data/misc/bluetooth/dynamic_auto_pairing.conf");
if(pa.exists()){
Log.v("tag", "does exists");
}else{
Log.v("tag", "does NOT exist");
}

If the file is on sdcard, try:
File pa = new File(Environment.getExternalStorageDirectory() + "/data/misc/bluetooth/dynamic_auto_pairing.conf");
Also try to add:
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
outside <application></application> in your manifest file.
EDIT
If the file is in internal memory: Your app can read only from a special folder in internal memory. The path to that folder is returned by:
getFilesDir().getAbsolutePath()
So put the file there and read it with openFileInput().
More info:
http://developer.android.com/guide/topics/data/data-storage.html#filesInternal

From the docs for File...
public File (String dirPath, String name)
Constructs a new File using the specified directory path and file name, placing a path separator between the two.
In your code you are using...
File pa = new File("/data/misc/bluetooth/","dynamic_auto_pairing.conf");
...and because your dirPath ends with a separator "/data/misc/bluetooth/" it will result in two separators. In other words, effective path will be...
/data/misc/bluetooth//dynamic_auto_pairing.conf
Note the // after 'bluetooth`

If you are using android 6.0 or higher. You must request permission in code.

save image to sdcard android Directory problem

Im trying to save data to sdCard first i tried to saave it privately within app directory on externalStorage using getExternalFilesDir but gives me nullPointerException so i tried the other way given below it worked but when i want to store files into a custom directory that i want to named myself it give me error:
FileOutputStream os;
dirName = "/mydirectory/";
try {
if (android.os.Environment.getExternalStorageState().equals(
android.os.Environment.MEDIA_MOUNTED)){
File sdCard = Environment.getExternalStorageDirectory();
File dir = new File (sdCard.getAbsolutePath() + dirName);
dir.mkdirs();
//File file = new File(this.getExternalFilesDir(null), this.dirName+fileName); //this function give null pointer exception so im using other one
File file = new File(dir, dirName+fileName);
os = new FileOutputStream(file);
}else{
os = context.openFileOutput(fileName, MODE_PRIVATE);
}
resizedBitmap.compress(CompressFormat.PNG, 100, os);
os.flush();
os.close();
}catch(Exception e){
}
ErrorLog:
java.io.FileNotFoundException: /mnt/sdcard/mvc/mvc/myfile2.png (No such file or directory)

Your directory "/mnt/sdcard/mvc/mvc" may not exist. What about changing your path to store the image in the Environment.getExternalStorageDirectory() path and then working from there?
Also, as Robert pointed out, make sure you have write permission to external storage in your manifest.
Edit - to create directories:
String root = Environment.getExternalStorageDirectory().toString();
new File(root + "/mvc/mvc").mkdirs();
Then you can save a file to root + "/mvc/mvc/foo.png".

Have you requested permission to write onto SD card? Add the following string to you app manifest:
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

You should check if you have added the required permission android.permission-group.STORAGE to your app. Without that permission you won't be able to access anything on the SD-Card.
BTW: On the Android system I know the SD-card is mounted on /sdcard not /mnt/sdcard

I found this book to be very helpful: "Pro Android Media: Developing Graphics, Music, Video, and Rich Media Apps for Smartphones and Tablets". I noticed a part that allows saving images and stuff to the SD card.