Cosc 4730

1. Cosc 4730 Files: Internal and External storage

2. Note about Streams. • In Java SE • We use BufferedWriter and BufferedReader streams for most io • These are only sort of implemented. • Generally we get InputStream and OutputStream • And pass them to DataInputStream and DataOutputStream • There are couple of other streams as well.

3. DataOutputStream • DyteArrayOutputStreambaos = new ByteArrayOutputStream(); • DataOutputStream dos = new DataOutputStream(baos); • Now you write records data to dos use one or more methods • write: writes an array of bytes, with an offset and length of byte array • writeBoolean: writes a boolean to the stream • writeByte: writes one byte to the stream • writeChar: writes one character to the stream • writeChars: write a String as a sequence of characters • writeDouble: converts Double to long (doubleToLongBits) and writes long to stream • writeFloat: converts float to a int (floatToIntBits) and writes the int to the stream • writeInt: writes an integer to the stream • writeLong: writes a long to the stream • writeShort: writes a short intger to the stream • writeUTF: writes a String using UTF-8 encoding to the stream • Once that's done, use baos variable to create the byte variable • byte[] bytes = boas.toByteArray();

4. DataInputStream • When reading back the data: • byteArrayInputStreambais = new ByteArrayInputStream(bytes); • DataInputStream dis = new DataINputStream(bais); • Now read it back the same way it written, using: • read: Reads an array of bytes from the stream • readBoolean: Reads a boolean from the stream • readByte: Reads a single byte from the stream • readChar: Reads a character from the stream • readDouble: Reads a long from the stream and converts it to a double • readFloat: reads an int from the stream and converts it to a float • readInt: reads an integer from the stream • readLong: reads long integer from the stream • readShort: read a short integer from the stream • readUTF: reads a string in UTF-8 enconding.

5. The other 2 streams (2) • input is a little harder, since InputStreamReader read() returns one character at a time and it's an integer value fc= (FileConnection) Connector.open(fs,Connector.READ); InputStreamReader in = new InputStreamReader(fc.openInputStream()); t = ""; //now read in the text file, one character at a time. inti = in.read(); while (i !=-1) { //To stop at end of line use (i !=-1 && (char) i != '\n') t += (char)i; i = in.read(); } fc.close(); System.out.println("read from file: "+t);

6. The other 2 streams (2) • Using these can make things simpler. • But • Now you have split up the strings • String tokenizers covered at the end of this lecture. • Convert numbers to the correct type. • Otherwise • Now you can read text files created on most machines and write files that can be read by most computers as well.

7. PrintStream • You may also find the printStream useful as well for output. • one doesn't throw exceptions, sets a status flag • Uses print and println • Example String t = "Hi There"; int x = 12; PrintStream out = new PrintStream(fc.openOutputStream()); out.println(t); out.print(x); out.print(" "); out.println(x);

8. FileSystem

9. Android and data Storage • Android has three different methods for data storage. • Private but stored in the application private area • Public but stored in the application area on the SDcard (or internal area) • For both of the above, when you uninstall the app, the data is already deleted (assuming SDcard is also installed). • Public stored in the public file system, normally on the SDcard (but maybe internal area if SDcard doesn’t exist) • We can also read files from the apk as well. • Note, you can’t write to the apk.

10. Internal vs External storage • Internal storage • You can save files directly on the device's internal storage. • By default, files saved to the internal storage are private to your application and other applications cannot access them (nor can the user). • When the user uninstalls your application, these files are removed. • External storage • This can be a removable storage media (such as an SD card) or an internal (non-removable) storage. • Files saved to the external storage are world-readable and can be modified by the user when they enable USB mass storage to transfer files on a computer.

11. Internal Storage • FileOutputStreamopenFileOutput(String File, MODE) • File: the filename for output • MODE: Context.MODE_PRIVATE, MODE_APPEND, MODE_WORLD_READABLE, and MODE_WORLD_WRITEABLE. • Note If the file already exists, then it will be overwritten, except with MODE_APPEND. • It returns a FileOutputStream, which we then send to DataOutputStream. • Close() when you are finished with the file.

12. Internal Storage (2) • FileInputStreamopenFileInput(String File) • Open the files named. • Again, send it to DataInputStream for ease of reading. • getFilesDir() • Gets the absolute path to the filesystem directory where your internal files are saved. • getDir() • Creates (or opens an existing) directory within your internal storage space. • deleteFile() • Deletes a file saved on the internal storage. • String[] fileList() • Returns an array of files currently saved by your application. A note, in a fragment, you will need to use getActivity(). and then the command Since it is methods come from context, which a fragment doesn’t have directly.

13. Internal Example • Output dos = new DataOutputStream( openFileOutput("FileExample", Context.MODE_PRIVATE)); dos.writeUTF("First line of the file"); dos.writeUTF(“Second line of the file"); dos.close(); • Input String flist[] = fileList(); in = new DataInputStream( openFileInput(flist[0]) ) ; while(true) try { label1.append(in.readUTF() + "\n"); //label1 is a TextView } catch (EOFException e) { //reach end of file in.close(); }

14. Files in the apk • If you have a static (read only) file to package with your application at compile time, you can save the file in your project in res/raw/myDataFile, and then open it with getResources().openRawResource (R.raw.myDataFile). • It returns an InputStream object that you can use to read from the file.

15. External files • Before accessing files on external storage, you’ll need to check to see if the media is available. • Code to check booleanmExternalStorageAvailable = false;booleanmExternalStorageWriteable = false;String state = Environment.getExternalStorageState();if (Environment.MEDIA_MOUNTED.equals(state)) {    // We can read and write the mediamExternalStorageAvailable = mExternalStorageWriteable = true;} else if (Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {    // We can only read the mediamExternalStorageAvailable = true;mExternalStorageWriteable = false;} else {    // Something else is wrong. It may be one of many other states, but all we need    //  to know is we can neither read nor writemExternalStorageAvailable = mExternalStorageWriteable = false;}

16. External Files (2) • //API 8 and above • getExternalFilesDir() //public but in app data. • For none shared files • Creates the directory /Android/data/<package_name>/files/ • Directory and all files deleted when app is uninstalled. • getExternalStoragePublicDirectory() //public • For files that are to be shared. • Not deleted when app is uninstalled.

17. Environment. directories

18. External Files (3) • File file = new File(getExternalFilesDir(null), “myfile.txt"); • Create directory if needed and the spot for the file, called myfile.txt • null: it’s a file for my application • If I wanted a music directory then • File file = new File(getExternalFilesDir( Environment.DIRECTORY_MUSIC), “file.mp3"); • Place in the a subdirectory of music.

19. External Files (4) • Read • in = new DataInputStream(new FileInputStream(file) ); • Write • dos = new DataOutputStream(new FileOutputStream(file) ); • Append: • dos = new DataOutputStream(new FileOutputStream(file,true) ); • Read or write as normal. Then close the file when you are done. • Other useful methods of file • file.exists() //return true if file exists • file.delete(); //deletes the file • See http://developer.android.com/reference/java/io/File.html for more.

20. external files (5) • getExternalStoragePublicDirectory() File path = Environment.getExternalStoragePublicDirectory( Environment.DIRECTORY_PICTURES); • There is no NULL version. File file = new File(path, "DemoPicture.jpg"); // Make sure the directory exists.path.mkdirs(); //NOT file, other it creates the file as a directory.//Now use file just like before.

21. BufferedWriter /Reader stream. • You can use the Buffered, but not completely implemented. • Examples: • Write a file BufferedWriterbW = new BufferedWriter(new FileWriter(file,true)); //append bW.write("Hi There"); //some some text bW.newLine(); //write out a newLine, no writeLinemethed bW.flush(); //flush may not be necessary, but good practice bW.close(); and close • Reading a file BufferedReaderin = new BufferedReader(new FileReader(file)); line = in.readLine(); while (line != null) { //null means end of file logger.append(line+"\n"); //logger is a TextView line = in.readLine(); } in.close();

22. Additional notes. Strings

23. Breaking up strings. • the string.split(String RegularExpression) is included on Android. • So String[] = line.split(“ “) would break up the string in line based on a space and put the resulting string array • Java.util has the StringTokenizer, but considered “legacy” and should not be used.

24. Example code • Filesystem.zip • Has three fragments • Each writes and reads a file in a different location • Local private, on the SD card public and into the download directory on the SD card. • You can click the run on each of them to have run again again, so see it work.

25. Q A &