Wie erstelle ich eine Datei in Android?

Wie erstelle ich eine Datei, schreibe Daten hinein und lese Daten daraus auf Android? Wenn möglich, geben Sie ein Code-Snippet an.

Von hier aus: http://www.anddev.org/working_with_files-t115.html

//Writing a file...  



try { 
       // catches IOException below
       final String TESTSTRING = new String("Hello Android");

       /* We have to use the openFileOutput()-method
       * the ActivityContext provides, to
       * protect your file from others and
       * This is done for security-reasons.
       * We chose MODE_WORLD_READABLE, because
       *  we have nothing to hide in our file */             
       FileOutputStream fOut = openFileOutput("samplefile.txt",
                                                            MODE_PRIVATE);
       OutputStreamWriter osw = new OutputStreamWriter(fOut); 

       // Write the string to the file
       osw.write(TESTSTRING);

       /* ensure that everything is
        * really written out and close */
       osw.flush();
       osw.close();

//Reading the file back...

       /* We have to use the openFileInput()-method
        * the ActivityContext provides.
        * Again for security reasons with
        * openFileInput(...) */

        FileInputStream fIn = openFileInput("samplefile.txt");
        InputStreamReader isr = new InputStreamReader(fIn);

        /* Prepare a char-Array that will
         * hold the chars we read back in. */
        char[] inputBuffer = new char[TESTSTRING.length()];

        // Fill the Buffer with data from the file
        isr.read(inputBuffer);

        // Transform the chars to a String
        String readString = new String(inputBuffer);

        // Check if we read back the same chars that we had written out
        boolean isTheSame = TESTSTRING.equals(readString);

        Log.i("File Reading stuff", "success = " + isTheSame);

    } catch (IOException ioe) 
      {ioe.printStackTrace();}

Ich habe den folgenden Code verwendet, um eine temporäre Datei zum Schreiben von Bytes zu erstellen. Und es funktioniert gut.

File file = new File(Environment.getExternalStorageDirectory() + "/" + File.separator + "test.txt");
file.createNewFile();
byte[] data1={1,1,0,0};
//write the bytes in file
if(file.exists())
{
     OutputStream fo = new FileOutputStream(file);              
     fo.write(data1);
     fo.close();
     System.out.println("file created: "+file);
}               

//deleting the file             
file.delete();
System.out.println("file deleted");

Ich habe beschlossen, eine Klasse aus diesem Thread zu schreiben, die für andere hilfreich sein kann. Beachten Sie, dass dies derzeit nur zum Schreiben in das Verzeichnis "files" vorgesehen ist (z. B. nicht zum Schreiben in "sdcard" -Pfade).

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;

import android.content.Context;

public class AndroidFileFunctions {

    public static String getFileValue(String fileName, Context context) {
        try {
            StringBuffer outStringBuf = new StringBuffer();
            String inputLine = "";
            /*
             * We have to use the openFileInput()-method the ActivityContext
             * provides. Again for security reasons with openFileInput(...)
             */
            FileInputStream fIn = context.openFileInput(fileName);
            InputStreamReader isr = new InputStreamReader(fIn);
            BufferedReader inBuff = new BufferedReader(isr);
            while ((inputLine = inBuff.readLine()) != null) {
                outStringBuf.append(inputLine);
                outStringBuf.append("\n");
            }
            inBuff.close();
            return outStringBuf.toString();
        } catch (IOException e) {
            return null;
        }
    }

    public static boolean appendFileValue(String fileName, String value,
            Context context) {
        return writeToFile(fileName, value, context, Context.MODE_APPEND);
    }

    public static boolean setFileValue(String fileName, String value,
            Context context) {
        return writeToFile(fileName, value, context,
                Context.MODE_WORLD_READABLE);
    }

    public static boolean writeToFile(String fileName, String value,
            Context context, int writeOrAppendMode) {
        // just make sure it's one of the modes we support
        if (writeOrAppendMode != Context.MODE_WORLD_READABLE
                && writeOrAppendMode != Context.MODE_WORLD_WRITEABLE
                && writeOrAppendMode != Context.MODE_APPEND) {
            return false;
        }
        try {
            /*
             * We have to use the openFileOutput()-method the ActivityContext
             * provides, to protect your file from others and This is done for
             * security-reasons. We chose MODE_WORLD_READABLE, because we have
             * nothing to hide in our file
             */
            FileOutputStream fOut = context.openFileOutput(fileName,
                    writeOrAppendMode);
            OutputStreamWriter osw = new OutputStreamWriter(fOut);
            // Write the string to the file
            osw.write(value);
            // save and close
            osw.flush();
            osw.close();
        } catch (IOException e) {
            return false;
        }
        return true;
    }

    public static void deleteFile(String fileName, Context context) {
        context.deleteFile(fileName);
    }
}

Schreiben Sie in eine Datei test.txt:

String filepath ="/mnt/sdcard/test.txt";
FileOutputStream fos = null;
try {
        fos = new FileOutputStream(filepath);
        byte[] buffer = "This will be writtent in test.txt".getBytes();
        fos.write(buffer, 0, buffer.length);
        fos.close();
    } catch (FileNotFoundException e) {
         e.printStackTrace();
    } catch (IOException e) {
         e.printStackTrace();
    }finally{
        if(fos != null)
            fos.close();
    }

Lesen Sie aus der Datei test.txt:

String filepath ="/mnt/sdcard/test.txt";        
FileInputStream fis = null;
try {
       fis = new FileInputStream(filepath);
       int length = (int) new File(filepath).length();
       byte[] buffer = new byte[length];
       fis.read(buffer, 0, length);
       fis.close();
    } catch (FileNotFoundException e) {
         e.printStackTrace();
    } catch (IOException e) {
         e.printStackTrace();
    }finally{
        if(fis != null)
            fis.close();
   }

Hinweis: Vergessen Sie nicht, diese beiden Berechtigungen in AndroidManifest.xml hinzuzufügen

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />