Wie erstelle ich eine Datei in Android?

Question

Wie erstelle ich eine Datei, schreibe Daten hinein und lese Daten davon auf Android? Wenn möglich, ein Code-Snippet bereitstellen.

Answer 1

From here: 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();} 

Answer 2

habe ich den folgenden Code eine temporäre Datei für das 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); 
    url = upload.upload(file); 
}    

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

Answer 3

Ich entschied mich, eine Klasse aus diesem Thread zu schreiben, die für andere hilfreich sein kann. Beachten Sie, dass derzeit nur im Verzeichnis "files" geschrieben werden soll (z. B. nicht in Pfade "sdcard" schreiben).

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); 
    } 
} 

Answer 4

schreiben 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 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 Erlaubnis in AndroidManifest hinzuzufügen. xml

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