Copiare un file da una parte all'altra del dispositivo.

Ho avuto non poche difficoltà nel copiare un file da una parte all'altra della memoria del cellulare.
Alla fine ci sono riuscito.
Credo di padroneggiare abbastanza le tecniche per la creazione di un file, ma ho avuto difficoltà nella copia mediante FileInputStream e FileOutputStream

Ora riprovo a trasferirmi un file dalla cartella DCIM/Camera alla cartella DCIM/Screenshots.
Il file è casa.jpg.

Ottengo l'accesso all'external storage.

File sd= Environment.getExternalStorageDirectory();

Voglio sapere qual è il Path di questo file. Come faccio?
Provo:

        File sd= Environment.getExternalStorageDirectory();
        System.out.println("Path: "+Environment.getExternalStorageDirectory().getAbsolutePath());

11-15 17:44:47.621 13976-13976/? I/System.out: Path: /storage/emulated/0

Ora voglio i nomi di tutti i sottofiles e le sottocartelle di questo External Storage.

        File sd= Environment.getExternalStorageDirectory();
        System.out.println("Path: "+Environment.getExternalStorageDirectory().getAbsolutePath());
        
        for(File f : sd.listFiles()){
            System.out.println(f.toString());
            
        }

Proviamo:

11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/Samsung
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/Android
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/DCIM
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/Music
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/Podcasts
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/Ringtones
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/Alarms
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/Notifications
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/Pictures
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/Movies
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/Download
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/Playlists
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/WhatsApp
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/.aide
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/AppProjects
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/docs
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/Voice Recorder
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/com.facebook.katana
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/runtastic
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/com.facebook.orca
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/.facebook_cache
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/MBSTPH
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/MBSTGO
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/VIRAL
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/LazyList
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/Tencent
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/pacer_steps_chart.jpg
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/JavaScript
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/.mrnom
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/adb
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/CallRecordings
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/.SMT
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/.Studio
11-15 17:48:49.941 15616-15616/? I/System.out: /storage/emulated/0/.SPenSDK30

Okay...

Ora voglio scendere in DCIM/Camera/casa.jpg.
DCIM è una sottocartella dell'External Storage.
Come faccio a ottenere un file?

        File sd= Environment.getExternalStorageDirectory();

        File src=new File(sd,"//DCIM//Camera//casa.jpg");

        File dst=new File(sd,"//DCIM//Screenshots//casa.jpg");

Ecco i files corrispondenti all'immagine originale e alla copia che voglio creare.

Ora devo usare gli Stream...
E qua c'è tutto l'apparato.

        File sd= Environment.getExternalStorageDirectory();

        File src=new File(sd,"//DCIM//Camera//casa.jpg");

        File dst=new File(sd,"//DCIM//Screenshots//casa.jpg");

        try {
            FileInputStream in=new FileInputStream(src);
            FileOutputStream out=new FileOutputStream(dst);
            byte[] buffer=new byte[1024];
            int len;
            while((len=in.read(buffer))!=-1) {
                out.write(buffer,0,len);
            }
            in.close();
            out.flush();
            out.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

Intanto vediamo se funziona...

Sì, è riuscito! In Screenshots mi trovo il file casa.jpg che funziona.

---

Ora vediamo come "funziona".
Il metodo read(buffer) di FileInputStream legge dei bytes dal file in un buffer di bytes..
Restituisce un int che rappresenta il numero di bytes letti, mentre se non ci sono più bytes da leggere dal file al buffer, restituisce -1.
Ecco perché

            while((len=in.read(buffer))!=-1) {
                out.write(buffer,0,len);
            }

...finché len, che è uguale al numero di bytes letto nel buffer, è diverso da -1, va scritto nel FileOutputStream quel numero di bytes preso dal buffer.

---

E forse, finalmente lo abbiamo capito.

FileInputStream

Ho messo un file wav nella memoria dell'emulatore: si tratta di un file che ho preso da qualche parte, contenente una canzoncina comica, tanto per mantenere l'allegria, e voglio leggere il file in un buffer.
Ecco il codice:

public class MainActivity extends Activity {

// dichiarazioni di variabili oggetto dell'activity
 Button button;
 Button button2;
 Button button3;
 Button button4;

//il percorso del file
 String filePath = Environment.getExternalStorageDirectory()
   .getAbsolutePath() + "/vaffanculo.wav";

// registratore e riproduttore (dichiarazioni)
 AudioRecord audioRecord;
 AudioTrack audioTrack;

//impostazioni audio
 int audioSource=AudioSource.MIC;
 int sampleRate=44100;
 int channelConfig=AudioFormat.CHANNEL_IN_STEREO;
 int audioFormat=AudioFormat.ENCODING_PCM_16BIT;
 int minBufferSize=AudioRecord.getMinBufferSize(sampleRate, 
             channelConfig, 
             audioFormat);
 
// dichiarazione del buffer
 byte[] buffer= new byte[minBufferSize];
 
 
 
 
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);

  
//istanziazione dei bottoni
  button = (Button) findViewById(R.id.button1);
  button2 = (Button) findViewById(R.id.button2);
  button3 = (Button) findViewById(R.id.button3);
  button4 = (Button) findViewById(R.id.button4);

//listeners
  button.setOnClickListener(new View.OnClickListener() {
   
   @Override
   public void onClick(View v) {
    try {
     
     FileInputStream fis=new FileInputStream(filePath);
     fis.read(buffer,0,minBufferSize);
     for(int i=0; i < minBufferSize;i++){
      Log.v(i+"",buffer[i]+"");
     }
    } catch (FileNotFoundException e) {
     e.printStackTrace();
    } catch (IOException e) {
     e.printStackTrace();
    }
    
    
   }
  });
    

  button2.setOnClickListener(new View.OnClickListener() {

   @Override
   public void onClick(View v) {
    
   }
  });
  button3.setOnClickListener(new View.OnClickListener() {
   
   @Override
   public void onClick(View v) {
    
   }
  });
  
  button4.setOnClickListener(new View.OnClickListener() {
   
   @Override
   public void onClick(View v) {
    
   }
  });
  
// termine listeners
 }

}

La parte notevole è questa:

  button.setOnClickListener(new View.OnClickListener() {
   
   @Override
   public void onClick(View v) {
    try {
     
     FileInputStream fis=new FileInputStream(filePath);
     fis.read(buffer,0,minBufferSize);
     for(int i=0; i < minBufferSize;i++){
      Log.v(i+"",buffer[i]+"");
     }
    } catch (FileNotFoundException e) {
     e.printStackTrace();
    } catch (IOException e) {
     e.printStackTrace();
    }
    
    
   }
  });

Creo un FileInputStream con l'indirizzo del file, e quindi con la riga scritta in verde "leggo" i bytes del file nel buffer.
Quindi schiaccio il bottone, produco il LogCat e mi leggo pezzo per pezzo ogni byte, di cui riporto i primi 100:

03-21 08:22:49.520: V/0(19511): 74
03-21 08:22:49.520: V/1(19511): 1
03-21 08:22:49.520: V/2(19511): 74
03-21 08:22:49.520: V/3(19511): 1
03-21 08:22:49.520: V/4(19511): 50
03-21 08:22:49.520: V/5(19511): 1
03-21 08:22:49.520: V/6(19511): 50
03-21 08:22:49.520: V/7(19511): 1
03-21 08:22:49.520: V/8(19511): 22
03-21 08:22:49.520: V/9(19511): 1
03-21 08:22:49.520: V/10(19511): 22
03-21 08:22:49.520: V/11(19511): 1
03-21 08:22:49.520: V/12(19511): -9
03-21 08:22:49.520: V/13(19511): 0
03-21 08:22:49.520: V/14(19511): -9
03-21 08:22:49.520: V/15(19511): 0
03-21 08:22:49.520: V/16(19511): -42
03-21 08:22:49.520: V/17(19511): 0
03-21 08:22:49.520: V/18(19511): -42
03-21 08:22:49.520: V/19(19511): 0
03-21 08:22:49.520: V/20(19511): -77
03-21 08:22:49.520: V/21(19511): 0
03-21 08:22:49.520: V/22(19511): -77
03-21 08:22:49.520: V/23(19511): 0
03-21 08:22:49.520: V/24(19511): -112
03-21 08:22:49.520: V/25(19511): 0
03-21 08:22:49.520: V/26(19511): -112
03-21 08:22:49.520: V/27(19511): 0
03-21 08:22:49.520: V/28(19511): 110
03-21 08:22:49.520: V/29(19511): 0
03-21 08:22:49.520: V/30(19511): 110
03-21 08:22:49.520: V/31(19511): 0
03-21 08:22:49.520: V/32(19511): 79
03-21 08:22:49.520: V/33(19511): 0
03-21 08:22:49.520: V/34(19511): 79
03-21 08:22:49.520: V/35(19511): 0
03-21 08:22:49.520: V/36(19511): 51
03-21 08:22:49.520: V/37(19511): 0
03-21 08:22:49.520: V/38(19511): 51
03-21 08:22:49.520: V/39(19511): 0
03-21 08:22:49.520: V/40(19511): 27
03-21 08:22:49.520: V/41(19511): 0
03-21 08:22:49.520: V/42(19511): 27
03-21 08:22:49.520: V/43(19511): 0
03-21 08:22:49.520: V/44(19511): 8
03-21 08:22:49.520: V/45(19511): 0
03-21 08:22:49.520: V/46(19511): 8
03-21 08:22:49.520: V/47(19511): 0
03-21 08:22:49.520: V/48(19511): -8
03-21 08:22:49.520: V/49(19511): -1
03-21 08:22:49.520: V/50(19511): -8
03-21 08:22:49.520: V/51(19511): -1
03-21 08:22:49.520: V/52(19511): -22
03-21 08:22:49.520: V/53(19511): -1
03-21 08:22:49.520: V/54(19511): -22
03-21 08:22:49.520: V/55(19511): -1
03-21 08:22:49.520: V/56(19511): -35
03-21 08:22:49.520: V/57(19511): -1
03-21 08:22:49.520: V/58(19511): -35
03-21 08:22:49.520: V/59(19511): -1
03-21 08:22:49.520: V/60(19511): -48
03-21 08:22:49.520: V/61(19511): -1
03-21 08:22:49.520: V/62(19511): -48
03-21 08:22:49.520: V/63(19511): -1
03-21 08:22:49.520: V/64(19511): -62
03-21 08:22:49.520: V/65(19511): -1
03-21 08:22:49.520: V/66(19511): -62
03-21 08:22:49.520: V/67(19511): -1
03-21 08:22:49.520: V/68(19511): -78
03-21 08:22:49.520: V/69(19511): -1
03-21 08:22:49.520: V/70(19511): -78
03-21 08:22:49.520: V/71(19511): -1
03-21 08:22:49.520: V/72(19511): -96
03-21 08:22:49.520: V/73(19511): -1
03-21 08:22:49.520: V/74(19511): -96
03-21 08:22:49.520: V/75(19511): -1
03-21 08:22:49.520: V/76(19511): -114
03-21 08:22:49.520: V/77(19511): -1
03-21 08:22:49.520: V/78(19511): -114
03-21 08:22:49.520: V/79(19511): -1
03-21 08:22:49.520: V/80(19511): 125
03-21 08:22:49.520: V/81(19511): -1
03-21 08:22:49.520: V/82(19511): 125
03-21 08:22:49.520: V/83(19511): -1
03-21 08:22:49.520: V/84(19511): 109
03-21 08:22:49.520: V/85(19511): -1
03-21 08:22:49.520: V/86(19511): 109
03-21 08:22:49.520: V/87(19511): -1
03-21 08:22:49.520: V/88(19511): 96
03-21 08:22:49.520: V/89(19511): -1
03-21 08:22:49.520: V/90(19511): 96
03-21 08:22:49.520: V/91(19511): -1
03-21 08:22:49.520: V/92(19511): 87
03-21 08:22:49.520: V/93(19511): -1
03-21 08:22:49.520: V/94(19511): 87
03-21 08:22:49.520: V/95(19511): -1
03-21 08:22:49.520: V/96(19511): 82
03-21 08:22:49.520: V/97(19511): -1
03-21 08:22:49.520: V/98(19511): 82
03-21 08:22:49.520: V/99(19511): -1
03-21 08:22:49.520: V/100(19511): 81

Sono 278 bytes in totale. Ma il buffer di che dimensione è?
Modifico il codice per ottenere minBufferSize in LogCat:

     FileInputStream fis=new FileInputStream(filePath);
     fis.read(buffer,0,minBufferSize);
     for(int i=0; i < minBufferSize;i++){
      Log.v("BUFFERSIZE",i+"",buffer[i]+"");
     }
.....   

Ottengo 640, che è pure il valore che ottengo come risultato della funzione fis.read(buffer,0,minBufferSize).

Ma adesso voglio trovare modi diversi di inserire i valori nel buffer.

     FileInputStream fis=new FileInputStream(filePath);
     for(int i=0; i < minBufferSize;i++){
      buffer[i]=(byte)fis.read();
     }
     for(int i=0; i < minBufferSize;i++){
      Log.v(i+"",buffer[i]+"");
     }

ed ecco il risultato:

03-21 08:59:47.970: V/0(26357): 74
03-21 08:59:47.970: V/1(26357): 1
03-21 08:59:47.970: V/2(26357): 74
03-21 08:59:47.970: V/3(26357): 1
03-21 08:59:47.970: V/4(26357): 50
03-21 08:59:47.970: V/5(26357): 1
03-21 08:59:47.970: V/6(26357): 50
03-21 08:59:47.970: V/7(26357): 1
03-21 08:59:47.970: V/8(26357): 22
03-21 08:59:47.970: V/9(26357): 1
03-21 08:59:47.970: V/10(26357): 22
03-21 08:59:47.970: V/11(26357): 1
03-21 08:59:47.970: V/12(26357): -9
03-21 08:59:47.970: V/13(26357): 0
03-21 08:59:47.970: V/14(26357): -9
03-21 08:59:47.970: V/15(26357): 0
03-21 08:59:47.970: V/16(26357): -42
03-21 08:59:47.970: V/17(26357): 0
03-21 08:59:47.970: V/18(26357): -42
03-21 08:59:47.970: V/19(26357): 0
03-21 08:59:47.970: V/20(26357): -77
03-21 08:59:47.970: V/21(26357): 0
03-21 08:59:47.970: V/22(26357): -77
03-21 08:59:47.970: V/23(26357): 0
03-21 08:59:47.970: V/24(26357): -112
03-21 08:59:47.970: V/25(26357): 0
03-21 08:59:47.970: V/26(26357): -112
03-21 08:59:47.970: V/27(26357): 0
03-21 08:59:47.970: V/28(26357): 110
03-21 08:59:47.970: V/29(26357): 0
03-21 08:59:47.970: V/30(26357): 110
03-21 08:59:47.970: V/31(26357): 0
03-21 08:59:47.970: V/32(26357): 79
03-21 08:59:47.970: V/33(26357): 0
03-21 08:59:47.970: V/34(26357): 79
03-21 08:59:47.970: V/35(26357): 0
03-21 08:59:47.970: V/36(26357): 51
03-21 08:59:47.970: V/37(26357): 0
03-21 08:59:47.970: V/38(26357): 51
03-21 08:59:47.970: V/39(26357): 0
03-21 08:59:47.970: V/40(26357): 27
03-21 08:59:47.970: V/41(26357): 0
03-21 08:59:47.970: V/42(26357): 27
03-21 08:59:47.970: V/43(26357): 0
03-21 08:59:47.970: V/44(26357): 8
03-21 08:59:47.970: V/45(26357): 0
03-21 08:59:47.970: V/46(26357): 8
03-21 08:59:47.970: V/47(26357): 0
03-21 08:59:47.970: V/48(26357): -8
03-21 08:59:47.970: V/49(26357): -1
03-21 08:59:47.970: V/50(26357): -8
03-21 08:59:47.970: V/51(26357): -1
03-21 08:59:47.970: V/52(26357): -22
03-21 08:59:47.970: V/53(26357): -1
03-21 08:59:47.970: V/54(26357): -22
03-21 08:59:47.970: V/55(26357): -1
03-21 08:59:47.970: V/56(26357): -35
03-21 08:59:47.970: V/57(26357): -1
03-21 08:59:47.970: V/58(26357): -35
03-21 08:59:47.970: V/59(26357): -1
03-21 08:59:47.970: V/60(26357): -48
03-21 08:59:47.970: V/61(26357): -1
03-21 08:59:47.970: V/62(26357): -48
03-21 08:59:47.970: V/63(26357): -1
03-21 08:59:47.970: V/64(26357): -62
03-21 08:59:47.970: V/65(26357): -1
03-21 08:59:47.970: V/66(26357): -62
03-21 08:59:47.970: V/67(26357): -1
03-21 08:59:47.970: V/68(26357): -78
03-21 08:59:47.970: V/69(26357): -1
03-21 08:59:47.970: V/70(26357): -78
03-21 08:59:47.970: V/71(26357): -1
03-21 08:59:47.970: V/72(26357): -96
03-21 08:59:47.970: V/73(26357): -1
03-21 08:59:47.970: V/74(26357): -96
03-21 08:59:47.970: V/75(26357): -1
03-21 08:59:47.970: V/76(26357): -114
03-21 08:59:47.970: V/77(26357): -1
03-21 08:59:47.970: V/78(26357): -114
03-21 08:59:47.970: V/79(26357): -1
03-21 08:59:47.970: V/80(26357): 125
03-21 08:59:47.970: V/81(26357): -1
03-21 08:59:47.970: V/82(26357): 125
03-21 08:59:47.970: V/83(26357): -1
03-21 08:59:47.970: V/84(26357): 109
03-21 08:59:47.970: V/85(26357): -1
03-21 08:59:47.970: V/86(26357): 109
03-21 08:59:47.970: V/87(26357): -1
03-21 08:59:47.970: V/88(26357): 96
03-21 08:59:47.970: V/89(26357): -1
03-21 08:59:47.970: V/90(26357): 96
03-21 08:59:47.970: V/91(26357): -1
03-21 08:59:47.970: V/92(26357): 87
03-21 08:59:47.970: V/93(26357): -1
03-21 08:59:47.970: V/94(26357): 87
03-21 08:59:47.970: V/95(26357): -1
03-21 08:59:47.970: V/96(26357): 82
03-21 08:59:47.970: V/97(26357): -1
03-21 08:59:47.970: V/98(26357): 82
03-21 08:59:47.970: V/99(26357): -1
03-21 08:59:47.970: V/100(26357): 81

Questi valori sono esattamente uguali a quelli ricavati prima.

Leggere i bytes da un file

Ed ecco ora il FileInputStream per leggere i bytes di un file in un buffer:

public class MainActivity extends Activity {

 Button button;
 Button button2;
 Button button3;
 Button button4;

 String filePath = Environment.getExternalStorageDirectory()
   .getAbsolutePath() + "/ilmiofiledalnomelungolungo";

 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);

  button = (Button) findViewById(R.id.button1);
  button2 = (Button) findViewById(R.id.button2);
  button3 = (Button) findViewById(R.id.button3);
  button4 = (Button) findViewById(R.id.button4);

  button.setOnClickListener(new View.OnClickListener() {

   @Override
   public void onClick(View v) {

    try {
     FileOutputStream fos = new FileOutputStream(filePath);
     byte[] nome = { 0x41, 0x4e, 0x54, 0x4f, 0x4e, 0x45, 0x4c,
       0x4c, 0x4f };
     fos.write(nome);
    } catch (Exception e) {
     e.printStackTrace();
    }

   }
  });
  button2.setOnClickListener(new View.OnClickListener() {

   @Override
   public void onClick(View v) {
    try {
     FileInputStream fis=new FileInputStream(filePath);
     byte[] buffer=new byte[50];
     fis.read(buffer);
     for(int i=0;i<50;i++){
      Log.d(i+"",buffer[i]+"");
     }
    } catch (Exception e) {
     // TODO Auto-generated catch block
     e.printStackTrace();
    }

   }
  });
 }

}

Ecco il risultato in LogCat:

03-19 17:03:03.740: D/0(15493): 65
03-19 17:03:03.740: D/1(15493): 78
03-19 17:03:03.740: D/2(15493): 84
03-19 17:03:03.740: D/3(15493): 79
03-19 17:03:03.740: D/4(15493): 78
03-19 17:03:03.740: D/5(15493): 69
03-19 17:03:03.740: D/6(15493): 76
03-19 17:03:03.740: D/7(15493): 76
03-19 17:03:03.740: D/8(15493): 79
03-19 17:03:03.740: D/9(15493): 0
03-19 17:03:03.740: D/10(15493): 0
03-19 17:03:03.740: D/11(15493): 0

...che sono i codici ASCII di "ANTONELLO" in notazione decimale.
65/16= 4 con resto di 1: 0x41
78/16= 4 con resto di 14 (E): 0x4e
84/16= 5 con resto di 4; 0x54
79/16= 4 con resto di 15 (F): 0x4f
...eccetera...

E' valso la pena, imparare la tabellina del 16, per fare i calcoli un po' più agevolmente! :D