问题
Can anyone tell me how to append data to a file that already has data in Android?
I wrote some code but it's not working. This is my activity:
package updatefile.developer.com.updatefiledemo;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintStream;
import java.nio.Buffer;
public class MainActivity extends ActionBarActivity {
Button create,update;
String data = "This is a sample";
File file;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
create = (Button)findViewById(R.id.btn_create);
create.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
File folder = new File("/sdcard/demo");
folder.mkdirs();
file = new File("/sdcard/demo/demotext.txt");
try {
FileOutputStream fileinput = new FileOutputStream(file);
PrintStream printstream = new PrintStream(fileinput);
printstream.print(data+"\n");
fileinput.close();
} catch (Exception e) {
Toast.makeText(MainActivity.this,e.getMessage(),Toast.LENGTH_SHORT).show();
}
}
});
update = (Button)findViewById(R.id.btn_update);
update.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if(!file.exists()) {
try {
file.createNewFile();
} catch (Exception e) {
Toast.makeText(MainActivity.this,e.getMessage(),Toast.LENGTH_SHORT).show();
}
}
try {
OutputStreamWriter file_writer = new OutputStreamWriter(new FileOutputStream(file,true));
BufferedWriter buffered_writer = new BufferedWriter(file_writer);
buffered_writer.write("This is a appended text");
buffered_writer.close();
} catch (IOException e) {
e.printStackTrace();
}
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
回答1:
FileOutputStream fileinput = new FileOutputStream(file, true);
It was a simple mistake, because of not setting the append flag to true. Just set it to true.
The default behavior is to overwrite the file content :)
回答2:
The only thing you have to do is simply add a "true" to FileOutputStream like
FileOutputStream fileinput = new FileOutputStream(file,true);
Here is the documentation
Constructs a new FileOutputStream that writes to file. If append is true and the file already exists, it will be appended to; otherwise it will be truncated. The file will be created if it does not exist.
回答3:
File file = new File(path);
if (!file.exists()) {
try {
file.createNewFile();
} catch (IOException ioe) {
ioe.printStackTrace();
}
}
try {
FileOutputStream fileOutputStream = new FileOutputStream(file);
OutputStreamWriter writer = new OutputStreamWriter(fileOutputStream);
writer.append(data);
writer.close();
fileOutputStream.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
回答4:
import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import android.app.Activity;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.widget.TextView;
public class WriteSDCard extends Activity {
private static final String TAG = "MEDIA";
private TextView tv;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
tv = (TextView) findViewById(R.id.TextView01);
checkExternalMedia();
writeToSDFile();
readRaw();
}
/** Method to check whether external media available and writable. This is adapted from
http://developer.android.com/guide/topics/data/data-storage.html#filesExternal */
private void checkExternalMedia(){
boolean mExternalStorageAvailable = false;
boolean mExternalStorageWriteable = false;
String state = Environment.getExternalStorageState();
if (Environment.MEDIA_MOUNTED.equals(state)) {
// Can read and write the media
mExternalStorageAvailable = mExternalStorageWriteable = true;
} else if (Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {
// Can only read the media
mExternalStorageAvailable = true;
mExternalStorageWriteable = false;
} else {
// Can't read or write
mExternalStorageAvailable = mExternalStorageWriteable = false;
}
tv.append("\n\nExternal Media: readable="
+mExternalStorageAvailable+" writable="+mExternalStorageWriteable);
}
/** Method to write ascii text characters to file on SD card. Note that you must add a
WRITE_EXTERNAL_STORAGE permission to the manifest file or this method will throw
a FileNotFound Exception because you won't have write permission. */
private void writeToSDFile(){
// Find the root of the external storage.
// See http://developer.android.com/guide/topics/data/data- storage.html#filesExternal
File root = android.os.Environment.getExternalStorageDirectory();
tv.append("\nExternal file system root: "+root);
// See http://stackoverflow.com/questions/3551821/android-write-to-sd-card-folder
File dir = new File (root.getAbsolutePath() + "/download");
dir.mkdirs();
File file = new File(dir, "myData.txt");
try {
FileOutputStream f = new FileOutputStream(file);
PrintWriter pw = new PrintWriter(f);
pw.println("Hi , How are you");
pw.println("Hello");
pw.flush();
pw.close();
f.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
Log.i(TAG, "******* File not found. Did you" +
" add a WRITE_EXTERNAL_STORAGE permission to the manifest?");
} catch (IOException e) {
e.printStackTrace();
}
tv.append("\n\nFile written to "+file);
}
/** Method to read in a text file placed in the res/raw directory of the application. The
method reads in all lines of the file sequentially. */
private void readRaw(){
tv.append("\nData read from res/raw/textfile.txt:");
InputStream is = this.getResources().openRawResource(R.raw.textfile);
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr, 8192); // 2nd arg is buffer size
// More efficient (less readable) implementation of above is the composite expression
/*BufferedReader br = new BufferedReader(new InputStreamReader(
this.getResources().openRawResource(R.raw.textfile)), 8192);*/
try {
String test;
while (true){
test = br.readLine();
// readLine() returns null if no more lines in the file
if(test == null) break;
tv.append("\n"+" "+test);
}
isr.close();
is.close();
br.close();
} catch (IOException e) {
e.printStackTrace();
}
tv.append("\n\nThat is all");
}
}
also add below permission in manifeast file
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
回答5:
In Kotlin, you can append data to a file by passing Context.MODE_APPEND as the second parameter of openFileOutput. It would look like this:
test_button.setOnClickListener {
main.openFileOutput(filename, Context.MODE_APPEND).use {
it.write("test".toByteArray())
}
}
There's some related info in the Android docs.
来源：https://stackoverflow.com/questions/29248600/how-to-append-data-in-a-file-in-android