如何在android中的文件中追加数据

Question

谁能告诉我如何将数据附加到 Android 中已有数据的文件中？

我写了一些代码，但它不起作用。这是我的活动：

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);
    }
}

Answer 1

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();
        }

Answer 2

您唯一需要做的就是简单地添加一个"true" to FileOutputStream 喜欢

FileOutputStream fileinput = new FileOutputStream(file,true);

这是文档

构造一个写入文件的新 FileOutputStream。如果追加是 true 并且文件已经存在，它将被追加到；否则它 将被截断。如果文件不存在，将创建该文件。

Answer 3

FileOutputStream fileinput = new FileOutputStream(file, true);

这是一个简单的错误，因为没有将 append 标志设置为 true。只需将其设置为true。

默认行为是覆盖文件内容:)

Answer 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"/>

Answer 5

在 Kotlin 中，您可以通过将 Context.MODE_APPEND 作为 openFileOutput 的第二个参数传递来将数据附加到文件中。它看起来像这样：

test_button.setOnClickListener {
            main.openFileOutput(filename, Context.MODE_APPEND).use {
                it.write("test".toByteArray())
            }
        }

有一些related info in the Android docs。