采用openFileOutput获取输出流

 package com.example.login.service;

 import java.io.BufferedReader;

 import java.io.File;

 import java.io.FileInputStream;

 import java.io.FileNotFoundException;

 import java.io.FileOutputStream;

 import java.io.InputStreamReader;

 import java.util.HashMap;

 import java.util.Map;

 import android.annotation.SuppressLint;

 import android.content.Context;

 /*

  * mode 1私有、2可读、3可写、4可读写

  */

 public class LoginService {

     public static boolean savaUserInfo(Context context, String username, String password,int mode)

     {

         try{

             //File file = new File("/data/data/com.example.login/info.txt");

             //File file = new File(context.getFilesDir(),"info.txt");

             //FileOutputStream fos = new FileOutputStream(file);

             //FileOutputStream fos = context.openFileOutput("private.txt", context.MODE_PRIVATE);

             FileOutputStream fos = null;

             switch(mode)

             {

             case 1:

                 fos = context.openFileOutput("private.txt", context.MODE_PRIVATE);

                 break;

             case 2:

                 fos = context.openFileOutput("readable.txt", context.MODE_WORLD_READABLE);

                 break;

             case 3:

                 fos = context.openFileOutput("writeable.txt", context.MODE_WORLD_WRITEABLE);

                 break;

             case 4:

                 fos = context.openFileOutput("public.txt", context.MODE_WORLD_READABLE + context.MODE_WORLD_WRITEABLE);

                 break;

             }

             fos.write((username + "##" + password).getBytes());

             fos.close();

             return true;

         }catch(Exception e){

             e.printStackTrace();

             return false;

         }

     }

 }

2、关于在另外项目测试文件的读写权限

 package com.example.other;

 import java.io.BufferedReader;

 import java.io.File;

 import java.io.FileInputStream;

 import java.io.FileOutputStream;

 import java.io.InputStreamReader;

 import android.os.Bundle;

 import android.app.Activity;

 import android.view.Menu;

 import android.view.View;

 import android.widget.Toast;

 public class MainActivity extends Activity {

     @Override

     protected void onCreate(Bundle savedInstanceState) {

         super.onCreate(savedInstanceState);

         setContentView(R.layout.activity_main);

     }

     public void readPrivate(View view)

     {

         try

         {

             File file = new File("/data/data/com.example.login/files/private.txt");

             FileInputStream fis = new FileInputStream(file);

             BufferedReader br = new BufferedReader(new InputStreamReader(fis));

             String result = br.readLine();

             Toast.makeText(this, result, 0).show();

         }catch(Exception e){

             e.printStackTrace();

             Toast.makeText(this, "读取私有文件失败!", 0).show();

         }

     }

     public void writePrivate(View view)

     {

         try

         {

             File file = new File("/data/data/com.example.login/files/private.txt");

             FileOutputStream fos = new FileOutputStream(file);

             fos.write("aaa".getBytes());

             fos.close();

         }catch(Exception e){

             e.printStackTrace();

             Toast.makeText(this, "写入私有文件失败!", 0).show();

         }

     }

     public void readPublic(View view)

     {

         try

         {

             File file = new File("/data/data/com.example.login/files/public.txt");

             FileInputStream fis = new FileInputStream(file);

             BufferedReader br = new BufferedReader(new InputStreamReader(fis));

             String result = br.readLine();

             Toast.makeText(this, result, 0).show();

         }catch(Exception e){

             e.printStackTrace();

             Toast.makeText(this, "读取私有文件失败!", 0).show();

         }

     }

     public void writePublic(View view)

     {

         try

         {

             File file = new File("/data/data/com.example.login/files/public.txt");

             FileOutputStream fos = new FileOutputStream(file);

             fos.write("aaa##bbb".getBytes());

             fos.close();

         }catch(Exception e){

             e.printStackTrace();

             Toast.makeText(this, "写入私有文件失败!", 0).show();

         }

     }

     @Override

     public boolean onCreateOptionsMenu(Menu menu) {

         // Inflate the menu; this adds items to the action bar if it is present.

         getMenuInflater().inflate(R.menu.main, menu);

         return true;

     }

 }