设置文件生成的权限：
    public static boolean saveInfo(  
                Context context, String userName, String userPass, int mode){              

            try {  
                FileOutputStream fos;  
                switch (mode) {  
                case 0:  
                    fos = context.openFileOutput(  
                            "private.txt", Context.MODE_PRIVATE);  
                    fos.write((userName+"##"+userPass).getBytes());  
                    fos.close();  
                    break;  
                case 1:  
                    fos = context.openFileOutput(  
                            "readable.txt", Context.MODE_WORLD_READABLE);  
                    fos.write((userName+"##"+userPass).getBytes());  
                    fos.close();  
                    break;  
                case 2:  
                    fos = context.openFileOutput(  
                            "writeable.txt", Context.MODE_WORLD_WRITEABLE);  
                    fos.write((userName+"##"+userPass).getBytes());  
                    fos.close();  
                    break;  
                case 3:  
                    fos = context.openFileOutput(  
                            "public.txt", Context.MODE_WORLD_READABLE+Context.MODE_WORLD_WRITEABLE);  
                    fos.write((userName+"##"+userPass).getBytes());  
                    fos.close();  
                    break;  
                default:  
                    break;  
                }  
                  
                  
                return true;  
            } catch (Exception e) {  
                e.printStackTrace();  
                return false;  
            }  
        } 

下面是读取文件和写入文件的程序代码：

读取文件：

    public void readInfo(View view){  
            File file = new File("/data/data/com.aaron.login/files/public.txt");  
            FileInputStream fis;  
            try {  
                fis = new FileInputStream(file);  
                BufferedReader br = new BufferedReader(new InputStreamReader(fis));  
                String result = br.readLine();  
                Toast.makeText(MainActivity.this,  
                        result,   
                        Toast.LENGTH_LONG).show();  
            } catch (Exception e) {  
                // TODO Auto-generated catch block  
                e.printStackTrace();  
                Toast.makeText(MainActivity.this,  
                        "读取文件失败",  
                        Toast.LENGTH_LONG).show();  
            }  
        } 

写入文件：

    public void writeInfo(View view){  
            File file = new File("/data/data/com.aaron.login/files/public.txt");  
            FileOutputStream fos;  
            try {  
                fos = new FileOutputStream(file);  
                fos.write("hahaha".getBytes());  
                fos.close();  
                Toast.makeText(MainActivity.this,  
                        "写入文件成功",   
                        Toast.LENGTH_LONG).show();  
            } catch (Exception e) {  
                // TODO Auto-generated catch block  
                e.printStackTrace();  
                Toast.makeText(MainActivity.this,   
                        "写入文件失败",   
                        Toast.LENGTH_LONG).show();  
            }  

              
        } 

Android的读写文件及权限设置