Android------文件与权限管理

//往手机内存写文件
          String str ="hello world";
                try {
                    FileOutputStream fos=openFileOutput("testfile",MODE_PRIVATE);
                    fos.write(str.getBytes());
                    fos.close();
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }

//往外存私有文件写，但其父目录 不容易
                File dir=getExternalFilesDir(null);
                File testfile=new File(dir,"testsdfile");
                FileOutputStream fos= null;
                try {
                    fos = new FileOutputStream(testfile);
                    fos.write(str.getBytes());
                    fos.close();
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }

String str ="hello world";
                //往其外存公有文件写，牵扯到一个问题，权限，得要权限
                File dir= Environment.getExternalStorageDirectory();
                File testfile=new File(dir,"testpublicsdfile");
                FileOutputStream fos= null;
                try {
                    fos = new FileOutputStream(testfile);
                    fos.write(str.getBytes());
                    fos.close();
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }