Android SD卡内的文件读写操作

private String readFromFile(Context context){
         
         
        if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())) {
             
            String foldername = Environment.getExternalStorageDirectory().getPath()+ "/eryaApp";
            File folder = new File(foldername);
             
            if (folder == null || !folder.exists()) {
                folder.mkdir();
            }
             
            File targetFile=new File("/sdcard/eryaApp/eryaShoppingList.txt");
            String readedStr="";
             
             try{
                if(!targetFile.exists()){
                    targetFile.createNewFile();
                    return "No File error ";
                }else{
                     InputStream in = new BufferedInputStream(new FileInputStream(targetFile));
                     BufferedReader br= new BufferedReader(new InputStreamReader(in,"UTF-8"));
                     String tmp;
                      
                     while((tmp=br.readLine())!=null){
                         readedStr+=tmp;
                     }
                     br.close();
                     in.close();
                      
                     return readedStr;
                }
             } catch (Exception e) {
                    Toast.makeText(context,e.toString(),Toast.LENGTH_LONG).show();
                    return e.toString();
             }
        }else{
            Toast.makeText(context,"未发现SD卡！",Toast.LENGTH_LONG).show();
            return "SD Card error";
        }
         
    }

private void SavedToText(Context context,String stringToWrite){
         
        if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())) {
             
            String foldername = Environment.getExternalStorageDirectory().getPath()+ "/eryaApp";
            File folder = new File(foldername);
             
            if (folder == null || !folder.exists()) {
                folder.mkdir();
            }
             
            String fileName="/eryaShoppingList"+".txt";
             
            File targetFile = new File(foldername + fileName);
            OutputStreamWriter osw;
             
             try{
                if(!targetFile.exists()){
                    targetFile.createNewFile();
                    osw = new OutputStreamWriter(new FileOutputStream(targetFile),"utf-8");
                    osw.write(stringToWrite);  
                    osw.close();
                }else{
                    osw = new OutputStreamWriter(new FileOutputStream(targetFile,true),"utf-8");
                    osw.write("n"+stringToWrite);
                    osw.flush();
                    osw.close();
                }
             } catch (Exception e) {
                Toast.makeText(context,Toast.LENGTH_LONG).show();
             }
        }else{
            Toast.makeText(context,Toast.LENGTH_LONG).show();
        }
         
          
         
      }