SDCard中檔案存取的實現

標籤：拼接

注意：

第一步要先添加許可權：

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

步驟：

         檔案流

         1、寫：

                   a）建立檔案輸出資料流（PATH）

                   b）將內容寫入檔案輸出資料流(str.getBytes())

                   bb）關閉流

         2、讀：

                   a）建立檔案輸入資料流

                   b）建立位元組數組緩衝(ByteArrayBufferarrayBuffer = new ByteArrayBuffer(1000);)——>為了後面分段讀取時拼接資料

                   c）建立位元組數組buffer（1024）（建立變數len=0）

                   d）迴圈讀入——while(-1!=(len=fis.read(buffer)){arrayBuffer.append(buffer, 0, len) }

                   e）通過建立String的形式將位元組數群組轉換成字串(new String(arrayBuffer.toByteArray()))

                   f）將內容顯示在文字框中

                   ff）關閉流

         物件流程

         1、寫：

                   a）建立對象

                   b）建立檔案輸出資料流（PATH）

                   c）建立對象輸出資料流（ObjectOutputStream，將檔案輸出資料流嵌套在裡面）

                   d）將對象寫入對象輸出資料流(oos.writeObject(person);)

                   dd）關閉最外層流（物件流程)

         2、讀：

                   a）建立檔案輸入資料流

                   b）建立對象輸入資料流

                   c）將讀到的Object對象強轉成所需對象（Personperson = (Person)ois.readObject();）

                   d）在文字框中顯示對象的各項內容

                   dd）關閉最外層流（物件流程）

 

代碼實現（檔案流）：

1、往sdcard中寫入資料

         FileOutputStreamfos = null;

                   try{

                            fos= new FileOutputStream(PATH);

                            Stringstr = writeToSdcard.getText().toString();

                            //將字串打散寫入流中

                            fos.write(str.getBytes());

                   }catch (FileNotFoundException e) {

                            //TODO Auto-generated catch block

                            e.printStackTrace();

                   }catch (IOException e) {

                            //TODO Auto-generated catch block

                            e.printStackTrace();

                   }finally{

                            if(fos!=null){

                                     try{

//如果path有問題，會跳到finally中，而fos此時為null，會發生null 指標異常

                                               fos.close();

                                     }catch (IOException e) {

                                               //TODO Auto-generated catch block

                                               e.printStackTrace();

                                     }

                            }

                   }

2、從sdcard中讀取資料

         FileInputStreamfis = null;

                   //1000表示的是預留空間

                   ByteArrayBufferarrayBuffer = new ByteArrayBuffer(1000);

                   try{

                            fis= new FileInputStream(PATH);

                            byte[]buffer = new byte[1024];

                            intlen = 0;

                            while(-1!=(len=fis.read(buffer))){

                                     //拼接

                                     arrayBuffer.append(buffer,0, len);

                            }

                            //通過建立字串的形式將arrayBuffer轉換成位元組數組

                            StringreadBuffer = new String(arrayBuffer.toByteArray());

                            writeToSdcard.setText(readBuffer);

                   }catch (FileNotFoundException e) {

                            //TODO Auto-generated catch block

                            e.printStackTrace();

                   }catch (IOException e) {

                            //TODO Auto-generated catch block

                            e.printStackTrace();

                   }finally{

                            if(fis!=null){

                                     try{

                                               fis.close();

                                     }catch (IOException e) {

                                               //TODO Auto-generated catch block

                                               e.printStackTrace();