Android---Java文件存取

android需声明文件权限：

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

java二进制文件的存储:

    try{
            File file = new File(fileName);
            if(!file.exists()) file.createNewFile();
            FileOutputStream outputStream = new FileOutputStream(file);
            outputStream.write("hello world");
            outputStream.flush();
            outputStream.close();
        }catch (FileNotFoundException e){
            e.printStackTrace();
        }catch (IOException e){
            e.printStackTrace();
        }

注意：输入输出流用完后及时关闭。

java二进制文件的读取：

String fileName = "/sdcard/feature.db";
        File file = new File(fileName);
        if(!file.exists()) return;
        try{
            FileInputStream fis = new FileInputStream(file);
            byte[] buffer = new byte[size];
            while(fis.read(buffer) > 0){
                Sysout(buffer.toString());
            }
            fis.close();
        }catch (Exception e){
            e.printStackTrace();
        }

按行写入数据

            file = new File(ind);
            if (!file.exists()) file.createNewFile();
            PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter(file, true)));
            out.println(filePath + "---" + faceimg.width + "---" + faceimg.height);
            out.close();

从文件中按行读取数据：

  File file = new File(path);
        try {
            FileInputStream instream = new FileInputStream(fileName);
            if (instream != null)
            {
                InputStreamReader inputreader = new InputStreamReader(instream);
                BufferedReader buffreader = new BufferedReader(inputreader);
                String line;
                //分行读取
                while (( line = buffreader.readLine()) != null) {
                    
                    ///
                }
                buffreader.close();
                inputreader.close();
                instream.close();
//注意关闭的顺序，先打开后关闭
            }
        }
        catch (FileNotFoundException e)
        {
            e.printStackTrace();
        }
        catch (IOException e)
        {
            e.printStackTrace();
        }

使用BufferedWriter写入文件，可以直接写字符串，数组，字符数据保存到文件中：

    try {
            String str = "hello";
            File file = new File(FileName);
            if (!file.exists()) {
                file.createNewFile();
            }
            FileWriter fw = new FileWriter(file);
            BufferedWriter bw = new BufferedWriter(fw);
            bw.write(str);
            bw.close();
            fw.close();
        } catch (IOException e) {
            e.printStackTrace();
        }

将NV21格式图片转成jpg压缩并存储：

//face为NV21格式
      public Bitmap pictureTrans(byte[] face, int width, int height){
        if(face == null) return null;
        YuvImage image = new YuvImage(face, ImageFormat.NV21, width, height, null);
        Rect rect = new Rect(0, 0, width, height);
        ByteArrayOutputStream os = new ByteArrayOutputStream(face.length);
        image.compressToJpeg(rect, 80, os);
        byte[] tmp = os.toByteArray();
        Bitmap bmp = BitmapFactory.decodeByteArray(tmp, 0, tmp.length);
        return bmp;
    }
----------------------------------  //文件操作
        File file = new File("/sdcard/myFolder");
        if(!file.exists())
            file.mkdir();
        String filePath = "/sdcard/myFolder/" + "hello.jpg";
        file = new File(filePath);
        try{
            file.createNewFile();
            FileOutputStream fos = new FileOutputStream(file);
            bmp.compress(Bitmap.CompressFormat.JPEG, 50, fos);
            fos.flush();
            fos.close();
        }catch (IOException e){
            e.printStackTrace();
        }

将图片读取出来

//android中直接使用BitmapFactory即可
    public Bitmap readImage(String filePath){
        Bitmap bitmap = BitmapFactory.decodeFile(filePath);
        return bitmap;
    }

获取文件的大小：

//文件大小小于2GB时可用，大文件需用其它方法
    public long getFileSize(File file){
        int size = 0;
        if(file.exists()){
            try{
                FileInputStream fis = new FileInputStream(file);
                size = fis.available();
                fis.close();
            }catch (Exception e){
                e.printStackTrace();
            }

        }
        return size;
    }

判断sd是否存在

public boolean isSDCardExist() {
        return Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED);
    }

获取sd卡根目录：

public String getSDCardPath() {
        boolean exist = isSDCardExist();
        String path = "";
        if (exist) {
            path = Environment.getExternalStorageDirectory().getAbsolutePath();
        } else {
            path = "error";
        }
        return path;
    }

!!!用于记录日常工作收获，后续更新及整理
引用：
http://blog.csdn.net/ccpat/article/details/45727427
http://www.cnblogs.com/rossoneri/p/3995096.html