图片Bitmap在本地的存储与读取 File

将Bitmap存储到本地：

    public void SaveImage(Bitmap image, String user_id){
        //照片通常存在DCIM文件夹中
        String sdCardDir = getApplicationContext().getCacheDir()+"/DCIM/";
//        String sdCardDir = Environment.getExternalStorageDirectory()+"/DCIM/";
        //为APP创建一个文件夹来存储图片
        File appDir = new File(sdCardDir, "MyGraduation");
        if(!appDir.exists()){
            appDir.mkdirs();
        }
        //图片名称
        String fileName = user_id+".jpg";
        //设置图片路径
        File imageDir = new File(appDir, fileName);
        FileOutputStream fos = null;
        try {
            fos = new FileOutputStream(imageDir);
            image.compress(Bitmap.CompressFormat.JPEG, 100, fos);
            fos.flush();
            fos.close();
            System.out.println(imageDir.toString());
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

从本地读取到Bitmap文件：

    public Bitmap getImage(String user_id){
        String sdCardDir = getApplicationContext().getCacheDir()+"/DCIM/";
//        String sdCardDir = Environment.getExternalStorageDirectory()+"/DCIM/";
        String path = sdCardDir+"MyGraduation/"+user_id+".jpg";
        Bitmap bitmap = null;
        FileInputStream fis = null;

        File f=new File(path);
        if(!f.exists())
        {
            return null;
        }

        try {
            fis = new FileInputStream(path);
            bitmap = BitmapFactory.decodeStream(fis);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        return bitmap;
    }

读取和改写SD卡需要权限：

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

 从imageView中获取bitmap：

Bitmap bitmap = ((BitmapDrawable)iv_user_head.getDrawable()).getBitmap();