第一步:先申请读写权限(读写权限都要申请)

  String base64 = (String) msg.obj;
                    bmp = ImageUtils.base64ToBitmap(base64);
                    if (Build.VERSION.SDK_INT >= M) {
                        if (ContextCompat.checkSelfPermission(WebViewActivity.this, Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager
                                .PERMISSION_GRANTED || ContextCompat.checkSelfPermission(WebViewActivity.this, Manifest.permission.READ_EXTERNAL_STORAGE) != PackageManager
                                .PERMISSION_GRANTED) {
                            //进行权限请求
                            ActivityCompat.requestPermissions(WebViewActivity.this, new String[]{Manifest.permission.READ_EXTERNAL_STORAGE,Manifest.permission.WRITE_EXTERNAL_STORAGE}, SAVE_BITMAP);
                        } else {
                            saveImageToGallery(bmp);
                        }
                    } else {
                        saveImageToGallery(bmp);
                    }



   /**
     * 图片保存相册方法
     *
     * @param bitmap
     */

    public void saveImageToGallery(Bitmap bitmap) {
        // 首先保存图片
        File file = null;
        String fileName = System.currentTimeMillis() + ".jpg";
        File root = new File(getExternalCacheDir(), getPackageName());
        if (!root.exists()) {
            root.mkdir();
        }
        file = new File(root, fileName);
        try {
            FileOutputStream fos = new FileOutputStream(file);
            bitmap.compress(Bitmap.CompressFormat.JPEG, 100, fos);
            fos.flush();
            fos.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
//        //其次把文件插入到系统图库
        try {
            String insertImage = MediaStore.Images.Media.insertImage(this.getContentResolver(), file.getAbsolutePath(), fileName, null);
            File file1 = new File(getRealPathFromURI(Uri.parse(insertImage),WebViewActivity.this));
            updatePhotoMedia(file1,this);
            Toast.makeText(this, "保存成功", Toast.LENGTH_SHORT).show();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }

    }
    //更新图库
    private  void updatePhotoMedia(File file ,Context context){
        Intent intent = new Intent();
        intent.setAction(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
        intent.setData(Uri.fromFile(file));
        context.sendBroadcast(intent);
    }
    //得到绝对地址
    private static String getRealPathFromURI(Uri contentUri,Context context) {
        String[] proj = { MediaStore.Images.Media.DATA };
        Cursor cursor = context.getContentResolver().query(contentUri, proj, null, null, null);
        int column_index = cursor.getColumnIndexOrThrow(MediaStore.Images.Media.DATA);
        cursor.moveToFirst();
        String fileStr = cursor.getString(column_index);
        cursor.close();
        return fileStr;
    }

//kotlin语法
fun saveImageToGallery(bitmap: Bitmap) {
        // 首先保存图片
        var file: File? = null
        val fileName = (System.currentTimeMillis()).toString() + ".jpg"
        val root = File(externalCacheDir, packageName)
        if (!root.exists()) {
            root.mkdir()
        }
        file = File(root, fileName)
        try {
            val fos = FileOutputStream(file!!)
            bitmap.compress(Bitmap.CompressFormat.JPEG, 100, fos)
            fos.flush()
            fos.close()
        } catch (e: FileNotFoundException) {
            e.printStackTrace()
        } catch (e: IOException) {
            e.printStackTrace()
        }

        //其次把文件插入到系统图库
        try {
            val insertImage = MediaStore.Images.Media.insertImage(this.contentResolver, file!!.absolutePath, fileName, null)
            val file1 = File(getRealPathFromURI(Uri.parse(insertImage), this))
            updatePhotoMedia(file1,this);

        } catch (e: FileNotFoundException) {
            e.printStackTrace()
        }

    }
  //更新图库
    fun updatePhotoMedia(file: File, context: Context) {
        val intent = Intent()
        intent.action = Intent.ACTION_MEDIA_SCANNER_SCAN_FILE
        intent.data = Uri.fromFile(file)
        context.sendBroadcast(intent)
    }

    //得到绝对地址
    fun getRealPathFromURI(contentUri: Uri, context: Context): String {
        val proj = arrayOf(MediaStore.Images.Media.DATA)
        val cursor = context.getContentResolver().query(contentUri, proj, null, null, null)
        val column_index = cursor.getColumnIndexOrThrow(MediaStore.Images.Media.DATA)
        cursor.moveToFirst()
        val fileStr = cursor.getString(column_index)
        cursor.close()
        return fileStr
    }

okay