下载类，可以url下载到相册，记得在清单加权限，6.0代码动态加权限判断，下载图片要在子线程中下载，下载完后广播更新相册

在清单文件里面添加权限：

    <!--网络-->
    <uses-permission android:name="android.permission.INTERNET" />
    <!-- 读写文件 -->
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

下载的url的工具类：

public class DonwloadSaveImg {
    private static Context context;
    private static String filePath;
    private static Bitmap mBitmap;
    private static String mSaveMessage = "失败";
    private final static String TAG = "PictureActivity";
    private static ProgressDialog mSaveDialog = null;
 
    public static void donwloadImg(Context contexts, String filePaths) {
        context = contexts;
        filePath = filePaths;
        mSaveDialog = ProgressDialog.show(context, "保存图片", "图片正在保存中，请稍等...", true);
        new Thread(saveFileRunnable).start();
    }
 
    private static Runnable saveFileRunnable = new Runnable() {
        @Override
        public void run() {
            try {
                if (!TextUtils.isEmpty(filePath)) { //网络图片
                    // 对资源链接
                    URL url = new URL(filePath);
                    //打开输入流
                    InputStream inputStream = url.openStream();
                    //对网上资源进行下载转换位图图片
                    mBitmap = BitmapFactory.decodeStream(inputStream);
                    inputStream.close();
                }
                saveFile(mBitmap);
                mSaveMessage = "图片保存成功！";
            } catch (IOException e) {
                mSaveMessage = "图片保存失败！";
                e.printStackTrace();
            } catch (Exception e) {
                e.printStackTrace();
            }
            messageHandler.sendMessage(messageHandler.obtainMessage());
        }
    };
 
    private static Handler messageHandler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            mSaveDialog.dismiss();
            Log.d(TAG, mSaveMessage);
            Toast.makeText(context, mSaveMessage, Toast.LENGTH_SHORT).show();
        }
    };
    /**
     * 保存图片
     * @param bm
     * @throws IOException
     */
    public static void saveFile(Bitmap bm ) throws IOException {
        File dirFile = new File(Environment.getExternalStorageDirectory().getPath());
        if (!dirFile.exists()) {
            dirFile.mkdir();
        }
        String fileName = UUID.randomUUID().toString() + ".jpg";
        File myCaptureFile = new File(Environment.getExternalStorageDirectory().getPath() + "/DCIM/Camera/" + fileName);
        BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(myCaptureFile));
        bm.compress(Bitmap.CompressFormat.JPEG, 80, bos);
        bos.flush();
        bos.close();
        //把图片保存后声明这个广播事件通知系统相册有新图片到来
        Intent intent = new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
        Uri uri = Uri.fromFile(myCaptureFile);
        intent.setData(uri);
        context.sendBroadcast(intent);
    }
}

在Activity中进行调用：

public class DownloadSavePictureActivity extends AppCompatActivity {
    private Button btn_pic;
    private Bitmap bitmap;
    privateString path = "https://s.vipkidstatic.com/fe-static/int/sale_tracking/3a96f033-b14c-40f1-98cf-79d40a95b837.jpg";
 
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_download_save_picture);
        btn_pic=findViewById(R.id.btn_pic);
        btn_pic.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                ImgDonwloads.donwloadImg(DownloadSavePictureActivity.this,path);//iPath
            }
        });
    }
}