C#同步、异步远程下载文件实例

1、使用httpwebrequest/httpwebresonse和webclient

httpwebrequest request = (httpwebrequest)webrequest.create(url);
webresponse response = request.getresponse();
stream stream = response.getresponsestream();

if (!response.contenttype.tolower().startswith("text/"))
{
    //value = savebinaryfile(response, filename);
    byte[] buffer = new byte[1024];
    stream outstream = system.io.file.create(filename);
    stream instream = response.getresponsestream();

    int l;
    do
    {
        l = instream.read(buffer, 0, buffer.length);
        if (l > 0)
            outstream.write(buffer, 0, l);
    }
    while (l > 0);

    outstream.close();
    instream.close();
}

2、使用webclient

string url = "http://www.mozilla.org/images/feature-back-cnet.png";
webclient mywebclient = new webclient();
mywebclient.downloadfile(url,"c:\\temp\\feature-back-cnet.png");

3、异步下载例子

        ///summary
        ///异步分析下载
        ///summary
        private void asyncanalyzeanddownload(string url, string savepath)
        {
            this.uristring = url;
            this.savepath = savepath;

            #region 分析计时开始

            count = 0;
            count1 = 0;
            freq = 0;
            result = 0;

            queryperformancefrequency(ref freq);
            queryperformancecounter(ref count);

            #endregion

            using (webclient wclient = new webclient())
            {
                autoresetevent waiter = new autoresetevent(false);
                wclient.credentials = credentialcache.defaultcredentials;
                wclient.downloaddatacompleted += new downloaddatacompletedeventhandler(asyncurianalyze);
                wclient.downloaddataasync(new uri(uristring), waiter);
                waiter.waitone();    阻止当前线程，直到收到信号
            }

        }

        ///summary
        ///异步分析
        ///summary
        protected void asyncurianalyze(object sender, downloaddatacompletedeventargs e)
        {
            autoresetevent waiter = (autoresetevent)e.userstate;
            try
            {
                if (!e.cancelled && e.error == null)
                {

                    string dndir = string.empty;
                    string domainname = string.empty;
                    string uri = uristring;

                    获得域名 [url]httpwww.sina.com[url]
                    match match = regex.match(uri, @((http(s)))+[w-.]+[^]);, regexoptions.ignorecase
                    domainname = match.value;

                    获得域名最深层目录 [url]httpwww.sina.commail[url]
                    if (domainname.equals(uri))
                        dndir = domainname;
                    else
                        dndir = uri.substring(0, uri.lastindexof(''));

                    dndir += '';

                    获取数据
                    string pagedata = encoding.utf8.getstring(e.result);
                    liststring urllist = new liststring();

                    匹配全路径
                    match = regex.match(pagedata, @((http(s)))+((()+[w-.]+()))+[w-.]+.+( + imagetype + )); , regexoptions.ignorecase
                    while (match.success)
                    {
                        string item = match.value;
                        短路径处理
                        if (item.indexof(http) == -1 && item.indexof(https) == -1)
                            item = (item[0] == ''  domainname  dndir) + item;

                        if (!urllist.contains(item))
                        {
                            urllist.add(item);
                            imgurllist.add(item);

                            实时显示分析结果
                            addlbshowitem(item);

                            边分析边下载
                            webrequest hwr = webrequest.create(item);
                            hwr.begingetresponse(new asynccallback(asyncdownload), hwr);
                            hwr.timeout = 0x30d40;        默认 0x186a0 - 100000 0x30d40 - 200000
                            hwr.method = post;
                            hwr.c;
                            hwr.maximumautomaticredirections = 3;
                            hwr.accept =imagegif, imagex-xbitmap, imagejpeg, imagepjpeg, applicationx-shockwave-flash, applicationvnd.ms-excel, applicationvnd.ms-powerpoint, applicationmsword, ;
                            hwr.accept = imagegif, imagex-xbitmap, imagejpeg, imagepjpeg, ;
                            iasyncresult iar = hwr.begingetresponse(new asynccallback(asyncdownload), hwr);
                            iar.asyncwaithandle.waitone();
                        }
                        match = match.nextmatch();
                    }
                }
            }
            finally
            {
                waiter.set();

                #region 分析计时结束

                queryperformancecounter(ref count1);
                count = count1 - count;
                result = (double)(count)  (double)freq;

                toolstripstatuslabel1.text = 分析完毕！;
                toolstripstatuslabel2.text = string.format(  分析耗时{0}秒, result);
                application.doevents();

                #endregion

                分析完毕
                isanalyzecomplete = true;
            }
        }

        /// <summary>
        /// 异步接受数据
        /// </summary>
        /// <param name="asyncresult"></param>
        public  void asyncdownload(iasyncresult asyncresult) 
        {
            #region 下载计时开始

            if (cfreq == 0)
            {
                queryperformancefrequency(ref cfreq);
                queryperformancecounter(ref ccount);
            }

            #endregion

            webrequest request = (webrequest)asyncresult.asyncstate;
            string url = request.requesturi.tostring();
            try
            {
                webresponse response = request.endgetresponse(asyncresult);
                using (stream stream = response.getresponsestream())
                {
                    image img = image.fromstream(stream);
                    string[] tmpurl = url.split('.');
                    img.save(string.concat(savepath, "/", datetime.now.tostring("yyyymmddhhmmssfff"), ".", tmpurl[tmpurl.length - 1]));
                    img.dispose();
                    stream.close();
                }
                alldone.set();

                //从未下载的列表中删除已经下载的图片
                imgurllist.remove(url);

                //更新列表框
                int indexitem = this.lbshow.items.indexof(url);
                if (indexitem >= 0 && indexitem <= this.lbshow.items.count)
                    setlbshowitem(indexitem);
            }
            catch (exception)
            {
                imgurllist.remove(url);
            }
        }