java – 如何从URL下载(使用http连接)检索文件的大小？

发布时间：2020-12-14 16:46:04 所属栏目：Java 来源：网络整理

导读：我正在使用一个使用http连接下载文件的项目.我在下载过程中显示一个进度条状态的水平进度条. 我的功能如下所示： .......try { InputStream myInput = urlconnect.getInputStream(); BufferedInputStream buffinput = new BufferedInputStream(myInput); Byt

我正在使用一个使用http连接下载文件的项目.我在下载过程中显示一个进度条状态的水平进度条.
我的功能如下所示：

.......
try {           
        InputStream myInput = urlconnect.getInputStream();
        BufferedInputStream buffinput = new BufferedInputStream(myInput);

        ByteArrayBuffer baf = new ByteArrayBuffer(capacity);
        int current = 0;
        while((current = buffinput.read()) != -1) {
            baf.append((byte) current);
        }
File outputfile = new File(createRepertory(app,0),Filename);
        FileOutputStream myOutPut = new FileOutputStream(outputfile);
        myOutPut.write(baf.toByteArray());
...
}

我提前知道我的文件的大小,所以我需要检索的大小在下载(在我的while块).因此,我可以确定进度条的状态.

progressBarStatus = ((int) downloadFileHttp(url,app) * 100)/sizefile;

长的downloadFileHttp(..,..)是我的函数的名字.

我已经尝试通过使用outputfile.length来检索它,但是他的值为“1”,也许这是我要下载的文件数.

Is there any way to figure it out?

更新1

I haven’t got any thread which allow me to figure this out.
Currently I have got a horizontal progress bar whch displays only 0 and 100% whitout intermediate values. I
think about another approach. If I know the rate of my wifi and the
size of the file I can determinate the time of downloading.

I know that I can retrieve the piece of information of my Wifi
connection and the size of my file to download.

Is anybody already have worked or have thread on it?

解决方法

AsyncTask可能是您的完美解决方案：

private class DownloadFileTask extends AsyncTask<URL,Integer,Long> {
 protected Long doInBackground(URL... urls) {
    Url url = urls[0];
    //connect to url here
    .......
    try {           
        InputStream myInput = urlconnect.getInputStream();
        BufferedInputStream buffinput = new BufferedInputStream(myInput);

        ByteArrayBuffer baf = new ByteArrayBuffer(capacity);
        int current = 0;
        while((current = buffinput.read()) != -1) {
            baf.append((byte) current);
            //here you can send data to onProgressUpdate
            publishProgress((int) (((float)baf.length()/ (float)sizefile) * 100));
        }
    File outputfile = new File(createRepertory(app,Filename);
    FileOutputStream myOutPut = new FileOutputStream(outputfile);
    myOutPut.write(baf.toByteArray());
    ...
 }

 protected void onProgressUpdate(Integer... progress) {
     //here you can set progress bar in UI thread
     progressBarStatus = progress;
 }

}

在您的方法中启动AsyncTask调用

new DownloadFileTask().execute(url);

（编辑：李大同）

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