📅  最后修改于: 2023-12-03 14:53:14.661000             🧑  作者: Mango
在编写程序时,我们经常需要下载文件或者数据,这些文件或数据有时候来源于不同的地方(例如网站、FTP、本地磁盘等),我们很难针对每一个来源编写单独的下载函数。因此,我们需要一个统一的下载函数来满足我们的需求。
一个好的下载函数应该满足以下几点要求:
以下是一个典型的下载函数的参数清单:
public static void Download(string url, string savePath, int maxThreadNum = 6, long range = 0)
{
// Implementation here
}
参数说明:
下载函数的实现比较复杂,需要涉及HTTP协议、网络编程、异步编程等知识,在这里我们只提供一个简单的实现思路,供大家参考。
以下是一个简单的实现:
public static void Download(string url, string savePath, int maxThreadNum = 6, long range = 0)
{
if (range < 0)
{
range = 0;
}
HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);
req.Proxy = null;
req.Method = "HEAD";
HttpWebResponse res = (HttpWebResponse)req.GetResponse();
long totalSize = res.ContentLength;
res.Close();
FileStream fs = new FileStream(savePath, FileMode.Create, FileAccess.Write);
fs.SetLength(totalSize);
fs.Close();
long blockSize = totalSize / maxThreadNum;
DownloadThread[] threads = new DownloadThread[maxThreadNum];
for (int i = 0; i < maxThreadNum; i++)
{
long startPos = i * blockSize + range;
long endPos = (i == maxThreadNum - 1) ? totalSize - 1 : (i + 1) * blockSize - 1;
threads[i] = new DownloadThread(url, savePath, startPos, endPos);
}
Task[] tasks = new Task[maxThreadNum];
for (int i = 0; i < maxThreadNum; i++)
{
tasks[i] = new Task(threads[i].Download);
tasks[i].Start();
}
Task.WaitAll(tasks);
using (FileStream fs2 = new FileStream(savePath, FileMode.Append))
{
foreach (DownloadThread item in threads)
{
using (FileStream part = new FileStream(item.TempFilePath, FileMode.Open))
{
byte[] buffer = new byte[4096];
int len = part.Read(buffer, 0, buffer.Length);
while (len > 0)
{
fs2.Write(buffer, 0, len);
len = part.Read(buffer, 0, buffer.Length);
}
}
}
}
foreach (DownloadThread item in threads)
{
File.Delete(item.TempFilePath);
}
}
以上实现中用到了DownloadThread类,以下是该类的实现:
class DownloadThread
{
private string url = "";
private string savePath = "";
private long startPos = 0;
private long endPos = 0;
public string TempFilePath { get; private set; }
public DownloadThread(string url, string savePath, long startPos, long endPos)
{
this.url = url;
this.savePath = savePath;
this.startPos = startPos;
this.endPos = endPos;
this.TempFilePath = savePath + ".tmp" + startPos;
}
public void Download()
{
HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);
req.Proxy = null;
req.AddRange(startPos, endPos);
req.Timeout = 5000;
using (HttpWebResponse res = (HttpWebResponse)req.GetResponse())
{
using (Stream input = res.GetResponseStream())
{
using (FileStream output = new FileStream(TempFilePath, FileMode.Create))
{
byte[] buffer = new byte[4096];
int len = 0;
while ((len = input.Read(buffer, 0, buffer.Length)) > 0)
{
output.Write(buffer, 0, len);
}
}
}
}
}
}
通过以上的实现,我们可以统一下载不同来源的文件或数据,并且支持断点续传和多线程下载。这样的设计具有良好的可扩展性和复用性,可以满足大部分下载需求。
需要注意,以上实现并没有考虑异常处理、网络状况判断等情况,实际开发中还需要进行更加严密的测试和优化。