本文是参照博客园【CAP&船长】的Demo衍生出来的。
主要是C#通过HttpWebRequest类通过Http协议并调用多线程下载Web资源。
思路: 1、获取文件的总大小 2、设置启动的线程数目,并分配每个线程的下载的开始位置与下载的字节数大小 3、子线程下载成功后保存到临时文件中 4、监听所有文件是否全部下载成功 5、如果所有子线程均下载完成则根据现在Id拼接起来 6、删除临时文件
简单封装的类:
1、新建一个【CHttpDownload.cs】类 2、声明必须的公共属性与私有属性以及变量
private int nThreadNum = 0; // 线程的个数 private string strUrl = ""; // 下载地址 private string strSavePath = ""; // 文件保存地址 private System.Threading.Thread[] threads = null; // 线程数组 private int[] nStartPosition = null; // 每个线程的开始地址 private int[] nFileSize = null; //每个线程下载的大小 private bool[] bThreadState = null; // 线程下载状态 public bool bHasMerge { get; private set; } // 是否合并成功 public long lFileSizeAll { get; private set; } // 文件总大小 public int nBufferSize { get; set; } // 下载文件缓冲区大小 private int id = 0; // 标记线程Id、临时变量 2、构造函数 /// <summary> /// 构造函数 /// </summary> /// <param name="strUrl">文件下载地址Url</param> /// <param name="nThreadNum">所需要的线程数</param> public CHttpDownload(string strUrl, int nThreadNum) { /* 初始化下载地址、线程数、缓冲流大小 */ this.strUrl = strUrl; this.nThreadNum = nThreadNum; this.nBufferSize = 1024; Init(); } /// <summary> /// 初始化数据、设置每个线程的开始字节位置与字节大小 /// </summary> private void Init() { threads = new System.Threading.Thread[this.nThreadNum]; nStartPosition = new int[this.nThreadNum]; nFileSize = new int[this.nThreadNum]; bThreadState = new bool[this.nThreadNum]; bHasMerge = false;
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(this.strUrl); lFileSizeAll = request.GetResponse().ContentLength; // 获取文件的总大小 request.Abort(); // 端口本次连接
int nFileNormalSize = (int)lFileSizeAll / nThreadNum; // 前面线程下载的大小,最后一个线程下载全部 int nFileLastSize = nFileNormalSize + (int)lFileSizeAll % nThreadNum; // 最后一个线程下载的大小
for (int i = 0; i < nThreadNum; i++) { bThreadState[i] = false; nStartPosition[i] = nFileNormalSize * i; if (i == nThreadNum - 1) { nFileSize[i] = nFileLastSize - 1; } else { nFileSize[i] = nFileNormalSize - 1; } } }
3、新建StartReceive方法,功能为启动指定一个线程进行下载,并保存到临时文件中 /// <summary> /// 多线程开始接收 /// </summary> private void StartReceive() { id++; int nId = id - 1; string strFileName = "C:\\\\" + nId + ".tmp"; byte[] buffer = new byte[nBufferSize]; int nReadSize = 0; // 标记本次读到多少个数据
FileStream fs = new FileStream(strFileName, System.IO.FileMode.Create); Stream s = null; try { HttpWebRequest request = (HttpWebRequest)WebRequest.Create(this.strUrl); request.AddRange(nStartPosition[nId], nStartPosition[nId] + nFileSize[nId]); // 设置流的开始位置与结束位置 s = request.GetResponse().GetResponseStream(); nReadSize = s.Read(buffer, 0, nBufferSize); while (nReadSize > 0) { fs.Write(buffer, 0, nReadSize); nReadSize = s.Read(buffer, 0, nBufferSize); } fs.Close(); s.Close(); } catch (Exception ex) { } bThreadState[nId] = true; }
4、新建MergeFiles方法,功能为当所有线程完成下载后进行文件合并保存、并删除临时文件 /// <summary> /// 合并文件 /// </summary> private void MergeFiles() { while (true) // 验证所有线程是否全部接收完毕 { bHasMerge = true; for (int i = 0; i < nThreadNum; i++) { if (bThreadState[i] == false) { bHasMerge = false; System.Threading.Thread.Sleep(100); break; } } if (bHasMerge == true) { break; } }
int nReadSize; byte[] bytes = new byte[nBufferSize]; FileStream fs = new FileStream(strSavePath, FileMode.Create); FileStream fsTmp = null; for (int i = 0; i < nThreadNum; i++) { fsTmp = new FileStream("C:\\\\" + i + ".tmp", FileMode.Open); while (true) { nReadSize = fsTmp.Read(bytes, 0, nBufferSize); if (nReadSize > 0) { fs.Write(bytes, 0, nReadSize); } else { break; } } fsTmp.Close(); if (File.Exists("C:\\\\" + i + ".tmp")) // 如果临时文件存在则删除 { File.Delete("C:\\\\" + i + ".tmp"); } } fs.Close(); }
5、新建StartDownload方法,为客户调用多线程下载的方法 /// <summary> /// 开始下载文件 /// </summary> /// <param name="strSaveFile">文件的保存地址</param> public void StartDownload(string strSaveFile) { this.strSavePath = strSaveFile; for (int i = 0; i < nThreadNum; i++) { threads[i] = new System.Threading.Thread(new System.Threading.ThreadStart(StartReceive)); threads[i].Start(); } System.Threading.Thread t = new System.Threading.Thread(new System.Threading.ThreadStart(MergeFiles)); t.Start(); }
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