412      阿裏雲  技術社區[雲棲]

使用Apache HttpClient實現多線程下載的小例子

網上類似的文章很多，參考了很多人的，大部分人都是用URLConnection寫的。

原理一：HTTP多線程下載原理

1、發送一個含有Rang頭的Head請求，如果返回狀態碼為206，則允許多線程下載

原理二：多線程下載原理

1、使用HttpClient的Head請求獲取請求文件的信息

2、發送一個Rang的Head請求判斷是否允許多線程下載

3、通過主任務創建多個分段下載線程，分段下載文件，然後用Java的隨機讀寫文件類保存下載的內容

（等有時間了再添加內容吧，先簡單寫這麼多）

調度功能代碼片段

	/**
	 * 開始下載
	 * @throws Exception
	 */
	public void startDown() throws Exception{
		HttpClient httpClient = new DefaultHttpClient();
		try {
			//獲取下載文件信息
			getDownloadFileInfo(httpClient);
			//啟動多個下載線程
			startDownloadThread();
			//開始監視下載數據
			monitor();
		} catch (Exception e) {
			throw e;
		} finally {
			httpClient.getConnectionManager().shutdown();
		}
	}

	/**
	 * 獲取下載文件信息
	 */
	private void getDownloadFileInfo(HttpClient httpClient) throws IOException,
			ClientProtocolException, Exception {
		HttpHead httpHead = new HttpHead(url);
		HttpResponse response = httpClient.execute(httpHead);
		//獲取HTTP狀態碼
		int statusCode = response.getStatusLine().getStatusCode();

		if(statusCode != 200) throw new Exception("資源不存在!");
		if(getDebug()){
			for(Header header : response.getAllHeaders()){
				System.out.println(header.getName()+":"+header.getValue());
			}
		}

		//Content-Length
		Header[] headers = response.getHeaders("Content-Length");
		if(headers.length > 0)
			contentLength = Long.valueOf(headers[0].getValue());

		httpHead.abort();
		
		httpHead = new HttpHead(url);
		httpHead.addHeader("Range", "bytes=0-"+(contentLength-1));
		response = httpClient.execute(httpHead);
		if(response.getStatusLine().getStatusCode() == 206){
			acceptRanges = true;
		}
		httpHead.abort();
	}

	/**
	 * 啟動多個下載線程
	 * @throws IOException
	 * @throws FileNotFoundException
	 */
	private void startDownloadThread() throws IOException,
			FileNotFoundException {
		//創建下載文件
		File file = new File(localPath);
		file.createNewFile();
		RandomAccessFile raf = new RandomAccessFile(file, "rw");
		raf.setLength(contentLength);
		raf.close();
		
		//定義下載線程事件實現類
		DownloadThreadListener listener = new DownloadThreadListener() {
			public void afterPerDown(DownloadThreadEvent event) {
				//下載完一個片段後追加已下載字節數
				synchronized (object) {
					DownloadTask.this.receivedCount += event.getCount();
				}
			}

			public void downCompleted(DownloadThreadEvent event) {
				//下載線程執行完畢後從主任務中移除
				threads.remove(event.getTarget());
				if(getDebug()){
					System.out.println("剩餘線程數："+threads.size());
				}
			}
		};
		
		//不支持多線程下載時
		if (!acceptRanges) {
			if(getDebug()){
				System.out.println("該地址不支持多線程下載");
			}
			//定義普通下載
			DownloadThread thread = new DownloadThread(url, 0, contentLength, file, false);
			thread.addDownloadListener(listener);
			thread.start();
			threads.add(thread);
			return;
		}
		
		//每個請求的大小
		long perThreadLength = contentLength / threadCount + 1;
		long startPosition = 0;
		long endPosition = perThreadLength;
		//循環創建多個下載線程
		do{
			if(endPosition >= contentLength)
				endPosition = contentLength - 1;

			DownloadThread thread = new DownloadThread(url, startPosition, endPosition, file);
			thread.addDownloadListener(listener);
			thread.start();
			threads.add(thread);

			startPosition = endPosition + 1;//此處加 1,從結束位置的下一個地方開始請求
			endPosition += perThreadLength;
		} while (startPosition < contentLength);
	}

 分段下載線程代碼片段：

Java代碼  

1.   
2. /**  
3.  * 現在過程代碼  
4.  */  
5. public void run() {   
6.     if(DownloadTask.getDebug()){   
7.         System.out.println("Start:" + startPosition + "-" +endPosition);   
8.     }   
9.     HttpClient httpClient = new DefaultHttpClient();   
10.     try {   
11.         HttpGet httpGet = new HttpGet(url);   
12.         if(isRange){//多線程下載   
13.             httpGet.addHeader("Range", "bytes="+startPosition+"-"+endPosition);   
14.         }   
15.         HttpResponse response = httpClient.execute(httpGet);   
16.         int statusCode = response.getStatusLine().getStatusCode();   
17.         if(DownloadTask.getDebug()){   
18.             for(Header header : response.getAllHeaders()){   
19.                 System.out.println(header.getName()+":"+header.getValue());   
20.             }   
21.             System.out.println("statusCode:" + statusCode);   
22.         }   
23.         if(statusCode == 206 || (statusCode == 200 && !isRange)){   
24.             InputStream inputStream = response.getEntity().getContent();   
25.             //創建隨機讀寫類   
26.             RandomAccessFile outputStream = new RandomAccessFile(file, "rw");   
27.             //跳到指定位置   
28.             outputStream.seek(startPosition);   
29.             int count = 0;byte[] buffer=new byte[1024];   
30.             while((count = inputStream.read(buffer, 0, buffer.length))>0){   
31.                 outputStream.write(buffer, 0, count);   
32.                 //觸發下載事件   
33.                 fireAfterPerDown(new DownloadThreadEvent(this,count));   
34.             }   
35.             outputStream.close();   
36.         }   
37.         httpGet.abort();   
38.     } catch (Exception e) {   
39.         e.printStackTrace();   
40.     } finally {   
41.         //觸發下載完成事件   
42.         fireDownCompleted(new DownloadThreadEvent(this, endPosition));   
43.         if(DownloadTask.getDebug()){   
44.             System.out.println("End:" + startPosition + "-" +endPosition);   
45.         }   
46.         httpClient.getConnectionManager().shutdown();   
47.     }   
48. }  

	
	/**
	 * 現在過程代碼
	 */
	public void run() {
		if(DownloadTask.getDebug()){
			System.out.println("Start:" + startPosition + "-" +endPosition);
		}
		HttpClient httpClient = new DefaultHttpClient();
		try {
			HttpGet httpGet = new HttpGet(url);
			if(isRange){//多線程下載
				httpGet.addHeader("Range", "bytes="+startPosition+"-"+endPosition);
			}
			HttpResponse response = httpClient.execute(httpGet);
			int statusCode = response.getStatusLine().getStatusCode();
			if(DownloadTask.getDebug()){
				for(Header header : response.getAllHeaders()){
					System.out.println(header.getName()+":"+header.getValue());
				}
				System.out.println("statusCode:" + statusCode);
			}
			if(statusCode == 206 || (statusCode == 200 && !isRange)){
				InputStream inputStream = response.getEntity().getContent();
				//創建隨機讀寫類
				RandomAccessFile outputStream = new RandomAccessFile(file, "rw");
				//跳到指定位置
				outputStream.seek(startPosition);
				int count = 0;byte[] buffer=new byte[1024];
				while((count = inputStream.read(buffer, 0, buffer.length))>0){
					outputStream.write(buffer, 0, count);
					//觸發下載事件
					fireAfterPerDown(new DownloadThreadEvent(this,count));
				}
				outputStream.close();
			}
			httpGet.abort();
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			//觸發下載完成事件
			fireDownCompleted(new DownloadThreadEvent(this, endPosition));
			if(DownloadTask.getDebug()){
				System.out.println("End:" + startPosition + "-" +endPosition);
			}
			httpClient.getConnectionManager().shutdown();
		}
	}

 附件說明：

1、Download.jar為編譯好的可運行程序

2、Download.zip為Eclipse項目文件

3、運行截圖

 

• Download.jar (928.1 KB)
• 下載次數: 44

• DownLoad.zip (832.5 KB)
• 下載次數: 70

最後更新：2017-04-02 06:51:46

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