Java实现多线程文件下载的代码示例

时间:2022-06-04 10:16:50

Java实现多线程文件下载思路:

1、基本思路是将文件分段切割、分段传输、分段保存。

2、分段切割用到HttpUrlConnection对象的setRequestProperty("Range", "bytes=" + start + "-" + end)方法。

3、分段传输用到HttpUrlConnection对象的getInputStream()方法。

4、分段保存用到RandomAccessFile的seek(int start)方法。

5、创建指定长度的线程池,循环创建线程,执行下载操作。 

 首先,我们要先写一个方法,方法的参数包含URL地址,保存的文件地址,切割后的文件开始位置和结束位置,这样我们就能把分段文件下载到本地。并且这个方法要是run方法,这样我们启动线程时就直接执行该方法。

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
public class DownloadWithRange implements Runnable
  {
    private String urlLocation;
 
    private String filePath;
 
    private long start;
 
    private long end;
 
    DownloadWithRange(String urlLocation, String filePath, long start, long end)
    {
      this.urlLocation = urlLocation;
      this.filePath = filePath;
      this.start = start;
      this.end = end;
    }
 
    @Override
    public void run()
    {
      try
      {
        HttpURLConnection conn = getHttp();
        conn.setRequestProperty("Range", "bytes=" + start + "-" + end);
 
        File file = new File(filePath);
        RandomAccessFile out = null;
        if (file != null)
        {
          out = new RandomAccessFile(file, "rwd");
        }
        out.seek(start);
        InputStream in = conn.getInputStream();
        byte[] b = new byte[1024];
        int len = 0;
        while ((len = in.read(b)) != -1)
        {
          out.write(b, 0, len);
        }
        in.close();
        out.close();
      }
      catch (Exception e)
      {
        e.getMessage();
      }
 
    }
 
    public HttpURLConnection getHttp() throws IOException
    {
      URL url = null;
      if (urlLocation != null)
      {
        url = new URL(urlLocation);
      }
      HttpURLConnection conn = (HttpURLConnection) url.openConnection();
      conn.setReadTimeout(5000);
      conn.setRequestMethod("GET");
 
      return conn;
    }
 
  }

然后我们创建线程池,线程池的长度可以自定义,然后循环创建线程来执行请求,每条线程的请求开始位置和结束位置都不同,本地存储的文件开始位置和请求开始位置相同,这样就可以实现多线程下载了。

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
public class DownloadFileWithThreadPool
{
  public void getFileWithThreadPool(String urlLocation,String filePath, int poolLength) throws IOException
  {
    Executor threadPool = Executors.newFixedThreadPool(poolLength);
    
    long len = getContentLength(urlLocation);
    for(int i=0;i<poolLength;i++)
    {
      long start=i*len/poolLength;
      long end = (i+1)*len/poolLength-1;
      if(i==poolLength-1)
      {
        end =len;
      }
      DownloadWithRange download=new DownloadWithRange(urlLocation, filePath, start, end);
      threadPool.execute(download);
    }
  }
 
  public static long getContentLength(String urlLocation) throws IOException
  {
    URL url = null;
    if (urlLocation != null)
    {
      url = new URL(urlLocation);
    }
    HttpURLConnection conn = (HttpURLConnection) url.openConnection();
    conn.setReadTimeout(5000);
    conn.setRequestMethod("GET");
    long len = conn.getContentLength();
 
    return len;
  }

以上就是本文的全部内容,希望对大家的学习有所帮助,也希望大家多多支持服务器之家。

原文链接:http://www.cnblogs.com/stsinghua/p/6418796.html