Java实现多线程文件下载的代码示例

Java实现多线程文件下载的代码示例

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。

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。

public class DownloadFileWithThreadPool

{

public void getFileWithThreadPool(String urlLocation,String filePath, int poolLength) throws IOException

{

Executor threadPool = Executors.newFixedThreadPool(poolLength);

long len = getContentLength(urlyZfhSnzVLocation);

for(int i=0;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) http://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;

}

{

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) http://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;

}

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