Java Multi-Threaded download Implementation method _java

Copy Code code as follows:

Package cn.me.test;

Import Java.io.InputStream;

Import Java.io.RandomAccessFile;

Import java.net.HttpURLConnection;

Import Java.net.URL;

/**

* Multi-threaded download

* 1: Write data in any location using Randomaccessfile.

* 2: The amount of data downloaded by the first thread needs to be calculated and distributed evenly. If the average is not enough,

* Direct the last thread to handle the relatively small amount of data

* 3: Must be prepared before downloading the same size of files, through the file header to get

*/

public class Multithreaddownload {

public static void Main (string[] args) throws Exception {

1: Declaring the filename and the address of the download

String fileName = "Aa.rar";

String urlstr = "Http://localhost:7777/day18";

2: Declaration URL

URL url = new URL (urlstr+ "/" +filename);

3: Get the connection

HttpURLConnection con =

(httpurlconnection) url.openconnection ();

4: Set the request mode

Con.setrequestmethod ("get");

5: Get the request header, that is, the length of the file

int length = Con.getcontentlength ();//Gets the length of the download file to calculate the amount of data each thread should download.

6: Create a file of the same size in the specified directory

Randomaccessfile file = new Randomaccessfile ("d:/a/" +filename, "RW");//Create a document of the same size.

7: Set the file size, placeholder

File.setlength (length);//Set File size.

File.close ();

8: Define the number of threads

int size = 3;

9: Calculate how many bytes each thread should download the data, if the exact division is the best, otherwise add 1

int block = length/size==0?length/size:length/size+1;//Calculates the amount of data that each thread should download.

SYSTEM.ERR.PRINTLN ("Each thread should be downloaded:" +block);

10: Run three threads and calculate from which byte to start to which byte end

for (int i=0;i<size;i++) {

int start = I*block;

int end = start+ (block-1);//calculate start and end bytes for each thread.

System.err.println (i+ "=" +start+ "," +end);

New Mydownthread (FileName, Start, End,url). Start ();

}

}

Static class Mydownthread extends thread{

Define file name

Private String FileName;

Define where to start the download

private int start;

Define which byte to download

private int end;

Private URL URL;

Public Mydownthread (String filename,int start,int end,url URL) {

This.filename=filename;

This.start=start;

This.end=end;

This.url=url;

}

@Override

public void Run () {

try{

11: Start downloading

HttpURLConnection con =

(httpurlconnection) url.openconnection ();

Con.setrequestmethod ("get");

12: Set the request header for the segmented download

Con.setrequestproperty ("Range", "bytes=" +start+ "-" +end),//sets the block of files read from the server.

13: Start downloading, need to Judge 206

if (Con.getresponsecode () ==206) {//Access succeeded, the returned status code is 206.

InputStream in = Con.getinputstream ();

14: Declare random Write file objects, note that RWD is to write data to the file immediately, without using a buffer

Randomaccessfile out = new Randomaccessfile ("d:/a/" +filename, "RWD");

Out.seek (start);/setting starts writing data from a location in the file.

Byte[] B=new byte[1024];

int len = 0;

while ((Len=in.read (b))!=-1) {

Out.write (B,0,len);

}

Out.close ();

In.close ();

}

System.err.println (This.getname () + "execution complete");

}catch (Exception e) {

throw new RuntimeException (e);

}

}

}

}