package download;

import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;


public class Downloader {

	public static void main(String[] args) throws Exception {
		String filename = "tim_pc.exe";

		String path = "https://qd.myapp.com/myapp/qqteam/tim/down/tim_pc.exe";

		URL url = new URL(path);
		HttpURLConnection conn = (HttpURLConnection) url.openConnection();
		conn.setConnectTimeout(5000);
		conn.setRequestMethod("GET");
		// 獲得需要下載的檔案的長度(大小)
		int filelength = conn.getContentLength();
		System.out.println("要下載的檔案長度" + filelength);
		// 生成一個大小相同的本地檔案
		RandomAccessFile file = new RandomAccessFile(filename, "rwd");
		file.setLength(filelength);
		file.close();
		conn.disconnect();
		// 設定有多少條執行緒下載
		int threadsize = 1;
		// 計算每個執行緒下載的量
		int threadlength = filelength % 3 == 0 ? filelength / 3
				: filelength + 1;
		for (int i = 0; i < threadsize; i++) {
			// 設定每條執行緒從哪個位置開始下載
			int startposition = i * threadlength;
			// 從檔案的什麼位置開始寫入資料
			RandomAccessFile threadfile = new RandomAccessFile(filename, "rwd");
			threadfile.seek(startposition);
			// 啟動三條執行緒分別從startposition位置開始下載檔案
			new DownLoadThread(i, startposition, threadfile, threadlength, path)
					.start();
		}
		int quit = System.in.read();
		while ('q' != quit) {
			Thread.sleep(2000);
		}

	}
}

// @Test
// public void download()throws Exception{
// String fileName="QQSetUp.exe";
//
// String path="https://qd.myapp.com/myapp/qqteam/tim/down/tim_pc.exe";
//
// URL url=new URL(path);
//
// HttpURLConnection conn=(HttpURLConnection)url.openConnection();
//
// conn.setConnectTimeout(5000);
// conn.setRequestMethod("GET");
//
// //獲得需要下載的檔案長度（大小）
// int filelength=conn.getContentLength();
// System.out.print("檔案大小："+filelength);
// //生成一個大小相同的本地檔案
// RandomAccessFile file=new RandomAccessFile(fileName,"rwd");
// file.setLength(filelength);
// file.close();
// conn.disconnect();
//
// //設定有多少個執行緒下載
// int threadsize=3;
// int threadlength=filelength%3==0?filelength/3:filelength+1;
//
// for(int i=0;i<threadsize;i++){
// int startposition=i*threadlength;
// RandomAccessFile threadfile =new RandomAccessFile(fileName,"rwd");
// threadfile.seek(startposition);
//
// //啟動三條執行緒分別從startposition位置開始下載檔案
// new DownLoadThread(i,startposition,threadfile,threadlength,path).start();
// }
//
// int quit=System.in.read();
// while('q'!=quit){
// Thread.sleep(2000);
// }
// }

// }
 

package download;

import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;

public class DownLoadThread extends Thread {
	private int threadid;
	private int startposition;
	private RandomAccessFile threadfile;
	private int threadlength;
	private String path;

	public DownLoadThread(int threadid, int startposition,
			RandomAccessFile threadfile, int threadlength, String path) {
		this.threadid = threadid;
		this.startposition = startposition;
		this.threadfile = threadfile;
		this.threadlength = threadlength;
		this.path = path;
	}

	public DownLoadThread() {
	}

	@Override
	public void run() {
		try {
			URL url = new URL(path);
			HttpURLConnection conn = (HttpURLConnection) url.openConnection();
			conn.setConnectTimeout(5000);
			conn.setRequestMethod("GET");
			// 指定從什麼位置開始下載
			conn.setRequestProperty("Range", "bytes=" + startposition + "-");
			// System.out.println(conn.getResponseCode());
			if (conn.getResponseCode() == 206) {
				InputStream is = conn.getInputStream();
				byte[] buffer = new byte[1024];
				int len = -1;
				int length = 0;
				while (length < threadlength && (len = is.read(buffer)) != -1) {
					threadfile.write(buffer, 0, len);
					// 計算累計下載的長度
					length += len;
				}
				threadfile.close();
				is.close();
				System.out.println("執行緒" + (threadid + 1) + "已下載完成");
			}
		} catch (Exception ex) {
			System.out.println("執行緒" + (threadid + 1) + "下載出錯" + ex);
		}
	}

}