多線程下載文件
平時開發中有時會用到文件下載，為了提高文件的下載速率，采用多線程下載能夠達到事半功倍的效果：
package test;
/**
* 文件下載類
* @author luweicheng
*
*/
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLConnection;
public class DownFile {
private URL fileUrl;// 文件下載路徑
private int threadCount;// 文件下載的線程數
private int startPos;// 每個線程下載文件的開始位置
private int size;// 每個線程下載文件的長度
private int fileLength;// 文件總程度
private String pathName;// 下載的文件路徑（包含文件名）
private Downthread[] tDownthreads;// 線程數組
public DownFile(URL url, int threadCount, String pathName) throws IOException {
fileUrl = url;
this.threadCount = threadCount;
this.pathName = pathName;
init();
}
/**
* 初始化
*
* @throws IOException
*/
private void init() throws IOException {
tDownthreads = new Downthread[threadCount];
HttpURLConnection conn = (HttpURLConnection) fileUrl.openConnection();
conn.setConnectTimeout(5000);
conn.setRequestMethod("GET");
conn.setRequestProperty("connection", "keep-alive");
fileLength = conn.getContentLength();
System.out.println("文件長度" + fileLength);
size = fileLength / threadCount;
System.out.println("每個下載量==" + size);
conn.disconnect();// 斷開鏈接
}
public URL getFileUrl() {
return fileUrl;
}
public int getThreadCount() {
return this.threadCount;
}
/**
* 開始下載
*/
public void startDown() {
for (int i = 0; i < threadCount; i++) {
try {
RandomAccessFile raFile = new RandomAccessFile(pathName, "rw");
tDownthreads[i] = new Downthread(i * size, raFile, i);
tDownthreads[i].start();
} catch (FileNotFoundException e) {
e.printStackTrace();
}
}
}
/**
* 下載線程類
*
* @author luweicheng
*
*/
class Downthread extends Thread {
private int startPos;// 開始的位置
private InputStream is;
private RandomAccessFile raFile;
private int length;// 下載的文件長度
private int flag;// 線程標志
public Downthread(int startPos, RandomAccessFile raFile, int i) {
this.startPos = startPos;
this.raFile = raFile;
flag = i;
}
@Override
public void run() {
try {
HttpURLConnection connection = (HttpURLConnection) fileUrl.openConnection();
connection.setRequestMethod("GET");
connection.setRequestProperty("connection", "keep-alive");
connection.setConnectTimeout(5 * 1000);
is = connection.getInputStream();
is.skip(startPos);
raFile.seek(startPos);
byte[] buf = new byte[8 * 1024];
int hasread = 0;// 讀出的字節數
// 將位置在 startPos - startPos 位置的數據讀出寫入
while (length < size && (hasread = is.read(buf)) != -1) {
raFile.write(buf, 0, hasread);
length += hasread;
System.out.println("*****線程" + flag + "下載了*********" + length);
}
System.out.println("*******線程" + flag + "下載完成*********");
} catch (IOException e) {
} finally {
try {
is.close();
raFile.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
