java多线程网页下载代码

1.使用了java.util.concurrent包里的线程池，可以飙升到满带宽，在100M带宽上，可以达到10MB/s。

2.使用了java.nio里的channels，性能比自己缓冲有一些提高。

import java.io.FileOutputStream;
import java.io.InputStream;
import java.net.URL;
import java.net.URLConnection;
import java.nio.channels.Channels;
import java.nio.channels.FileChannel;
import java.nio.channels.ReadableByteChannel;
import java.util.Calendar;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;


public class HttpDownloader implements Callable<String> {
URLConnection connection;
FileChannel outputChann;
public static volatile int count = 0;


public static void main(String[] args) throws Exception {


ExecutorService poll = Executors.newFixedThreadPool(100);


for (int i = 0; i < 100; i++) {
Calendar now = Calendar.getInstance();
String fileName = "../data/" + now.get(Calendar.YEAR) + "年"
+ (now.get(Calendar.MONTH) + 1) + "月"
+ now.get(Calendar.DAY_OF_MONTH) + "日--" + i + ".txt";
poll.submit(new HttpDownloader("http://www.sina.com",
(new FileOutputStream(fileName)).getChannel()));
}


poll.shutdown();


long start = System.currentTimeMillis();
while (!poll.isTerminated()) {
Thread.sleep(1000);
System.out.println("已运行"
+ ((System.currentTimeMillis() - start) / 1000) + "秒，"
+ HttpDownloader.count + "个任务还在运行");
}
}


public HttpDownloader(String url, FileChannel fileChannel) throws Exception {
synchronized (HttpDownloader.class) {
count++;
}
connection = (new URL(url)).openConnection();
this.outputChann = fileChannel;
}


@Override
public String call() throws Exception {
connection.connect();
InputStream inputStream = connection.getInputStream();
ReadableByteChannel rChannel = Channels.newChannel(inputStream);
outputChann.transferFrom(rChannel, 0, Integer.MAX_VALUE);
// System.out.println(Thread.currentThread().getName() + " completed!");
inputStream.close();
outputChann.close();
synchronized (HttpDownloader.class) {
count--;
}
return null;
}
}