您的位置:首页 > 编程语言 > Java开发

用java实现简单的多线程下载

2005-12-03 19:44 1181 查看
今天用java写了一个简单的HTTP多线程下载程序,主要用了HTTP协议和RandomAccessFile类来实现。很容易再加上断点续传功能,这样就可以实现类似“小小网络蚂蚁”的功能了。

public class DownloadNetTest {
private File fileOut;
private URL url;
private long fileLength=0;
//初始化线程数
private int ThreadNum=5;

public DownloadNetTest(){
try{
System.out.println("正在链接URL");
url=new URL("http://211.64.201.201/uploadfile/nyz.mp3");
HttpURLConnection urlcon=(HttpURLConnection)url.openConnection();
fileLength=urlcon.getContentLength();
if(urlcon.getResponseCode()>=400){
System.out.println("服务器响应错误");
System.exit(-1);
}
if(fileLength<=0)
System.out.println("无法获知文件大小");
//打印信息
printMIME(urlcon);
System.out.println("文件大小为"+fileLength/1024+"K");
//获取文件名
String trueurl=urlcon.getURL().toString();
String filename=trueurl.substring(trueurl.lastIndexOf('/')+1);
fileOut=new File("D://",filename);
}
catch(MalformedURLException e){
System.err.println(e);
}
catch(IOException e){
System.err.println(e);
}
init();
}
private void init(){
DownloadNetThread [] down=new DownloadNetThread[ThreadNum];
try {
for(int i=0;i<ThreadNum;i++){
RandomAccessFile randOut=new RandomAccessFile(fileOut,"rw");
randOut.setLength(fileLength);
long block=fileLength/ThreadNum+1;
randOut.seek(block*i);
down[i]=new DownloadNetThread(url,randOut,block,i+1);
down[i].setPriority(7);
down[i].start();
}
//循环判断是否下载完毕
boolean flag=true;
while (flag) {
Thread.sleep(500);
flag = false;
for (int i = 0; i < ThreadNum; i++)
if (!down[i].isFinished()) {
flag = true;
break;
}
}// end while
System.out.println("文件下载完毕,保存在"+fileOut.getPath() );
} catch (FileNotFoundException e) {
System.err.println(e);
e.printStackTrace();
}
catch(IOException e){
System.err.println(e);
e.printStackTrace();
}
catch (InterruptedException e) {
System.err.println(e);
}

}
private void printMIME(HttpURLConnection http){
for(int i=0;;i++){
String mine=http.getHeaderField(i);
if(mine==null)
return;
System.out.println(http.getHeaderFieldKey(i)+":"+mine);
}
}

public static void main(String[] args) {
DownloadNetTest app=new DownloadNetTest();
}

}

//线程类
public class DownloadNetThread extends Thread{
private InputStream randIn;
private RandomAccessFile randOut;
private URL url;
private long block;
private int threadId=-1;
private boolean done=false;

public DownloadNetThread(URL url,RandomAccessFile out,long block,int threadId){
this.url=url;
this.randOut=out;
this.block=block;
this.threadId=threadId;
}
public void run(){
try{
HttpURLConnection http=(HttpURLConnection)url.openConnection();
http.setRequestProperty("Range","bytes="+block*(threadId-1)+"-");
randIn=http.getInputStream();
}
catch(IOException e){
System.err.println(e);
}

////////////////////////
byte [] buffer=new byte[1024];
int offset=0;
long localSize=0;
System.out.println("线程"+threadId+"开始下载");
try {
while ((offset = randIn.read(buffer)) != -1&&localSize<=block) {
randOut.write(buffer,0,offset);
localSize+=offset;
}
randOut.close();
randIn.close();
done=true;
System.out.println("线程"+threadId+"完成下载");
this.interrupt();
}
catch(Exception e){
System.err.println(e);
}
}
public boolean isFinished(){
return done;
}
}
内容来自用户分享和网络整理,不保证内容的准确性,如有侵权内容,可联系管理员处理 点击这里给我发消息
标签: