多个RandomAccessFile 同时往一个文件中写数据如何保证写入的正确性

Question

rt

Answer 1

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
public class ThreadDownload implements Runnable {
private URL url;
private File file;
private int offset;
private int len;
private String net;
private InputStream in;
private RandomAccessFile random;
private HttpURLConnection httpConnection;
@Override
public void run() {
StartDownload();
}
public ThreadDownload(String net,File file,int offset,int len)
{
this.net=net;
this.file=file;
this.offset=offset;
this.len=len;
}
public void StartDownload() 
{
long start = System.currentTimeMillis();
int byteread=0;
System.out.println("begin to download the file");
System.out.println("the offset is "+offset);
byte[] b=new byte[1024];
try {
url=new URL(net);
} catch (MalformedURLException e) {
e.printStackTrace();
}
try {
httpConnection=(HttpURLConnection) url.openConnection();
httpConnection.setRequestProperty("RANGE","bytes=" + offset + "-");
in=httpConnection.getInputStream();
random = new RandomAccessFile(file,"rw");
random.seek(offset);
while(in.read(b)!=-1&&byteread<=len)
{
random.write(b);
byteread+=b.length;
}
} catch (IOException e) {
e.printStackTrace();
}
System.out.println("this thread is complete");
long end= System.currentTimeMillis();
System.out.println(end-start);
}
}
import java.io.File;
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.URL;public class b { /**
 * @param args
 * @throws IOException 
 */
public static void main(String[] args) throws IOException {
ThreadDownload[] d= new ThreadDownload[4];
Thread[] thread=new Thread[4];
File file = new File("4.mp3");
String net ="http://224.cachefile7.rayfile.com/a8c6/zh-cn/preview/e58932fb329b88afe7f4bbe252f70012/preview.mp3";
URL url=new URL(net);
HttpURLConnection http = (HttpURLConnection) url.openConnection();
int length=http.getContentLength();
System.out.println(length/4);
System.out.println(http.getContentType());
d[0]=new ThreadDownload(net, file, length*0,  length/4);
d[1]= new ThreadDownload(net,file,length/4,length/4);
d[2]= new ThreadDownload(net,file,length/2,length/4);
d[3]= new ThreadDownload(net,file,length/4*3,length/4);

for(int i=0;i<4;i++){
thread[i]=new Thread(d[i]);
thread[i].start();
}
}
}
实验的代码 能改一下么

Answer 2

RandomAccessFile是可以获得lock的.
在写之前,先获得要写入数据位置的lock.这样别人就动不了这块地方了.
写完之后unlock.接口就在RandomAccessFile里,lz自己找找吧:)

Answer 3

哦 原来要用FileLock啊  原来是这个样子 明白了 谢谢了啊~~