java 读取远程文件 实现继传。。。

import java.io.BufferedInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;

public class TestGetFile {

private boolean FileExist(String pathAndFile)// 确定文件是否已经下载，但没有下载完成
{
File file = new File(pathAndFile);
if (file.exists())
return true;
else
return false;
}

private long FileSize(String pathAndFile)// 确定已经下载了的文件大小
{
File file = new File(pathAndFile);
return file.length();
}

public static void main(String[] args) {

TestGetFile tgf = new TestGetFile();
URL url = null;
HttpURLConnection ulc = null;
DataOutputStream dos = null;
BufferedInputStream bis = null;
FileOutputStream fos = null;
RandomAccessFile raFile = null;
long TotalSize = 0;// 要下载的文件总大小
long fileSize = 0; // 当前文件大小
try {
url = new URL("http://www.baidu.com");
ulc = (HttpURLConnection)url.openConnection();
String fileName = "g:/text.txt";
TotalSize = Long.parseLong(ulc.getHeaderField("Content-Length"));
ulc.disconnect();// 先断开，下面再连接，否则下面会报已经连接的错误
ulc = (HttpURLConnection) url.openConnection();

if(tgf.FileExist(fileName))
{
System.out.println("文件续传中...");
fileSize = tgf.FileSize(fileName);
ulc.setRequestProperty("RANGE", "bytes=" + fileSize + "-");
// urlc.setRequestProperty("RANGE",
// "bytes="+fileSize);//这样写不行，不能少了这个"-".
// 设置接受信息
ulc.setRequestProperty(
"Accept",
"http://www.huomo.cn/developer/image/gif,image/x-xbitmap,application/msword,*/*");
raFile = new RandomAccessFile(fileName, "rw");// 随机方位读取
raFile.seek(fileSize);// 定位指针到fileSize位置
bis = new BufferedInputStream(ulc.getInputStream());
byte[] bt = new byte[1024];
int len = 0;
while(-1!=(len = bis.read(bt)))
{
raFile.write(bt, 0, len);
}
}
else
{
int len = 0;byte[] bt = new byte[1024];
fos = new FileOutputStream(fileName); // 没有下载完毕就将文件的扩展名命名.bak
dos = new DataOutputStream(fos);
bis = new BufferedInputStream(ulc.getInputStream());
System.out.println("正在接收文件...");
while ((len = bis.read(bt)) > 0)// 循环获取文件
{
dos.write(bt, 0, len);
}
System.out.println("文件正常接收完毕！");
}
if (bis != null)
bis.close();
if (dos != null)
dos.close();
if (fos != null)
fos.close();
if (raFile != null)
raFile.close();

} catch (Exception e) {
e.printStackTrace();
}
}
}