断点续传JAVA实现

public class BreakpointResume {
private static Logger log = Logger.getLogger(BreakpointResume.class);
/**下载操作，支持断点续传*/
public static void download(HttpServletRequest req,HttpServletResponse resp,String filepath) throws NumberFormatException, IOException{
//请求头参数
File file = new File(filepath);
Long fileSize = file.length();
Long lasttime = file.lastModified();
Long size = fileSize;
int i = 0;
String range = req.getHeader("Range");
String ifm = req.getHeader("If-Modified-Since");
if(ifm!=null&&Long.parseLong(ifm)<lasttime){//检查文件修改时间判断是否启用缓存
resp.setStatus(304);
}else{
byte[] buff = new byte[524288];//1024*1024/2
RandomAccessFile raf  = new RandomAccessFile(file, "rw");
BufferedOutputStream bfo = new BufferedOutputStream(resp.getOutputStream());
try {
if(range!=null){//断点续传请求
size = (long)(5242880);//限制每次视频输出的大小 
String[] ranges = range.replace("bytes=", "").split("-");
if(ranges.length<2){//为Content-Range参数做铺垫
ranges = new String[]{ranges[0],"0"};
if(fileSize-Long.parseLong(ranges[0])>size){
ranges[1] = String.valueOf(Long.parseLong(ranges[0])+size);
}else{
ranges[1] = String.valueOf(fileSize-1);
}
}
raf.seek(Long.parseLong(ranges[0]));//从指定位置开始读取
resp.setHeader("Last-Modified", String.valueOf(lasttime));//文件最后修改时间
resp.setHeader("Content-Range", "bytes "+StringUtils.join(ranges, "-")+"/"+fileSize);//请求的数据 开始-结束/文件总大小
resp.setStatus(206);
}
int len = 0;
while((len=raf.read(buff))>0&&i<size){
bfo.write(buff);
bfo.flush();
i+=len;
log.debug("本次输出："+buff.length);
}
} catch (Exception e) {
log.info("输出流非正常关闭：");
} finally{
raf.close();
bfo.close();
log.info("当前请求共输出："+i);
}
}
}
}