断点续传(Range的使用)

package com.fileserver;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpServletResponse;

import org.apache.log4j.Logger;

/**
 *用于支持视频的拖动 
 * @author Gabriel
 */
public class PartialRender {
	private ServletContext sc;
	private HttpServletResponse response;
	private int range = -1;
	
	public PartialRender(ServletContext sc,HttpServletResponse response,int range){
		this.sc = sc;
		this.response = response;
		if(range>=0){
			this.range = range;
		}
	}
	
	/**
	 * 输出文件流
	 * @param file 输出文件位置
	 */
	public void doRender(File file){
		String contentType = sc.getMimeType(file.getName());
		if(contentType==null)
			contentType = Const.DEFAULT_FILE_CONTENT_TYPE; //"application/octet-stream"
		
		int fileSize = (int)file.length();
		response.setContentType(contentType);
		if(range!=-1){
			response.setHeader("Content-Range","bytes "+ range+"-"+(fileSize-1)+"/"+fileSize);
			response.setContentLength(fileSize-range);
			response.setStatus(HttpServletResponse.SC_PARTIAL_CONTENT);
		}else{
			response.setContentLength(fileSize);
			response.setStatus(HttpServletResponse.SC_OK);
		}
		InputStream is = null;
		OutputStream os = null;
		try{
			byte[] buf = new byte[1024];
			is = new FileInputStream(file);
			os = response.getOutputStream();
			if(range>0){
				is.skip(range);
			}
			int len;
			while((len=is.read(buf))!=-1){
				os.write(buf, 0, len);
			}
			os.flush();
		}catch (Exception e) {
			//当终止下载或者播放视频时会抛出异常
		}finally{
			if(is!=null)
				try {
					is.close();
				} catch (IOException e1) {
				}
			if(os!=null)
				try {
					os.close();
				} catch (IOException e1) {
				}
		}
	}
}