大神帮我看看这段代码什么意思

大神帮我看看这段代码什么意思

package control;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import util.Info;

public class Upload extends HttpServlet {

/**
 * Constructor of the object.对象的构造函数
 */
public Upload() {
	super();
}

/**
 * Destruction of the servlet. <br>
 */
public void destroy() {
	super.destroy(); // Just puts "destroy" string in log 只需在日志中输入“destroy”字符串即可
	// Put your code here
}

/**
 * The doGet method of the servlet. <br>
 *
 * This method is called when a form has its tag value method equals to get.
 * 
 * @param request the request send by the client to the server
 * @param response the response send by the server to the client
 * @throws ServletException if an error occurred
 * @throws IOException if an error occurred
 */
public void doGet(HttpServletRequest request, HttpServletResponse response)
		throws ServletException, IOException {

	this.doPost(request, response);
}

/**
 * The doPost method of the servlet. <br>
 *
 * This method is called when a form has its tag value method equals to post.
 * 
 * @param request the request send by the client to the server
 * @param response the response send by the server to the client
 * @throws ServletException if an error occurred
 * @throws IOException if an error occurred
 */
public void doPost(HttpServletRequest request, HttpServletResponse response)
		throws ServletException, IOException {

	StringBuffer   sb   =   new   StringBuffer(50);   
	 response.setContentType("application/x-msdownload;charset=GB2312");   
    try {
		response.setHeader("Content-Disposition",   new   String(sb.toString()   
		         .getBytes(),   "ISO8859-1"));
	} catch (UnsupportedEncodingException e1) {
		// TODO Auto-generated catch block
		e1.printStackTrace();
	}
	 String filename = request.getParameter("filename");
	  if (request.getHeader("User-Agent").toLowerCase().indexOf("firefox") > 0){
	     try {
			filename = new String(filename.getBytes("gb2312"), "ISO8859-1");
		} catch (UnsupportedEncodingException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	 }
	 else 
	      if (request.getHeader("User-Agent").toUpperCase().indexOf("MSIE") > 0){
	           try {
				filename = URLEncoder.encode(filename, "gb2312");
			} catch (UnsupportedEncodingException e) {
				// TODO Auto-generated catch block
				 
			}
	      }
	 response.setContentType("text/plain");
	 response.setHeader("Location",filename);
	 response.reset();
	 response.setHeader("Cache-Control", "max-age=0" );
	 response.setHeader("Content-Disposition", "attachment; filename=" + filename);
	   

	    try {
			       BufferedInputStream bis = null;
				   BufferedOutputStream bos = null;
				   OutputStream fos = null;
				  // File f = new File(request.getRealPath("/upfile/")+"/"+filename);
				   //System.out.println(f);
				   bis = new BufferedInputStream((InputStream)new FileInputStream(request.getRealPath("/upfile/")+"/"+filename));
				    fos = response.getOutputStream();
				    bos = new BufferedOutputStream(fos);

				    int bytesRead = 0;
				    byte[] buffer = new byte[5 * 1024];
				    while ((bytesRead = bis.read(buffer)) != -1) {
				     bos.write(buffer, 0, bytesRead);
				    }
				    bos.close();
				    bis.close();
				    fos.close();
			
	               new Info().delPic(request.getRealPath("/upfile/")+"/", filename);
	     } catch (Exception e) {
			 
		}finally{
		}
}

/**
 * Initialization of the servlet. <br>
 *
 * @throws ServletException if an error occurs
 */
public void init() throws ServletException {
	// Put your code here
}

}