import java.io.*;
import java.text.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.net.*;
public class Download extends HttpServlet
{public void downLoad(File file,HttpServletResponse response)throws IOException{if(file.exists()){if(file.getName().length()-file.getName().lastIndexOf(".jpg")==4){response.setContentType("image/jpeg");response.addHeader("Content-Disposition","filename="+URLEncoder.encode(file.getName(),"UTF-8"));}else{response.setContentType("application/octet-stream");response.addHeader("Content-Disposition","attachment;filename="+URLEncoder.encode(file.getName(),"UTF-8"));}response.addHeader("Content-Length",String.valueOf(file.length()));InputStream in=new FileInputStream(file);byte[] b=new byte[8192];int count=0;ServletOutputStream out=response.getOutputStream();while((count=in.read(b))>0){out.write(b,0,count);}in.close();out.close();}}private void listDir(File dir,HttpServletResponse response)throws IOException{response.setContentType("text/html;charset=UTF-8");PrintWriter out=response.getWriter();for(File file:dir.listFiles()){if(file.isFile()){out.print("<a href='Download?filename="+URLEncoder.encode(file.getName(),"UTF-8")+"'>");out.println(file.getName()+"</a><br />");}}}public void service(HttpServletRequest request,HttpServletResponse response)throws ServletException ,IOException{response.setContentType("text/html;charset=UTF-8");String path=this.getServletConfig().getInitParameter("path");String filename=request.getParameter("filename");File dir=new File(path);if(dir.exists()){if(filename!=null){filename=dir.getPath()+File.separator+filename;System.out.println(filename);File downLoadFile=new File(filename);downLoad(downLoadFile,response);}else{listDir(dir,response);}}PrintWriter out=response.getWriter();SimpleDateFormat dateFormat=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");out.println(dateFormat.format(new java.util.Date()));}}//总结//在下载文件时 必须设置 Content-Type和Content-Disposition 字段 其中Content-Type字段的值是application/octet-stream表示下载二进制文件
//Content-Disposition 的值为attachment;filename= 其中attachment表示下载的是附件 浏览器会弹出一个下载对话框 如果不设置 要下载的文件将在
//浏览器打开//

• 由于是初学servlet，这个小程序是通过记事本写的。目的是为了了解servlet的配置过程，以更好的理解servlet。