简单实现Servlet文件下载功能

package down;

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

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

public class CodeServlet extends HttpServlet {

  
  private static final long serialVersionUID = -2142723162865292420L;

  @Override
  protected void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    // TODO Auto-generated method stub
    response.setHeader("content-type", "application/jar");
    response.addHeader("content-disposition", "attachment;filename=utils.jar");
    ServletContext ctx = this.getServletContext();
    InputStream is = ctx.getResourceAsStream("/utils.jar");
    
    int read = 0;
    byte[] bytes = new byte[1024];
    
    OutputStream os = response.getOutputStream();
    while((read = is.read(bytes)) != -1) {
      os.write(bytes, 0, read);
    }
    os.flush();
    os.close();
  }
}

 OutputStream o = response.getOutputStream();
 byte b[] = new byte[500];
 File fileLoad = new File("e:/tmpxls.xls");
 response.reset();
 //response.setCharacterEncoding("gb2312");
 response.setContentType("application/vnd.ms-excel");
 response
  .setHeader("content-disposition", "attachment; filename=abc.xls");
 long fileLength = fileLoad.length();  //这里的length()返回的是文件的长度,以字节为单位,Long类型
 String length1 = String.valueOf(fileLength);
 response.setHeader("Content_Length", length1); //content-length指的是有效负载的字节(Byte)长度
 FileInputStream in = new FileInputStream(fileLoad);
 int n;
 while ((n = in.read(b)) != -1) {
  o.write(b, 0, n);
 }
 in.close();
 o.close();