package shiyao.frist.test.文件下载;

import java.io.FileInputStream;
import java.io.IOException;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**

• Servlet implementation class FileDownLoad
  */
  @WebServlet("/FileDownLoad")
  public class FileDownLoad extends HttpServlet {
  private static final long serialVersionUID = 1L;

  /**
  • @see HttpServlet#HttpServlet()
    */
    public FileDownLoad() {
    super();
    // TODO Auto-generated constructor stub
    }
  /**

  • @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
    */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub
    response.getWriter().append("Served at: ").append(request.getContextPath());

    //1.获取文件请求参数，也就是文件名称
    String Filename=request.getParameter("Filename");
    //2.获取文件的服务器路径即真实路径
    ServletContext sc=this.getServletContext();
    String path=sc.getRealPath("/img/"+Filename);
    //3.将文件和相关的流关联起来
    FileInputStream fis=new FileInputStream(path);

    //为了解决输入流已经被调用的情况
    response.reset();

    //为了解决文件名是中文的问题：使用DownLoadUtils工具类
    //获取User-Agent请求头得知浏览器种类
    String user_agent=request.getHeader("user-agent");
    Filename=DownLoadUtils.getFileName(user_agent, Filename);

    //4.设置响应头
    //4.1设置content-type
    String mimeType=sc.getMimeType(Filename);
    response.setHeader("content-type", mimeType);
    //4.2设置响应头打开方式：content-disposition为附件打开方式
    response.setHeader("content-disposition","attachment;filename="+Filename);
    //5将输入流的数据读出到输出流中
    ServletOutputStream sos=response.getOutputStream();
    byte[] buff=new byte[1024*8];
    int len=0;
    while((len=fis.read(buff))!=-1)
    {
    sos.write(buff,0,len);
    }
    fis.close();
    }

  /**
  • @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
    */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub
    doPost(request, response);
    }

}

这里只有一个getOutputStream没有getWrite为什么也报getWriter() has already been called for this response错误？