servlet下载文件实现代码详解（五）

package com.learn;import javax.servlet.ServletConfig;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.File;import java.io.IOException;import java.io.InputStream;import java.io.OutputStream;public class DownLoadServlet extends HttpServlet {  private String filePath;  @Override  public void init(ServletConfig config) throws ServletException {    super.init(config);    filePath = config.getInitParameter("filePath");    //初始化路径    //filePath = config.getServletContext().getRealPath(filePath);    System.out.println("初始化文件路径："+filePath);  }  @Override  protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {    doPost(req,resp);  }  @Override  protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {    OutputStream out; //输出流    InputStream in; //输入流    String fileName = req.getParameter("fileName");    System.out.println("文件名称："+fileName);    //如果把文件名为null则提示用户    if(fileName == null){      out = resp.getOutputStream();      out.write("please input fileName".getBytes());      out.close();    }    //获取文件流    in = getServletContext().getResourceAsStream(filePath+ File.separator+fileName);    System.out.println(in==null?true:false);    int length = in.available();        //设置返回消息头部信息    resp.setContentType("application/force-download");    resp.setHeader("Content-Length",String.valueOf(length));    resp.setHeader("content-disposition","attachment;filename=\""+fileName+"\"");    //输出文件到客户端    out = resp.getOutputStream();    int bytesend = 0 ;    byte[] buff = new byte[512];    while ((bytesend = in.read(buff))!= -1){      out.write(buff,0,bytesend);    }    in.close();    out.close();  }}