Java Web应用程序实现基础的文件下载功能的实例讲解

window.location.href =“后台方法地址"。

String filePath = this.getClass().getClassLoader().getResource("").toURI().getPath()
     + "/exportPdf.pdf"; //文件在项目中的路径
  File outfile = new File(filePath);
  String filename = outfile.getName();// 获取文件名称
  InputStream fis = new BufferedInputStream(new FileInputStream(
     filePath));
  byte[] buffer = new byte[fis.available()]; 
  fis.read(buffer); //读取文件流
  fis.close();
  response.reset(); //重置结果集
  response.addHeader("Content-Disposition", "attachment;filename="
    + new String(filename.replaceAll(" ", "").getBytes("utf-8"),
    "iso8859-1")); //返回头 文件名
  response.addHeader("Content-Length", "" + outfile.length()); //返回头 文件大小
  response.setContentType("application/octet-stream"); //设置数据种类
  //获取返回体输出权
  OutputStream os = new BufferedOutputStream(response.getOutputStream()); 
  os.write(buffer); // 输出文件
  os.flush();
  os.close();

package cn.itcast.day06.web.servlet;
 
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URLEncoder;
 
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 DownloadServlet extends HttpServlet {
 
 public void doGet(HttpServletRequest request, HttpServletResponse response)
  throws ServletException, IOException {
 
 // 实现防盗链功能
 // 获得 referer 头 用于说明来访者来自哪里
 String referer = request.getHeader("referer");
 if(referer==null || !referer.startsWith("http://localhost")) {
  // 是盗链者
  response.sendRedirect("/day06/index.jsp");
  return ;
 }
 
 
 // 解决response中文乱码问题
 response.setContentType("text/html;charset=utf-8"); // 设置消息体的编码
 
 
 // 通过 http 协议 发送的http响应消息头 不能出现中文 中文必须要经过url编码
 String filename = URLEncoder.encode("美女.jpg", "utf-8");
 
 // 通知浏览器以下载的方式读取资源
 response.setHeader("content-disposition", "attachment;filename="+filename);
 
 // 读取图片数据 发给ie浏览器
 String webPath = "/download/美女.jpg"; // 相当于当前web应用的path
 
 ServletContext servletContext = super.getServletContext();
 
 InputStream in = servletContext.getResourceAsStream(webPath);
 
 
 OutputStream out = response.getOutputStream();
 
 
 int len;
 byte[] buffer = new byte[1024];
 while((len=in.read(buffer))!=-1)
  out.write(buffer, 0, len);
 
 }
 
 public void doPost(HttpServletRequest request, HttpServletResponse response)
  throws ServletException, IOException {
 doGet(request, response);
 }
 
}