@WebServlet("/DownloadServlet02")
public class DownloadServlet02 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取文件名称
        String filename = request.getParameter("filename");
        //获取ServletContext域对象
        ServletContext servletContext = this.getServletContext();
        //获取文件的路径
        String realPath = servletContext.getRealPath("/img/" + filename);
        //输入流读取文件
        FileInputStream fis = new FileInputStream(realPath);
        //获取文件的类型
        String mimeType = servletContext.getMimeType(filename);
        //设置content-type
        response.setHeader("content-type",mimeType);
        //防乱码
        String agent = request.getHeader("user-agent");
        filename = DownLoadUtils.getFileName(agent, filename);

        //设置将文件作为附件加载
        response.setHeader("content-disposition","attachment;filename="+filename);
        //写出文件
        ServletOutputStream ops = response.getOutputStream();
        byte[] buff = new byte[1024*5];
        int len=0;
        while((len=fis.read(buff))!=-1){
        ops.write(buff,0,len);
        }
        fis.close();
    }

@WebServlet("/DownloadServlet02")
public class DownloadServlet02 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取文件名称
        String filename = request.getParameter("filename");
        //获取ServletContext域对象
        ServletContext servletContext = this.getServletContext();
        //获取文件的路径
        String realPath = servletContext.getRealPath("/img/" + filename);
        //输入流读取文件
        FileInputStream fis = new FileInputStream(realPath);
        //获取文件的类型
        String mimeType = servletContext.getMimeType(filename);
        //设置content-type
        response.setHeader("content-type",mimeType);
        //防乱码
        String agent = request.getHeader("user-agent");
        filename = DownLoadUtils.getFileName(agent, filename);

        //设置将文件作为附件加载
        response.setHeader("content-disposition","attachment;filename="+filename);
        //写出文件
        ServletOutputStream ops = response.getOutputStream();
        byte[] buff = new byte[1024*5];
        int len=0;
        while((len=fis.read(buff))!=-1){
        ops.write(buff,0,len);
        }
        fis.close();
    }