Java＞＞Servlet，response.getOutputStream().write(byte[], 0, len)；文件下载

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.FileInputStream;
import java.io.IOException;


@WebServlet(urlPatterns = "/fileDownLoad")
public class FileDownLoad extends HttpServlet {
    
    

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
    
        // 获取域对象
        ServletContext servletContext = req.getServletContext();

        // 获取请求内的文件名称
        String filename = req.getParameter("filename");
        // 获取请求文件的绝对路径
        String realPath = servletContext.getRealPath("./image/" + filename);

        // 获取响应头的MIME类型名称
        String mimeType = servletContext.getMimeType(filename);
        // 设置响应头的类型为文件所对应的Mime类型
        resp.setHeader("content-type", mimeType);

        // 设置中文乱码问题
        filename = DownLoadUtils.getFileName(req.getHeader("user-agent"),filename);

        // 设置与文件对应的MIME类型
        resp.setHeader("content-disposition", "attachment;filename=" + filename);

        // inputStream 读取到内存
        FileInputStream fileInputStream = new FileInputStream(realPath);

        // 将获取到的数据先展示到控制台
        byte[] temp_arr = new byte[1024 * 8];
        // 获取到的每一行的数据的长度
        int len = 0;

        // 写出数据到页面
        while ((len = fileInputStream.read(temp_arr)) != -1) {
    
    
           /* System.out.println(temp_arr);
            System.out.println("Length is : " + len);*/
            // 写出数据到页面
            resp.getOutputStream().write(temp_arr, 0, len);
        }
        fileInputStream.close();


    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
    
        this.doPost(req, resp);
    }
}