Servlet之文件下载

    通过浏览器客户端访问Servlet，实现存储于Tomcat服务器上的资源文件的下载效果，主要结合ServletResponse与IO流文件操作实现。原理图示如下：

    首先新建项目servletDemo2，指定用于存放文件的路径为：

servletDemo2/files/

    通过继承HttpServlet，重写doGet()和doPost()方法，实现文件下载功能，此处约定使用GET请求，请求参数为：fname。

package com.xwd.demo;

import jdk.internal.util.xml.impl.Input;

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;
import java.io.*;
import java.lang.reflect.Field;


public class FileDownLoad extends HttpServlet {
    private static final String FILE_DIR="files";

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

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //super.doPost(req, resp);
        request.setCharacterEncoding("UTF-8");
        //解析参数
        String fname = request.getParameter("fname");
        System.out.println(fname);
        //获取ServletContext对象
        ServletContext servletContext = request.getServletContext();
        //获取相对路径
        String realPath = servletContext.getRealPath(FILE_DIR+ File.separator + fname);
        System.out.println(realPath);
        //获取媒体类型
        String mimeType = servletContext.getMimeType(fname);

        //设置响应头
        response.setHeader("Content-Disposition","attachment;filename="+realPath);
        //设置响应体编码格式
        response.setCharacterEncoding("UTF-8");
        //设置媒体类型
        response.setContentType(mimeType);
        System.out.println(mimeType);

        //以字节流输出文件
        InputStream is = new FileInputStream(realPath);
        ServletOutputStream os = response.getOutputStream();
        byte[] buffer=new byte[1024];
        int len=-1;
        while ((len = is.read(buffer)) != -1) {
            os.write(buffer,0,len);
        }
        //关闭流
        os.close();
        is.close();
    }
}

    使用Servlet3.0以上的版本，也可直接使用@WebServlet注解配置

    
        filedownLoad
        com.xwd.demo.FileDownLoad
    
    
        filedownLoad
        /filedownLoad
    

@WebServlet(
        name = "filedownload",
        value = {"/filedownload"}
)
public class FileDownLoad extends HttpServlet {
}