response下载文件

Servlet实现文件下载

一. servlet项目创建

1. 新建maven项目

• 新建maven项目

  • 记得更换jdk版本

• 项目设置

  • 在模块那添加web

• 编译配置

  • 添加本地tomcat

• 运行

  • 如果有创建index.jsp文件的话默认打开，没有的话会报错500，没资源

2. 添加servlet包

• 配置pom.xml文件

  •     <dependencies>
            <dependency>
                <groupId>javax.servlet</groupId>
                <artifactId>javax.servlet-api</artifactId>
                <version>4.0.1</version>
            </dependency>
        </dependencies>
    

  • <build>
        <resources>
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
        </resources>
    </build>
    

记得关闭tomcat，不然依赖源不会实时更新，导入后长这样!

3. 新建java类

• 拓展类，自动导包

package com.yorha.Servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class ResponseServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        
    }

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

二. 资源路径的获取和使用

1. 获取下载路径

String realPath = this.getServletContext().getRealPath("/WEB-INF/classes/路标.png");

2. 下载文件名

String fileName = realPath.substring(realPath.lastIndexOf("\\")+1);

3. 浏览器提供支持

resp.setHeader("Content-disposition","attachment;filename=" + URLEncoder.encode(fileName,"utf-8"));

4. 获取文件输入流

FileInputStream in = new FileInputStream(realPath);

5. 创建缓冲区

int len = 0;
byte[] buffer = new byte[1024];

6. 获取outputSteam对象

ServletOutputStream out = resp.getOutputStream();

7. 将fileOutputSteam写入缓冲区

使用OutputSteam将缓冲区内推输出到客户端

while ((len = in.read(buffer))>0){
    out.write(buffer,0,len);
}

8. 用完记得关闭文件，保证安全性

in.close();
out.close();

class类完整代码

//        1.    获取下载路径
        String realPath = this.getServletContext().getRealPath("/WEB-INF/classes/路标.png");
//        2.   下载文件名
        System.out.println(realPath);
        String fileName = realPath.substring(realPath.lastIndexOf("\\")+1);
//        3.   浏览器提供支持
        resp.setHeader("Content-disposition","attachment;filename=" + URLEncoder.encode(fileName,"utf-8"));
//        4.   获取文件输入流
        FileInputStream in = new FileInputStream(realPath);
//        5.   创建缓冲区
        int len = 0;
        byte[] buffer = new byte[1024];
//        6.   获取outputSteam对象
        ServletOutputStream out = resp.getOutputStream();
//        7.   将fileOutputSteam写入缓冲区,使用OutputSteam将缓冲区内推输出到客户端
        while ((len = in.read(buffer))>0){
            out.write(buffer,0,len);
        }
        in.close();
        out.close();

注意事项

使用绝对路径时报错

ava.lang.NullPointerException: Cannot invoke "String.lastIndexOf(String)" because "realPath" is null

使用/加文件名

String realPath = this.getServletContext().getRealPath("/路标.png");

时得到的路径为

D:\javaweb\response\out\artifacts\response_Web_exploded\.png

这时点开输出的资源包里面发现是没有.png文件的，所以我们需要在pom.xml文件中添加如下代码

<include>**/*.png</include>

所选段完整代码如下

    <build>
        <resources>
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                    <include>**/*.png</include>

                </includes>
                <filtering>true</filtering>
            </resource>
        </resources>
    </build>

这时就能在WEB-INF文件中看到.png文件了

然后对照sout输出的内容修改路径

String realPath = this.getServletContext().getRealPath("/WEB-INF/classes/路标.png");

此时就能正常下载了，这里注意是WEB"-"INF,不要写成WEB"_"INF,输入法按住shift是"-"是"__"

URLEncoder类

URLEncoder.encode(fileName,"utf-8")