[Java知识库]springmvc(3)-上传下载文件

1.基于springmvc的文件上传

1.1导入依赖

?????? 依赖包：spring-webmvc??? servlet-api???? commons-fileupload

<!-- https://mvnrepository.com/artifact/org.springframework/spring-webmvc -->

??? <dependency>

????? <groupId>org.springframework</groupId>

????? <artifactId>spring-webmvc</artifactId>

????? <version>5.1.5.RELEASE</version>

??? </dependency>

??? <!-- 配置ServletAPI依赖 -->

??? <!-- https://mvnrepository.com/artifact/javax.servlet/javax.servlet-api -->

??? <dependency>

????? <groupId>javax.servlet</groupId>

????? <artifactId>javax.servlet-api</artifactId>

????? <version>3.0.1</version>

????? <scope>provided</scope>

??? </dependency>

??? <!-- commons-fileupload组件 -->

??? <!-- https://mvnrepository.com/artifact/commons-fileupload/commons-fileupload -->

??? <dependency>

????? <groupId>commons-fileupload</groupId>

????? <artifactId>commons-fileupload</artifactId>

????? <version>1.3.1</version>

</dependency>

1.2 配置web.xml

? ?? 由于SpringMVC不支持静态资源的访问，因此可以配置default允许访问静态资源

? default的mapping的配置，一定要写在dispatcherServle的mapping的配置之前。

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"

???? xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

???? xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee

???? http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"

???? version="4.0">

??? <display-name>Archetype Created Web Application</display-name>

??? <servlet>

??????? <servlet-name>DispatcherServlet</servlet-name>

??????? <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>

??????? <init-param>

??????????? <param-name>contextConfigLocation</param-name>

??????????? <param-value>classpath:springmvc.xml</param-value>

??????? </init-param>

??? </servlet>

??? <servlet-mapping>

??????? <servlet-name>default</servlet-name>

??????? <url-pattern>*.jpg</url-pattern>

??? </servlet-mapping>

??? <servlet-mapping>

??????? <servlet-name>default</servlet-name>

??????? <url-pattern>*.html</url-pattern>

??? </servlet-mapping>

??? <servlet-mapping>

??????? <servlet-name>default</servlet-name>

??????? <url-pattern>*.js</url-pattern>

??? </servlet-mapping>

??? <servlet-mapping>

??????? <servlet-name>default</servlet-name>

??????? <url-pattern>*.css</url-pattern>

??? </servlet-mapping>

??? <servlet-mapping>

??????? <servlet-name>DispatcherServlet</servlet-name>

??????? <url-pattern>*.do</url-pattern>

??? </servlet-mapping>

</web-app>

1.3 需要的接口和方法

1.3.1 MultipartResolver接口

MultipartResolver 用于处理文件上传，当收到请求时 DispatcherServlet 的 checkMultipart() 方法会调用 MultipartResolver 的 isMultipart() 方法判断请求中是否包含文件。如果请求数据中包含文件，则调用 MultipartResolver 的 resolveMultipart() 方法对请求的数据进行解析，然后将文件数据解析成 MultipartFile 并封装在 MultipartHttpServletRequest (继承了 HttpServletRequest) 对象中，最后传递给 Controller。

在 MultipartResolver 接口中有如下方法：

boolean isMultipart(HttpServletRequest request); // 是否是一个文件上传请求

MultipartHttpServletRequest resolveMultipart(HttpServletRequest request); // 解析请求

void cleanupMultipart(MultipartHttpServletRequest request);//清理上传的资源

我们用它的实现类CommonsMultipartResolver

1.3.2 CommonsMultipartResolver类

MultipartResolver 是一个接口，它的实现类如下图所示，分为CommonsMultipartResolver 类和 StandardServletMultipartResolver 类。

?

它的构造方法需要一个servletContext对象

?? public CommonsMultipartResolver(ServletContext servletContext) {

??????? this();

??????? this.setServletContext(servletContext);

}

????????其中 CommonsMultipartResolver 使用 commons Fileupload 来处理 multipart 请求，所以在使用时，必须要引入相应的 jar 包；而 StandardServletMultipartResolver 是基于 Servlet 3.0来处理 multipart 请求的，所以不需要引用其他 jar 包，但是必须使用支持 Servlet 3.0的容器才可以，以tomcat为例，从 Tomcat 7.0.x的版本开始就支持 Servlet 3.0了。

配置文件中配置：

<!-- 定义文件上传解析器-->

<!-- Spring 组件 CommonsMultipartResolver 类的主要作用是配置文件上传的一些属性，也可以控制上传文件的大小。 -->

??? <!--必须保证 id 是 multipartResolver-->

<bean id="multipartResolver"

class="org.springframework.web.multipart.commons.CommonsMultipartResolver">

??????? <!--设置默认编码-->

??????? <property name="defaultEncoding" value="UTF-8"/>

??????? <!-- 设定文件上传的最大值为5M，5*1024*1024-->

??????? <property name="maxUploadSize" value="5242880"></property>

??????? <!--设定文件最大缓存大小，如果小于这个参数不会生成临时文件，默认为10240-->???

<property name="maxInMemorySize" value="10240"/>

</bean>

上传表单：

要在 form 标签中加入 enctype="multipart/form-data" 表示该表单要提交文件。

<form action="xxxxx " method="xxx" enctype="multipart/form-data">

???? <input type="file" name="file">

???? <input type="submit" value="提交">

</form>

1.3.3 MultipartRequest接口和实现类MultipartHttpServletRequest

MultipartRequest接口下有如下方法：

??

MultipartHttpServletRequest类

1.3.4 MultipartFile接口

MultipartFile 封装了请求数据中的文件，此时这个文件存储在内存中或临时的磁盘文件中，需要将其转存到一个合适的位置，因为请求结束后临时存储将被清空。

在 MultipartFile 接口中有如下方法：

String getName(); // 获取参数的名称

String getOriginalFilename(); // 获取文件的原名称

String getContentType(); // 文件内容的类型

boolean isEmpty(); // 文件是否为空

long getSize(); // 文件大小

byte[] getBytes(); // 将文件内容以字节数组的形式返回

InputStream getInputStream(); // 将文件内容以输入流的形式返回

void transferTo(File dest); // 将文件内容传输到指定文件中

1.4 springmvc.xml

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

?????? xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

?????? xmlns:mvc="http://www.springframework.org/schema/mvc"

?????? xmlns:context="http://www.springframework.org/schema/context"

?????? xsi:schemaLocation="http://www.springframework.org/schema/beans

?????? http://www.springframework.org/schema/beans/spring-beans.xsd

?????? http://www.springframework.org/schema/mvc

?????? http://www.springframework.org/schema/mvc/spring-mvc.xsd

?????? http://www.springframework.org/schema/context

?????? http://www.springframework.org/schema/context/spring-context.xsd">

<!--开启注解-->

??? <mvc:annotation-driven/>

<!-- 开启自动扫描包-->

??? <context:component-scan base-package="com.weiwei.springmvcfile"/>

<!-- 定义文件上传解析器-->

<!-- Spring 组件 CommonsMultipartResolver 类的主要作用是配置文件上传的一些属性，也可以控制上传文件的大小。 -->

??? <!--必须保证 id 是 multipartResolver-->

??? <bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">

??????? <!--设置默认编码-->

??????? <property name="defaultEncoding" value="UTF-8"/>

??????? <!-- 设定文件上传的最大值为5M，5*1024*1024-->

??????? <property name="maxUploadSize" value="5242880"/>

??????? <!--设定文件最大缓存大小，如果小于这个参数不会生成临时文件，默认为10240-->

??????? <property name="maxInMemorySize" value="10240"/>

??? </bean>

</beans>

1.5 文件上传页面

<!DOCTYPE html>

<html lang="en">

<head>

??? <meta charset="UTF-8">

??? <title>上传文件</title>

</head>

<body>

??? <form action="upload.do" method="post" enctype="multipart/form-data">

??????? <input type="file" name="myfile1">

<input type="file" name="myfile2">

??????? <input type="submit" value="上传">

??? </form>

</body>

</html>

1.6 uploadController类

??????

package com.weiwei.springmvcfile.controller;



import org.springframework.stereotype.Controller;

import org.springframework.web.bind.annotation.RequestMapping;

import org.springframework.web.bind.annotation.RequestMethod;

import org.springframework.web.bind.annotation.ResponseBody;

import org.springframework.web.multipart.MultipartFile;

import org.springframework.web.multipart.MultipartHttpServletRequest;

import org.springframework.web.multipart.MultipartRequest;

import org.springframework.web.multipart.commons.CommonsMultipartResolver;

import org.springframework.web.servlet.ModelAndView;

import sun.security.krb5.internal.tools.Klist;



import javax.servlet.ServletContext;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import java.io.File;

import java.io.IOException;

import java.util.ArrayList;

import java.util.Iterator;

import java.util.List;



@Controller

public class UploadController {

??? @RequestMapping(value = "upload.do",method = RequestMethod.POST)

??? @ResponseBody

??? public ModelAndView uploadFile(HttpServletRequest request){

??????? List<String> list=new ArrayList();

??????? ModelAndView modelAndView = new ModelAndView();

??????? //创建CommonsMultipartResolver对象

??????? ServletContext servletContext = request.getSession().getServletContext();

??????? CommonsMultipartResolver commonsMultipartResolver = new CommonsMultipartResolver(servletContext);

??????? //检验请求是否是一个文件上传请求，commonsMultipartResolver中有一个方法isMultipart

??????? if(commonsMultipartResolver.isMultipart(request)){

??????????? //将HttpServletRequest转换成 MultipartHttpServletRequest文件上传请求对象

??????????? MultipartHttpServletRequest multipartRequest = (MultipartHttpServletRequest) request;

??????????? //从文件上传请求中得到文件名称，返回迭代器

??????????? Iterator<String> fileNames = multipartRequest.getFileNames();

??????????? //遍历迭代器

??????????? while(fileNames.hasNext()){

??????????????? String filehttpUrl="";

??????????????? //得到input元素的name属性值

??????????????? String shuxingname = fileNames.next().toString();//myfile1? myfile2

??????????????? //根据name属性值得到上传来的文件名称,返回MultipartFile对象

??????????????? MultipartFile multipartFile = multipartRequest.getFile(shuxingname);

??????????????? if(multipartFile!=null){

??????????????????? //得到被传上来的文件的真实名称【图片1.jpg】

??????????????????? String originalFilename = multipartFile.getOriginalFilename();



??????????????? ????//重新组织文件名名称，防止出现上传的文件名称相同而失败

??????????????????? //得到文件真实名称的后缀名

??????????????????? String houzhuiname = originalFilename.substring(originalFilename.lastIndexOf("."));

??????????????????? //以系统时间毫秒数命名文件名称

??????????????????? long currentTimeMillis = System.currentTimeMillis();

??????????????????? String newfilename = currentTimeMillis + houzhuiname;

??????????????????? //System.out.println(newfilename);



??????????????????? //保存上传的文件到服务器

?????????????????? ?//获取项目的根目录,创建保存文件的目录

??????????????????? //F:\Tomcat8.0\apache-tomcat-8.0.52\webapps\demofile\fileupload

??????????????????? String rootpath = servletContext.getRealPath("/fileupload");

??????????????????? System.out.println(rootpath);

?????????????????? ?File uploadfile = new File(rootpath);

??????????????????? if (!uploadfile.exists()) {

??????????????????????? //创建upload目录

??????????????????????? uploadfile.mkdirs();

??????????????????? }

??????????????????? //保存文件的目录带文件名称

??????????????????? String pathfile = rootpath + File.separator + newfilename;

?????????????????? // System.out.println(pathfile);//F:\Tomcat8.0\apache-tomcat-8.0.52\webapps\demofile\fileupload\1646997723418.jpg

??????????????????? File savefile = new File(pathfile);

????????????????? ??try {

??????????????????????? //保存文件到本地磁盘

??????????????????????? multipartFile.transferTo(savefile);

??????????????????? } catch (IOException e) {

??????????????????????? e.printStackTrace();

??????????????????? }

??????????????????? //保存的文件在服务器的地址http://localhost:8080/demofile/fileupload/1646998210613.jpg

??????????????????? //想办法组成这个地址，需要返回给前端

??????????????????? String requrl = request.getRequestURL().toString();

?????????????????? //System.out.println(requrl);//http://localhost:8080/demofile/upload.do

???????????????????? filehttpUrl=requrl.substring(0,requrl.lastIndexOf("/"))+"/fileupload/"+newfilename;

??????????????????? System.out.println(filehttpUrl);

??????????????????? list.add(newfilename);



??????????????? }else{

??????????????????? System.out.println("上传的是一个空文件");

??????????????? }

??????????? }

??????????? modelAndView.addObject("mypicture", list);

??????????? modelAndView.setViewName("downfile.jsp");//设置跳转路径

??????? }else {

??????????? System.out.println("http请求中没有文件");

??????? }

??????? return modelAndView;

??? }

}

?

2. 基于Springmvc的文件下载

2.1 下载页面jsp

<%--

? Created by IntelliJ IDEA.

? User: Betty

? Date: 2022/3/12

? Time: 12:00

? To change this template use File | Settings | File Templates.

--%>

<%@ page contentType="text/html;charset=UTF-8" language="java" isELIgnored="false" %>

<html>

<head>

??? <title>下载文件</title>

</head>

<body>

??? <h3><a href="download.do?mypicture=${mypicture[0]}">下载图片${mypicture[0]}</a></h3>

??? <h3><a href="download.do?mypicture=${mypicture[1]}">下载图片${mypicture[1]}</a></h3>

</body>

</html>

?

2.2 下载控制类

package com.weiwei.springmvcfile.controller;



import org.apache.commons.io.FileUtils;

import org.springframework.http.HttpHeaders;

import org.springframework.http.HttpStatus;

import org.springframework.http.MediaType;

import org.springframework.http.ResponseEntity;

import org.springframework.stereotype.Controller;

import org.springframework.web.bind.annotation.RequestMapping;

import org.springframework.web.bind.annotation.RequestMethod;



import javax.servlet.http.HttpServletRequest;

import java.io.File;



@Controller

public class DownloadController {



??? @RequestMapping(value = "download.do",method = RequestMethod.GET)

??? public ResponseEntity<byte[]> getDownload(HttpServletRequest request){

??????? //得到指定下载的文件名称

??????? String downname = request.getParameter("mypicture");

??????? String realpath = request.getSession().getServletContext().getRealPath("/fileupload");

??????? //创建保存文件目录的文件对象

??????? File savedownfilepath = new File(realpath);

??????? //创建被下载的文件对象

??????? File file = new File(savedownfilepath, downname);

??????? System.out.println(file.getAbsoluteFile());

??????? //设置http协议头

??????? HttpHeaders headers = new HttpHeaders();

??????? headers.setContentDispositionFormData("attachment",downname);

??????? headers.setContentType(MediaType.APPLICATION_OCTET_STREAM);

??????? ResponseEntity<byte[]>? responseEntity=null;

?????? ?try {

??????????? responseEntity = new ResponseEntity<byte[]>(FileUtils.readFileToByteArray(file), headers, HttpStatus.CREATED);

??????? }catch (Exception e){

??????????? e.printStackTrace();

??????? }

??????? return responseEntity;

??? }



}

?