spring mvc文件上传和下载

首先要导入2个包(上传文件包和io的包)

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配置文件spring-servlet.xml文件中

<!-- 配置文件上传MultipartResolver -->
    <bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
        <property name="maxUploadSize" value="5000000"></property>
    </bean>

如果id="multipartResolver"没传，就会报以下的错（小心小心）

Request processing failed; nested exception is java.lang.IllegalArgumentException: Expected MultipartHttpServletRequest: is a MultipartResolver configured?

添加文件的显示页面add.sjp

a、enctype="multipart/form-data"这句就是告诉，要添加文件，很重要

b、 attach：<input type="file" name="attach"><br/>

    <form:form modelAttribute="user" method="post" enctype="multipart/form-data">
        ID:<form:input path="id"/><br/>
        userName:<form:input path="userName"/><form:errors path="userName"/><br/>
        password:<form:input path="password"/><form:errors path="password"/><br/>
        email:<form:input path="email"/><form:errors path="email"/><br/>
        attach：<input type="file" name="attach"><br/>
        <input type="submit" value="提交"/>
      </form:form>

修改添加的方法

a、指定路径

b、上传文件，就要文件保存的目标位置

@RequestMapping(value="/add",method=RequestMethod.POST)
        public String add(@Validated User user,BindingResult bindingResult,MultipartFile attach,HttpServletRequest request){
            //上传文件就是要上传的路径所以就需要request对象
            if(bindingResult.hasErrors()){
                return "user/add";
            }
            //指定上传位置
            String uploadFilePath = request.getSession().getServletContext().getRealPath("statics/upload");
            System.out.println(uploadFilePath);

            System.out.println(attach.getOriginalFilename());//原始名
            System.out.println(attach.getContentType());//类型
            System.out.println(attach.getName());//页面表单控件name的值

            if(!attach.isEmpty()){
                try {
                    //"/" 更换成自动识别分隔符File.separator
                    File saveFile = new File(uploadFilePath+File.separator+attach.getOriginalFilename());
                    //第一个是拿到输入流，第二个参数是保存到哪里
                    FileUtils.copyInputStreamToFile(attach.getInputStream(), saveFile);
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            //把user对象放进去key（id）
            userList.put(user.getId(), user);

//            return "user/userlist";//返回到逻辑视图名
            //（添加后，不能把添加过的数据展示出来）服务器端行为
            return "redirect:/user/list";//客户端重新发送请求（把添加进去的展示出来）
        }

多文件的上传

因为是多文件所以一定要加@RequestParam不加的话报如下异常

//Could not instantiate bean class [[Lorg.springframework.web.multipart.MultipartFile;]: No default constructor found;nested exception is java.lang
//不能实例化bean类[[Lorg.springframework.web.multipart。MultipartFile;]:没有默认构造函数发现,嵌套异常. lang。
//页面500

//文件上传（多文件）
        @RequestMapping(value="/add",method=RequestMethod.POST)
        public String add(@Validated User user,BindingResult bindingResult,@RequestParam("attachs") MultipartFile[] attachs,HttpServletRequest request){
            //上传文件就是要上传的路径所以就需要request对象
            if(bindingResult.hasErrors()){
                return "user/add";
            }
            //指定上传位置
            String uploadFilePath = request.getSession().getServletContext().getRealPath("statics/upload");
            try {
                for(MultipartFile attach:attachs){

                    if(!attach.isEmpty()){

                            //"/" 更换成自动识别File.separator
                            File saveFile = new File(uploadFilePath+File.separator+attach.getOriginalFilename());
                            //第一个是拿到输入流，第二个参数是保存到哪里
                            FileUtils.copyInputStreamToFile(attach.getInputStream(), saveFile);
                        }
                }
            }catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            //把user对象放进去key（id）
            userList.put(user.getId(), user);

//            return "user/userlist";//返回到逻辑视图名
            //（添加后，不能把添加过的数据展示出来）服务器端行为
            return "redirect:/user/list";//客户端重新发送请求（把添加进去的展示出来）
        }

因为多文件是一个数组，attach：<input type="file" name="attachs"><br/>

这边的name要是attachs，否则就找不到

<form:form modelAttribute="user" method="post" enctype="multipart/form-data">
        ID:<form:input path="id"/><br/>
        userName:<form:input path="userName"/><form:errors path="userName"/><br/>
        password:<form:input path="password"/><form:errors path="password"/><br/>
        email:<form:input path="email"/><form:errors path="email"/><br/>
        attach：<input type="file" name="attachs"><br/>
        attach1：<input type="file" name="attachs"><br/>
        attach2：<input type="file" name="attachs"><br/>
        <input type="submit" value="提交"/>
      </form:form>