一. commons-fileupload组件上传

1. 导入jar包依赖

        <!--文件上传组件-->
        <!-- https://mvnrepository.com/artifact/commons-fileupload/commons-fileupload -->
        <dependency>
            <groupId>commons-fileupload</groupId>
            <artifactId>commons-fileupload</artifactId>
            <version>1.4</version>
        </dependency>
        <dependency>
            <groupId>commons-io</groupId>
            <artifactId>commons-io</artifactId>
            <version>2.4</version>
        </dependency>

2. 编写文件上传的前台页面

<h3>文件上传</h3>        
    <form action="upload" method="post" enctype="multipart/form-data">        
    选择文件：<input type="file" name="upload"/><br/>        
    <input type="submit" value="上传文件"/>    
</form>

3. 编写Controller控制器

    /**
     * 组件上传（commons-fileupload）
     * @param request
     * @return
     * @throws Exception
     */
    @PostMapping("upload")
    @ResponseBody
    public String uploadFile(HttpServletRequest request) throws Exception {
        System.out.println("文件上传 start...");

        //上传位置
        String realPath = request.getSession().getServletContext().getRealPath("/uploads/");

        //判断路径是否存在
        File file = new File(realPath);
        if(!file.isDirectory()){
            //创建文件夹
            boolean mkdir = file.mkdir();
            System.out.println("位置："+mkdir+":"+file.getAbsolutePath());

        }

        //解析request对象，获取上传文件项
        //磁盘文件项工厂
        DiskFileItemFactory factory = new DiskFileItemFactory();
        ServletFileUpload upload = new ServletFileUpload(factory);
        List<FileItem> items = upload.parseRequest(request);
        for (FileItem i:items) {
            if(i.isFormField()){
                //普通表单项，不处理
            }else{
                //文件上传项
                //获取上传文件的名称
                String fileName = i.getName();

                fileName = System.currentTimeMillis() + fileName;
                System.out.println("文件名："+fileName);
                //上传
                i.write(new File(realPath,fileName));
                //删除临时文件
                i.delete();
            }
        }

        return "ok";
    }

二. SpringMVC文件上传

1. SpringMVC框架提供了MultipartFile对象，该对象表示上传的文件，要求变量名称必须和表单file标签的 name属性名称相同。
2.Controller如下：

    /**
     * springMVC上传
     * @param request
     * @param upload
     * @return
     * @throws IOException
     */
    @PostMapping("upload")
    @ResponseBody
    public String springMVCFileUpload(HttpServletRequest request,MultipartFile upload) throws IOException {
        System.out.println("文件上传 start...");

        //上传位置
        String realPath = request.getSession().getServletContext().getRealPath("/uploads/");

        //判断路径是否存在
        File file = new File(realPath);
        if(!file.isDirectory()){
            //创建文件夹
            boolean mkdir = file.mkdir();
            System.out.println("创建文件夹"+mkdir+":"+file.getAbsolutePath());

        }

        //获取上传文件的名称
        String fileName = upload.getOriginalFilename();

        fileName = System.currentTimeMillis() + fileName;
        System.out.println("文件名："+fileName);

        upload.transferTo(new File(realPath,fileName));
        return "ok";
    }

3.配置文件解析器对象

    <!--配置文件上传解析器-->
    <bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
        <!--文件上传大小限制-->
        <property name="maxUploadSize" value="10485760"/> <!-- 10M = 10*1024*1024 =  10485760 -->
    </bean>

三. SpringMVC跨服务器文件上传

1.准备图片服务器（Server-image），并配置允许读写操作（以 http://localhost:9090/uploads/ （图片服务器的路径） 为例：）

<servlet>
    <servlet-name>default</servlet-name>
    <servlet-class>org.apache.catalina.servlets.DefaultServlet</servlet-class>
    
    <!-- 添加，解决jersey上传服务器403错误 -->
    <init-param>
      <param-name>readonly</param-name>
      <param-value>false</param-value>
    </init-param>
    <init-param>
      <param-name>debug</param-name>
      <param-value>0</param-value>
    </init-param>
    <init-param>
      <param-name>listings</param-name>
      <param-value>false</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
  </servlet>

web.xml

    /**
     * 跨域上传
     * @param upload
     * @return
     * @throws IOException
     */
    @PostMapping("upload")
    @ResponseBody
    public String httpFileUpload(MultipartFile upload) throws IOException {
        System.out.println("文件上传 start...");

        // 上传位置
        String realPath = "http://localhost:9090/uploads/";

        String fileName = System.currentTimeMillis() + upload.getOriginalFilename();

        // 创建客户端对象
        Client client = Client.create();
        // 连接图片服务器
        WebResource resource = client.resource(realPath + fileName);
        // 上传文件
        resource.put(upload.getBytes());
        return "ok";
    }

3.上传测试结果

Server-image