檔案上傳的必要條件：

　　1.form表單的enctype取值必須是：mutipart/form-data (預設是:application/x-www-form-urlencoded)

　　2.method屬性為：post

　　3.提供一個文字選擇域<input type="file" />

        <dependency>
            <groupId>commons-fileupload</groupId>
            <artifactId>commons-fileupload</artifactId
 
>
            <version>1.3.3</version>
        </dependency>
        <dependency>
            <groupId>commons-io</groupId>
            <artifactId>commons-io</artifactId>
            <version>2.6</version>
        </dependency>

1.傳統的方式上傳

form表單

    <form action="/fileupload/f1" method="post" enctype="multipart/form-data" >
        選擇檔案:<input type="file" name="upload">
                <input type="submit" value="上傳">
    </form>

controller類，生成的檔案在target根目錄下的uploads資料夾中

@Controller
@RequestMapping("/fileupload")
 
public class FileuploadController {

    /**
     * 傳統的檔案上傳方式
     */
    @RequestMapping("/f1")
    public String f1(HttpServletRequest request) throws Exception {
        //用fileupload元件完成檔案上傳
        String path = request.getSession().getServletContext().getRealPath("/uploads");
        //判斷該路徑是否存在
        File file = new File(path);
        if(!file.exists()){
            //建立該資料夾
            file.mkdirs();
        }

        //解析request物件，獲取檔案上傳項
        DiskFileItemFactory factory = new DiskFileItemFactory();
        ServletFileUpload upload = new ServletFileUpload(factory);
        //解析request
        List<FileItem> items = upload.parseRequest(request);
        for (FileItem item : items) {
            //判斷當前item物件是否是檔案上傳項
            if(item.isFormField()){
                //說明普通表單項
            }else {
                //說明檔案上傳項
                String fileName = item.getName();
                //把檔名稱設定為唯一值 uuid
                String uuid = UUID.randomUUID().toString().replace("-", "");
                fileName = uuid +"_"+fileName;
                //完成檔案上傳
                item.write(new File(path,fileName));
                //刪除臨時檔案
                item.delete();
            }
        }
        return "success";
    }
}

2.springmvc檔案上傳

1.配置檔案解析器

    <!-- 配置檔案解析器物件，要求id名稱必須是multipartResolver -->
    <bean id="multipartResolver"
          class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
        <!--位元組單位-->
        <property name="maxUploadSize" value="10485760"/>
    </bean>

2.頁面表單

    <%--springmvc模式--%>
    <form action="/fileupload/f2" method="post" enctype="multipart/form-data" >
        選擇檔案:<input type="file" name="upload">
        <input type="submit" value="上傳">
    </form>

3.controller

    /**
     * springmvc模式的上傳
     */
    @RequestMapping("/f2")
    public String f2(HttpServletRequest request, MultipartFile upload) throws IOException {
        String path = request.getSession().getServletContext().getRealPath("/uploads");
        File file = new File(path);
        if(!file.exists()){
            file.mkdirs();
        }
        //獲取檔名字
        String filename = upload.getOriginalFilename();
        String uuid = UUID.randomUUID().toString().replace("-", "");
        filename = uuid +"_"+filename;
        //完成上傳
        upload.transferTo(new File(path,filename));
        return "success";
    }