依赖

   <dependency>
      <groupId>commons-fileupload</groupId>
      <artifactId>commons-fileupload</artifactId>
      <version>${commons-fileupload.version}</version>
    </dependency>

    <dependency>
      <groupId>commons-io</groupId>
      <artifactId>commons-io</artifactId>
      <version>${commons-io.version}</version>
    </dependency>

jsp的form表单

文件要以二进制的形式传输 enctype="multipart/form-data"

<form name="addNewCategoryForm" action="addNewCategory" method="post" enctype="multipart/form-data" onsubmit="return check(this)">
...
</form>

提交的二进制数据处理

        DiskFileItemFactory itemFactory = new DiskFileItemFactory();
        ServletFileUpload fileUpload = new ServletFileUpload(itemFactory);
        //设置缓冲区的大小：
        itemFactory.setSizeThreshold(1024 * 1024);
        List items = null;
        try {
            //获得表单项集合
            items = fileUpload.parseRequest(request);
            for (Object item : items) {
                FileItem fileItem = (FileItem)item;
                //如果不是普通表单,即是文件类型
                if(!fileItem.isFormField()) {
                    //获取文件存储目录
                    String fileFolder = request.getSession().getServletContext().getRealPath("img/category");
                    //获取文件名称
                    String fileName = fileItem.getName();
                    //获取文件后缀名
                    String suffix = fileName.substring(fileName.lastIndexOf("."));
                    //构建文件名
                    String newFileName = new Date().getTime() + suffix;                 
                    File file = new File(fileFolder,newFileName);
                    try {
                        if(!file.exists()) {
                            file.createNewFile();
                        }
                        //将表单内容写入该文件
                        fileItem.write(file);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                    //删除临时文件
                    fileItem.delete();
                }
                //普通表单
                if(fileItem.isFormField()) {
                    //获取name的值
                    System.out.println(fileItem.getFieldName());
                    try {
                        //获取value的值
                        String value = fileItem.getString("UTF-8");
                    } catch (UnsupportedEncodingException e) {
                        e.printStackTrace();
                    }
                }
            }
        } catch (FileUploadException e) {
            e.printStackTrace();
        }