思路：先提交form，成功后触发上传图片按钮（隐藏）

一、html

        <div class="layui-row " style="width: 900px; padding: 20px; margin: auto auto; background-color: #f2f2f2">
            <form class="layui-form" action="" >
            <div class="layui-upload layui-col-md4 layui-col-space30" style="margin-left: 80px">
                <label class="layui-form-label" style="font-size: 15px;">图书封面</label>
                <div class="layui-upload-list ">
                    <p id="demoText"></p>
                    <div style="width:220px;height:300px;background: white;margin-top: 20px"><img class="layui-upload-img" id="demo1"></div>

                </div>

                <button type="button" class="layui-btn" id="test1" style="margin-left: 20px" >选择图片</button>
                <button id="hideUpload" type="button" style="display: none"></button>
            </div>

            <div class="layui-col-md7 layui-col-space10 " style="font-size: 15px;" >
                <div class="layui-form-item" >
                        <label class="layui-form-label">ID</label>
                        <div class="layui-input-inline" style="width: 45%">
                            <input id="bookId" lay-verify="number" type="text" name="bookId" placeholder="请输入图书Id(唯一)"
                                   autocomplete="off" class="layui-input" >
                        </div>
                </div>

                <div class="layui-form-item">
                    <label class="layui-form-label">书 名</label>
                    <div class="layui-input-inline" style="width: 45%">
                        <input required lay-verify="required" id="bookName" type="text" name="bookName"
                               placeholder="请输入书名" autofocus
                               class="layui-input" autocomplete="off">
                    </div>
                </div>

                <div class="layui-form-item">
                    <label class="layui-form-label">作 者</label>
                    <div class="layui-input-inline" style="width: 45%">
                        <input id="bookAuthor" lay-verify="required" type="text" name="bookAuthor" placeholder="请输入作者"
                               autocomplete="off" class="layui-input">
                    </div>
                </div>

                <div class="layui-form-item">
                    <label class="layui-form-label">出版社</label>
                    <div class="layui-input-inline" style="width: 45%">
                        <input id="publish" lay-verify="required" type="text" name="publish"
                               placeholder="请输入出版社" autocomplete="off"
                               class="layui-input">
                    </div>
                </div>

                <div class="layui-form-item">
                    <label class="layui-form-label">页 数</label>
                    <div class="layui-input-inline" style="width: 45%" >
                        <input id="pages" lay-verify="number" type="text" name="pages"
                               placeholder="请输入页数" autocomplete="off"
                               class="layui-input">
                    </div>
                </div>

                <div class="layui-form-item">
                    <label class="layui-form-label">价 格</label>
                    <div class="layui-input-inline" style="width: 45%">
                        <input id="price" lay-verify="number" type="text" name="price" placeholder="￥"
                               autocomplete="off" class="layui-input">
                    </div>
                </div>

                <div class="layui-form-item">
                    <label class="layui-form-label">评分</label>
                    <div class="layui-input-inline" style="width: 45%">
                        <input id="bookGrade" lay-verify="number" type="text" name="bookGrade"
                               placeholder="请输入评分" autocomplete="off"
                               class="layui-input">
                    </div>
                </div>

                <div class="layui-form-item">
                    <label class="layui-form-label">ISBN</label>
                    <div class="layui-input-inline" style="width: 45%">
                        <input id="isbn" lay-verify="required" type="text" name="isbn"
                               placeholder="请输入ISBN" autocomplete="off"
                               class="layui-input">
                    </div>
                </div>

                <div class="layui-form-item layui-form-text">
                    <label class="layui-form-label">简 介</label>
                    <div class="layui-input-inline" style="width: 45%" >
                    <textarea id="bookIntro" lay-verify="required" name="bookIntro" placeholder="请输入简介"
                              class="layui-textarea "
                              autocomplete="off"></textarea>
                    </div>
                </div>
        </div>



            <div class="layui-form-item layui-row">
                <div class="layui-input-block" style="width:300px;margin: auto; margin-top: 20px">
                    <button class="layui-btn" lay-submit="" lay-filter="submit" id="add">立即提交</button>
                </div>
            </div>
            </form>
        </div>


    </div>






</body>
</html>

二、js

layui.use(["jquery", "upload", "form", "layer", "element"], function () {
    var $ = layui.$,
        element = layui.element,
        layer = layui.layer,
        upload = layui.upload,
        form = layui.form;
    //监听提交
    form.on('submit(submit)', function(data){
        var date = new Date();
            subData = {
            bookId: data.field.bookId,
            bookName:data.field.bookName,
            bookAuthor: data.field.bookAuthor,
            publish: data.field.publish,
            pages: data.field.pages,
            price: data.field.price,
            bookGrade: data.field.bookGrade,
            isbn: data.field.isbn,
            bookIntro: data.field.bookIntro
        }
        $.ajax({
            type:'post',
            url:'/addBook',
            data:subData,
            success:(res)=>{
                if(res.code == 0){
                    // 触发隐藏按的上传按钮
                    $('#hideUpload').trigger('click');
                    layer.msg("图书信息提交成功!", {
                        time: 1000
                    });


                }else{
                    layer.msg("图书信息提交失败!请重新填写！", {
                        time: 3000
                    }, function() {
                        //重新加载页面
                        location.reload();
                    })
                }
            },
            error:(err)=>{
                layer.msg("图书信息提交失败!", {
                    time: 1000
                }, function() {
                    //重新加载页面
                    location.reload();
                })
            }
        });
        return false;
    });

    //图片上传
    var uploadInst = upload.render({
        elem: '#test1'         //绑定点击按钮
        ,url: '/upload'     //访问后台路径
        ,accept: 'images'               //图片格式
        ,auto:false                     //取消自动上传
        ,method: 'post'                 //请求上传的 http 类型
        ,bindAction:'#hideUpload'       //绑定真正的上传按钮
        ,data:{                         //访问后台提交的数据
            // name: $('#a').val()
            fileName:()=>{
                return $('#bookId').val();//官方文档说明：实现动态传值
            }
        }
        ,choose: function(obj){
            //预读本地文件示例，不支持ie8
            obj.preview(function(index, file, result){
                $('#demo1').attr({src: result,width:"220",height:"300"});//图片链接（base64）
            });
        }
        ,done: function(res){

            //如果上传失败
            if(res.code > 0){
                return layer.msg('图片上传失败！');
            }
            //上传成功
            layer.msg("图片上传成功!", {
                time: 1000
            }, function() {
                //重新加载页面
                location.reload();
            });
        }
        ,error: function(){
            //演示失败状态，并实现重传
            var demoText = $('#demoText');
            demoText.html('<span style="color: #FF5722;">上传失败</span> <a class="layui-btn layui-btn-xs demo-reload">重试</a>');
            demoText.find('.demo-reload').on('click', function(){
                uploadInst.upload();
            });
        }
    });
});

三、后端

    /**
     * 管理员：添加图书
     * @return
     */
    @PostMapping("/addBook")
    @ResponseBody
    public Object addBook(Book book){
        HashMap<String, Object> map = new HashMap<>();
        // 存储图书信息到数据库
        Integer flag = null;
        try {
            flag = bookService.addBook(book);
            if (flag!=0){
                map.put("msg", "ok");
                map.put("code", 0);
            }else {
                map.put("msg", "error");
                map.put("code", 1);
            }
        } catch (Exception e) {
            e.printStackTrace();
            // 防止id重复
            map.put("msg", "error");
            map.put("code", 1);
        }

        return map;
    }
    /**
     * 管理员：保存图片
     */
    @PostMapping("/upload")
    @ResponseBody
    public Object upload(MultipartFile file, String fileName){
        HashMap<String, Object> map = new HashMap<>();
        // 上传图片
        // 存储地址
        String realPath = "E:\\JAVA\\book_system\\src\\main\\resources\\static\\img";

        // 获取文件后缀
        String extension = FilenameUtils.getExtension(file.getOriginalFilename());
        // 文件名
        String newFileName= fileName +"."+extension;
        //处理文件上传
        try {
            file.transferTo(new File(realPath,newFileName));
        } catch (IOException e) {
            e.printStackTrace();
            map.put("msg", "error");
            map.put("code", 1);
        }
        map.put("msg", "ok");
        map.put("code", 0);
        return map;
    }