("[name='hobby']"):定位遍历的元素
$("[name='hobby']").eq(i)：精确定位到所有元素中的某一个

$(function () {
        //点击全选框，选中所有购物车商品
        var  a = 1;
        $("[name= 'all']").click(function () {
            a++;
            //获取选中的订单项金额
            var money = parseInt($("[name='hobby']").siblings(".mid-je").children("span").text());
            //获取当前总计中的金额
            var sum = parseInt($(".jshj-p2").children("span").text());
            if(a % 2 ==0){
                $("[name='hobby']").attr("checked",true);
                $("[name='all']").attr("checked",true);
                var b = document.getElementsByName("hobby");
                var total = 0 ;
                for(var i = 0 ; i < b.length ; i++){
                    total = total +  parseInt($("[name='hobby']").eq(i).siblings(".mid-je").children("span").text());
                    console.log(total);
                }
                $(".jshj-p2").children("span").text(total);
            }else{
                $("[name='hobby']").attr("checked",false);
                $("[name='all']").attr("checked",false);
                $(".jshj-p2").children("span").text(0);
            }
        });
    });

 <c:forEach items="${sessionScope.cart.cartItem}" var="cartI">
        <div class="cart-con-info">
            <div class="info-top">
            </div>
            <div class="info-mid">
                <input type="checkbox" value="" name="hobby" class="mid-ipt f-l"></input>
                <div class="mid-tu f-l">
                    <a href="#"><img src="${pageContext.request.contextPath}/images/dai1.gif" /></a>
                </div>
                <div class="mid-font f-l">
                    <a href="#">登高阁紫菜肉松鸡蛋卷 海苔蛋卷 糕点<br />江西特产小吃 休闲办公零食</a>
                    <span>满赠</span>
                </div>
                <div class="mid-guige f-l">
                    <p>颜色：蓝色</p>
                    <p>尺码：XL</p>
                    <a href="JavaScript:;" class="xg" xg="xg1">修改</a>
                    <div class="guige-xiugai" xg-g="xg1">
                        <div class="xg-left f-l">
                            <dl>
                                <dt>颜  色</dt>
                                <dd>
                                    <a href="JavaScript:;" class="current">黑色</a>
                                    <a href="JavaScript:;">白色</a>
                                </dd>
                                <div style="clear:both;"></div>
                            </dl>
                            <dl>
                                <dt>尺  码</dt>
                                <dd>
                                    <a href="JavaScript:;" class="current">M</a>
                                    <a href="JavaScript:;">L</a>
                                    <a href="JavaScript:;">XL</a>
                                </dd>
                                <div style="clear:both;"></div>
                            </dl>
                            <a href="JavaScript:;" class="qd">确定</a>
                            <a href="JavaScript:;" class="qx" qx="xg1">取消</a>
                        </div>
                        <div class="xg-right f-l">
                            <a href="#"><img src="${pageContext.request.contextPath}/images/dai2.gif" /></a>
                        </div>
                        <div style="clear:both;"></div>
                    </div>
                </div>
                <div class="mid-sl f-l">
                    <a href="JavaScript:;" class="sl-left" id="${cartI.productExt.pid}" name="reduce">-</a>
                    <input type="number" name="num" id="${cartI.productExt.pid}" value="${cartI.count}" />
                    <a href="JavaScript:;" class="sl-right" id="${cartI.productExt.pid}" name="plus">+</a>
                </div>
                <p class="mid-dj f-l">¥ <span>${cartI.price}</span></p>
                <p class="mid-je f-l">¥ <span>${cartI.sum}</span></p>
                <div class="mid-chaozuo f-l">
                    <a href="#">移入收藏夹</a>
                    <a href="#">删除</a>
                </div>
                <div style="clear:both;"></div>
            </div>
        </div>
    </c:forEach>

    <div class="cart-con-footer">
        <div class="quanxuan f-l">
            <input type="checkbox" value="" name="all"></input>
            <span>全选</span>
            <a href="#">删除</a>
            <a href="#">加入收藏夹</a>
            <p>（此处始终在屏幕下方）</p>
        </div>
        <div class="jiesuan f-r">
            <div class="jshj f-l">
                <p>合计（不含运费）</p>
                <p class="jshj-p2">
                    ￥：<span>0</span>.00
                </p>
            </div>
            <a href="JavaScript:;" class="js-a1 f-l">结算</a>
            <div style="clear:both;"></div>
        </div>
        <div style="clear:both;"></div>
    </div>