从servlet

Question

我正在开发一个spring hibernate项目。我试图以Json对象的形式获取数据，并根据该Json数据填充下拉列表。我正在使用ajax jquery调用，但作为回报我只得到[对象对象] [对象对象] ...我在google开发者控制台中调试jquery并且我收到错误（json对象包含两个字段brandID和BrandName）

Uncaught SyntaxError: Unexpected token o in JSON at position 1
    at JSON.parse (<anonymous>)
    at Object.success (AddItem:51)
    at i (jquery.min.js:2)
    at Object.fireWith [as resolveWith] (jquery.min.js:2)
    at A (jquery.min.js:4)
    at XMLHttpRequest.<anonymous> (jquery.min.js:4)
success @ AddItem:51
i @ jquery.min.js:2
fireWith @ jquery.min.js:2
A @ jquery.min.js:4
(anonymous) @ jquery.min.js:4

这是jquery代码

<script type="text/javascript">
$(document).ready(function(){
    $('#ItemCategory').change(function(){
        $.ajax({
            type       : 'post',
            url        : "${home}/Admin/AddItem",
            data       : {dropdown: $('#ItemCategory').find(":selected").val()},
            datatype   : 'html',
            success    : function(responseText)
            {
                $('#BrandList').empty().append($('<option>').val('-1').text('select brand..'));
                $.each(JSON.parse(responseText),function(index,element){
                    $('#BrandList').append($('<option>',{value:element.BrandID,text:element.BrandName}));
                });
                $('#BrandList').selectpicker('refresh');
            }
        });
    });
});
</script>

servlet代码

    public String getbrand(String catid){
        List<BrandLoader> list = brand_Service.getItemBrand(catid);
        json = null;
        json = gson.toJson(list);
        System.out.println(list);
        System.out.println(json);/* output see below */
        return json;
    }

我得到了正确的json但仍然是同样的问题

[{"BrandID":"brand-21","BrandName":"HTC"},{"BrandID":"brand-22","BrandName":"Sony"},{"BrandID":"brand-23","BrandName":"Lenovo"},{"BrandID":"brand-24","BrandName":"Micromax"},{"BrandID":"brand-25","BrandName":"Panasonic"},{"BrandID":"brand-26","BrandName":"Vivo"}]

实体类

@Entity
@Table(name="brand")
public class BrandLoader {

    @Id
    private String BrandID;

    @Column(name="brandname")
    private String BrandName;

    @Column(name="cat_id")
    private transient String Cat_ID;

    @Override
    public String toString() {
        return "id :"+BrandID+" brand_name :"+BrandName;
    }

    public String getBrandID() {
        return BrandID;
    }

    public void setBrandID(String brandID) {
        BrandID = brandID;
    }

    public String getBrandName() {
        return BrandName;
    }

    public void setBrandName(String brandName) {
        BrandName = brandName;
    }

    public String getCat_ID() {
        return Cat_ID;
    }

    public void setCat_ID(String cat_ID) {
        Cat_ID = cat_ID;
    }
}