struts2 action 接受數組參數爲Null的問題

 public List<FormulaDetail> formulaDetails;
public List<FormulaDetail> getFormulaDetails() {
        return formulaDetails;
    }
    public void setFormulaDetails(List<FormulaDetail> formulaDetails) {
        this.formulaDetails = formulaDetails;
    }

JSP傳過來的數組formulaDetails[0].count不能被struts2接收，通過查詢發現是FormulaDetail類沒有缺省的構造函數

public FormulaDetail() {
    }

只有一個帶參數的函數

/** full constructor */
    public FormulaDetail(Integer formulaId, Integer goodsCategory,
            Integer percent) {
        this.formulaId = formulaId;
        this.goodsCategory = goodsCategory;
        this.percent = percent;
    }

講缺省構造函數添加以後,成功接收數組參數