Jasper 中如何将数据拆成多行并跨行累计

【问题】

I have a query that returns some summary records.  For instance,

loan amount, loan term, interest rate.  Then I want to have a second row that builds out the detailed payment schedule.  so the report would look like this:

Loan Amt         Term                 Rate
100,000            05months          4.75
             payment              interest     principal      principlebalance
             20,238.13           395.83       19,842.30   80,157.70
             20,238.13           317.29       19,920.84   60,236.86
             20,238.13           238.44       19,999.69   40,237.17
             20,238.13           159.27       20,078.86   20,158.31
             20,238.10           79.79         20,158.31   0
 20,000            2months           5
             payment              interest     principal      remaining
             10,062.55             83.33          9,979.22     10,020.78
              10,062.53            41.75         10,020.78   0

As you can see, for each loan the amortization table can be calculated solely from the 3 values supplied.  But my question is, how do I write the for loop under the detail1?  For the record the loan fields are detail 2 and each amortization section is the detail2 band. I came to know that i can implement this using table/subdataset..But i'm new to jasper not getting to know how to use table/subdataset..Any help with sample code is highly appreciated and of great help..Thanks in advance..

【回答】

       根据贷款额计算贷款分期时需要进行循环计算和跨行计算，用存储过程或Scriptlets实现的难度较大，这种情况用SPL协助Jasper更合适：

A1：sql取数

A2：增加两个计算列mRate和mPayment

A3：创建由LoanID，LoanAmt，payment，Term，Rate，interest，principal，principlebalance组成的新序表，并根据A2每条记录的Term值，将A2的每条记录拆分成Term条新记录插入到创建的新序表中

结果如下：

以A2中L01这条记录为例：Term=5，该条记录被拆分为5条记录插入到新序表中，通过t=t-principal，t被重新赋值，因此这5条记录中，interest，principal，principlebalance列都在逐条变化。

这个脚本如何嵌入到Jasper里执行，具体可参考Java 如何调用 SPL 脚本