1.将list元素用单引号引起来：
List<TransferFocusxfSummaryTop3> topList = getTransferFocusxfSummaryTop3(userId);
List<String> otherSidelist=new ArrayList<String>();

for(int i=0;i<topList.size();i++){
    otherSidelist.add("‘"+topList.get(i).getOtherSide()+"‘");
}

2.将list转化为mysql中集合查询条件in ():

("+String.join(",",otherSidelist)+")

3.mysql最近三个月数据：

t.tradetime>=DATE_SUB(now(), INTERVAL 3 MONTH)

4.BigDecimal数据类型除法并转换为百分比：

getFormatNum(amountTop3.divide(totalAmount, RoundingMode.HALF_UP).toPlainString()

百分比：
private String getFormatNum(String n) {
    NumberFormat num = NumberFormat.getPercentInstance();
    num.setMaximumFractionDigits(0);
    return num.format(new BigDecimal(n));
}

List与字符串转换