先直接上測試程式碼

public static void main(String[] args){
    List<DealerInfoOut> list = new ArrayList<>();
    List<DealerInfoOut> otherList = new ArrayList<>();
    for(int i=0 ; i<=10000;i++){
        DealerInfoOut infoOut = new DealerInfoOut();
        DealerInfoOut otherInfoOut = new 
 
DealerInfoOut();
        infoOut.setDealerId(i);
        otherInfoOut.setDealerId(10000-i);
        otherInfoOut.setDealerSimpleName((10000-i)+"");
        list.add(infoOut);
        otherList.add(otherInfoOut);
    }
    //
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss.ms");// 其中
//處理方式1
System.out
 
.println("start1="+sdf.format(new Date()));
    Map<Integer,DealerInfoOut> map = new HashMap<>();
    for(DealerInfoOut otherInfoOut:otherList){
        map.put(otherInfoOut.getDealerId(),otherInfoOut);
    }
    for(DealerInfoOut infoOut:list){
        if(map.containsKey(infoOut.getDealerId())){
            infoOut.setDealerSimpleName(map.get(infoOut.getDealerId()).getDealerSimpleName());
        }
    }
    System.out
 
.println("end1="+sdf.format(new Date()));

    //處理方式2
System.out.println("start2="+sdf.format(new Date()));
    for(DealerInfoOut infoOut:list){
        for(DealerInfoOut otherInfoOut:otherList){
            if(infoOut.getDealerId().equals(otherInfoOut.getDealerId())){
                infoOut.setDealerSimpleName(otherInfoOut.getDealerSimpleName());
                break;
            }
        }
    }
    System.out.println("end2="+sdf.format(new Date()));
}

通過輸出的時間可以看到方式1所用時間基本不超過1毫秒,方式2在有1萬資料的時候所用時間大概在1秒左右.當資料量為10萬時,方式2我大概等了10幾秒都沒處理完.