java list分組，從list中隨機抽取不重複

（1）list 分組

private Map<String, List<SimUser>> listGroup2MapTwo(List<SimUser> list) {
        Map<String, List<SimUser>> userSignSerialMap = Maps.newConcurrentMap();
        if (CollectionUtils.isNotEmpty(list)) {
            // 分組
            for (SimUser vo : list) {
                String pernr = vo.getFrom();
                List<SimUser> tempList = userSignSerialMap.get(pernr);
                /*如果取不到數據,那麼直接new一個空的ArrayList**/
                if (tempList == null) {
                    tempList = Lists.newArrayList();
                    tempList.add(vo);
                    userSignSerialMap.put(pernr, tempList);
                } else {
            /*某個vo之前已經存放過了,則直接追加數據到原來的List裏**/
                    tempList.add(vo);
                }
            }
        }
        return userSignSerialMap;
    }

 

（2）從list 中隨機抽取幾個

public static <T>List<T> getRandomListDocVo(List<T> sourceList) {
        List<Integer> tempList=new ArrayList<Integer>();
        List<T> result = new ArrayList<>();
        for (int i = 0; i < 5; i++) {
            int random = new Random().nextInt(sourceList.size());
            if(!tempList.contains(random)){
                tempList.add(random);
                result.add(sourceList.get(random));
            }else{
                i--;
            }
        }
        return result;
    }

 

或者 

Collections.shuffle(stringList); 直接打亂list順序，然後截取前幾個也行