集合与字符串之间进行转化

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 public String listToString(List list){
        if(list.size() == 0)
            return "";
        StringBuilder stringBuilder = new StringBuilder();
        for(int i=0; i<list.size(); i++){
            stringBuilder.append(list.get(i)).append(",");
        }
        return stringBuilder.toString().substring(0,stringBuilder.toString().length()-1);
    }

    public List<Integer> stringToList(String s){
        List<Integer> list = new ArrayList<Integer>();
        if(StringUtil.isEmpty(s))
            return list;
        String [] strings = s.split(",");
        for(String et : strings){
            list.add(Integer.parseInt(et));
        }
        return list;
    }

将list转化成String，元素中间加“，”。