list.stram 抽取属性转成数字并汇总

List<Title> list = ..... list.stream().mapToInt(s -> Integer.valueOf(s.getScore())).sum();

避开null，数据库中存的字符串，列表中需转成数字并汇总

int sum = list.stream().collect(Collectors.summingInt(f->f.getScore()==null?0:Integer.valueOf(f.getScore())));