Spring3.x不支持stream写法

Question

Map<String, List> collect = list.stream().collect(Collectors.groupingBy(d -> fetchGroupKey(d)));
public static String fetchGroupKey(ScrapSpecial scrapSpecial) {
return scrapSpecial.getMaterialCode().toString() + scrapSpecial.getScrapReason().toString();
}
问题描述：项目Spring版本是3.x，不支持stream()的写法，如何将上面的stream流转变成普通写法。

Answer 1

可以使用for循环和HashMap来实现，如下：

HashMap<String, List<ScrapSpecial>> collect = new HashMap<>();

for (ScrapSpecial scrapSpecial : list) {
    String key = fetchGroupKey(scrapSpecial);
    if (collect.containsKey(key)) {
        // 如果HashMap中已经存在key对应的集合，则将元素添加到集合中
        collect.get(key).add(scrapSpecial);
    } else {
        // 如果HashMap中不存在key对应的集合，则创建新的集合并将元素添加进去
        List<ScrapSpecial> tempList = new ArrayList<>();
        tempList.add(scrapSpecial);
        collect.put(key, tempList);
    }
}

public static String fetchGroupKey(ScrapSpecial scrapSpecial) {
    return scrapSpecial.getMaterialCode().toString() + scrapSpecial.getScrapReason().toString();
}

for (String key : collect.keySet()) {
    System.out.println(key + ": " + collect.get(key));
}