9.5.3 集合（Collection）类型的使用范例

Redisson提供的RSet、 RSetCache、 RList、 RSortedSet、 RScoredSortedSet、 RQueue、 RBlockingQueue、 RDeque、 RBlockingDeque、 RPriorityQueue和RPriorityDeque这几种集合（Collection）类型的对象均可以使用这种分布式映射归纳（MapReduce）服务。

以下是在集合（Collection）类型的基础上采用映射归纳（MapReduce）来实现字数统计的范例：

    public class WordMapper implements RCollectionMapper<String, String, Integer> {
        @Override
        public void map(String value, RCollector<String, Integer> collector) {
            String[] words = value.split("[^a-zA-Z]");
            for (String word : words) {
                collector.emit(word, 1);
            }
        }
    }

    public class WordReducer implements RReducer<String, Integer> {
        @Override
        public Integer reduce(String reducedKey, Iterator<Integer> iter) {
            int sum = 0;
            while (iter.hasNext()) {
               Integer i = (Integer) iter.next();
               sum += i;
            }
            return sum;
        }
    }

    public class WordCollator implements RCollator<String, Integer, Integer> {
        @Override
        public Integer collate(Map<String, Integer> resultMap) {
            int result = 0;
            for (Integer count : resultMap.values()) {
                result += count;
            }
            return result;
        }
    }

    RList<String> list = redisson.getList("myList");
    list.add("Alice was beginning to get very tired");
    list.add("of sitting by her sister on the bank and");
    list.add("of having nothing to do once or twice she");
    list.add("had peeped into the book her sister was reading");
    list.add("but it had no pictures or conversations in it");
    list.add("and what is the use of a book");
    list.add("thought Alice without pictures or conversation");
    RCollectionMapReduce<String, String, Integer> mapReduce
             = list.<String, Integer>mapReduce()
                   .mapper(new WordMapper())
                   .reducer(new WordReducer());
    // 统计词频
    Map<String, Integer> mapToNumber = mapReduce.execute();
    // 统计字数
    Integer totalWordsAmount = mapReduce.execute(new WordCollator());