9.5.2 映射（Map）类型的使用范例

Redisson提供的RMap、 RMapCache和RLocalCachedMap这三种映射（Map）类型的对象均可以使用这种分布式映射归纳（MapReduce）服务。

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

1. Mapper对象将每个映射的值用空格且分开。

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

2. Reducer对象计算统计所有单词的使用情况。

    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;
        }
    }

3. Collator对象统计所有单词的使用情况。

    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;
        }
    }

4. 把上面的各个对象串起来使用：

    RMap<String, String> map = redisson.getMap("wordsMap");
    map.put("line1", "Alice was beginning to get very tired");
    map.put("line2", "of sitting by her sister on the bank and");
    map.put("line3", "of having nothing to do once or twice she");
    map.put("line4", "had peeped into the book her sister was reading");
    map.put("line5", "but it had no pictures or conversations in it");
    map.put("line6", "and what is the use of a book");
    map.put("line7", "thought Alice without pictures or conversation");
    RMapReduce<String, String, String, Integer> mapReduce
             = map.<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());