【word count 程序】 通过 java8实现

hadoop的入门程序，java8也能实现

txt统计单词数量程序

@Test
public void fileWordCount() throws IOException {
    //特殊文件需要格式转换为txt
    Files.readAllLines(Paths.get("D:\\jd.txt"), StandardCharsets.UTF_8).parallelStream()
            //将多个流融合为一个
            .flatMap(line -> Arrays.stream(line.trim().split("\\s")))
            .filter(word -> word.length() > 0)
            .map(word -> new AbstractMap.SimpleEntry<>(word, 1))
            .collect(groupingBy(AbstractMap.SimpleEntry :: getKey, counting()))
            .entrySet().forEach(System.out :: println);
}

List统计单词数量程序
@Test
public void listWordCount(){
    List stringList = Arrays.asList("a","b","c","a");
    stringList.stream()
            .map(s -> new AbstractMap.SimpleEntry<>(s, 1))
            .collect(groupingBy(AbstractMap.SimpleEntry :: getKey, counting()))
            .entrySet().stream()
            .forEach(System.out :: println);
    System.out.println("---------------------------------------------------");
    //通过自定义reduce统计，其实counting（）也使用的是reduce
    //记住：凡是在中间操作使用了map，接口定义都需要声明出来，直接使用lambda表达式会有1.无法读取method，2.类型检查不到 的问题
    BinaryOperator binaryOperator2 = Integer::sum;
    //排序的转换规则接口
    ToIntFunction sortMapFunction = (Map.Entry se) -> Integer.valueOf(se.getValue().toString()).intValue();
    stringList
            .stream()
            .map(s -> new AbstractMap.SimpleEntry<>(s, 1))
            .collect(groupingBy(AbstractMap.SimpleEntry::getKey,
                    reducing(0, AbstractMap.SimpleEntry::getValue,binaryOperator2)))
            .entrySet()
            .stream()
            .sorted(Comparator.comparingInt(sortMapFunction))
            .forEach(System.out::println);
}