java8 stream流操作实现List Count/Word Count

话不多说，直接上代码

• List Count

代码语言：javascript复制

public static void main(String[] args) {
    List<String> list = Arrays.asList("beijing", "shanghai", "guangzhou", "shenzhen", "beijing");
    Map<String, Long> collect = list.stream()
            .collect(Collectors.groupingBy(o -> o, Collectors.counting()));
    System.out.println(collect);
    // out => {guangzhou=1, shanghai=1, shenzhen=1, beijing=2}
}

• List Word Count

代码语言：javascript复制

public static void main(String[] args) {
    List<String> list = Arrays.asList("beijing shanghai guangzhou"
                                    , "beijing guangzhou"
                                    , "beijing", "beijing");
    Map<String, Long> collect = list.stream()
            .flatMap(o -> Stream.of(o.split(" ")))
            .collect(Collectors.groupingBy(o -> o, Collectors.counting()));
    System.out.println(collect);
    // out => {guangzhou=2, shanghai=1, beijing=4}
}

如果要包含元素

• 使用JDK自带集合类

代码语言：javascript复制

public static void main(String[] args) {
    List<String> list = Arrays.asList("beijing", "shanghai", "guangzhou", "shenzhen", "beijing");
    Map<String, List<String>> collect
            = list.stream().collect(Collectors.groupingBy(o -> o));
    System.out.println(collect);
    // out => {guangzhou=[guangzhou], shanghai=[shanghai], shenzhen=[shenzhen], beijing=[beijing, beijing]}
}

• 使用Spring 的 LinkedMultiValueMap

代码语言：javascript复制

public static void main(String[] args) {
    List<String> list = Arrays.asList("beijing", "shanghai", "guangzhou", "shenzhen", "beijing");
    LinkedMultiValueMap<String, String> map = new LinkedMultiValueMap();
    list.stream().forEach(o -> map.add(o, o));
    System.out.println(map);
    // out => {beijing=[beijing, beijing], shanghai=[shanghai], guangzhou=[guangzhou], shenzhen=[shenzhen]}
}

spring jdk list word 集合

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