WordCounting.java

package com.insightfullogic.java8.examples.chapter6;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.Map;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import static java.util.Comparator.comparing;
import static java.util.stream.Collectors.counting;
import static java.util.stream.Collectors.groupingBy;

public class WordCounting {

    public static void main(String[] args) {
        InputStream enWiki = WordCounting.class.getResourceAsStream("enwiki-20131230-stubs-meta-hist-incr.xml");
        new WordCounting().countUsers(enWiki);
        // InputStream huckleberryFinn = WordCounting.class.getResourceAsStream("huckleberry_finn");
        // new WordCounting().countWords(huckleberryFinn);
    }

    private static final Pattern username = Pattern.compile("\\s+<username>(.*?)</username>");

    public void countUsers(InputStream stream) {
        try (BufferedReader reader = new BufferedReader(new InputStreamReader(stream))) {
            Map<String, Long> counts = reader
                    .lines()
                    .parallel()
                    .filter(line -> line.contains("<username>"))
                    .map(line -> {
                        Matcher matcher = username.matcher(line);
                        matcher.find();
                        return matcher.group(1);
                    })
                    .collect(groupingBy(word -> word, counting()));

            counts.forEach((word, count) -> System.out.println(word + " -> " + count));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private static final Pattern space = Pattern.compile("\\s+");

    public void countWords(InputStream stream) {
        try (BufferedReader reader = new BufferedReader(new InputStreamReader(stream))) {
            Map<String, Long> counts = reader
                                        .lines()
                                        .flatMap(space::splitAsStream)
                                        .map(String::trim)
                                        .filter(word -> !word.isEmpty())
                                        .collect(groupingBy(word -> word, counting()));

            counts.forEach((word, count) -> System.out.println(word + " -> " + count));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

}