Read file word by word solution.

Main.java

public static void main(String[] args) throws IOException {
//      OptionalInt max = Files.lines(Paths.get("/", "1.txt"), Charset.forName("windows-1251"))
//        .flatMap(s -> Arrays.stream(s.split("[\\P{L}]+")))
//              .peek(System.out::println)
//              .mapToInt(s -> s.length())
//              .max();
//
//(max.getAsInt());
        String content = new String(Files.readAllBytes(Paths.get("/", "1.txt")), Charset.forName("windows-1251"));
        //System.out.println(content);
//        OptionalInt max = Arrays.stream(content.split("[\\P{L}]+"))
//                .peek(System.out::println)
//                .mapToInt(s -> s.length())
//                .max();
//        System.out.println(max.getAsInt());
        String maxWord = "";
        //String s// = "This is how I tried to split a paragraph into a sentence. But, there is a problem. My paragraph includes dates like Jan.13, 2014 , words like U.S and numbers like 2.2. They all got splitted by the above code.";
        Pattern re = Pattern.compile("[^.!?\\s][^.!?]*(?:[.!?](?!['\"]?\\s|$)[^.!?]*)*[.!?]?['\"]?(?=\\s|$)", Pattern.MULTILINE | Pattern.COMMENTS);
        Matcher reMatcher = re.matcher(content);
        while (reMatcher.find()) {
           String[] words = reMatcher.group().split("[\\P{L}]+");
            for(String word : words){
                System.out.print(word.toLowerCase() + " ");
                if(word.length() > maxWord.length()){
                    maxWord = word;
                }
            }
            System.out.println();
        }

        System.out.println(maxWord);
    }