FullTextExample.java

import lombok.Data;

import java.util.*;

public class MainIndex {
    public static void main(String[] args) {
        Map<String, Set<Post>> postFullText = new HashMap<>();

        Post p1 = new Post();
        p1.id = 1L;
        p1.categoryId = 2L;
        p1.createdAt = 123213213L;
        p1.text = "Hello world";

        // image, hel, ell, llo, wor, orl, rld
        for (String term: p1.text.split(" ")) {
            Set<Post> postsByTerm = postFullText.getOrDefault(term.toLowerCase(), new HashSet<>());
            postsByTerm.add(p1);
        }


        // cup
        // cat
        // 1  - (ld / max("cat".length", "cup".length)) = 0.3333



        String search = "hello kittens";
        Map<Post, Float> searchResult = new HashMap<>();

        for (String term: search.split(" ")) {
            Set<Post> posts = postFullText.getOrDefault(term.toLowerCase(), new HashSet<>());
            posts.forEach(p -> {
                Float prevScore = searchResult.getOrDefault(p, 0f);

                searchResult.put(p, prevScore + (1/posts.size()));
            });
        }
    }

    @Data
    static class Post {
        private Long id;
        private Long categoryId;
        private Long createdAt;
        private String text;
    }
}