M101J-Homework-3.2,3.3- Updating the java BlogPostDAO

package course;

import com.mongodb.client.MongoCollection;
import com.mongodb.client.MongoDatabase;
import com.mongodb.client.model.Filters;
import com.mongodb.client.model.Sorts;
import com.mongodb.client.model.Updates;
import org.bson.Document;
import org.bson.conversions.Bson;

import java.util.ArrayList;
import java.util.Date;
import java.util.List;

public class BlogPostDAO {
    MongoCollection<Document> postsCollection;

    public BlogPostDAO(final MongoDatabase blogDatabase) {
        postsCollection = blogDatabase.getCollection("posts");
    }

    // Return a single post corresponding to a permalink    public Document findByPermalink(String permalink) {

        // XXX HW 3.2,  Work Here        Document post = null;
        Bson filter = Filters.eq("permalink",permalink);
        List<Document> list = postsCollection.find(filter).into(new ArrayList<Document>());
        if (list.size() > 0)
            post = list.get(0);


        return post;
    }

    // Return a list of posts in descending order. Limit determines    // how many posts are returned.    public List<Document> findByDateDescending(int limit) {

        // XXX HW 3.2,  Work Here        // Return a list of DBObjects, each one a post from the posts collection        List<Document> posts = null;
           posts = postsCollection.find().sort(Sorts.descending("date")).limit(limit).into(new ArrayList<Document>());

        return posts;
    }


    public String addPost(String title, String body, List tags, String username) {

        System.out.println("inserting blog entry " + title + " " + body);

        String permalink = title.replaceAll("\\s", "_"); // whitespace becomes _        permalink = permalink.replaceAll("\\W", ""); // get rid of non alphanumeric        permalink = permalink.toLowerCase();


        // XXX HW 3.2, Work Here        // Remember that a valid post has the following keys:        // author, body, permalink, tags, comments, date, title        //        // A few hints:        // - Don't forget to create an empty list of comments        // - for the value of the date key, today's datetime is fine.        // - tags are already in list form that implements suitable interface.        // - we created the permalink for you above.
        // Build the post object and insert it        Document post = new Document();
        post.append("title",title).append("author",username).append("body",body).append("permalink",permalink).append("tags",tags).append("comments",new ArrayList<String>()). append("date",new Date());
        postsCollection.insertOne(post);

        return permalink;
    }




    // White space to protect the innocent







    // Append a comment to a blog post    public void addPostComment(final String name, final String email, final String body,
                               final String permalink) {

        // XXX HW 3.3, Work Here        // Hints:        // - email is optional and may come in NULL. Check for that.        // - best solution uses an update command to the database and a suitable        //   operator to append the comment on to any existing list of comments        if (permalink != null) {

            Document post = null;
            Bson filter = Filters.eq("permalink",permalink);
            List<Document> list = postsCollection.find(filter).into(new ArrayList<Document>());
            if (list.size() > 0)
                post = list.get(0);
            if (post != null) {
                Bson comments = Updates.push("comments",new Document("author",name).append("body",body).append("email",email));
                postsCollection.updateOne(post,comments);
            }

        }
    }
}