在Spring Boot框架下的web评论系统，实体有评论、子评论、用户和回复，实现检索、分页和排序功能。

首先，你需要定义实体类，如下所示：

@Entity
@Table(name = "comment")
public class Comment {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String content;
    private LocalDateTime createdTime;
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "user_id")
    private User user;
    @OneToMany(mappedBy = "comment", cascade = CascadeType.ALL)
    private List<Reply> replies;
    // getters and setters
}

@Entity
@Table(name = "reply")
public class Reply {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String content;
    private LocalDateTime createdTime;
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "user_id")
    private User user;
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "comment_id")
    private Comment comment;
    // getters and setters
}

@Entity
@Table(name = "user")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String username;
    private String password;
    // getters and setters
}

然后，你需要创建一个DAO层，使用Spring Data JPA实现对实体的增删改查操作，如下所示：

@Repository
public interface CommentRepository extends JpaRepository<Comment, Long> {
    Page<Comment> findAllByOrderByIdDesc(Pageable pageable);
    Page<Comment> findByContentContainingIgnoreCaseOrderByIdDesc(String keyword, Pageable pageable);
}

@Repository
public interface ReplyRepository extends JpaRepository<Reply, Long> {
    Page<Reply> findAllByCommentIdOrderByIdDesc(Long commentId, Pageable pageable);
}

@Repository
public interface UserRepository extends JpaRepository<User, Long> {
    User findByUsername(String username);
}

最后，你需要创建一个Service层，实现对DAO层的调用和业务逻辑处理，如下所示：

@Service
public class CommentService {
    @Autowired
    private CommentRepository commentRepository;
    @Autowired
    private ReplyRepository replyRepository;

    public Page<Comment> findComments(Integer pageNo, Integer pageSize, String keyword) {
        Pageable pageable = PageRequest.of(pageNo - 1, pageSize);
        if (StringUtils.isEmpty(keyword)) {
            return commentRepository.findAllByOrderByIdDesc(pageable);
        } else {
            return commentRepository.findByContentContainingIgnoreCaseOrderByIdDesc(keyword, pageable);
        }
    }

    public Page<Reply> findReplies(Long commentId, Integer pageNo, Integer pageSize) {
        Pageable pageable = PageRequest.of(pageNo - 1, pageSize);
        return replyRepository.findAllByCommentIdOrderByIdDesc(commentId, pageable);
    }

    public Comment saveComment(Comment comment) {
        comment.setCreatedTime(LocalDateTime.now());
        return commentRepository.save(comment);
    }

    public Reply saveReply(Reply reply) {
        reply.setCreatedTime(LocalDateTime.now());
        return replyRepository.save(reply);
    }
}

最后，在控制器中调用Service层方法，实现路由和响应数据的处理，如下所示：

@RestController
@RequestMapping("/api")
public class CommentController {
    @Autowired
    private CommentService commentService;

    @GetMapping("/comments")
    public Page<Comment> findComments(@RequestParam(defaultValue = "1") Integer pageNo,
                                      @RequestParam(defaultValue = "10") Integer pageSize,
                                      @RequestParam(required = false) String keyword) {
        return commentService.findComments(pageNo, pageSize, keyword);
    }

    @GetMapping("/comments/{commentId}/replies")
    public Page<Reply> findReplies(@PathVariable Long commentId,
                                   @RequestParam(defaultValue = "1") Integer pageNo,
                                   @RequestParam(defaultValue = "10") Integer pageSize) {
        return commentService.findReplies(commentId, pageNo, pageSize);
    }

    @PostMapping("/comments")
    public Comment saveComment(@RequestBody Comment comment) {
        return commentService.saveComment(comment);
    }

    @PostMapping("/replies")
    public Reply saveReply(@RequestBody Reply reply) {
        return commentService.saveReply(reply);
    }
}

以上就是一个简单的评论系统的实现，其中包括了检索、分页和排序功能。