@Entity(name = "Post")
@Table(name = "post")
public static class Post {

    @Id
    private Long id;

    private String title;

    @OneToMany(fetch = FetchType.EAGER)
    private List<PostComment> comments = new ArrayList<>();

    @ManyToMany(fetch = FetchType.EAGER)
    @JoinTable(name = "post_tag",
        joinColumns = @JoinColumn(name = "post_id"),
        inverseJoinColumns = @JoinColumn(name = "tag_id")
    )
    private List<Tag> tags = new ArrayList<>();
}

Post post = entityManager.find(Post.class, 1L);

SELECT  eagerfetch0_.id AS id1_0_0_ ,
        eagerfetch0_.title AS title2_0_0_ ,
        comments1_.Post_id AS Post_id1_2_1_ ,
        eagerfetch2_.id AS comments2_2_1_ ,
        eagerfetch2_.id AS id1_1_2_ ,
        eagerfetch2_.review AS review2_1_2_ ,
        tags3_.post_id AS post_id1_3_3_ ,
        eagerfetch4_.id AS tag_id2_3_3_ ,
        eagerfetch4_.id AS id1_4_4_ ,
        eagerfetch4_.name AS name2_4_4_
FROM    post eagerfetch0_
        LEFT OUTER JOIN post_post_comment comments1_ ON eagerfetch0_.id = comments1_.Post_id
        LEFT OUTER JOIN post_comment eagerfetch2_ ON comments1_.comments_id = eagerfetch2_.id
        LEFT OUTER JOIN post_tag tags3_ ON eagerfetch0_.id = tags3_.post_id
        LEFT OUTER JOIN tag eagerfetch4_ ON tags3_.tag_id = eagerfetch4_.id
WHERE   eagerfetch0_.id = 1

Post post = entityManager.createQuery(
    "select p " +
    "from Post p " +
    "join fetch p.tags " +
    "join fetch p.comments " +
    "where p.id = :id", Post.class)
.setParameter("id", postId)
.getSingleResult();