java - 哪种数据格式适合将数据(左连接数据库查询的结果)从 servlet 传输到 JSP？

Question

[使用 JPA、MySQL、MVC、Servlet、JSP] 如果我从数据库LEFT JOIN读取一些数据 - 三个表(DAO对象的内部方法)我应该如何格式化该结果，以便我可以将其设置为请求属性(在servlet中)并转发到JSP页面？

实体(数据库中的表):

发布:

@Entity
@Table(name = "post")
public class Post implements Serializable {
    @Id
    @GeneratedValue(strategy = IDENTITY)
    @Column(name = "post_id", unique = true, nullable = false)
    private Integer id; 

    @Column(name = "post_title", length=300, unique = false, nullable = false)
    private String title;

    @Column(name = "post_date", unique = false, nullable = false)
    private Date date;

    @Column(name = "post_summary", length=1000, unique = false, nullable = true)
    private String summary;

    @Column(name = "post_content", length=50000, unique = false, nullable = false)
    private String content;

    @Column(name = "post_visitors", unique = false, nullable = false)
    private Integer visitors;

    @ManyToOne
    @JoinColumn (name = "user_id", referencedColumnName="user_id", nullable = false)
    private User user;

    @ManyToOne
    @JoinColumn (name = "category_id", referencedColumnName="category_id", nullable = false)
    private Category category;

    @OneToMany(cascade = { ALL }, fetch = LAZY, mappedBy = "post")
    private Set<Comment> comments = new HashSet<Comment>();
...

实体评论:

@Entity
@Table(name = "comment")
public class Comment implements Serializable {
    @Id
    @GeneratedValue(strategy = IDENTITY)
    @Column(name = "comment_id", unique = true, nullable = false)
    private Integer id; 

    @Column(name = "comment_title", length=300, unique = false, nullable = false)
    private String title;

    @Column(name = "comment_date", unique = false, nullable = false)
    private Date date;

    @Column(name = "comment_content", length=600, unique = false, nullable = false)
    private String content;

    @ManyToOne
    @JoinColumn (name = "user_id", referencedColumnName="user_id", nullable = false)
    private User user;

    @ManyToOne
    @JoinColumn (name = "post_id", referencedColumnName="post_id", nullable = false)
    private Post post;
...

实体用户:

@Entity
@Table(name = "user")
public class User implements Serializable {
    @Id
    @GeneratedValue(strategy = IDENTITY)
    @Column(name = "user_id", unique = true, nullable = false)
    private Integer id; 

    @Column(name = "user_name", length=45, unique = false, nullable = false)
    private String name; // "first_name" + ' ' + "last_name"    

    //URL address to user's image 
    @Column(name = "user_image", length=500, unique = false, nullable = true)
    private String image;

    @Column(name = "user_username", length=45, unique = false, nullable = false)
    private String username;

    @Column(name = "user_password", length=45, unique = false, nullable = false)
    private String password;
...

所以，我想创建一个方法，可能在 PostDAO 对象内，看起来像这样:

public <SomeDataTypeFormat???> getPostsSummaries(){

   Query q = em.createNativeQuery("SELECT
        post_title,
        post_summary,
        post_date,
        COUNT(comment_id) AS comment_cnt,
        user.user_name
    FROM
        post
        LEFT JOIN user USING(user_id)
        LEFT JOIN comment USING(post_id)
    GROUP BY
        post_id
    ORDER BY
        comment_cnt DESC");
    ...
}

方法返回数据库中所有三个表的一些字段。 我是否需要创建单独的类并将这些数据存储在该类的对象中？或者 JSON(虽然我还没有使用过它)？

具体做法是什么？对于连接几个表而获得的某些字段，最容易使用并从 servlet 转发到 JSP 的数据格式是什么？

Answer 1

这取决于您的目标；为了将数据传输到浏览器，JSON 和 AJAX 不是一个坏的选择。要将数据获取到 JSP(从 Servlet)，您可能需要 Data Transfer Object (或者可能是不可变的 Value Object )。