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

[使用通用语言处理器、MySQL、MVC、服务包、JSP]如果我从数据库 LEFT JOIN-ing 三个表（DAO 对象的方法内部）读取一些数据，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>();
...

实体注释：

@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;
...

因此，我想创建一个方法，可能在＜code＞PostDAO＜/code＞对象中，它看起来像这样：

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");
    ...
}

方法从数据库中的所有三个表中返回一些字段。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？还是JSON（尽管我还没有使用它）？

做法是什么？对于由于连接多个表而获得的某些字段，从 servlet 到 JSP 的最简单使用和转发的数据格式是什么？

Answer 1

这取决于您的目标；要将数据传输到浏览器，JSON和AJAX是一个不错的选择。要将数据传输到JSP（从Servlet），您可能需要一个数据传输对象（或者可能是一个不可变的值对象）。