如何访问从 servlet 传递的 .jsp 中的变量？

Question

我有一个对象列表，我从 servlet 传递到 jsp，如下所示：

List<LifeEvent> lifeEvents = null;
if (initialDate.equals(finalDate))
lifeEvents = ontAccess.getPhotosOfTheDay(initialDate,null);
else
lifeEvents = ontAccess.getPhotosOfTheDay(initialDate,finalDate);

request.setAttribute("lifeEvents", lifeEvents);

LifeEvent 类具有以下全局变量：

@Id
    @GeneratedValue(strategy = GenerationType.TABLE)
    private long id;

    @OneToOne(optional = true, cascade = {CascadeType.ALL})
    @JoinColumn
    private IDContainer idContainer;

    @ManyToOne(optional = true, cascade = {CascadeType.PERSIST, CascadeType.REFRESH, CascadeType.MERGE})
    private Place place;

    @OneToMany(cascade = {CascadeType.PERSIST, CascadeType.REFRESH, CascadeType.MERGE}, fetch = FetchType.EAGER)
    @Fetch(value = FetchMode.SUBSELECT)
    private List<Comment> comments;

    @ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.REFRESH, CascadeType.MERGE}, fetch = FetchType.EAGER)
    @Fetch(value = FetchMode.SUBSELECT)
    @JoinTable(name = "lifeevent_withFriends")
    private List<Friend> withFriends;

    @ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.REFRESH, CascadeType.MERGE}, fetch = FetchType.EAGER)
    @Fetch(value = FetchMode.SUBSELECT)
    @JoinTable(name = "lifeevent_likedBy")
    private List<Friend> likedBy;

    private String text;

    private boolean highlyRelevant = false;


    @ManyToOne(optional=true, cascade = {CascadeType.PERSIST, CascadeType.REFRESH, CascadeType.MERGE})
    @JoinColumn
    private MediaObject mediaObject;


    private boolean archived=false;

例如 Place 对象有以下全局变量：

@Id
    @GeneratedValue(strategy = GenerationType.TABLE)
    private long id;

    @OneToOne(optional = true, cascade = {CascadeType.ALL})
    @JoinColumn
    protected IDContainer idContainer;

    private boolean isPublic;

    private String placeName;

    @ManyToOne
    private MediaObject media;

    @ManyToOne(optional = true, cascade = {CascadeType.PERSIST, CascadeType.REFRESH, CascadeType.MERGE})
    private Location location;

    private boolean archived=false;

在 .jsp 页面中，我想显示有关 LifeEvent 的信息，例如，我希望访问 LifeEvent 类中 Place 内的地名。我怎样才能访问它？

只是 ${lifeEvent.place.placeName} 吗？

Answer 1

零是一个非常好的数字。不要将List 初始化为null。将其初始化为一个空列表。 isPublic 不是布尔值的好名字。

由于您已将lifeEvents 设为请求属性，因此您可以使用JSTL c:forEach JSP 标记来遍历列表：

<table>
    <thead>
        <tr>
            <th>Place Name</th>
            <th>Public</th>
        </tr>
    </thead>
    <tfoot>
        <tr>
            <th colspan="2">${fn:length(lifeEvents)} Events</th>
        </tr>
    </tfoot>
    <tbody>
        <c:forEach items="${lifeEvents}" var="event">
            <tr>
                <td>${event.place.placeName}</td>
                <td>${event.place.isPublic}</td>
            </tr>
        </c:forEach>
     </tbody>
</table>

当然，您需要导入 JSTL 核心标签库。