JSF：绝对需要将昂贵的业务逻辑放入访问器方法中。如何避免多次调用这种昂贵的BL

发布于 2024-11-08 03:09:32 字数 1180 浏览 0 评论 0原文

这是我的困境，我知道在 JSF 中访问器方法将被多次调用，因此我知道不要将昂贵的业务逻辑（如数据库访问）放在访问器方法中。如果我绝对必须将业务逻辑放入我的访问器中怎么办？这种情况我该怎么办？以下是我的困境的高级布局。（Mojarra 2.1，GF 3.1）

<h:dataTable value="#{myBean.comments}" var="item1">
    <h:column>
          #{item1.name} says: #{item1.comment}
          <h:dataTable value="#{myBean.handleReplies(item1)}" var="item2">
               <h:column>
                   #{item2.name} replies: #{item2.comment}
               </h:column>
          </h:dataTable>    
    </h:column>
</h:dataTable>    

@ManagedBean
@ViewScoped
public void myBean(){
    private List<Comment> comments;

    @EJB
    private MyEJB myEJB;

    @PostConstruct
    public void init(){
        comments = myEJB.getAllComments();
    }

    //getters and setters for List<Comment> comments

    public List<Comment> handleReplies(Comment comment){
         //Return a List of replies of the comment
         return myEJB.getRepliesFromComment(comment); 
    }
}

如您所见，inner 数据表采用outer 数据表的item 来生成其列表。有没有办法以某种方式停止 handleReplies() 被多次调用，因为此访问器方法访问数据库。

原文

Here is my dilemma, I know in JSF the accessor method will get call mutilple times, therefore I know not to put expensive business logic (like DB access) in accessor method. What if I absolutely have to put business logic into my accessor. What should I do in this case? Below are a high level layout of my dilemma. (Mojarra 2.1, GF 3.1)

<h:dataTable value="#{myBean.comments}" var="item1">
    <h:column>
          #{item1.name} says: #{item1.comment}
          <h:dataTable value="#{myBean.handleReplies(item1)}" var="item2">
               <h:column>
                   #{item2.name} replies: #{item2.comment}
               </h:column>
          </h:dataTable>    
    </h:column>
</h:dataTable>    

@ManagedBean
@ViewScoped
public void myBean(){
    private List<Comment> comments;

    @EJB
    private MyEJB myEJB;

    @PostConstruct
    public void init(){
        comments = myEJB.getAllComments();
    }

    //getters and setters for List<Comment> comments

    public List<Comment> handleReplies(Comment comment){
         //Return a List of replies of the comment
         return myEJB.getRepliesFromComment(comment); 
    }
}

As you can see, the inner dataTable take in the item of the outer dataTable to generate its List. Is there a way for somehow stop handleReplies() to be called multiple times, since this accessor method access DB.

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讽刺将军 2024-11-15 03:09:32

使用 HashMap 创建视图范围的缓存怎么样？

类似于：

private Map<Comment, List<Comment>> replies = new HashMap<Comment, List<Comment>>();

public List<Comment> handleReplies(Comment comment){
    if (!replies.containsKey(comment)) {
        replies.put(comment, myEJB.getRepliesFromComment(comment));
    }

    return replies.get(comment);
}

这样，您的视图范围 bean 会存储先前的请求结果，并在请求已完成时返回它们。如果没有，则提出请求。最终没有重复请求！

How about using a HashMap to create a view-scoped cache?

Something like:

private Map<Comment, List<Comment>> replies = new HashMap<Comment, List<Comment>>();

public List<Comment> handleReplies(Comment comment){
    if (!replies.containsKey(comment)) {
        replies.put(comment, myEJB.getRepliesFromComment(comment));
    }

    return replies.get(comment);
}

This way, your view-scoped bean store previous request results, and returns them if the request has already been done. If it hasn't, the request is made. In the end, no duplicate request!

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迷鸟归林 2024-11-15 03:09:32

您还可以让 JPA 执行延迟加载和缓存工作（使用适当的二级缓存）。

假设您的 Comment 实体如下所示，

@Entity
@NamedQuery(name="Comment.list", query="SELECT c FROM Comment c WHERE c.parent IS NULL")
public class Comment implements Serializable {

    @ManyToOne(optional=false)
    private Comment parent;

    @OneToMany(mappedBy="parent", fetch=LAZY, cascade=ALL);
    private List<Comment> children;

    // ...
}

您可以使用 #{comment.children} 来（懒惰地）获取 中的子级。。

You can also just let JPA do the lazy loading and caching job (with a proper second level cache).

Assuming that your Comment entity look like this

@Entity
@NamedQuery(name="Comment.list", query="SELECT c FROM Comment c WHERE c.parent IS NULL")
public class Comment implements Serializable {

    @ManyToOne(optional=false)
    private Comment parent;

    @OneToMany(mappedBy="parent", fetch=LAZY, cascade=ALL);
    private List<Comment> children;

    // ...
}

You could just use #{comment.children} to (lazily) get the children in a <h:dataTable>.

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