JSF：绝对需要将昂贵的业务逻辑放在访问器方法中。如何避免称这个昂贵的BL倍数时间 [英] JSF: Absolutely need to put expensive Business Logic inside accessor method. How to avoid calling this expensive BL multiples time

问题描述

这是我的困境，我知道在JSF中访问器方法会多次调用，因此我知道不要在访问器方法中放置昂贵的业务逻辑（如DB访问）。如果我必须将业务逻辑放入我的访问器中该怎么办？在这种情况下我该怎么办？以下是我的困境的高层次布局。 （Mojarra 2.1，GF 3.1）

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); 
    }
}

如你所见， inner dataTable接受外部 dataTable的项以生成其List。有没有办法以某种方式停止 handleReplies（）被多次调用，因为这个访问器方法访问DB。

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.

推荐答案

如何使用 HashMap 创建视图范围的缓存？

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

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，您的视图范围的bean存储先前的请求结果，并返回它们如果请求已经完成。如果没有，则发出请求。最后，没有重复请求！

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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