Java ArrayList 在两次用户交互之间变为空？

Question

我正在使用 JDeveloper 开发一个在 Weblogic Server 12c 上运行的 ADF 融合应用程序。

该应用程序包含一个 JSF 页面，其中包括一个文件输入、一个 table 和一个按钮。用户上传文件后，它会被解析，结果按预期显示在 table 中。用户的下一步是单击按钮将解析结果保存到数据库（通过支持 bean）。

这些是 JSF 文档中提到的元素：

<af:inputFile label="file" 
              id="if1"
              valueChangeListener="#{ResultMatching.valueChangeListener}"
              binding="#{ResultMatching.bindingInputFileCSV}"/>

<af:button text="upload" 
           id="b1"
           action="#{ResultMatching.readFile}"
           binding="#{ResultMatching.bindingButtonReadFile}"/>    

<af:table var="row" 
          rowBandingInterval="0" 
          id="t3"
          value="#{ResultMatching.Results}"
          binding="#{ResultMatching.bindingTableResults}"
          fetchSize="32" 
          width="800"                        
          partialTriggers="::b1 ::b21">
    <!--column definitions--> 
</af:table>

<af:button id="b21"
           text="save"
           action="#{ResultMatching.saveResults}"/>

这些是支持 bean 中的连贯方法 ResultMatching.java:

private ArrayList<Result> Results= new ArrayList<Result>();
private RichTable bindingTableResults;

public void readFile() {
            
    Results.clear();
                    
    if (fileInputStream != null) {
        for (HashMap<String, String> dataSet : FileHandler.parseCFFile(fileInputStream)) {          
            Result r = new Result("values from the dataSet");
            Results.add(r);
        }
        matchResults();
    } else {
        String msg = "No file was selected for upload";
        FacesContext.getCurrentInstance().addMessage(
            null, new FacesMessage(FacesMessage.SEVERITY_INFO,msg, msg));
    }
}

private void matchResults() {
    
    //very complicated matching logic

    bindingTableResults.setValue(Results);
    AdfFacesContextImpl.getCurrentInstance().addPartialTarget(bindingTableResults);
    System.out.println(Results.size()); //prints the correct amount of results like in the file
}

public void saveResults() {
    if (Results.isEmpty()) {
        System.out.println("Results is empty!");
        return;
        //here is where I end up
        //i did no other GUI interaction meanwhile
        //neither has the getter nor setter of Results been called
        //why is it suddenly empty? Where are my objects???
    }
    for(Result r : Results){
        //as Results is empty this loop always gets skipped
        //and so does the actual update statement
    }
}

bean 是视图范围的。有什么想法我的结果去了哪里？提前致谢！

Answer 1

从您的代码来看，ResultMatching bean 似乎在请求范围内：

value="#{ResultMatching.Results}"

如果你想访问视图范围内的 bean，EL 应该是

value="#{viewScope.ResultMatching.Results}"

您必须为所有 EL 中每次出现的 ResultMatching 更改 EL。确保在任务流的 viewScope 中定义了该 bean。

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