修改后jsf视图不更新后备bean列表属性

Question

I have a strange problem that I could not resolve. I have two entities, Dept and Division . A Dept must belong to a Division . Thus, there is a list of depts for each Division . I also have two views, dept.xhtml and division.xhtml to manage the two entities (CRUD Operations). Both views are backed by DeptManager and DivManager , which are both ViewScoped.

There is a DELETE button on division.xhtml , which is to be disabled when the selected Division has some Dept entities attached to it. When I go to dept.xhtml and change the Division assigned to a particular Dept , the Dept table on dept.xhtml is updated correctly. However, when I navigate to division.xhtml , the Division table does not capture the update. The value in the column showing the number of Depts for the recently-modified Division retains previous values before the modification. This affects the DELETE button on division.xhtml , which might be disabled when it shouldnt be. I have to close the browser and re-open it before the update is captured. I believe this should not be because my navigation causes a new view to be created each time and I have verified that by some print-outs. Here are my codes:

dept.xhtml

<h:body>
        <ui:composition template="adminTemplate.xhtml">
            <ui:define name="content">
                <h:form id="form">
                    <p:dataTable id="dtable" value="#{deptManager.orderedDepts}" var="dept" 
                                 selectionMode="single" selection="#{deptManager.dept}" rowIndexVar="index"  
                                 rowKey="#{dept.deptCode}" scrollable="true" scrollHeight="270">
                        <p:ajax event="rowSelect" listener="#{deptManager.onRowSelect}" update=":form:fields"  />

                        <f:facet name="header">List of Departments</f:facet>
                        <p:column headerText="S/No">#{index+1}</p:column>
                        <p:column headerText="Department Code" sortBy="deptCode">#{dept.deptCode}</p:column>
                        <p:column headerText="Department Name" sortBy="description" >#{dept.description}</p:column>
                        <p:column headerText="Division" sortBy="description" >#{dept.divCode.description}</p:column>
                        <f:facet name="footer">Number of Departments #{deptManager.count}</f:facet>
                    </p:dataTable>
                    <br/><br/>
                    <p:panel  header="Create/Modify Dept" toggleable="true" toggleOrientation="vertical">
                        <p:panelGrid columns="2" id="fields">
                            <p:outputLabel value="Department Code:"/> <p:inputText value="#{deptManager.dept.deptCode}" disabled="true" />
                            <p:outputLabel value="Department Description:"/> <p:inputText value="#{deptManager.dept.description}" />                  
                            <p:outputLabel value="Department Division"/> 
                            <p:selectOneMenu value="#{deptManager.dept.divCode}" converter="omnifaces.SelectItemsConverter">
                                <f:selectItem itemLabel="Select.." noSelectionOption="true" />
                                <f:selectItems value="#{divManager.orderedDivs}" itemLabel="#{division.description}" var="division" itemValue="#{division}" />
                            </p:selectOneMenu>  
                        </p:panelGrid>
                        <p:commandButton ajax="true" actionListener="#{deptManager.createNew}" value="NEW" update="@form" />
                        <p:commandButton ajax="true" actionListener="#{deptManager.deleteDept}" value="DELETE" update="@form" />
                        <p:commandButton ajax="true" actionListener="#{deptManager.saveDept}" value="SAVE" update="@form"  />
                    </p:panel>  

                </h:form>                                
            </ui:define>            
        </ui:composition>
    </h:body>

DeptManager

@Named
@ViewScoped
public class DeptManager implements Serializable{  
    @EJB
    private DeptFacade service;   

    private Dept dept;
    private List<Dept> depts;

    @Inject
    private DivManager divManager;

    public DeptManager() {

    }

    public DivManager getDivManager() {
        return divManager;
    }

    public void setDivManager(DivManager divManager) {
        this.divManager = divManager;
    }

    @PostConstruct
    public void Init(){
        dept = new Dept();
        updateList();
    }

    public void setService(DeptFacade service) {
        this.service = service;
    }

    public Dept getDept() {
        if(dept == null){
            dept = new Dept();
        }
        return dept;
    }

    public void updateList(){
        depts = service.findOrderedAll("Dept", "deptCode");
    }    

    public void setDept(Dept dept) {
        this.dept = dept;
    }

    public int getCount(){
        return service.count();
    }

    public List<Dept> getDepts(){
        return service.findAll();
    }

    public List<Dept> getOrderedDepts(){
        return depts;
    }

    public String createNew(){
        dept = new Dept();
        dept.setDeptCode("");
        dept.setDivCode(null);
        dept.setDescription("");
        return "";
    }

    public String saveDept(){
        //code to create or edit Dept
        updateList();
        divManager.updateList();
        return "dept.xhtml?faces-redirect=true";
    }

    public String deleteDept(){
        if (dept.getDeptCode() == null || dept.getDeptCode().isEmpty()){
            return "dept";
        }
        service.remove(dept);
        dept = new Dept();
        updateList();
        divManager.updateList();
        return "dept";
    }

    public String onRowSelect(SelectEvent event) {  
        dept = (Dept) event.getObject();
        return "";
    } 

    public String navigate(String page){
        return page;
    }

}

division.xhtml

<h:body>
        <ui:composition template="adminTemplate.xhtml">
            <ui:define name="content">
                <h:form id="form">
                    <p:dataTable id="dtable" value="#{divManager.orderedDivs}" var="division" 
                                 selectionMode="single" selection="#{divManager.division}" rowIndexVar="index"  
                                 rowKey="#{division.divCode}" scrollable="true" scrollHeight="300">
                        <p:ajax event="rowSelect" listener="#{divManager.onRowSelect}" update=":form:fields"  />

                        <f:facet name="header">List of Divisions</f:facet>
                        <p:column headerText="S/No">#{index+1}</p:column>
                        <p:column headerText="Division Code" sortBy="divCode">#{division.divCode}</p:column>
                        <p:column headerText="Division Name" sortBy="description" >#{division.description}</p:column>
                        <p:column headerText="No Of Depts"  >#{division.invDeptList.size()}</p:column>
                        <f:facet name="footer">Number of Divisions: #{divManager.count}</f:facet>
                    </p:dataTable>
                    <br/><br/>
                    <p:panel id="fields" header="Create/Modify Division" toggleable="true" toggleOrientation="vertical">
                        <p:panelGrid columns="2" >
                            <p:outputLabel value="Division Code:"/> <p:inputText value="#{divManager.division.divCode}" disabled="true" />
                            <p:outputLabel value="Division Description:"/> <p:inputText value="#{divManager.division.description}" />                  
                        </p:panelGrid>
                        <p:commandButton ajax="true" actionListener="#{divManager.createNew}" value="NEW" update="@form" />
                        <p:commandButton ajax="true" actionListener="#{divManager.deleteDiv}" disabled="#{divManager.division.deptList.size() > 0}" value="DELETE" update="@form" />
                        <p:commandButton ajax="true" actionListener="#{divManager.saveDiv}" value="SAVE" update="@form"  />
                    </p:panel>  

                </h:form>                                
            </ui:define>            
        </ui:composition>
    </h:body>

DivisionManager

@Named
@ViewScoped
public class DivManager implements Serializable{

    @EJB
    private DivFacade service;

    private Div division;   
    private ArrayList<Div> divisions;  
    private boolean newInstance;

    public DivManager() {

    }

    @PostConstruct
    public void Init(){
        newInstance = true;
        division = new Div();
        divisions = new ArrayList<Div>();
        updateList();
        System.out.println("DivManager bean "+this.toString()+" was created");
    }

    public Div getDivision() {
        if(division == null){
            division = new Div();
        }
        return division;
    }

    public void setService(DivFacade service) {
        this.service = service;
    }

    public void updateList(){
        divisions.clear();
        divisions.addAll(service.findOrderedAll("Div", "divCode"));
        // Also tried: divisions = service.findOrderedAll("Div", "divCode"); same result
    }    

    public void setDivision(Div div) {
        this.division = div;
    }

    public int getCount(){
        return service.count();
    }

    public List<Div> getDivisions(){
        return service.findAll();
    }

    public List<Div> getOrderedDivs(){
        if(newInstance){
            updateList();
            newInstance = false;
        }
        return divisions;
    }

    public String createNew(){
        division = new Div();
        division.setDivCode("");        
        division.setDescription("");
        return null;
    }

    public String saveDiv(){
        //code to modify or create Division
        updateList();
        return "division.xhtml?faces-redirect=true";
    }

    public String deleteDiv(){
        if (division.getDivCode() == null || division.getDivCode().isEmpty()){
            return null;
        }
        service.remove(division);
        division = new Div();
        updateList();        
        return null;
    }

    public String onRowSelect(SelectEvent event) {  
        division = (Div) event.getObject();
        return null;
    } 

    public String navigate(String page){
        return page;
    }

}

From my observation, it looks as if the field divisions is cached and new instances of viewScoped bean DivManager get the same list when updateList() is called, unless the session is invalidated. Thus the same List of Divisions in the cache is returned instead of calling the find method on the Session Bean service .

Any idea on what could be causing this? Thanks a lot.

Answer 1

After several days of troubleshooting, I discovered that the EntityManager used by the Stateless Session Bean keeps a cache of Entities retrieved from the database. Therefore, as long as the same Session Bean is assigned to the backing bean of a View fetching those Entities will always return the cached copy, which might not be up-to-date.

To solve the problem, I made use of boolean field newInstance in my backing bean. This field is checked whenever there is a call to fetch the list of Entities . If newInstance is true, I loop through all the entities and refresh them from the database.This way, as long as the View being visited is new (which is verified by checking if the Viewscoped backing bean is new), calling updateList will cause the Entities in the list to be refreshed. Here is the modified code:

@DivManager
public void updateList(){
    service.refreshList(divisions);
}   

And in the SSB service, I have the method:

public void refreshList(List<Div> divisions){
    EntityManager em = getEntityManager();
    for(Div divison : divisions){
        division = em.find(Div.class, division.getDivCode());
        em.refresh(division);
    }
}

Although this solved the problem, I envisage performance issue if the number of records is large. If there is a way to monitor only the entities that have been modified since the last call to refreshList() and refresh only those, it will be better. I am thinking about implementing such a solution.

Hope this will help someone.