SelectedItem return null when hit the NEXT page or Submit

Question

Hello All,
I try to add the paging to the open source Alfresco content management. We need to process a large dataset (e.g. > 50K files) so after we gather a list of data files we display them with the checkbox and each checkbox has default checked status.
If the value="#{FixItemList.selectedItems} is omitted in the <h:selectManyCheckbox> then the paging is fine when hitting the NEXT page or Submit button. If we set the value in the selectManyCheckbox then it returns null for selectedItems.
Would please point out what I have done wrong? Appreciate for all yours helps.
This is the managed bean object.
public class ToolsContext
     private FixItemList fixItemList;
     private ToolsContext()
          this.fixItemList = new FixItemList();
     public void addFix(Fix fix) {
          if(fix != null) {               
               fixItemList.addFixItem(new SelectItem(fix, fix.getPath(), fix.getDetails(), false));
               fixItemList.addFixSelectedItems("" + fix + "");
public class FixItemList implements Serializable
     private static final long serialVersionUID = 123784764562L;          
     private List<SelectItem> items;
     private List<String> selectedItems;
     private int displayItemPerPage;
     public FixItemList() {
          displayItemPerPage = 100;
          items = new ArrayList<SelectItem>();
          selectedItems = new ArrayList<String>();
     public void setItems(List<SelectItem> items) {
          this.items = items;
     public List<SelectItem> getItems() {
          return this.items;          
     public int getItemsSize() {
          return this.items.size();
     public int getDisplayItemPerPage() {
          return this.displayItemPerPage;
     public void setDisplayItemPerPage(int displayItemPerPage) {
          this.displayItemPerPage = displayItemPerPage;
     public void addFixItem(SelectItem selectItem) {          
          items.add(selectItem);
     public List<String> getSelectedItems() {
          return selectedItems;
     public void setSelectedItems(List<String> selectedItems) {
          this.selectedItems = selectedItems;
     public void addFixSelectedItems(String selectedItem) {          
          selectedItems.add(selectedItem);
}My faces-config.xml
    <managed-bean>
     <description>
        This bean is to display in the Web Project tool as the pagination. HOPEFULLY SO
     </description>
     <managed-bean-name>FixItemList</managed-bean-name>
     <managed-bean-class>org.alfresco.module.websitetools.util.FixItemList</managed-bean-class>
     <managed-bean-scope>session</managed-bean-scope>
    </managed-bean>The JSP page.
<%@ taglib uri="http://java.sun.com/jsf/html" prefix="h" %>
<%@ taglib uri="http://java.sun.com/jsf/core" prefix="f" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ taglib uri="/WEB-INF/alfresco.tld" prefix="a" %>
<%@ taglib uri="/WEB-INF/repo.tld" prefix="r" %>
<%@ taglib uri="/WEB-INF/wcm.tld" prefix="w" %>
<w:avmList id="files-list" viewMode="details" pageSize="#{FixItemList.displayItemPerPage}" styleClass="recordSet"
headerStyleClass="recordSetHeader" rowStyleClass="recordSetRow" altRowStyleClass="recordSetRowAlt" width="100%"
value="#{FixItemList.items}" var="row">
<%-- checkbox column --%>
<a:column id="col1" primary="true" width="5" style="padding:2px;text-align:left">
   <h:selectManyCheckbox id="wpt" value="#{FixItemList.selectedItems}">
        <f:selectItem itemLabel="#{row.label}" itemValue="#{row.value}" />
   </h:selectManyCheckbox>
</a:column>
<%-- file name column --%>
<a:column id="col2" primary="true" width="50%" style="padding:2px;text-align:left">
     <h:outputText value="#{row.description}" />
</a:column>
<a:dataPager id="pager1" styleClass="pager" />
</w:avmList>When I hit the NEXT page the #FixItemList.selectedItem return null. We use myface version 1.1.5. And below is the stack error
SEVERE: Servlet.service() for servlet Faces Servlet threw exception
java.lang.NullPointerException
     at javax.faces.component._SelectItemsIterator.hasNext(_SelectItemsIterator.java:73)
     at javax.faces.component.UISelectMany.validateValue(UISelectMany.java:268)
     at javax.faces.component.UIInput.validate(UIInput.java:354)
     at javax.faces.component.UISelectMany.validate(UISelectMany.java:297)
     at javax.faces.component.UIInput.processValidators(UIInput.java:184)
     at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:627)
     at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:627)
     at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:627)
     at javax.faces.component.UIForm.processValidators(UIForm.java:73)
     at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:627)
     at javax.faces.component.UIViewRoot.processValidators(UIViewRoot.java:149)
     at org.apache.myfaces.lifecycle.ProcessValidationsExecutor.execute(ProcessValidationsExecutor.java:32)
     at org.apache.myfaces.lifecycle.LifecycleImpl.executePhase(LifecycleImpl.java:95)
     at org.apache.myfaces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:70)
     at javax.faces.webapp.FacesServlet.service(FacesServlet.java:139)
     at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
     at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
     at org.alfresco.web.app.servlet.AuthenticationFilter.doFilter(AuthenticationFilter.java:104)Appreciate for all yours helps,
Anh

Answer 1

I put the print out statement in the _SelectItemsIterator and found out that the selected item's value doesn't binding. How would I be able to select an item? Attached is the code with debug print out in the SelectItemsIterator.
Would some one please point me a direction? Appreciate.
    public boolean hasNext()
        if(_nextItem != null)
            return true;
        if(_nestedItems != null)
            if(_nestedItems.hasNext())
                return true;
            _nestedItems = null;
        if(_childs.hasNext())
            UIComponent child = (UIComponent)_childs.next();
            getLogger().debug("-----_SelectItemsIterator---child is UIComponent---" + child.getChildCount());
            getLogger().debug("-----_SelectItemsIterator---child is UIComponent---" + child.getAttributes());
            Map m = child.getAttributes();
            Set s = m.keySet();
            Iterator i= s.iterator();
            while (i.hasNext()) {                 
                 getLogger().debug("value  = " + m.get(i.next()));
            if(child instanceof UISelectItem)
                 UISelectItem uiSelectItem = (UISelectItem)child;
                Object item = uiSelectItem.getValue();
                getLogger().debug("-----_SelectItemsIterator---child is UISelectItem---getValue()--" + item);
                if(item == null)
                    Object itemValue = ((UISelectItem)child).getItemValue();
                    String label = ((UISelectItem)child).getItemLabel();
                    String description = ((UISelectItem)child).getItemDescription();
                    boolean disabled = ((UISelectItem)child).isItemDisabled();
                    if(label == null)
                        label = itemValue.toString(); //////////////////////IT THROWS THE EXCEPTION HERE, BECAUSE THE
                                                             ///itemValue is null
                    item = new SelectItem(itemValue, label, description, disabled);
                    getLogger().debug("-----_SelectItemsIterator---create item - label---" + label);
                    getLogger().debug("-----_SelectItemsIterator---create item - descp---" + description);
                    getLogger().debug("-----_SelectItemsIterator---create item - disable---" + disabled);
                    getLogger().debug("-----_SelectItemsIterator---create item - itemValue--" + itemValue);
                }