Exception while implementing LazyModel for primefaces datalist - spring

Question

I am trying to implement the lazy loading model for the primefaces datalist similar to datatable as shown here.
My initial code with the normal AJAX pagination feature works absolutely fine. However, when I try using the lazy loading model, I get the exception below when the page loads :
com.sun.faces.application.view.FaceletViewHandlingStrategy handleRenderException
SEVERE: Error Rendering View[/pages/index.xhtml]
java.io.NotSerializableException: java.util.ArrayList$SubList
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1180)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1528)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1493)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1416)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1528)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1493)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1416)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:346)
at java.util.HashMap.writeObject(HashMap.java:1100)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:975)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1480)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1416)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1528)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1493)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1416)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
at java.io.ObjectOutputStream.writeArray(ObjectOutputStream.java:1362)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1170)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:346)
at java.util.HashMap.writeObject(HashMap.java:1100)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:975)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1480)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1416)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:346)
at com.sun.faces.renderkit.ClientSideStateHelper.doWriteState(ClientSideStateHelper.java:325)
at com.sun.faces.renderkit.ClientSideStateHelper.writeState(ClientSideStateHelper.java:173)
at com.sun.faces.renderkit.ResponseStateManagerImpl.writeState(ResponseStateManagerImpl.java:122)
at com.sun.faces.application.StateManagerImpl.writeState(StateManagerImpl.java:166)
at com.sun.faces.application.view.WriteBehindStateWriter.flushToWriter(WriteBehindStateWriter.java:225)
at com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:418)
at com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:131)
at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:121)
at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:139)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:594)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:929)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1002)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:585)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
at java.lang.Thread.run(Thread.java:722)
Here's the code of index.html
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
xmlns:ui="http://java.sun.com/jsf/facelets"
xmlns:h="http://java.sun.com/jsf/html"
xmlns:f="http://java.sun.com/jsf/core"
xmlns:p="http://primefaces.org/ui">
<ui:composition template="/pages/templates/template.xhtml">
<ui:define name="content">
<h:form prependId="false" id="form">
<p:dataList value="#{movies.lazyMovieModel}" var="movie" id="movies" paginator="true" rows="10"
paginatorTemplate="{FirstPageLink} {PreviousPageLink} {PageLinks} {NextPageLink} {LastPageLink}"
type="none" paginatorAlwaysVisible="false" lazy="true">
<h:outputText value="#{movie.movieName}, #{movie.releaseYear}" style="margin-left:10px">
</h:outputText>
<br/>
</p:dataList>
</h:form>
</ui:define>
</ui:composition>
</html>
MovieListBean.java
import org.primefaces.model.LazyDataModel;
import com.clixflix.enitities.Movie;
import com.clixflix.jsf.extensions.LazyMovieDataModel;
#ManagedBean(name = "movies")
#ViewScoped
public class MovieListBean extends BaseBean implements Serializable
{
private static final long serialVersionUID = -5719443344065177588L;
private LazyDataModel<Movie> lazyMovieModel;
#PostConstruct
public void initialize() {
lazyMovieModel = new LazyMovieDataModel();
}
public LazyDataModel<Movie> getLazyMovieModel()
{
List<Movie> movieList = getServiceLocator().getMovieService().getMovieList();
((LazyMovieDataModel) lazyMovieModel).setMovieList(movieList);
return lazyMovieModel;
}
}
LazyMovieDataModel.java (LazyModel implementation)
public class LazyMovieDataModel extends LazyDataModel<Movie>
{
private static final long serialVersionUID = 8745562148994455749L;
private List<Movie> movieList;
public LazyMovieDataModel() {
this.movieList = Collections.emptyList();
}
#Override
public List<Movie> load(int first, int pageSize, String sortField, SortOrder sortOrder, Map<String, String> filters) {
// Sorting
if (null != sortField) {
LazySorter sorter = new LazySorter(sortField, sortOrder);
Collections.sort(movieList, sorter);
sorter = null;
}
// RowCount
int rowCount = movieList.size();
this.setRowCount(rowCount);
// Pagination
if (rowCount > pageSize) {
return movieList.subList(first, (first + pageSize));
}
else {
return movieList;
}
}
private class LazySorter implements Comparator<Movie>
{
private String sortField;
private SortOrder sortOrder;
LazySorter(String sortField, SortOrder sortOrder) {
this.sortField = sortField;
this.sortOrder = sortOrder;
}
#SuppressWarnings("unchecked")
#Override
public int compare(Movie movie1, Movie movie2) {
Object value1 = null, value2 = null;
try {
value1 = Movie.class.getField(this.sortField).get(movie1);
value2 = Movie.class.getField(this.sortField).get(movie2);
int value = ((Comparable<Object>) value1).compareTo(value2);
return SortOrder.ASCENDING.equals(sortOrder) ? value : -1 * value;
}
catch (IllegalArgumentException | IllegalAccessException | NoSuchFieldException | SecurityException e) {
e.printStackTrace();
return 0;
}
}
}
public void setMovieList(List<Movie> movieList) {
this.movieList = movieList;
}
}
I am assuming the exception is at this line:
return movieList.subList(first, (first + pageSize));
Could anyone please guide me as to what am I missing?
Also, I observe in the logs, that when I use the lazymodel, the DB gets queried three times but when I use the normal AJAX pagination, the DB is queried only once :|
UPDATE: I figured out the reason for the DB being queried 3 times. It was because I was calling my service in the getter of the LazyModel instead of only in the load method.
I made the following changes in the classes:
LazyMovieDataModel.java
public class LazyMovieDataModel extends LazyDataModel<Movie>
{
private static final long serialVersionUID = 8745562148994455749L;
public LazyMovieDataModel() {}
#Override
public List<Movie> load(int first, int pageSize, String sortField, SortOrder sortOrder, Map<String, String> filters) {
List<Movie> movieList = getServiceLocator().getMovieService().getMovieList(first, (first + pageSize));
// RowCount
int rowCount = ((Number)getServiceLocator().getMovieService().getMovieCount()).intValue();
this.setRowCount(rowCount);
}
}
LazyModel getter in MovieListBean.java
/* Removed PostConstruct init method */
public LazyDataModel<Movie> getLazyMovieModel()
{
return lazyMovieModel;
}
The above changes work fine on the initial page load. However, when I hit the next page button (or any pagination button) I get an NPE for getServiceLocator() in the load method.
The serviceLocator is a protected access modified managed property inherited from BaseBean and injected using Spring.
Any reason why the getter returns null on subsequent invokes ???

Answer 1

ArrayList$SubList is a problem. The subList returned does not implement serializable.
Try using:
return new ArrayList(movieList.subList(first, (first + pageSize)));

Answer 2

Same problem in this link.There are 2 load methods in LazyDataModel:
public List<T> load(int first, int pageSize, String sortField, SortOrder sortOrder, Map<String,String> filters) {
throw new UnsupportedOperationException("Lazy loading is not implemented.");
}
public List<T> load(int first, int pageSize, List<SortMeta> multiSortMeta,Map<String,String> filters) {
throw new UnsupportedOperationException("Lazy loading is not implemented.");
}
This is where the error is thrown. You are using multisort, so you should override the second.Default method is the first one.