Vaadin - Lazy Query Container - lazy-loading

Question

I'm doing my project in Vaadin 7. I need to implement a Lazy Query Container for a Treetable. I will get data for the Treetable from a web service.
Could someone please show how to use a Lazy Query Container with a web service as my data source?
Please let me know the steps required to implement this or show sample code to get me started.

Answer 1

There is good documentation for LQC here: https://vaadin.com/wiki/-/wiki/Main/Lazy%20Query%20Container
The examples in documentation are implementing MovieQuery using javax.persistence API, but it might be easier to use the simple MockQuery example as basis and replace the actual data fetching with webservice calls.

Answer 2

Have a look at the following lazy loading Hierarchical interface. All data is read from a webservice IViewService. The example uses the Tree component but it also works for TreeTable.
It's very important to store all elements in a local structure (in my case in the HashMap hierarchy), do not read elements multiple times this does not work. I think because Vaadin does not use equals() and hashCode().
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import com.softmodeler.common.CommonPlugin;
import com.softmodeler.model.OutputNode;
import com.softmodeler.service.IViewService;
import com.vaadin.data.Container.Hierarchical;
import com.vaadin.data.Item;
import com.vaadin.data.Property;
import com.vaadin.data.util.BeanItem;
/**
* #author Flavio Donzé
* #version 1.0
*/
public class OutputNodeHierachical implements Hierarchical {
private static final long serialVersionUID = 8289589835030184018L;
/** the view service */
private IViewService service = CommonPlugin.getService(IViewService.class);
/** collection of all root nodes */
private List<OutputNode> rootNodes = null;
/** parent=>children mapping */
private Map<OutputNode, List<OutputNode>> hierarchy = new HashMap<>();
/**
* constructor
*
* #param rootNodes collection of all root nodes
*/
public OutputNodeHierachical(List<OutputNode> rootNodes) {
this.rootNodes = Collections.unmodifiableList(rootNodes);
addToHierarchy(rootNodes);
}
#Override
public Collection<?> getChildren(Object itemId) {
try {
List<OutputNode> children = hierarchy.get(itemId);
if (children == null) {
OutputNode node = (OutputNode) itemId;
children = service.getChildren(node.getNodeId(), false);
hierarchy.put(node, children);
// add children to hierarchy, their children will be added on click
addToHierarchy(children);
}
return children;
} catch (Exception e) {
VaadinUtil.handleException(e);
}
return null;
}
/**
* add each element to the hierarchy without their children hierarchy(child=>null)
*
* #param children elements to add
*/
private void addToHierarchy(List<OutputNode> children) {
for (OutputNode child : children) {
hierarchy.put(child, null);
}
}
#Override
public boolean areChildrenAllowed(Object itemId) {
return !((OutputNode) itemId).getChilds().isEmpty();
}
#Override
public boolean hasChildren(Object itemId) {
return !((OutputNode) itemId).getChilds().isEmpty();
}
#Override
public Object getParent(Object itemId) {
String parentId = ((OutputNode) itemId).getParentId();
for (OutputNode node : hierarchy.keySet()) {
if (node.getNodeId().equals(parentId)) {
return node;
}
}
return null;
}
#Override
public Collection<?> rootItemIds() {
return rootNodes;
}
#Override
public boolean isRoot(Object itemId) {
return rootNodes.contains(itemId);
}
#Override
public Item getItem(Object itemId) {
return new BeanItem<OutputNode>((OutputNode) itemId);
}
#Override
public boolean containsId(Object itemId) {
return hierarchy.containsKey(itemId);
}
#Override
public Collection<?> getItemIds() {
return hierarchy.keySet();
}
#Override
public int size() {
return hierarchy.size();
}
#Override
public boolean setParent(Object itemId, Object newParentId) throws UnsupportedOperationException {
throw new UnsupportedOperationException();
}
#Override
public boolean setChildrenAllowed(Object itemId, boolean areChildrenAllowed) throws UnsupportedOperationException {
throw new UnsupportedOperationException();
}
#Override
public Item addItem(Object itemId) throws UnsupportedOperationException {
throw new UnsupportedOperationException();
}
#Override
public Object addItem() throws UnsupportedOperationException {
throw new UnsupportedOperationException();
}
#Override
public boolean removeItem(Object itemId) throws UnsupportedOperationException {
throw new UnsupportedOperationException();
}
#Override
public boolean removeAllItems() throws UnsupportedOperationException {
throw new UnsupportedOperationException();
}
#Override
public Class<?> getType(Object propertyId) {
throw new UnsupportedOperationException();
}
#Override
public Collection<?> getContainerPropertyIds() {
throw new UnsupportedOperationException();
}
#Override
public Property<?> getContainerProperty(Object itemId, Object propertyId) {
throw new UnsupportedOperationException();
}
#Override
public boolean addContainerProperty(Object propertyId, Class<?> type, Object defaultValue) throws UnsupportedOperationException {
throw new UnsupportedOperationException();
}
#Override
public boolean removeContainerProperty(Object propertyId) throws UnsupportedOperationException {
throw new UnsupportedOperationException();
}
}
Adding the container to the Tree like this:
OutputNodeHierachical dataSource = new OutputNodeHierachical(rootNodes);
Tree mainTree = new Tree();
mainTree.setSizeFull();
mainTree.setContainerDataSource(dataSource);
mainTree.addItemClickListener(new ItemClickListener() {
private static final long serialVersionUID = -413371711541672605L;
#Override
public void itemClick(ItemClickEvent event) {
OutputNode node = (OutputNode) event.getItemId();
openObject(node.getObjectId());
}
});