Update V1/V2 NavigationItemImpl to use child supplier

Updates `NavigationItemImpl` constructor to accept a `Supplier` which
supplies a list of children instead of passing the list its self in
the constructor.

This allows the work of constructing a navigation sub-tree to be
deferred and only completed if the `NavigationItem#getChildren()`
method is called.

----
refs adobe#2526

bundles/core/src/main/java/com/adobe/cq/wcm/core/components/internal/models/v1/NavigationItemImpl.java

@@ -17,6 +17,7 @@
 
 import java.util.Collections;
 import java.util.List;
+import java.util.function.Supplier;
 
 import org.jetbrains.annotations.NotNull;
 
@@ -26,21 +27,63 @@
 import com.day.cq.wcm.api.components.Component;
 import com.fasterxml.jackson.annotation.JsonIgnore;
 
+/**
+ * V1 Navigation Item Implementation.
+ */
 public class NavigationItemImpl extends PageListItemImpl implements NavigationItem {
 
-    protected List<NavigationItem> children = Collections.emptyList();
-    protected int level;
-    protected boolean active;
-    private boolean current;
+    /**
+     * List of children.
+     * Note - this will be null until populated from {@link #childrenSupplier} and so should remain private.
+     */
+    private List<NavigationItem> children;
 
-    public NavigationItemImpl(Page page, boolean active, boolean current, @NotNull LinkManager linkManager, int level,
-                              List<NavigationItem> children,
-                              String parentId, Component component) {
+    /**
+     * Navigation level.
+     */
+    private final int level;
+
+    /**
+     * Flag indicating if this navigation item is active.
+     */
+    private final boolean active;
+
+    /**
+     * Flag indicating if this navigation item is for the current page.
+     */
+    private final boolean current;
+
+    /**
+     * Supplier for child navigation items.
+     */
+    @NotNull
+    private final Supplier<@NotNull List<NavigationItem>> childrenSupplier;
+
+    /**
+     * Construct a Navigation Item.
+     *
+     * @param page             The page for which to create a navigation item.
+     * @param active           Flag indicating if the navigation item is active.
+     * @param current          Flag indicating if the navigation item is current page.
+     * @param linkManager      Link manager service.
+     * @param level            Depth level of the navigation item.
+     * @param childrenSupplier The child navigation items supplier.
+     * @param parentId         ID of the parent navigation component.
+     * @param component        The parent navigation {@link Component}.
+     */
+    public NavigationItemImpl(@NotNull final Page page,
+                              final boolean active,
+                              final boolean current,
+                              @NotNull final LinkManager linkManager,
+                              final int level,
+                              @NotNull final Supplier<List<NavigationItem>> childrenSupplier,
+                              final String parentId,
+                              final Component component) {
         super(linkManager, page, parentId, component);
         this.active = active;
         this.current = current;
         this.level = level;
-        this.children = children;
+        this.childrenSupplier = childrenSupplier;
     }
 
     @Override
@@ -62,6 +105,9 @@ public boolean isCurrent() {
 
     @Override
     public List<NavigationItem> getChildren() {
+        if (this.children == null) {
+            this.children = Collections.unmodifiableList(this.childrenSupplier.get());
+        }
         return children;
     }
 

bundles/core/src/main/java/com/adobe/cq/wcm/core/components/internal/models/v2/NavigationItemImpl.java

@@ -17,6 +17,7 @@
 
 import java.util.Collections;
 import java.util.List;
+import java.util.function.Supplier;
 
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
@@ -28,20 +29,63 @@
 import com.day.cq.wcm.api.components.Component;
 import com.fasterxml.jackson.annotation.JsonIgnore;
 
+/**
+ * V2 Navigation Item Implementation.
+ */
 public class NavigationItemImpl extends PageListItemImpl implements NavigationItem {
 
-    protected List<NavigationItem> children = Collections.emptyList();
-    protected int level;
-    protected boolean active;
-    private boolean current;
+    /**
+     * List of children.
+     * Note - this will be null until populated from {@link #childrenSupplier} and so should remain private.
+     */
+    private List<NavigationItem> children;
 
-    public NavigationItemImpl(Page page, boolean active, boolean current, @NotNull LinkManager linkManager, int level, List<NavigationItem> children,
-                              String parentId, Component component) {
+    /**
+     * Navigation level.
+     */
+    private final int level;
+
+    /**
+     * Flag indicating if this navigation item is active.
+     */
+    private final boolean active;
+
+    /**
+     * Flag indicating if this navigation item is for the current page.
+     */
+    private final boolean current;
+
+    /**
+     * Supplier for child navigation items.
+     */
+    @NotNull
+    private final Supplier<@NotNull List<NavigationItem>> childrenSupplier;
+
+    /**
+     * Construct a Navigation Item.
+     *
+     * @param page The page for which to create a navigation item.
+     * @param active Flag indicating if the navigation item is active.
+     * @param current Flag indicating if the navigation item is current page.
+     * @param linkManager Link manager service.
+     * @param level Depth level of the navigation item.
+     * @param childrenSupplier The child navigation items supplier.
+     * @param parentId ID of the parent navigation component.
+     * @param component The parent navigation {@link Component}.
+     */
+    public NavigationItemImpl(@NotNull final Page page,
+                              final boolean active,
+                              final boolean current,
+                              @NotNull final LinkManager linkManager,
+                              final int level,
+                              @NotNull final Supplier<@NotNull List<@NotNull NavigationItem>> childrenSupplier,
+                              final String parentId,
+                              final Component component) {
         super(linkManager, page, parentId, component);
         this.active = active;
         this.current = current;
         this.level = level;
-        this.children = children;
+        this.childrenSupplier = childrenSupplier;
     }
 
     @Override
@@ -63,6 +107,9 @@ public boolean isCurrent() {
 
     @Override
     public List<NavigationItem> getChildren() {
+        if (this.children == null) {
+            this.children = Collections.unmodifiableList(this.childrenSupplier.get());
+        }
         return children;
     }
 

bundles/core/src/test/java/com/adobe/cq/wcm/core/components/internal/models/v2/NavigationItemImplTest.java

@@ -44,7 +44,7 @@ protected void test() {
         when(linkBuilder.build()).thenReturn(link);
         when(linkManager.get(page)).thenReturn(linkBuilder);
         Component component = mock(Component.class);
-        NavigationItemImpl navigationItem = new NavigationItemImpl(page, true, true, linkManager, 0, Collections.emptyList(), "id", component);
+        NavigationItemImpl navigationItem = new NavigationItemImpl(page, true, true, linkManager, 0, Collections::emptyList, "id", component);
         assertEquals(page, navigationItem.getPage());
         assertTrue(navigationItem.isActive());
         assertEquals(Collections.emptyList(), navigationItem.getChildren());