新增 TreeBuilder 工具类。

src/main/java/xyz/zhouxy/plusone/commons/util/TreeBuilder.java

@@ -0,0 +1,39 @@
+package xyz.zhouxy.plusone.commons.util;
+
+import java.util.Collection;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.function.BiConsumer;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+
+public class TreeBuilder<T, TIdentity> {
+    private final Collection<T> nodes;
+    private final Function<T, TIdentity> identityGetter;
+    private final Function<T, Optional<TIdentity>> parentIdentityGetter;
+    private final BiConsumer<T, T> addChildrenMethod;
+
+    public TreeBuilder(Collection<T> nodes, Function<T, TIdentity> identityGetter,
+            Function<T, Optional<TIdentity>> parentIdentityGetter, BiConsumer<T, T> addChildren) {
+        this.nodes = nodes;
+        this.identityGetter = identityGetter;
+        this.parentIdentityGetter = parentIdentityGetter;
+        this.addChildrenMethod = addChildren;
+    }
+
+    public List<T> buildTree() {
+        Map<TIdentity, T> identityNodeMap = MoreCollections.toHashMap(nodes, identityGetter);
+        List<T> result = this.nodes.stream()
+                .filter(node -> !this.parentIdentityGetter.apply(node).isPresent())
+                .collect(Collectors.toList());
+        for (T node : this.nodes) {
+            Optional<TIdentity> parentIdentity = parentIdentityGetter.apply(node);
+            if (parentIdentity.isPresent() && identityNodeMap.containsKey(parentIdentity.get())) {
+                T parentNode = identityNodeMap.get(parentIdentity.get());
+                addChildrenMethod.accept(parentNode, node);
+            }
+        }
+        return result;
+    }
+}