optimize BuildTree of ClassLoader -t

core/src/main/java/com/taobao/arthas/core/command/klass100/ClassLoaderCommand.java

@@ -449,31 +449,37 @@ public class ClassLoaderCommand extends AnnotatedCommand {
 
     // 以树状列出ClassLoader的继承结构
     private static List<ClassLoaderVO> processClassLoaderTree(List<ClassLoaderVO> classLoaders) {
-        List<ClassLoaderVO> rootClassLoaders = new ArrayList<ClassLoaderVO>();
-        List<ClassLoaderVO> parentNotNullClassLoaders = new ArrayList<ClassLoaderVO>();
+        List<ClassLoaderVO> rootClassLoaders = new ArrayList<>();
+        Map<String, List<ClassLoaderVO>> childMap = new HashMap<>();
+
+        // 分离根节点和非根节点，并构建父子关系映射
         for (ClassLoaderVO classLoaderVO : classLoaders) {
             if (classLoaderVO.getParent() == null) {
                 rootClassLoaders.add(classLoaderVO);
             } else {
-                parentNotNullClassLoaders.add(classLoaderVO);
+                childMap.computeIfAbsent(classLoaderVO.getParent(), k -> new ArrayList<>()).add(classLoaderVO);
             }
         }
 
-        for (ClassLoaderVO classLoaderVO : rootClassLoaders) {
-            buildTree(classLoaderVO, parentNotNullClassLoaders);
+        // 构建树
+        for (ClassLoaderVO root : rootClassLoaders) {
+            buildTree(root, childMap);
         }
+
         return rootClassLoaders;
     }
 
-    private static void buildTree(ClassLoaderVO parent, List<ClassLoaderVO> parentNotNullClassLoaders) {
-        for (ClassLoaderVO classLoaderVO : parentNotNullClassLoaders) {
-            if (parent.getName().equals(classLoaderVO.getParent())){
-                parent.addChild(classLoaderVO);
-                buildTree(classLoaderVO, parentNotNullClassLoaders);
+    private static void buildTree(ClassLoaderVO parent, Map<String, List<ClassLoaderVO>> childMap) {
+        List<ClassLoaderVO> children = childMap.get(parent.getName());
+        if (children != null) {
+            for (ClassLoaderVO child : children) {
+                parent.addChild(child);
+                buildTree(child, childMap);
             }
         }
     }
 
+
     private static Set<ClassLoader> getAllClassLoaders(Instrumentation inst, Filter... filters) {
         Set<ClassLoader> classLoaderSet = new HashSet<ClassLoader>();