fixed strcutre errors

data/1.Java初阶/1.Java概览/1.编辑Java源代码/HelloWorld.json

@@ -2,6 +2,6 @@
   "type": "code_options",
   "author": "ccat",
   "source": "HelloWorld.md",
-    "exercise_id":"1190bb7834904da0b1f20915960714d5",
+  "exercise_id": "1190bb7834904da0b1f20915960714d5",
   "notebook_enable": true
 }
\ No newline at end of file

data/1.Java初阶/10.类和接口/1.类和面向对象/config.json

 {
-  "keywords": [],
+  "keywords": ["class", "类", "面向对象", "oo"],
   "children": [],
   "node_id": "java-0593e0b9c9f74799a204d697f0db488b",
   "export": [

data/1.Java初阶/11.IO初步/1.字节流/config.json

 {
   "node_id": "java-3ea06f6d049d4c079a88747ffd0cc51e",
-  "keywords": [],
+  "keywords": ["字节流", "bytestream"],
   "children": [],
   "export": [
     "bytestream.json"

data/1.Java初阶/11.IO初步/2.File类/config.json

 {
   "node_id": "java-046d129404f14676af135da42fea658b",
-  "keywords": [],
+  "keywords": ["文件", "文件类", "file"],
   "children": [],
   "export": [
     "file.json"

data/1.Java初阶/2.Java的基本语法/1.Java的基本语法格式/app.json

@@ -2,5 +2,6 @@
   "type": "code_options",
   "author": "ccat",
   "source": "app.md",
-  "exercise_id": "f83bb3ca8a7d4070a5cdb850c8745d43"
+  "exercise_id": "f83bb3ca8a7d4070a5cdb850c8745d43",
+  "notebook_enable": true
 }
\ No newline at end of file

data/1.Java初阶/2.Java的基本语法/2.Java中的注释/comment.json

@@ -2,5 +2,6 @@
   "type": "code_options",
   "author": "ccat",
   "source": "comment.md",
-    "exercise_id":"a666420ebe28430dab8ad4bd99306dfb"
+  "exercise_id": "a666420ebe28430dab8ad4bd99306dfb",
+  "notebook_enable": true
 }
\ No newline at end of file

data/1.Java初阶/2.Java的基本语法/3.Java中的关键字/keyword.json

@@ -2,5 +2,6 @@
   "type": "code_options",
   "author": "ccat",
   "source": "keyword.md",
-  "exercise_id": "57b6f2510fde488486f73ab8597370c6"
+  "exercise_id": "57b6f2510fde488486f73ab8597370c6",
+  "notebook_enable": true
 }
\ No newline at end of file

data/1.Java初阶/3.Java中的变量与常量/1.变量的定义/swap.json

@@ -2,5 +2,6 @@
   "type": "code_options",
   "author": "ccat",
   "source": "swap.md",
-    "exercise_id":"accd5c6fca914d69990826e6123de37e"
+  "exercise_id": "accd5c6fca914d69990826e6123de37e",
+  "notebook_enable": true
 }
\ No newline at end of file

data/1.Java初阶/3.Java中的变量与常量/1.变量的定义/vars.json

@@ -2,5 +2,6 @@
   "type": "code_options",
   "author": "ccat",
   "source": "vars.md",
-    "exercise_id":"f990d6473c1c4b0c8947c27681c8f476"
+  "exercise_id": "f990d6473c1c4b0c8947c27681c8f476",
+  "notebook_enable": true
 }
\ No newline at end of file

data/1.Java初阶/3.Java中的变量与常量/3.Java中的常量/solidity.json

@@ -2,5 +2,6 @@
   "type": "code_options",
   "author": "ccat",
   "source": "solidity.md",
-    "exercise_id":"45bc14d503364f999f98e5d2faad2fec"
+  "exercise_id": "45bc14d503364f999f98e5d2faad2fec",
+  "notebook_enable": true
 }
\ No newline at end of file

data/1.Java初阶/3.Java中的变量与常量/4.变量的作用域/scope.json

@@ -2,5 +2,6 @@
   "type": "code_options",
   "author": "ccat",
   "source": "scope.md",
-    "exercise_id":"009d35ca11a24baa809d0eeb5e2f66e2"
+  "exercise_id": "009d35ca11a24baa809d0eeb5e2f66e2",
+  "notebook_enable": true
 }
\ No newline at end of file

data/1.Java初阶/4.Java中的运算符/1.比较运算符/find.json

@@ -2,5 +2,6 @@
   "type": "code_options",
   "author": "ccat",
   "source": "find.md",
-    "exercise_id":"61cca0fdecc34b00b173f4edc575ce48"
+  "exercise_id": "61cca0fdecc34b00b173f4edc575ce48",
+  "notebook_enable": true
 }
\ No newline at end of file

data/1.Java初阶/4.Java中的运算符/1.比较运算符/max.json

@@ -2,5 +2,6 @@
   "type": "code_options",
   "author": "ccat",
   "source": "max.md",
-    "exercise_id":"5025886554e5470e82710ed84735e419"
+  "exercise_id": "5025886554e5470e82710ed84735e419",
+  "notebook_enable": true
 }
\ No newline at end of file

data/1.Java初阶/7.集合/12.遗留的集合/config.json

 {
   "node_id": "java-98b609c0de1544bf955cd3e1996224f7",
-  "keywords": [],
+  "keywords": ["集合", "legacy"],
   "children": [
     {
       "属性映射": {

data/1.Java初阶/7.集合/6.Java集合框架/config.json

 {
   "node_id": "java-af0bf70f564b4ac68a7fadda69d55086",
-  "keywords": [],
+  "keywords": ["集合", "collection"],
   "children": [
     {
       "集合接口与实现分离": {

data/1.Java初阶/9.控制执行流程/1.if-else/ifelse.json

@@ -2,5 +2,6 @@
   "type": "code_options",
   "author": "ccat",
   "source": "ifelse.md",
-    "notebook_enable": false
+  "notebook_enable": false,
+  "exercise_id": "6feafab76cba4d91a083c1dc0b14a80b"
 }
\ No newline at end of file

data/2.Java中阶/6.深入研究容器/1.Collection的功能方法/config.json

 {
   "node_id": "java-20cad95081b4475aaac1c1ebf7af0253",
-  "keywords": [],
+  "keywords": ["容器", "collection", "方法"],
   "children": [],
   "export": [
     "Collection.json"

data/2.Java中阶/7.注解/3.基于注解的单元测试/junit.json

@@ -2,5 +2,6 @@
   "type": "code_options",
   "author": "ccat",
   "source": "junit.md",
-    "notebook_enable": false
+  "notebook_enable": false,
+  "exercise_id": "38a9581c24d9427598c83112d0af0c34"
 }
\ No newline at end of file

data/3.Java高阶/1.行为抽象和Lambda/5.分组/group_by.json

+{
+  "type": "code_options",
+  "author": "ccat",
+  "source": "group_by.md",
+  "notebook_enable": true,
+  "exercise_id": "a2249d4d426c403da4382c62e64f37e5"
+}
\ No newline at end of file

data/tree.json

@@ -433,7 +433,10 @@
                   {
                     "Java集合框架": {
                       "node_id": "java-af0bf70f564b4ac68a7fadda69d55086",
-                      "keywords": [],
+                      "keywords": [
+                        "集合",
+                        "collection"
+                      ],
                       "children": [
                         {
                           "集合接口与实现分离": {
@@ -561,7 +564,10 @@
                   {
                     "遗留的集合": {
                       "node_id": "java-98b609c0de1544bf955cd3e1996224f7",
-                      "keywords": [],
+                      "keywords": [
+                        "集合",
+                        "legacy"
+                      ],
                       "children": [
                         {
                           "属性映射": {
@@ -1037,7 +1043,12 @@
                   {
                     "类和面向对象": {
                       "node_id": "java-0593e0b9c9f74799a204d697f0db488b",
-                      "keywords": [],
+                      "keywords": [
+                        "class",
+                        "类",
+                        "面向对象",
+                        "oo"
+                      ],
                       "children": []
                     }
                   },
@@ -1085,14 +1096,21 @@
                   {
                     "字节流": {
                       "node_id": "java-3ea06f6d049d4c079a88747ffd0cc51e",
-                      "keywords": [],
+                      "keywords": [
+                        "字节流",
+                        "bytestream"
+                      ],
                       "children": []
                     }
                   },
                   {
                     "File类": {
                       "node_id": "java-046d129404f14676af135da42fea658b",
-                      "keywords": [],
+                      "keywords": [
+                        "文件",
+                        "文件类",
+                        "file"
+                      ],
                       "children": []
                     }
                   }
@@ -2028,7 +2046,11 @@
                   {
                     "Collection的功能方法": {
                       "node_id": "java-20cad95081b4475aaac1c1ebf7af0253",
-                      "keywords": [],
+                      "keywords": [
+                        "容器",
+                        "collection",
+                        "方法"
+                      ],
                       "children": []
                     }
                   },

src/tree.py

@@ -326,8 +326,12 @@ class TreeWalker:
 
     def ensure_exercises_meta(self, meta_path, source):
         _, mfile = os.path.split(meta_path)
+        meta = None
         if os.path.exists(meta_path):
-            meta = load_json(meta_path)
+            with open(meta_path) as f:
+                content = f.read()
+            if content:
+                meta = json.loads(content)
                 if "exercise_id" not in meta:
                     meta["exercise_id"] = uuid.uuid4().hex
                 if "notebook_enable" not in meta:
@@ -338,7 +342,7 @@ class TreeWalker:
                     meta["author"] = user_name()
                 if "type" not in meta:
                     meta["type"] = "code_options"
-        else:
+            if meta is None:
                 meta = {
                     "type": "code_options",
                     "author": user_name(),