数据:

{
                    "children": [
                        {
                            "children": [
                                
                            ],
                            "content": "{\"requestHeaders\":[],\"requestMethod\":\"GET\",\"dataType\":\"X-WWW-FORM-URLENCODED\",\"requestArgs\":[{\"children\":[],\"defaultValue\":\"0\",\"name\":\"start\",\"require\":\"false\",\"type\":\"string\",\"testValue\":\"\"},{\"children\":[],\"defaultValue\":\"1\",\"name\":\"count\",\"require\":\"false\",\"type\":\"string\",\"testValue\":\"\"}],\"description\":\"\",\"contentType\":\"JSON\",\"url\":\"https://mobile.mdaxue.com/bbs-forumdetail-48199.json\",\"responseArgs\":[],\"example\":\"{\\n    \\\"id\\\": \\\"48199\\\", \\n    \\\"name\\\": \\\"海报招贴\\\", \\n    \\\"collegeid\\\": \\\"tsinghua\\\", \\n    \\\"threadnum\\\": \\\"112\\\", \\n    \\\"newthreadnum\\\": \\\"0\\\", \\n    \\\"postnum\\\": \\\"4\\\", \\n    \\\"lastthread_at\\\": \\\"1494143370\\\", \\n    \\\"extra\\\": \\\"poster\\\", \\n    \\\"level\\\": 1, \\n    \\\"collegename\\\": \\\"清华大学\\\", \\n    \\\"subforums\\\": [\\n        {\\n            \\\"id\\\": \\\"48200\\\", \\n            \\\"parentid\\\": \\\"48199\\\", \\n            \\\"name\\\": \\\"租房\\\", \\n            \\\"extra\\\": \\\"poster\\\", \\n            \\\"newthreadnum\\\": \\\"0\\\", \\n            \\\"level\\\": 2\\n        }, \\n        {\\n            \\\"id\\\": \\\"48201\\\", \\n            \\\"parentid\\\": \\\"48199\\\", \\n            \\\"name\\\": \\\"讲座\\\", \\n            \\\"extra\\\": \\\"poster\\\", \\n            \\\"newthreadnum\\\": \\\"0\\\", \\n            \\\"level\\\": 2\\n        }, \\n        {\\n            \\\"id\\\": \\\"48202\\\", \\n            \\\"parentid\\\": \\\"48199\\\", \\n            \\\"name\\\": \\\"活动\\\", \\n            \\\"extra\\\": \\\"poster\\\", \\n            \\\"newthreadnum\\\": \\\"0\\\", \\n            \\\"level\\\": 2\\n        }, \\n        {\\n            \\\"id\\\": \\\"48203\\\", \\n            \\\"parentid\\\": \\\"48199\\\", \\n            \\\"name\\\": \\\"赛事\\\", \\n            \\\"extra\\\": \\\"poster\\\", \\n            \\\"newthreadnum\\\": \\\"0\\\", \\n            \\\"level\\\": 2\\n        }, \\n        {\\n            \\\"id\\\": \\\"48205\\\", \\n            \\\"parentid\\\": \\\"48199\\\", \\n            \\\"name\\\": \\\"失物\\\", \\n            \\\"extra\\\": \\\"poster\\\", \\n            \\\"newthreadnum\\\": \\\"0\\\", \\n            \\\"level\\\": 2\\n        }, \\n        {\\n            \\\"id\\\": \\\"48206\\\", \\n            \\\"parentid\\\": \\\"48199\\\", \\n            \\\"name\\\": \\\"公益\\\", \\n            \\\"extra\\\": \\\"poster\\\", \\n            \\\"newthreadnum\\\": \\\"0\\\", \\n            \\\"level\\\": 2\\n        }, \\n        {\\n            \\\"id\\\": \\\"48207\\\", \\n            \\\"parentid\\\": \\\"48199\\\", \\n            \\\"name\\\": \\\"其他\\\", \\n            \\\"extra\\\": \\\"poster\\\", \\n            \\\"newthreadnum\\\": \\\"0\\\", \\n            \\\"level\\\": 2\\n        }\\n    ], \\n    \\\"admins\\\": null\\n}\",\"status\":\"有效\"}",
                            "id": "8Gbprvxm1",
                            "name": "获取海报二级分类",
                            "parentId": "8GVhbjEbh",
                            "projectId": "LNJIh7zgQ",
                            "sort": 0,
                            "type": "sys.http"
                        }
                    ],
                    "id": "8GVhbjEbh",
                    "name": "海报",
                    "parentId": "LNJMNG5ul",
                    "projectId": "LNJIh7zgQ",
                    "sort": 5,
                    "type": "sys.folder"
}

$json = json_decode($json,1);
var_dump($json);

却打印出了NULL,懵逼