英文:
Java: Gson: fromJson: Get element value
问题
以下是翻译好的内容：
我有一个 JSON 字符串：
string jsonString = "{
\"Header\":{
\"ID\": \"103\",
\"DateTime\": \"2020-07-29 09:14:23.802-4:00 1\",
\"PlazaID\": \"01\",
\"Lane\": \"Lane 20\",
\"IPAddr\": \"192.9.0.123\"
},
\"Body\": {
\"EventMsg\": \"Status: Online\",
\"EventNum\": \"99999\"
}
}";
我正试图使用 Gson 从上述 JSON 中获取 ID 的值，但是它给了我一个 NullPointerException。我的代码：
JsonObject jsonObject = new Gson().fromJson(jsonString, JsonObject.class );
//System.out.println("jsonObject: " + jsonObject.toString());
String _ID = jsonObject.get("ID").getAsString();
我不确定我的代码哪里出错了。非常感谢帮助。
编辑：
根据 @Arvind 的建议，我尝试了他的代码，但是我得到了这个错误：
[![查看图片描述][1]][1]
根据 @Arvind 的建议，这段代码有效：
String _ID = jsonObject.get("Header").getAsJsonObject().get("ID").getAsString();
英文:
I have a json string as:
string jsonString = "{"Header":{"ID": "103","DateTime": "2020-07-29 09:14:23.802-4:00 1","PlazaID": "01","Lane": "Lane 20","IPAddr": "192.9.0.123"},"Body": {"EventMsg": "Status: Online","EventNum": "99999"}}";
I am trying to get the value if ID from the above json by using Gson and it gives me NullPointerException. My code:
JsonObject jsonObject = new Gson().fromJson(jsonString, JsonObject.class );
//System.out.println("jsonObject: " + jsonObject.toString());
String _ID = jsonObject.get("ID").getAsString();
I am not sure where the error in my code is. Any help is appreciated.
Edit:
As per @Arvind's suggestion, I tried his code and am getting this error:
As per @Arvind's suggestion, this works:
String _ID = jsonObject.get("Header").getAsJsonObject().get("ID").getAsString();
答案1
得分: 1
让我们首先美化你的 jsonString 以便更清晰地看到：
{
"Header": {
"ID": "103",
"DateTime": "2020-07-29 09:14:23.802-4:00 1",
"PlazaID": "01",
"Lane": "Lane 20",
"IPAddr": "192.9.0.123"
},
"Body": {
"EventMsg": "Status: Online",
"EventNum": "99999"
}
}
注意 "ID" 位于 "Header" 内部，因此您需要以这种方式解析：
String _ID = jsonObject.getJsonObject("Header").get("ID").getAsString();
此外，避免使用 get()，因为有更好的便利方法：
String _ID = jsonObject.getJsonObject("Header").getString("ID");
英文:
Let's prettify your jsonString first for clarity:
{
"Header": {
"ID": "103",
"DateTime": "2020-07-29 09:14:23.802-4:00 1",
"PlazaID": "01",
"Lane": "Lane 20",
"IPAddr": "192.9.0.123"
},
"Body": {
"EventMsg": "Status: Online",
"EventNum": "99999"
}
}
Notice that "ID" is inside "Header", so you'd have to parse it this way:
String _ID = jsonObject.getJsonObject("Header").get("ID").getAsString();
Also, avoid using get() since there are better convenience methods:
String _ID = jsonObject.getJsonObject("Header").getString("ID");
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