I have a JsonObject named "mapping" with the following content:
{
"client": "127.0.0.1",
"servers": [
"8.8.8.8",
"8.8.4.4",
"156.154.70.1",
"156.154.71.1"
]
}
I know I can get the array "servers" with:
mapping.get("servers").getAsJsonArray()
And now I want to parse that JsonArray into a java.util.List...
What is the easiest way to do this?
Definitely the easiest way to do that is using Gson's default parsing function fromJson().
There is an implementation of this function suitable for when you need to deserialize into any ParameterizedType (e.g., any List), which is fromJson(JsonElement json, Type typeOfT).
In your case, you just need to get the Type of a List<String> and then parse the JSON array into that Type, like this:
import java.lang.reflect.Type;
import com.google.gson.reflect.TypeToken;
JsonElement yourJson = mapping.get("servers");
Type listType = new TypeToken<List<String>>() {}.getType();
List<String> yourList = new Gson().fromJson(yourJson, listType);
In your case yourJson is a JsonElement, but it could also be a String, any Reader or a JsonReader.
You may want to take a look at Gson API documentation.
I was able to get the list mapping to work with just using @SerializedName for all fields.. no logic around Type was necessary.
Running the code - in step #4 below - through the debugger, I am able to observe that the List<ContentImage> mGalleryImages object populated with the JSON data
Here's an example:
1. The JSON
{
"name": "Some House",
"gallery": [
{
"description": "Nice 300sqft. den.jpg",
"photo_url": "image/den.jpg"
},
{
"description": "Floor Plan",
"photo_url": "image/floor_plan.jpg"
}
]
}
2. Java class with the List
public class FocusArea {
@SerializedName("name")
private String mName;
@SerializedName("gallery")
private List<ContentImage> mGalleryImages;
}
3. Java class for the List items
public class ContentImage {
@SerializedName("description")
private String mDescription;
@SerializedName("photo_url")
private String mPhotoUrl;
// getters/setters ..
}
4. The Java code that processes the JSON
for (String key : focusAreaKeys) {
JsonElement sectionElement = sectionsJsonObject.get(key);
FocusArea focusArea = gson.fromJson(sectionElement, FocusArea.class);
}
Given you start with mapping.get("servers").getAsJsonArray(), if you have access to Guava Streams, you can do the below one-liner:
List<String> servers = Streams.stream(jsonArray.iterator())
.map(je -> je.getAsString())
.collect(Collectors.toList());
Note StreamSupport won't be able to work on JsonElement type, so it is insufficient.
I read solution from official website of Gson at here
And this code for you:
String json = "{"client":"127.0.0.1","servers":["8.8.8.8","8.8.4.4","156.154.70.1","156.154.71.1"]}";
JsonObject jsonObject = new Gson().fromJson(json, JsonObject.class);
JsonArray jsonArray = jsonObject.getAsJsonArray("servers");
String[] arrName = new Gson().fromJson(jsonArray, String[].class);
List<String> lstName = new ArrayList<>();
lstName = Arrays.asList(arrName);
for (String str : lstName) {
System.out.println(str);
}
Result show on monitor:
8.8.8.8
8.8.4.4
156.154.70.1
156.154.71.1
Below code is using com.google.gson.JsonArray.
I have printed the number of element in list as well as the elements in List
import java.util.ArrayList;
import com.google.gson.Gson;
import com.google.gson.JsonArray;
import com.google.gson.JsonObject;
import com.google.gson.JsonParser;
public class Test {
static String str = "{ "+
"\"client\":\"127.0.0.1\"," +
"\"servers\":[" +
" \"8.8.8.8\"," +
" \"8.8.4.4\"," +
" \"156.154.70.1\"," +
" \"156.154.71.1\" " +
" ]" +
"}";
public static void main(String[] args) {
// TODO Auto-generated method stub
try {
JsonParser jsonParser = new JsonParser();
JsonObject jo = (JsonObject)jsonParser.parse(str);
JsonArray jsonArr = jo.getAsJsonArray("servers");
//jsonArr.
Gson googleJson = new Gson();
ArrayList jsonObjList = googleJson.fromJson(jsonArr, ArrayList.class);
System.out.println("List size is : "+jsonObjList.size());
System.out.println("List Elements are : "+jsonObjList.toString());
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
OUTPUT
List size is : 4
List Elements are : [8.8.8.8, 8.8.4.4, 156.154.70.1, 156.154.71.1]
Source: Stackoverflow.com