使用GSON解析JSON数组和对象

Question

I have a JSON file like this:

{
 "waypoints": [
    {
        "waypoint_index": 0,
        "trips_index": 0,
        "hint": "u_FYj4uKI=",
        "name": "",
        "location": [
            28.068655,
            41.180774
        ]
    },
    {
        "waypoint_index": 4,
        "trips_index": 0,
        "hint": "KiKhg4uKI=",
        "name": "",
        "location": [
            20.75179,
            29.031869
        ]
    }
}

I know if you want to create java objects, well, you have just to understand how JSON works.

{} -> object

[] -> array

but I could not!

How to convert Java object to This json file?

public class ResultOsrm {
    public Waypoints waypoints;
}

public class Waypoints {
    public List waypoint_index;

}

Main -

Gson gson = new GsonBuilder().create();                             
ResultOsrm resultOsrm=gson.fromJson(JsonFile,ResultOsrm.class); 
System.out.println(resultOsrm);    

I need just waypoint_index and location values

Answer 1

I think ResultOsrm should hold list of Waypoint and class Waypoint will hold the data

public class ResultOsrm
{
    public List<Waypoint> waypoints;
}

public class Waypoint
{
    public int waypoint_index;
    public int trips_index;
    public String hint;
    public String name;
    public List<float> location;
}

waypoint_index is a variable in Waypoint , not a list by itself.

Answer 2

Use Kotlin to define the data classes.

WayPoint.kt

data class WayPoint(
    @SerializedName("waypoint_index") var wayPointIndex: String,
    @SerializedName("trips_index") var tripIndex: String,
    @SerializedName("hint") var hint: String,
    @SerializedName("name") var name: String,
    @SerializedName("location") var location: ArrayList<String>

)

Response.kt

data class Response(
    @SerializedName("waypoints") var wayPoints: ArrayList<WayPoint>

)

then to convert the string to JSON and to objects in Java class

    String data = "{\n" +
            " \"waypoints\": [\n" +
            "    {\n" +
            "        \"waypoint_index\": 0,\n" +
            "        \"trips_index\": 0,\n" +
            "        \"hint\": \"u_FYj4uKI=\",\n" +
            "        \"name\": \"\",\n" +
            "        \"location\": [\n" +
            "            28.068655,\n" +
            "            41.180774\n" +
            "        ]\n" +
            "    },\n" +
            "    {\n" +
            "        \"waypoint_index\": 4,\n" +
            "        \"trips_index\": 0,\n" +
            "        \"hint\": \"KiKhg4uKI=\",\n" +
            "        \"name\": \"\",\n" +
            "        \"location\": [\n" +
            "            20.75179,\n" +
            "            29.031869\n" +
            "        ]\n" +
            "    }\n" +
            "\t]\n" +
            "}";

    Response response = new Gson().fromJson(
            data,
            Response.class
    );

The response class has all your data converted to the data class values.

Do try this solution. this will surely solve your issue.

Answer 3

Your JSON structure is little incorrect here -

{
     "waypoints": [
        {
            "waypoint_index": 0,
            "trips_index": 0,
            "hint": "u_FYj4uKI=",
            "name": "",
            "location": [
                28.068655,
                41.180774
            ]
        },
        {
            "waypoint_index": 4,
            "trips_index": 0,
            "hint": "KiKhg4uKI=",
            "name": "",
            "location": [
                20.75179,
                29.031869
            ]
        }
    ]
}

You don't have closing array bracket for waypoints .

Also, you need to modify your class structure as per the JSON -

public class ResultOsrm {
    private List<Waypoints> waypointsList;
    // getter setter
}

public class Waypoints {
    private Integer waypoint_index;
    private List<Double> location;
    // other fields & all getter setters

}

You should map every fields into objects & then use whatever you need out of it.

Note - Make your instance variable private & provide getters & setters for fields. This is a good practice to have in POJO classes.

Answer 4

As the Sagar Nayak mentioned above is correct.

Kotlin

if you want to convert mockup data to ArrayList you could use this. It is the other options in case of you don't want to create a model, which contains ArrayList attribute within.

// when json variable is your mockup data

val list= Gson().fromJson<ArrayList<WayPoint>>(json, Array<WayPoint>::class.java).toCollection(ArrayList())