Gson, enum and Attempt to invoke virtual method 'java.lang.Class java.lang.Object.getClass()' on a null object reference

Question

There is a json, contains String value for parameter, e.g. status and this json maps by Gson on POJO, and this parameter maps on custom enum. JSON:

{"status":"on"}

POJO

public class StatusData {
    @SerializedName("status")
    @Expose
    private Status status;
}

enum:

public enum Status {
   @SerializedName("on")ON,
   @SerializedName("off")OFF;
}

And if json contains correct values ("on" or "off") - all right, but if there is unsupported value e.g. "unknown" - then it crushes with Attempt to invoke virtual method 'java.lang.Class java.lang.Object.getClass()' on a null object reference. And question: is there way to change message of exception for understanding what went wrong?

Goku · Accepted Answer · 2018-04-05 08:27:35Z

1

No need to create new class of enum

Use http://www.jsonschema2pojo.org/ to generate pojo class

Try this

public class StatusData
{
    @SerializedName("status")
    @Expose
    private String status;

    public String getStatus() {
        return status;
    }

    public void setStatus(String status) {
        this.status = status;
    }
}

edited Apr 5, 2018 at 8:27

answered Apr 5, 2018 at 8:21

Goku

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1 Comment

TheSecond Over a year ago

I wanna then work with enum, but no String, I know that I can change getters and setters and maps String and Enum there, but I just want throw exception with understandable description

Navneet Krishna · Accepted Answer · 2018-04-05 10:44:24Z

0

public class StatusData {
@SerializedName("status")
@Expose
private Status status;

public String getStatus() {
    return status;
}
}

Save your response as an object of StatusData

StatusData statusData=response;
String status=statusData.getStatus();
if(status.equals("on")){
  //code when status is "on"
} else if(status.equals("off")){
  //code when status is "off"
}

or use gson

Gson gson = new Gson();
StatusData statusData = gson.fromJson("json response",
                                        StatusData.class);

edited Apr 5, 2018 at 10:44

answered Apr 5, 2018 at 9:29

Navneet Krishna

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1 Comment

TheSecond Over a year ago

Yes, it will help to get around the problem, but I want just set custom message for exception, maybe some Strategies of Gson can help to solve this problem

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