改型返回空响应Android

Question

I'm using Retrofit to make API call, When I handle the response I get the next error (Need to get the data from the API call) -

Attempt to invoke interface method 'java.lang.Object java.util.List.get(int)' on a null object reference

I don't know if I'm doing it right. Anyway here's my code.

Here's the url link: https://data.gov.il/api/

Retrofit call -

@GET("datastore_search?resource_id=2c33523f-87aa-44ec-a736-edbb0a82975e")
Call<Result> getRecords();

Retrofit base call -

private static Retrofit retrofit;
public static final String BASE_URL = "https://data.gov.il/api/action/";

public static Retrofit getRetrofitInstance() {
    if (retrofit == null) {
        retrofit = new retrofit2.Retrofit.Builder()
                .baseUrl(BASE_URL)
                .addConverterFactory(GsonConverterFactory.create())
                .build();
    }
    return retrofit;
}

Model class -

public class Result {

@SerializedName("include_total")
@Expose
private Boolean includeTotal;
@SerializedName("resource_id")
@Expose
private String resourceId;
@SerializedName("fields")
@Expose
private List<Field> fields = null;
@SerializedName("records_format")
@Expose
private String recordsFormat;
@SerializedName("records")
@Expose
private List<Record> records = null;
@SerializedName("limit")
@Expose
private Integer limit;
@SerializedName("_links")
@Expose
private Links links;
@SerializedName("total")
@Expose
private Integer total;

public Boolean getIncludeTotal() {
    return includeTotal;
}

public void setIncludeTotal(Boolean includeTotal) {
    this.includeTotal = includeTotal;
}

public String getResourceId() {
    return resourceId;
}

public void setResourceId(String resourceId) {
    this.resourceId = resourceId;
}

public List<Field> getFields() {
    return fields;
}

public void setFields(List<Field> fields) {
    this.fields = fields;
}

public String getRecordsFormat() {
    return recordsFormat;
}

public void setRecordsFormat(String recordsFormat) {
    this.recordsFormat = recordsFormat;
}

public List<Record> getRecords() {
    return records;
}

public void setRecords(List<Record> records) {
    this.records = records;
}

...

Main Activity -

    RecallService service = RetrofitClientInstance.getRetrofitInstance().create(RecallService.class);
    Call<Result> records = service.getRecords();

    records.enqueue(new Callback<Result>() {

        @Override
        public void onResponse(Call<Result> call, Response<Result> response) {
            Log.d(TAG, String.valueOf(response.body().getRecords().get(0).getId())); // ERROR
        }

        @Override
        public void onFailure(Call<Result> call, Throwable t) {
            Log.e(TAG, t.getMessage());

        }
    });

Answer 1

The API link you've shared returns the response in the format below:

{"help": "https://data.gov.il/api/3/action/help_show?name=datastore_search", "success": true, "result": {...}}

You are setting the response object to be of type Result which is actually a sub-element within the root element help in the json response. response.body() would include help and the result would be it's sub-element. Since it is not parsed correctly, you're getting a null response.

You will need to include the root element in your model class and update the API call to use that class type as the response type.

Answer 2

The response, which you are getting from the API, doesn't fit the Result POJO.

The response you get from API is like below:

{
  "help": "https://data.gov.il/api/3/action/help_show?name=datastore_search",
  "success": true,
  "result": {...}
}

By using the Result POJO, you are assuming that you get the response as below, which is a json inside the actual response json, and is not what you actually receive. So, just create a POJO which fairly represents the actual response.

{
    "include_total": true,
    "resource_id": "2c33523f-87aa-44ec-a736-edbb0a82975e",
    "fields": [...],
    "records_format": "objects",
    "records":[...]
}

Try making a class like below (set the annotations yourself):

class Resp{
    Result result;
}

Replace the class Result with Resp , like below and other usages:

@GET("datastore_search?resource_id=2c33523f-87aa-44ec-a736-edbb0a82975e")
Call<Resp> getRecords();

Then, finally you can do:

response.body().getResult().getRecords()