Cannot deserialize instance of `java.lang.String` out of START_OBJECT token (Jackson)

Question

I want to send a JSON Object from my angular 8 front-end to my spring boot API. I'm new on those frameworks and I'm a little lost.

I have a world map, with leaflet, and i want to send the coordinates of the polygon to my backend.

The backend get the body as a String, but i want to make an Object with those coordinates(first step, then other stuff).

I search some solution but I don't find similar cases.

Here is the code =>

Angular :

getFeed(data): Observable<boolean> {
        var q = {coordinates:data};
        console.log(q);
        return this.http.get<Answer>(`${this.baseUrl}api/searchs?data=`+encodeURIComponent(JSON.stringify(q))).pipe(
            map(res => true),
            catchError(err => {
                console.error(err);
                return of(false);
            })
        );
    }

Spring ModelDTO: (the problem's certainly there, not sur about the ArrayList)

public class QueryDTO {
//  @JsonFormat(shape=JsonFormat.Shape.ARRAY)
    @JsonDeserialize(as=ArrayList.class)
    private ArrayList<String> coordinates=new ArrayList();
    public QueryDTO (ArrayList<String> coo) {
        this.coordinates=coo;
    }
    public QueryDTO() {}
    public ArrayList<String> getCoordinates() {
        return this.coordinates; 
    }

    public void setCoordinate(ArrayList<String> coo) {
        this.coordinates=coo;
    }

}

Spring Controller:

    @CrossOrigin(origins = "http://localhost:4200")
    @Produces("application/json")
    @RequestMapping(value = "/searchs")

    public Collection<SearchFeedDTO> getFeed(@RequestParam(value = "data") String data) throws JsonMappingException, JsonProcessingException {
        System.out.println(data);
        System.out.println("I'm here");
        final QueryDTO queryDTO = new ObjectMapper().readValue(data, QueryDTO.class);
        System.out.println("you");
        return null;
    }

The error:

"Cannot deserialize instance of java.lang.String out of START_OBJECT token↵ at [Source: (String)"{"coordinates":[{"lat":76.00542202728906,"lng":-71.76493508359451},{"lat":62.96921913888247,"lng":-113.6539800675124},{"lat":63.601007712290695,"lng":-56.583665780107154}]}"; line: 1, column: 17] (through reference chain: com.freemind.leaflet_test.Models.DTO.QueryDTO["coordinates"]->java.util.ArrayList[0])"

Edit:

Updated Controller:

    @CrossOrigin(origins = "http://localhost:4200")
    @Produces("application/json")
    @RequestMapping(value = "/searchs")

    public Collection<SearchFeedDTO> getFeed(@RequestParam(value = "data") QueryDTO data) throws JsonMappingException, JsonProcessingException {
        System.out.println(data);
        System.out.println("I'm here");
        return null;
    }

Coordinates class:

@Getter
@Setter
public class CoordinateDTO {
    private int lat;
    private int lng;
    public CoordinateDTO() {}
}


public class QueryDTO {
//  @JsonFormat(shape=JsonFormat.Shape.ARRAY)
    @JsonDeserialize(as=ArrayList.class)
    private ArrayList<CoordinateDTO> coordinates=new ArrayList<CoordinateDTO>();
    public QueryDTO (ArrayList<CoordinateDTO> coo) {
        this.coordinates=coo;
    }
    public QueryDTO() {}
    public ArrayList<CoordinateDTO> getCoordinates() {
        return this.coordinates; 
    }

    public void setCoordinate(ArrayList<CoordinateDTO> coo) {
        this.coordinates=coo;
    }

}

new error : failed to convert value of type 'java.lang.String' to required type 'com.freemind.leaflet_test.Models.DTO.QueryDTO'; nested exception is java.lang.IllegalStateException: Cannot convert value of type 'java.lang.String' to required type 'com.freemind.leaflet_test.Models.DTO.QueryDTO': no matching editors or conversion strategy found

Coordinates is not a list of Strings. It is a list which contains objects with two properties — Jens
– Jens, Commented Mar 20, 2020 at 17:15
Also your paramater sould not be a string it should be QueryDTO Then you do not explizitly use the objectMapper. it will be done by spring itself — Jens
– Jens, Commented Mar 20, 2020 at 17:18
@Jens Thanks, I add a class with the lat and the lng, Getter Setter public class CoordinateDTO { private String lat; private String lng; public CoordinateDTO() {} } and change the String by the QueryDTO but now i have another issue: failed to convert value of type 'java.lang.String' to required type 'com.freemind.leaflet_test.Models.DTO.QueryDTO'; nested exception is java.lang.IllegalStateException: Cannot convert value of type 'java.lang.String' to required type 'com.freemind.leaflet_test.Models.DTO.QueryDTO': no matching editors or conversion strategy found — Girbouillle
– Girbouillle, Commented Mar 20, 2020 at 18:38
Why don't you simply use a POST to send a Json object and let Jackson unmarshal it? — Yann Huissoud
– Yann Huissoud, Commented Mar 20, 2020 at 19:10
You can send it as json. But than it should be part of the requestBody not as the url — Jens
– Jens, Commented Mar 23, 2020 at 6:26

Alejandro Gonzalez · Accepted Answer · 2020-03-20 17:11:43Z

-1

you only need to do the next

const it= JSON.stringify(Object);

Now in the spring, the webservice should recieve a string,

answered Mar 20, 2020 at 17:11

Alejandro Gonzalez

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