Java Spring rest java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to Cuestionario

Question

I have developed the following code using Spring Rest.

MyProxy

public Respuesta reject(Integer id,Integer uid, Integer asociation, String reason,Integer type, Cuestionario cuestionario){
    UriComponentsBuilder builder = UriComponentsBuilder.fromHttpUrl(METHOD_REJECT_FULLPATH);
    Map<String,Serializable> map = new HashMap<String,Serializable>(2);
    map.put("cuestionario",cuestionario);
    map.put("motivo",motivo);
    ResponseEntity<RespuestaServidor> respuesta = restTemplate.exchange(builder.buildAndExpand(id,uid,type, idTipo,asociation).encode().toUri(),
HttpMethod.POST,
    new HttpEntity<Map<String,Serializable>>(map),
    new ParameterizedTypeReference<Respuesta>(){});
    return respuesta.getBody();
}

The URI calls this method.

@RequestMapping(value = Proxy.METHOD_REJECT,method = RequestMethod.POST)
public @ResponseBody
ResponseEntity<Respuesta>reject(@PathVariable Integer id,@PathVariable Integer uid,@PathVariable Integer asociation, @PathVariable Integer type,@RequestBody(required=false)Map<String,Object>map){
    final String motivo = (String)map.get("motivo");
    final Cuestionario cuestionario = (Cuestionario)map.get("cuestionario");

The problem is in this line

    final Cuestionario cuestionario = (Cuestionario)map.get("cuestionario");

Given below is the Cuestionario POJO

public class Cuestionario implements Serializable {

   private static final long serialVersionUID = -2669540728368524646L;
   private String respuesta1;
   private String respuesta2;
   private String respuesta3;
   private String respuesta4;
   private boolean fullfilled;

for which I am getting the following exception

java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to com.Cuestionario

I have read in other posts similar to this issue which state that it is a kind of Java quirk while other opinions state that a mapper can be used to retreive/cast the Cuestionario object. But I am not aware of any mappers due to my limited expertise on REST.

I have a very similiar code but with a

Map<List<Integer>,List<Integer>>

And works perfect. But it is failing for Cuestionario. I have also tried using Spring LinkedMultiValueMap but that doesn't work either.

MultiValueMap<String,Serializable> map = new LinkedMultiValueMap<String, Serializable>(2);
map.add("motivo",motivo);
map.add("cuestionario",cuestionario);

I need to have to parse the request body somewhere and construct a Cuestionario instance from the data but how can i do that.

(Cuestionario)(map.get("cuestionario")); what is the diff with final Cuestionario cuestionario = (Cuestionario)map.get("cuestionario"); — chiperortiz
– chiperortiz, Commented Jan 25, 2018 at 14:27
In the second scenario, you're trying to cast map to Cuestionario — Rahul Raj
– Rahul Raj, Commented Jan 25, 2018 at 14:29
There are many posts on stackoverflow that looks similar, did you try google out? google.com/… — Rahul Raj
– Rahul Raj, Commented Jan 25, 2018 at 17:29

SrThompson · Accepted Answer · 2018-01-26 20:52:47Z

1

You're trying to cast an Object to a Cuestionario, that won't work

@RequestMapping(value = Proxy.METHOD_REJECT,method = RequestMethod.POST)
public @ResponseBody
ResponseEntity<Respuesta>reject(@PathVariable Integer id,@PathVariable Integer uid,@PathVariable Integer asociation, @PathVariable Integer type,@RequestBody(required=false)Map<String,Object>map){
    final String motivo = (String)map.get("motivo");
    // Here map is of type Map<String, Object>
    final Cuestionario cuestionario = (Cuestionario)map.get("cuestionario");

You'll have to deserialize manually the response body.

Since you're using Spring, you probably already have Jackson in your dependencies. You can extend JsonDeserializer

public class CuestionarioDeserializer extends JsonDeserializer<Cuestionario> {
  @Override
  public Cuestionario deserialize(JsonParser parser, DeserializationContext context) throws IOExcention {
    //Your deserialization logic
  }
}

and then annotate your Cuestionario like:

@JsonDeserialize(using = YourCuestionarioDeserializer.class)
public class Cuestionario

Or do the same thing but deserialize to a DTO, then use the DTO to create a Cuestionario

edited Jan 26, 2018 at 20:52

answered Jan 25, 2018 at 15:18

SrThompson

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4 Comments

chiperortiz Over a year ago

You're trying to cast an Object to a Cuestionario! Yep. But is a Cuestionario indeed. Whose get transform it into a LinkedHashMap... I need to get the cuestionario object.

SrThompson Over a year ago

Casting only works up the inheritance hierarchy. You can cast a Cuestionario to an Object because Cuestionario inherits from Object (just like every other Java class), the inverse is not possible. Even if that Object is always a Cuestionario, the JVM has no way to know that. If you need to extract a Cuestionario from the request body, you have to parse the request body somewhere and construct a Cuestionario instance from the data

chiperortiz Over a year ago

and how i can do that??

SrThompson Over a year ago

I added an edit with the general steps for deserializing with Jackson. There are a lot of good tutorials for that if you need something more specific

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