RestTemplate和Jackson-自定义JSON反序列化？

Question

The webservice returns an empty string instead of NULL which causes Jackson to crash. So I created a custom parser, and I'm trying to parse it manually? Any idea How I could achieve this?

What Am I doing wrong here? All I'm trying to do is to parse JSON to object as I normally would. The field names are added to my properties using @JsonProperty so the parser should know how to convert it.

public class InsertReplyDeserializer extends JsonDeserializer<ListingReply> {

    @Override
    public ListingReply deserialize(JsonParser jsonParser, DeserializationContext arg1)
            throws IOException, JsonProcessingException {

        ObjectCodec oc = jsonParser.getCodec();
        JsonNode node = oc.readTree(jsonParser);

        // If service returns "" instead of null return a NULL object and don't try to parse
        if (node.getValueAsText() == "")
            return null;


       ObjectMapper objectMapper = new ObjectMapper();
       ListingReply listingReply = objectMapper.readValue(node, ListingReply.class);


       return listingReply;
    }

}

Answer 1

Here is how I resolved it

@Override
public MyObject deserialize(JsonParser jsonParser, DeserializationContext arg1)
        throws IOException, JsonProcessingException {

    ObjectCodec oc = jsonParser.getCodec();
    JsonNode node = oc.readTree(jsonParser);

    if (node.getValueAsText() == "")
        return null;

    MyObject myObject = new MyObject();
    myObject.setMyStirng(node.get("myString").getTextValue());

    JsonNode childNode = node.get("childObject");
    ObjectMapper objectMapper = new ObjectMapper();
    ChildObject childObject = objectMapper.readValue(childNode,
            ChildObject.class);

             myObject.setChildObject(childObject);
             return myObject;
}

Answer 2

I am not sure you need to manually parse response. You solution would work but seems sub-optimal in my opinion. Since it looks like that you are using RestTemplate, you should rather write (or move your parser code to) your own message converter. Then add this converter to your rest template object which will internally deserialize the value for you. Something along the lines,

public class CustomHttpmsgConverter extends  AbstractHttpMessageConverter<Object> {
private ObjectMapper objectMapper = new ObjectMapper();
@Override
protected Object readInternal(Class clazz, HttpInputMessage inputMessage) throws IOException, HttpMessageNotReadableException {
   InputStream istream = inputMessage.getBody();
   String responseString = IOUtils.toString(istream);
   if(responseString.isEmpty()) //if your response is empty
     return null;
   JavaType javaType = getJavaType(clazz);
   try {
       return this.objectMapper.readValue(responseString, javaType);
   } catch (Exception ex) {
    throw new HttpMessageNotReadableException(responseString);
    }
}

//add this converter to your resttemplate
    RestTemplate template = new RestTemplate();
    List<HttpMessageConverter<?>> converters = new ArrayList<HttpMessageConverter<?>>();
    converters.add(new CustomHttpmsgConverter());
    template.setMessageConverters(converters);