Force spring RestTemplate to process plain text as JSON?

Question

A web API is responding to a request with Content-Type:text/plain; charset=utf-8, but the messageis formatted as if it were a JSON, eg.

{
"total": 168,
"page": 0,
"pageCount": 1,
...
}

In Spring, this message is processed with a RestTemplate and the JSON is automagically mapped into a ModelDto POJO,

restTemplate.getForObject(url, ModelDto::class.java)

This gives the following error:

org.springframework.web.client.RestClientException: Could not extract response: no suitable HttpMessageConverter found for response type [class api.ModelDto] and content type [text/plain;charset=utf-8]

Is there any way to have spring treat this message as if it were a JSON and parse it as such, despite the Content-Type being plaintext?

score 8 · Accepted Answer · edited Oct 05 '19 at 06:46

UPDATED

There's no need to create a custom HttpMessageConverter since AbstractHttpMessageConverter has a method setSupportedMediaTypes which can be used to change supported media type:

MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();
converter.setSupportedMediaTypes(Arrays.asList(MediaType.TEXT_PLAIN, MediaType.APPLICATION_JSON));
restTemplate.getMessageConverters().add(0, converter);

I think it's possible via implementing own HttpMessageConverter<T>.

RestTemplate uses it to convert a raw response to some representation (for instance, POJO). Since it has a list of converters, it finds specific converter for a particular response by its type (e.g application/json, etc).

So your implementation of HttpMessageConverter<T> should be something like default MappingJackson2HttpMessageConverter but with changed supported media type:

public class MappingJackson2HttpMessageConverter2 extends AbstractJackson2HttpMessageConverter {

    private String jsonPrefix;

    public MappingJackson2HttpMessageConverter2() {
        this(Jackson2ObjectMapperBuilder.json().build());
    }

    public MappingJackson2HttpMessageConverter2(ObjectMapper objectMapper) {
        // here changed media type
        super(objectMapper, MediaType.TEXT_PLAIN);
    }

    public void setJsonPrefix(String jsonPrefix) {
        this.jsonPrefix = jsonPrefix;
    }

    public void setPrefixJson(boolean prefixJson) {
        this.jsonPrefix = (prefixJson ? ")]}', " : null);
    }


    @Override
    protected void writePrefix(JsonGenerator generator, Object object) throws IOException {
        if (this.jsonPrefix != null) {
            generator.writeRaw(this.jsonPrefix);
        }
        String jsonpFunction =
                (object instanceof MappingJacksonValue ? ((MappingJacksonValue) object).getJsonpFunction() : null);
        if (jsonpFunction != null) {
            generator.writeRaw("/**/");
            generator.writeRaw(jsonpFunction + "(");
        }
    }

    @Override
    protected void writeSuffix(JsonGenerator generator, Object object) throws IOException {
        String jsonpFunction =
                (object instanceof MappingJacksonValue ? ((MappingJacksonValue) object).getJsonpFunction() : null);
        if (jsonpFunction != null) {
            generator.writeRaw(");");
        }
    }

}

Then you can add this to RestTemplate object:

restTemplate.getMessageConverters().add(0, new MappingJackson2HttpMessageConverter2());

Looks like another approach is to just change in the inbound header. https://stackoverflow.com/questions/42592440/how-to-change-response-http-header-in-get-request-by-spring-resttemplate?rq=1 — Adam Hughes, Mar 25 '18 at 16:22
@MykolaYashchenko `MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter(); converter.setSupportedMediaTypes(Arrays.asList(TEXT_PLAIN, MediaType.APPLICATION_JSON)); restTemplate.getMessageConverters().add(0, converter);` I have added the TEXT_PLAIN in converter still facing the same issue. `[class com.fasterxml.jackson.databind.JsonNode] and content type [text/plain;charset=ISO-8859-1];` — Nagendra Nigade, Aug 28 '19 at 11:06
@NagendraNigade I guess the reason is that "text/plain;charset=ISO-8859-1" is not the same as "text/plain" — Mykola Yashchenko, Aug 29 '19 at 12:04
try to do `converter.setSupportedMediaTypes(Arrays.asList("text/plain;charset=ISO-8859-1", MediaType.APPLICATION_JSON))` — Mykola Yashchenko, Aug 29 '19 at 12:05

Force spring RestTemplate to process plain text as JSON?

1 Answers1

Linked