With all configurations DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES not working

Question

I tried all the solutions provided on these below SO threads:

Jackson FAIL_ON_UNKNOWN_PROPERTIES to false not working

Spring Boot Web- Set FAIL_ON_UNKNOWN_PROPERTIES to false in Jackson

And around 10 more similar SO threads.

Here is my Spring Boot application:

@SpringBootApplication(exclude = { DataSourceAutoConfiguration.class })
public class MyApplication {

    @Autowired
    private WebClient webClient;

    public static void main(String args[]) {
        SpringApplication.run(MyApplication.class, args);

    }

    @Bean
    public CommandLineRunner demo() {
        return (args) -> {
            getDetails("abcd12345");

        };
    }

    private void getDetails(String nodeId) throws IOException {
        Mono<String> mono = webClient.get().uri("/end/point").retrieve().bodyToMono(String.class);
        System.out.println(mono.block());
        final ObjectNode node = objectMapper().readValue(mono.block(), ObjectNode.class);
        System.out.println(node.get("parent").get("properties").get("nonExisting:keyhere").asText());  // NPE here
    }

    @Bean
    public ObjectMapper objectMapper() {
        return Jackson2ObjectMapperBuilder.json().featuresToEnable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES)
                .build();
    }

    @Bean
    public Jackson2ObjectMapperBuilder objectMapperBuilder() {
        Jackson2ObjectMapperBuilder builder = new Jackson2ObjectMapperBuilder();
        builder.failOnUnknownProperties(false);
        return builder;
    }

}

And my application.properties file has:

spring.jackson.deserialization.FAIL_ON_UNKNOWN_PROPERTIES=false

Output:

Caused by: java.lang.NullPointerException: null
    at com.springbatch.parallel.processing.Application.getDetails(MyApplication .java:43)

But still I am getting NullPointerException (NPE) for non-existing key. I am trying to disable FAIL_ON_UNKNOWN_PROPERTIES. What I am missing here?

Unknown properties don't cause an NPE. Show the full output. — shmosel, Dec 13 '21 at 18:18
It seems to me that one of the `get()` calls in `node.get("parent").get("properties").get("nonExisting:keyhere")` is null, hence the NPE. — João Dias, Dec 13 '21 at 18:27
I understand. Question is - how to avoid it? As in my situation, for few calls there is some value present and in some cases its not. When the key is present, there is no error whatsoever. — Ajay Kumar, Dec 13 '21 at 18:49
The easiest way is to use [`path()`](https://fasterxml.github.io/jackson-databind/javadoc/2.7/com/fasterxml/jackson/databind/JsonNode.html#path(java.lang.String)). — shmosel, Dec 13 '21 at 20:09

score 1 · Accepted Answer · edited Dec 13 '21 at 19:05

1

You will need to cope with the possibility of null being returned by any of the calls in that chained method call as follows:

private void getDetails(String nodeId) throws IOException {
    Mono<String> mono = webClient.get().uri("/end/point").retrieve().bodyToMono(String.class);
    System.out.println(mono.block());
    final ObjectNode node = objectMapper().readValue(mono.block(), ObjectNode.class);
    JsonNode parentNode = node.get("parent");
    if (parentNode != null) {
        JsonNode parentPropertiesNode = parentNode.get("properties");
        if (parentPropertiesNode != null) {
            JsonNode nonExistingKeyNode = parentPropertiesNode.get("nonExisting:keyhere");
            if (nonExistingKeyNode != null) {
                System.out.println(nonExistingKeyNode.asText());
            }
        }
    }
}

Additionally, avoid at all costs using block() in a Reactive stack. By doing this you are wasting all the benefits of using Spring WebFlux. Here is a very interesting online resource about common mistakes while using the Reactive stack: https://medium.com/javarevisited/five-mistakes-to-avoid-in-reactive-java-786927ffd2f6.

edited Dec 13 '21 at 19:05

Ajay Kumar

2,906
3
23
46

answered Dec 13 '21 at 18:33

João Dias

16,277
6
33
45

I totally get your point @Joao Dias. But the question remains why FAIL_ON_UNKNOWN_PROPERTIES config is not working? – Ajay Kumar Dec 13 '21 at 19:04
That has no effect when you deserialize to `ObjectNode`. `FAIL_ON_UNKNOWN_PROPERTIES` has only an effect if were deserializing your JSON to a custom Java class that actually matches your JSON. In the case that that JSON would include properties that were not included in your Java model then Jackson would simply ignore them with `FAIL_ON_UNKNOWN_PROPERTIES = false`. It has nothing to do with the way you are using Jackson. – João Dias Dec 13 '21 at 19:07
Ah got it. Thanks. – Ajay Kumar Dec 13 '21 at 19:09
Thanks for editing my answer and actually fixing a bug in it ;) – João Dias Dec 13 '21 at 19:11

With all configurations DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES not working

1 Answers1