How to fix JSON decoding error in Spring?

Question

I'm sending a User object through REST which contains a Set of SimpleGrantedAuthority objects. On the receiver side, I'm getting an exception:

org.springframework.core.codec.DecodingException: JSON decoding error: Cannot construct instance of org.springframework.security.core.authority.SimpleGrantedAuthority (although at least one Creator exists): cannot deserialize from Object value (no delegate- or property-based Creator);

I'm using the default JSON mapper which Spring Boot 2.1.2 provides. On the receiving side, I'm using WebFlux's WebClient (WebTestClient in this case).

Can anyone explain to me why am I getting this error and how to solve it?

stackoverflow.com/questions/47570931/…

xingbin
– xingbin

2019-01-15 14:55:28 +00:00
Commented Jan 15, 2019 at 14:55 — xingbin
– xingbin, Commented Jan 15, 2019 at 14:55

rustyx · Accepted Answer · 2019-01-15 15:49:42Z

9

SimpleGrantedAuthority is not suitable for automatic mapping with Jackson; it has no no-arg constructor and no setter for the authority field.

So it needs a custom deserializer. Something like this:

class SimpleGrantedAuthorityDeserializer extends StdDeserializer<SimpleGrantedAuthority> {
    public SimpleGrantedAuthorityDeserializer() {
        super(SimpleGrantedAuthority.class);
    }
    @Override
    public SimpleGrantedAuthority deserialize(JsonParser p, DeserializationContext ctxt) throws IOException, JsonProcessingException {
        JsonNode tree = p.getCodec().readTree(p);
        return new SimpleGrantedAuthority(tree.get("authority").textValue());
    }
}

Register it with Jackson globally like this:

objectMapper.registerModule(new SimpleModule().addDeserializer(
                      SimpleGrantedAuthority.class, new SimpleGrantedAuthorityDeserializer()));

Or annotate the field(s) with:

@JsonDeserialize(using = SimpleGrantedAuthorityDeserializer.class)

Note: you don't need a serializer because SimpleGrantedAuthority has the getAuthority() method, which is usable by Jackson.

answered Jan 15, 2019 at 15:49

rustyx

86.5k28 gold badges224 silver badges298 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

OCPi Over a year ago

Thank you very much! Works like a charm.

Simon Over a year ago

If you're annotating the signature public Collection<GrantedAuthority> getAuthorities() make sure to use contentUsing, so @JsonDeserialize(contentUsing = SimpleGrantedAuthorityDeserializer.class), otherwise the deserializer gets the entire collection node to deserialize at once.

Collectives™ on Stack Overflow

How to fix JSON decoding error in Spring?

1 Answer 1

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related