parse versus mapping exception in custom deserializers

[Daniel Lipofsky]

I'm converting an enum to/from and int using a custom serializer/deserializer.

I've been throwing a JsonParseException if deserialization fail.

Somewhere between 2.2.1 and 2.5.0 the Jackson libraries started

wrapping my JsonParseException with a JsonMappingException.  The most

immediate problem is that causes my unit tests to fail.  I could fix

the tests, but I am wondering why Jackson is doing this, and I am also

wonder the logical difference between a parse and a mapping exception

and whether or not I should be throwing a mapping exception instead?

@JsonSerialize(using = com.foo.FooType.FooTypeSerializer.class)
@JsonDeserialize(using = com.foo.FooType.FooTypeDeserializer.class)
public enum FooType {
    NONE(0, "None"),
    RELATIVE(1, "Relative"),
    ABSOLUTE(2, "Absolute"),
    STANDARD_DEVIATION(3, "Std Dev");


    public static final FooType getByCode(final int i) {
        // ... returns null if not found ...
    }


    private final int code;
    private final String display;


    FooType(final int code, final String display) {
        this.code = code;
        this.display = display;
    }


    public int getCode() {
        return code;
    }


    static class FooTypeSerializer extends JsonSerializer<FooType> {
        @Override
        public void serialize(
                final FooType value,
                final JsonGenerator generator,
                final SerializerProvider provider) throws IOException, JsonGenerationException {
            generator.writeNumber(value.getCode());
        }
    }


    static class FooTypeDeserializer extends JsonDeserializer<FooType> {
        @Override
        public FooType deserialize(final JsonParser jp, final DeserializationContext ctxt)
                throws IOException, JsonParseException {
            final int c = jp.getIntValue();
            final FooType type = getByCode(c);
            if (type == null) {
                throw new JsonParseException("Could not convert " + c + " to FooType", jp.getCurrentLocation());
            }
            return type;
        }
    }
}

Caused by: com.fasterxml.jackson.databind.JsonMappingException: Could not convert 4 to FooType
 at [Source: {"id":9,"sShockType":0,"sShock":0.0,"volShockType":4,"volShock":0.0}; line: 1, column: 53] (through reference chain: com.foo.Foo["volShockType"])
 at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:210)
 at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:177)
 at com.fasterxml.jackson.databind.deser.impl.BeanPropertyMap.wrapAndThrow(BeanPropertyMap.java:439)
 at com.fasterxml.jackson.databind.deser.impl.BeanPropertyMap._findDeserializeAndSet2(BeanPropertyMap.java:315)
 at com.fasterxml.jackson.databind.deser.impl.BeanPropertyMap.findDeserializeAndSet(BeanPropertyMap.java:291)
 at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:248)
 at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:136)
 at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3560)
 at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2576)
 at com.foo.FooTest.testReadErrorBadVolatilityType(FooTest.java:82)
 ...
Caused by: com.fasterxml.jackson.core.JsonParseException: Could not convert 4 to FooType
 at [Source: {"id":9,"sShockType":0,"sShock":0.0,"volShockType":4,"volShock":0.0}; line: 1, column: 53]
 at com.foo.FooType$FooTypeDeserializer.deserialize(FooType.java:114)
 at com.foo.FooType$FooTypeDeserializer.deserialize(FooType.java:1)
 at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:523)
 at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:95)
 at com.fasterxml.jackson.databind.deser.impl.BeanPropertyMap._findDeserializeAndSet2(BeanPropertyMap.java:313)
 ... 16 more

Thanks,

Dan

[Tatu Saloranta]

I was about to answer that this sounds like a bug, before remembering actual reason why this is done: to add location information (where the problem occurred) regarding logical location within POJO, which is useful in troubleshooting. JsonParseException (and JsonGenerationException) are more low-level things from streaming parser/generator, and thus can only report physical input/output location.

JsonMappingException would not be wrapped, since location information can be augmented easily in cases where it has not yet been added.

In your case I do think that JsonMappingException is a better type to use; JsonParseException would refer to problem with decoding JSON (missing comma, wrong closing marker, duplicate key), but in this case JSON itself is well-formed, and problem is with mapping/binding.

Apologies for the change here. But it was made to give more useful information regarding problem; and there are no plans to change this behavior.

-+ Tatu +-

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[Daniel Lipofsky]

No problem, I can change! I just wasn't sure what I should even be using. Your response clarifies it for me. Thanks,

Dan

[Tatu Saloranta]

No problem -- and it is a good question, hopefully answer is useful to others as well.

-+ Tatu +-