I got an error ...(no Creators, like default constructor, exist): cannot deserialize from Object value (no delegate- or property-based Creator) which indicates that I need a property-based creator. I have a few constructors with different parameters, but no default.
My solution was to add a default constructor SomeClass() {}. My question is: why does this happen? Also, what is a delegate/property-based constructor?
If there is no constructors that is annotated with @JsonCreator, by default, Jackson needs a default no-args constructor in order to parse the JSON into POJO or bean classes. That is why when you add a default constructor, it will work fine.
And if you don't actually need the usage of the default constructor, just add it for Jackson only, you can set it to private, protected or package-protected. Jackson is still able to fill all the fields via reflection.
Regarding the no delegate- or property-based Creator, they are constructors that is annotated with @JsonCreator. In Jackson, there are 2 types of Creator/JsonCreator which are delegate-based Creator and property-based Creator.
Delegate-based creators take just one argument, which is NOT annotated with @JsonProperty. Type of that property is used by Jackson to bind the whole JSON value (JSON Object, array or scalar value), to be passed as value of that one argument.
Property-based creators take one or more arguments; all of which MUST be annotated with @JsonProperty, to specify JSON name used for property. They can only be used to bind data from JSON Objects; and each parameter represents one property of the JSON Object; type of property being used for binding data to be passed as that parameter when calling creator.
You can read for more details about these 2 creators in the article below. http://www.cowtowncoder.com/blog/archives/2011/07/entry_457.html
