Ankur
c438afc33b
37 runnable examples covering the eight feature posts on ankurm.com, verified against Jackson 3.2.1 on Temurin 21.0.5. Every output committed under docs/ was produced by run-all.sh. Also documents 11 places where the published snippets do not compile or do not behave as printed against a real Jackson 3 build - most notably that writeValueAsString(List<Base>) silently drops the polymorphic type discriminator, so the post's serialised output cannot be read back.
56 lines
2.5 KiB
Java
56 lines
2.5 KiB
Java
package com.ankurm.jackson3.part3annotations;
|
|
|
|
import com.fasterxml.jackson.annotation.JsonAlias;
|
|
import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
|
|
import tools.jackson.databind.DeserializationFeature;
|
|
import tools.jackson.databind.json.JsonMapper;
|
|
|
|
/**
|
|
* Post: Jackson Annotations Cheat Sheet — https://ankurm.com/jackson-annotations-guide/
|
|
* Sections: "@JsonAlias" and "@JsonIgnoreProperties"
|
|
*
|
|
* Correction to the post: it frames @JsonIgnoreProperties(ignoreUnknown = true) as the
|
|
* per-class alternative to configuring FAIL_ON_UNKNOWN_PROPERTIES globally. In Jackson 3
|
|
* that feature is already DISABLED by default, so unknown fields are tolerated with no
|
|
* annotation at all. The annotation now matters mainly when you have deliberately turned
|
|
* strictness back ON — which is what the `strict` mapper below does.
|
|
*/
|
|
public class D03AliasAndUnknownFields {
|
|
|
|
public record SearchQuery(
|
|
@JsonAlias({ "q", "query", "search_term" }) String searchKeyword) { }
|
|
|
|
public record LenientResponse(String status, String message) { }
|
|
|
|
@JsonIgnoreProperties(ignoreUnknown = true)
|
|
public record OptedOutResponse(String status, String message) { }
|
|
|
|
public static void main(String[] args) {
|
|
JsonMapper mapper = JsonMapper.builder().build();
|
|
|
|
for (String json : new String[] {
|
|
"{\"q\":\"jackson\"}", "{\"query\":\"jackson\"}", "{\"search_term\":\"jackson\"}" }) {
|
|
System.out.println("alias " + String.format("%-24s", json)
|
|
+ " -> " + mapper.readValue(json, SearchQuery.class).searchKeyword());
|
|
}
|
|
|
|
String extra = "{\"status\":\"OK\",\"message\":\"done\",\"undocumentedField\":42}";
|
|
|
|
// Default Jackson 3 mapper: unknown fields are already ignored.
|
|
System.out.println("default mapper : " + mapper.readValue(extra, LenientResponse.class));
|
|
|
|
// A mapper with strictness deliberately re-enabled.
|
|
JsonMapper strict = JsonMapper.builder()
|
|
.enable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES)
|
|
.build();
|
|
try {
|
|
strict.readValue(extra, LenientResponse.class);
|
|
System.out.println("strict mapper : unreachable");
|
|
} catch (Exception e) {
|
|
System.out.println("strict mapper : " + e.getClass().getSimpleName() + " (as expected)");
|
|
}
|
|
// ...but the annotation opts this one class back out of the strictness.
|
|
System.out.println("strict + anno : " + strict.readValue(extra, OptedOutResponse.class));
|
|
}
|
|
}
|