Ankur
ef05f9024e
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.
52 lines
2.2 KiB
Java
52 lines
2.2 KiB
Java
package com.ankurm.jackson3.part2modernjava;
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import com.fasterxml.jackson.annotation.JsonInclude;
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import tools.jackson.databind.json.JsonMapper;
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import java.util.Optional;
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/**
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* Post: Jackson with Records, Optionals, Sealed Classes
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* https://ankurm.com/jackson-java-records-optionals/
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* Section: "Jackson with Optional<T>"
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*
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* Jackson 3 handles Optional natively. There is no jackson-datatype-jdk8
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* dependency in the pom and no registerModule(new Jdk8Module()) call — those are
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* Jackson 2 requirements, and the Jdk8Module class does not exist under
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* tools.jackson at all.
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*/
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public class C02OptionalFields {
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public record CustomerProfile(String customerName, Optional<String> middleName) { }
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/** NON_ABSENT is the inclusion value that understands Optional.empty(). */
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@JsonInclude(JsonInclude.Include.NON_ABSENT)
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public record CompactProfile(String customerName, Optional<String> middleName) { }
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public static void main(String[] args) {
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JsonMapper mapper = JsonMapper.builder().build();
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// Present value: the Optional is unwrapped, not wrapped in {"present":true}.
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System.out.println("present : "
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+ mapper.writeValueAsString(new CustomerProfile("Alice", Optional.of("Marie"))));
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// Empty Optional: serialises as null by default.
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System.out.println("empty : "
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+ mapper.writeValueAsString(new CustomerProfile("Bob", Optional.empty())));
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// NON_ABSENT omits the property entirely instead of writing null.
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System.out.println("absent : "
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+ mapper.writeValueAsString(new CompactProfile("Bob", Optional.empty())));
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// Deserialise back.
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String json = "{\"customerName\":\"Alice\",\"middleName\":\"Marie\"}";
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CustomerProfile restored = mapper.readValue(json, CustomerProfile.class);
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System.out.println("isPresent: " + restored.middleName().isPresent());
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// A missing property deserialises to Optional.empty(), never to null.
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CustomerProfile missing = mapper.readValue("{\"customerName\":\"Carol\"}", CustomerProfile.class);
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System.out.println("missing -> " + missing.middleName() + " (null? "
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+ (missing.middleName() == null) + ")");
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}
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}
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