Example of using the `@Size` Annotation with Spring and Jackson.

ValidjacksonspringApplication.java

package com.docutools.demo.validjacksonspring;

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RestController;

import javax.validation.Valid;
import javax.validation.constraints.Size;
import java.util.Objects;

@RestController
@SpringBootApplication
public class ValidjacksonspringApplication {

	public static void main(String[] args) {
		SpringApplication.run(ValidjacksonspringApplication.class, args);
	}

	@PostMapping(path = "/hello")
	public String greet(@RequestBody @Valid Person person) {
		return String.format("Hello %s", person.getName());
	}

	public static class Person {

		@Size(max = 5, message = "A persons name must not be longer than 5 characters.")
		private String name;

		@JsonCreator
		public Person(@JsonProperty(value = "name", required = true) String name) {
			this.name = name;
		}

		public String getName() {
			return name;
		}

		@Override
		public boolean equals(Object o) {
			if (this == o) return true;
			if (o == null || getClass() != o.getClass()) return false;
			Person person = (Person) o;
			return Objects.equals(name, person.name);
		}

		@Override
		public int hashCode() {
			return Objects.hash(name);
		}

		@Override
		public String toString() {
			return "Person{" +
							"name='" + name + '\'' +
							'}';
		}
	}

}

Thanks for such a good explanation of @ Size. But, if you don't mind, could you comment what @ JsonCreator and @ JsonProperty does exactly in this code or in general ?
Thanks in advance.