Jackson Mapper - 如何在 null 或空值上失败

Question

我们在代码中使用 Jackson JSON 映射器来反序列化一些配置对象。我们希望 Jackson 在特定字段缺失或为空时反序列化失败

Jackson 中支持此行为的唯一功能是针对基元的：

final DeserializationConfig.Feature failOnPremitives = DeserializationConfig.Feature.FAIL_ON_NULL_FOR_PRIMITIVES;

问题是有问题的字段主要是字符串

非常感谢任何帮助

Answer 1

你考虑过Bean Validation吗？

虽然 Jackson 专注于 JSON 解析，但 Bean 验证完全是关于对 bean 进行声明和执行验证。

您可以使用 @NotNull or @NotBlank from Hibernate Validator，Bean 验证参考实现。

或者您可以使用 JSON Schema。

Answer 2

必须创建特定于对象的自定义反序列化器。

import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.core.ObjectCodec;
import com.fasterxml.jackson.core.Version;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.deser.std.StdDeserializer;
import com.fasterxml.jackson.databind.module.SimpleModule;

import java.io.IOException;

class JacksonDeserializerTest {

    public static void main(String[] args) throws Exception {
        ObjectMapper mapper = new ObjectMapper();
        SimpleModule module = new SimpleModule("CustomPersonDeserializer", new Version(1, 0, 0, null, null, null));
        module.addDeserializer(Person.class, new CustomPersonDeserializer());
        mapper.registerModule(module);

        String jsonString = "{ \"id\": 1, \"name\": \"User 1 \"}";
        Person user = mapper.readValue(jsonString, Person.class);
        System.out.println("User: " + user.toString());

        jsonString = "{ \"id\": 1}";
        user = mapper.readValue(jsonString, Person.class);
    }

    static class CustomPersonDeserializer extends StdDeserializer<Person> {

        private static final long serialVersionUID = -4100181951833318756L;

        public CustomPersonDeserializer() {
            this(null);
        }

        public CustomPersonDeserializer(Class<?> vc) {
            super(vc);
        }

        @Override
        public Person deserialize(JsonParser parser, DeserializationContext deserializer) throws IOException, JsonProcessingException {
            Person person = new Person();
            ObjectCodec codec = parser.getCodec();
            JsonNode node = codec.readTree(parser);

            JsonNode idNode = node.get("id");
            int id = idNode.asInt();
            person.setId(id);

            JsonNode nameNode = node.get("name");
            if(nameNode == null){
                throw new IOException("name must be provided");
            }

            String name = nameNode.asText();
            if (name.trim().length() < 1){
                throw new IOException("name can not be empty");
            }

            person.setName(name);
            return person;
        }
    }

    static class Person {
        private int id;
        private String name;

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public int getId() {
            return id;
        }

        public void setId(int id) {
            this.id = id;
        }

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

Answer 3

有一个选项叫做：FAIL_ON_NULL_FOR_CREATOR_PARAMETERS。

所以我假设它可以在以下位置访问：DeserializationConfig.Feature.FAIL_ON_NULL_FOR_CREATOR_PARAMETERS;

或在yml中：

jackson:
    serialization:
      indent-output: false
    deserialization:
      fail-on-unknown-properties: true
      fail-on-missing-creator-properties: true
      fail-on-null-creator-properties: true

这适用于所有类型，字符串、整数、双精度等。

Answer 4

替代方式：
这也适用于对象

ObjectMapper mapper= new ObjectMapper();
mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);

Jackson Mapper - 如何在 null 或空值上失败

Jackson Mapper - how to fail on null or empty values

java

jackson

mapper

deserialization