如何忽略 json 字段并使用 Jackson ObjectMapper 获取其值进行映射答案

【问题标题】：How to ignore a json field and get its value to map using Jackson ObjectMapper如何忽略 json 字段并使用 Jackson ObjectMapper 获取其值进行映射
【发布时间】：2017-02-14 18:27:44
【问题描述】：

鉴于以下 json

  {
    "countries":{
        "country":[{
            "name":"USA",
             "independence":"July 4, 1776",
         }],
     },
  }

我想忽略“国家”并获得国家的价值。因此，映射后我的 json 应该是这样的

{
  "countries": [{
            "name":"USA",
             "independence":"July 4, 1776",
         }],
 }

ObjectMapper 目前可以做到这一点吗？

编辑：以下是 Pojo

public class Result {
private static final long serialVersionUID = 6403654749443599206L;

@Getter @Setter @JsonProperty("country") private List<Country> countries;
}

public class Country {
private static final long serialVersionUID = 6403654749443599206L;

@Getter @Setter private String name;
@Getter @Setter private String independence;
}

我正在这样做

    return new ObjectMapper().readValue({jsonValue}, Result.class);

【问题讨论】：

你的代码是什么样的？
@CássioMazzochiMolin return mapper.readValue({jsonValue}, {pojo.class});
你的 POJO 类是什么样的？
@CássioMazzochiMolin 我更新了帖子。

标签： java spring jackson objectmapper

【解决方案1】：

输入的 json 语法错误。应该是这样的

  {
    "countries":{
        "country":[{
            "name":"USA",
             "independence":"July 4, 1776"
         }]
     }
  }

ObjectMapper 用于将 json 转为 Object，将 Object 转为 json。无论如何，要将第一个 json 转换为您想要的另一个，您可以执行以下操作：

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;

import java.io.IOException;
import java.util.List;

public class ConvertExample {

    public static void main(String[]args) {

        String inputJson = new String("{\"countries\":{\"country\":[{\"name\":\"USA\", \"independence\":\"July 4, 1776\"}]}}");

        ObjectMapper mapper = new ObjectMapper();
        mapper.enable(SerializationFeature.INDENT_OUTPUT); //To indent output, optional
        try {
            StartPojo startPojo = mapper.readValue(inputJson, StartPojo.class);
            EndPojo endPojo = new EndPojo();
            endPojo.countries = startPojo.getCountries().getCountry();
            String outputJson = mapper.writeValueAsString(endPojo);

            System.out.println("Output:");
            System.out.println(outputJson);

        } catch (IOException e) {
            e.printStackTrace(); //Cannot read the input json
        }
    }

    @JsonIgnoreProperties(ignoreUnknown = true)
    public static class StartPojo {
        private Countries countries;

        public Countries getCountries() {
            return countries;
        }

        public void setCountries(Countries countries) {
            this.countries = countries;
        }
    }

    @JsonIgnoreProperties(ignoreUnknown = true)
    public static class EndPojo {
        private List<Country> countries;

        public List<Country> getCountries() {
            return countries;
        }

        public void setCountries(List<Country> countries) {
            this.countries = countries;
        }
    }

    @JsonIgnoreProperties(ignoreUnknown = true)
    public static class Countries {
        private List<Country> country;

        public List<Country> getCountry() {
            return country;
        }

        public void setCountry(List<Country> country) {
            this.country = country;
        }
    }

    @JsonIgnoreProperties(ignoreUnknown = true)
    public static class Country {
        private String name;
        private String independence;

        public String getName() {
            return name;
        }

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

        public String getIndependence() {
            return independence;
        }

        public void setIndependence(String independence) {
            this.independence = independence;
        }
    }
}

这个类接受输入 json 并通过将其打印到控制台将其转换为其他格式。这段代码的输出是：

{
  "countries" : [ {
    "name" : "USA",
    "independence" : "July 4, 1776"
  } ]
}

【讨论】：