如何将json解析为对象

Question

我想创建一个包含一个字段的对象：List

public class Responce {

List<String> cities 

// some methods

}

JSON 本身看起来是这样的（它在对象中有一个对象）：

{"responce" : {
   "list" : {
    "1": "А",
    "2": "B",
    "3": "C",
      .....  
    }
  }

我只想获取 A、B、C 的列表以及所有这些，而不需要创建大量的类：)

我已经尝试过 JsonNons 和 @JsonPropery，但到目前为止还没有运气。

Answer 1

我没有得到你的问题，但如果你需要反序列化 json 数据，那么你可以试试这个。

为 List 创建一个 pojo 类

public class cityListPojo{

   private List<String> cityList;

   public List<String> getCityList() {
       return cityList;
   }

   public void setCityList(List<String> cityList) {
       this.cityList = cityList;
   }
}

然后使用jackson库，您可以将收到的json字符串转换为cityListPojo类对象

// jsonString:- 从 db 或任何你得到的地方获取 json 并将其转换为字符串。

cityListPojo obj = new ObjectMapper().readValue(jsonString, cityListPojo.class);

然后使用 obj 对象将 List 返回为。

List<String> cityList = obj.getCityList();

// 这些jackson依赖仅供参考。

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-core</artifactId>
    <version>2.11.0</version>
</dependency>
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.11.0</version>
</dependency>

Answer 2

如下设置城市，

Response.java

public class Response {

    @JsonProperty
    private Map<String, String> list;

    @JsonIgnore
    List<String> cities = new ArrayList<>();

    public Map<String, String> getList() {
        return list;
    }

    public void setList(Map<String, String> list) {
        Set<String> keys = list.keySet();
        for (String key : keys) {
            cities.add(list.get(key));
        }
        this.list = list;
    }

    public List<String> getCities() {
        return cities;
    }

    public void setCities(List<String> cities) {
        this.cities = cities;
    }
}

测试方法

    public static void main(String... args) throws Exception {
        ObjectMapper mapper = new ObjectMapper();

        String json = " {\r\n" + 
                "   \"list\" : {\r\n" + 
                "    \"1\": \"А\",\r\n" + 
                "    \"2\": \"B\",\r\n" + 
                "    \"3\": \"C\",\r\n" + 
                "    \"4\":\"D\",\r\n" + 
                "    \"5\":\"E\"\r\n" + 
                "    }\r\n" + 
                "  }";

        Response response = mapper.readValue(json, Response.class);

        System.out.println("Object:" + mapper.writeValueAsString(response));

        System.out.println("Cities:");
        for (String city : response.getCities()) {
            System.out.print("\t" + city);
        }
    }

或可以使用自定义序列化器

Response.java

@JsonSerialize(using = ResponseSerializer.class)
public class Response {

    private Map<String, String> list;

    List<String> cities = new ArrayList<>();

    public Map<String, String> getList() {
        return list;
    }

    public void setList(Map<String, String> list) {
        this.list = list;
    }

    public List<String> getCities() {
        return cities;
    }

    public void setCities(List<String> cities) {
        this.cities = cities;
    }
}

ResponseSerializer.java

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.Set;

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.ser.std.StdSerializer;

public class ResponseSerializer extends StdSerializer<Response> {

    public ResponseSerializer() {
        this(null);
    }

    public ResponseSerializer(Class<Response> t) {
        super(t);
    }

    @Override
    public void serialize(Response value, JsonGenerator jgen, SerializerProvider provider)
            throws IOException, JsonProcessingException {

        jgen.writeStartObject();

        Map<String, String> list = value.getList();

        List<String> cities = new ArrayList<>();
        Set<String> keys = list.keySet();
        for (String key : keys) {
            cities.add(list.get(key));
        }
        jgen.writeObjectField("cities", cities);
        jgen.writeEndObject();
    }
}

测试方法

public static void main(String... args) throws Exception {
        ObjectMapper mapper1 = new ObjectMapper();
        Response response1=new Response() ;

        Map<String, String> map=new HashMap<>();

        map.put("1", "A");      
        map.put("2", "B");
        map.put("3", "C");

        response1.setList(map);

        System.out.println("Object:" +  mapper1.writeValueAsString(response1));

        System.out.println("Cities:");
        for (String city : response1.getCities()) {
            System.out.print("\t" + city);
        }
    }