web-dev-qa-db-ja.com

Jacksonを使用してJSON文字列を配列に解析する方法

次の値を持つStringがあります。

[
  {
    "key1": "value11",
    "key2": "value12"
  },
  {
    "key1": "value21",
    "key2": "value22"
  }
]

そして、次のクラス：

public class SomeClass {
    private String key1;
    private String key2;
    /* ... getters and setters omitted ...*/
}

そして、それをList<SomeClass>またはSomeClass[]に解析したい

JacksonObjectMapperを使用して行う最も簡単な方法はどれですか？

javajsonjackson
89
mmutilva

私はついにそれを得た：

ObjectMapper objectMapper = new ObjectMapper();
TypeFactory typeFactory = objectMapper.getTypeFactory();
List<SomeClass> someClassList = objectMapper.readValue(jsonString, typeFactory.constructCollectionType(List.class, SomeClass.class));
157
mmutilva

他の答えは正しいですが、完全を期すために、他の方法があります：

List<SomeClass> list = mapper.readValue(jsonString, new TypeReference<List<SomeClass>>() { });
SomeClass[] array = mapper.readValue(jsonString, SomeClass[].class);
78
StaxMan

配列を使用した完全な例。 「constructArrayType（）」を「constructCollectionType（）」または必要な他のタイプに置き換えます。

import Java.io.IOException;

import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.type.TypeFactory;

public class Sorting {

    private String property;

    private String direction;

    public Sorting() {

    }

    public Sorting(String property, String direction) {
        this.property = property;
        this.direction = direction;
    }

    public String getProperty() {
        return property;
    }

    public void setProperty(String property) {
        this.property = property;
    }

    public String getDirection() {
        return direction;
    }

    public void setDirection(String direction) {
        this.direction = direction;
    }

    public static void main(String[] args) throws JsonParseException, IOException {
        final String json = "[{\"property\":\"title1\", \"direction\":\"ASC\"}, {\"property\":\"title2\", \"direction\":\"DESC\"}]";
        ObjectMapper mapper = new ObjectMapper();
        Sorting[] sortings = mapper.readValue(json, TypeFactory.defaultInstance().constructArrayType(Sorting.class));
        System.out.println(sortings);
    }
}
4
Didasko

JSONLint.comでjsonを検証してからJacksonを使用して、この問題を分類しました。以下は同じコードです。

 Main Class:-

String jsonStr = "[{\r\n" + "       \"name\": \"John\",\r\n" + "        \"city\": \"Berlin\",\r\n"
                + "         \"cars\": [\r\n" + "            \"FIAT\",\r\n" + "          \"Toyata\"\r\n"
                + "     ],\r\n" + "     \"job\": \"Teacher\"\r\n" + "   },\r\n" + " {\r\n"
                + "     \"name\": \"Mark\",\r\n" + "        \"city\": \"Oslo\",\r\n" + "        \"cars\": [\r\n"
                + "         \"VW\",\r\n" + "            \"Toyata\"\r\n" + "     ],\r\n"
                + "     \"job\": \"Doctor\"\r\n" + "    }\r\n" + "]";

        ObjectMapper mapper = new ObjectMapper();

        MyPojo jsonObj[] = mapper.readValue(jsonStr, MyPojo[].class);

        for (MyPojo itr : jsonObj) {

            System.out.println("Val of getName is: " + itr.getName());
            System.out.println("Val of getCity is: " + itr.getCity());
            System.out.println("Val of getJob is: " + itr.getJob());
            System.out.println("Val of getCars is: " + itr.getCars() + "\n");

        }

POJO:

public class MyPojo {

private List<String> cars = new ArrayList<String>();

private String name;

private String job;

private String city;

public List<String> getCars() {
    return cars;
}

public void setCars(List<String> cars) {
    this.cars = cars;
}

public String getName() {
    return name;
}

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

public String getJob() {
    return job;
}

public void setJob(String job) {
    this.job = job;
}

public String getCity() {
    return city;
}

public void setCity(String city) {
    this.city = city;
} }

  RESULT:-
         Val of getName is: John
         Val of getCity is: Berlin
         Val of getJob is: Teacher
         Val of getCars is: [FIAT, Toyata]

          Val of getName is: Mark
          Val of getCity is: Oslo
          Val of getJob is: Doctor
          Val of getCars is: [VW, Toyata]
0
Atul Sharma