I'm receiving JSON which I want to parse:

[
    {
        "id": "f9952c24-1b44-4379-9aef-b10075e93562",
        "sections": [
            {
                "id": "7fe9f47e-9cfe-46c7-9c77-f729b9fb98a4",
                "type": "vehicle",
                "summary": {
                    "duration": 23377,
                    "length": 480501,
                    "baseDuration": 22140
                }
            }
        ]
    }
]

My Java model classes (generated by json2pojo):

public class HereRoute {
  @SerializedName("routes")
  @Expose
  private List<Route> routes = null;
}

public class Route {
  @SerializedName("id")
  @Expose
  private String id;
  @SerializedName("sections")
  @Expose
  private List<Section> sections = null;
}

public class Section {
  @SerializedName("id")
  @Expose
  private String id;
  @SerializedName("type")
  @Expose
  private String type;
  @SerializedName("summary")
  @Expose
  private Summary summary;
  }

public class Summary {
  @SerializedName("duration")
  @Expose
  private Integer duration;
  @SerializedName("length")
  @Expose
  private Integer length;
  @SerializedName("baseDuration")
  @Expose
  private Integer baseDuration;
}

I'm only interested about Summary length which I want to save in db. How can I parse it to get only summary length for every object from json? Do I need something like Gson?

CodePudding user response：

First of all include the JSON Library in your project.

Then iterate through your JSON like this:

JSONArray firstLevelArrray = new JSONArray(jsonString); // Getting the big array

for(int i = 0 ; i < firstLevelArrray.length(); i  )
{
    Integer length = firstLevelArray.getJSONObject(i) // getting the first object of the array
               .getJSONArray("sections") // Getting the sections array
               .getJSONObject(0) // Getting the first element of the sections array
               .getJSONObject("summary")
               .getInt("length");
               
    // But how sure are you that you won't have a null in there?
}

I still wouldn't go this way, there is a big possibility of a NullPointerException in there. You can always handle it and treat it as if the field was not in there, but still...

CodePudding user response：

You can use the 'jackson' for deserializing.

Include the dependency using maven

<dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-core</artifactId>
        <version>2.13.0</version>
</dependency>

use ObjectMapper for deserializing your JSON string.

ObjectMapper mapper = new ObjectMapper();
data = mapper.readValue(json, Data[].class);

A complete working example would be as follows

import java.io.IOException;

import com.fasterxml.jackson.databind.ObjectMapper;

public class Test {

static String json = "[\r\n"
          "    {\r\n"
          "        \"id\": \"f9952c24-1b44-4379-9aef-b10075e93562\",\r\n"
          "        \"sections\": [\r\n"
          "            {\r\n"
          "                \"id\": \"7fe9f47e-9cfe-46c7-9c77- 
f729b9fb98a4\",\r\n"
          "                \"type\": \"vehicle\",\r\n"
          "                \"summary\": {\r\n"
          "                    \"duration\": 23377,\r\n"
          "                    \"length\": 480501,\r\n"
          "                    \"baseDuration\": 22140\r\n"
          "                }\r\n"
          "            }\r\n"
          "        ]\r\n"
          "    }\r\n"
          "]";
public static void main(String[] args) {
    ObjectMapper mapper = new ObjectMapper();
    Test.Data data[] = null;
    try {
        data = mapper.readValue(json, Data[].class);
    } catch (IOException e) {
        e.printStackTrace();
    }

    System.out.println(data[0].sections[0].summary.length);

}

private static class Data {
    String id;
    Sections sections[];

    public Data() {
        super();
    }

    public Data(String id, Test.Sections[] sections) {
        super();
        this.id = id;
        this.sections = sections;
    }

    public String getId() {
        return id;
    }

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

    public Sections[] getSections() {
        return sections;
    }

    public void setSections(Sections[] sections) {
        this.sections = sections;
    }

}

private static class Sections {
    private String id;
    private String type;
    private Summary summary;

    public Sections() {
        super();
    }

    public Sections(String id, String type, Test.Summary summary) {
        super();
        this.id = id;
        this.type = type;
        this.summary = summary;
    }

    public String getId() {
        return id;
    }

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

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public Summary getSummary() {
        return summary;
    }

    public void setSummary(Summary summary) {
        this.summary = summary;
    }

}

private static class Summary {
    private Integer duration;
    private Integer length;
    private Integer baseDuration;

    public Summary() {
        super();
    }

    public Summary(Integer duration, Integer length, Integer baseDuration) {
        super();
        this.duration = duration;
        this.length = length;
        this.baseDuration = baseDuration;
    }

    public Integer getDuration() {
        return duration;
    }

    public void setDuration(Integer duration) {
        this.duration = duration;
    }

    public Integer getLength() {
        return length;
    }

    public void setLength(Integer length) {
        this.length = length;
    }

    public Integer getBaseDuration() {
        return baseDuration;
    }

    public void setBaseDuration(Integer baseDuration) {
        this.baseDuration = baseDuration;
    }

}
}