Why does an error occur when converting json to Java object (gson library)?

Question

Java

I need to convert json to java object. An error occurs when trying to extract temp from main.
json:

{
    "coord": {
        "lon": 30.2642,
        "lat": 59.8944
    },
    "weather": [
        {
            "id": 800,
            "main": "Clear",
            "description": "clear sky",
            "icon": "01n"
        }
    ],
    "base": "stations",
    "main": {
        "temp": 257.74,
        "feels_like": 253.56,
        "temp_min": 256.15,
        "temp_max": 259.82,
        "pressure": 1022,
        "humidity": 85
    },
    "visibility": 10000,
    "wind": {
        "speed": 1,
        "deg": 230
    },
    "clouds": {
        "all": 0
    },
    "dt": 1612803730,
    "sys": {
        "type": 1,
        "id": 8926,
        "country": "RU",
        "sunrise": 1612763713,
        "sunset": 1612794668
    },
    "timezone": 10800,
    "id": 498817,
    "name": "Saint Petersburg",
    "cod": 200
}

Java code:

Tree tree = gson.fromJson(line, Tree.class);
System.out.println(tree);

class Tree {
    private String name;
    Weather[] weather;
    <b>@SerializedName("main")
    Temp[] temp;</b>

    @Override
    public String toString() {
        return "Tree{" +
                "name='" + name + '\'' +
                ", weather=" + Arrays.toString(weather) +
                '}';
    }
}

class Weather {
    private String main;

    @Override
    public String toString() {
        return "Weather{" +
                "main='" + main + '\'' +
                '}';
    }
}

class Temp {
    private double temp;
}

Code that causes the error:

@SerializedName("main")
Temp[] temp;

mistake:

Caused by: java.lang.IllegalStateException: Expected BEGIN_ARRAY but was BEGIN_OBJECT at line 1 column 143 path $.main

I understand that the problem is that "main" occurs before this, but I don't understand how to solve it.

Answer 1

Your object structure is incorrect.
Here, look at this

-----------------------------------com.example.Clouds.java-----------------------------------

package com.example;

import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;

public class Clouds {

@SerializedName("all")
@Expose
public int all;

}
-----------------------------------com.example.Coord.java-----------------------------------

package com.example;

import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;

public class Coord {

@SerializedName("lon")
@Expose
public double lon;
@SerializedName("lat")
@Expose
public double lat;

}
-----------------------------------com.example.Example.java-----------------------------------

package com.example;

import java.util.List;
import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;

public class Example {

@SerializedName("coord")
@Expose
public Coord coord;
@SerializedName("weather")
@Expose
public List<Weather> weather = null;
@SerializedName("base")
@Expose
public String base;
@SerializedName("main")
@Expose
public Main main;
@SerializedName("visibility")
@Expose
public int visibility;
@SerializedName("wind")
@Expose
public Wind wind;
@SerializedName("clouds")
@Expose
public Clouds clouds;
@SerializedName("dt")
@Expose
public int dt;
@SerializedName("sys")
@Expose
public Sys sys;
@SerializedName("timezone")
@Expose
public int timezone;
@SerializedName("id")
@Expose
public int id;
@SerializedName("name")
@Expose
public String name;
@SerializedName("cod")
@Expose
public int cod;

}
-----------------------------------com.example.Main.java-----------------------------------

package com.example;

import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;

public class Main {

@SerializedName("temp")
@Expose
public double temp;
@SerializedName("feels_like")
@Expose
public double feelsLike;
@SerializedName("temp_min")
@Expose
public double tempMin;
@SerializedName("temp_max")
@Expose
public double tempMax;
@SerializedName("pressure")
@Expose
public int pressure;
@SerializedName("humidity")
@Expose
public int humidity;

}
-----------------------------------com.example.Sys.java-----------------------------------

package com.example;

import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;

public class Sys {

@SerializedName("type")
@Expose
public int type;
@SerializedName("id")
@Expose
public int id;
@SerializedName("country")
@Expose
public String country;
@SerializedName("sunrise")
@Expose
public int sunrise;
@SerializedName("sunset")
@Expose
public int sunset;

}
-----------------------------------com.example.Weather.java-----------------------------------

package com.example;

import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;

public class Weather {

@SerializedName("id")
@Expose
public int id;
@SerializedName("main")
@Expose
public String main;
@SerializedName("description")
@Expose
public String description;
@SerializedName("icon")
@Expose
public String icon;

}
-----------------------------------com.example.Wind.java-----------------------------------

package com.example;

import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;

public class Wind {

@SerializedName("speed")
@Expose
public int speed;
@SerializedName("deg")
@Expose
public int deg;

}

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