getting nested maps in Java

Question

I've the below json code.

{
"main": {
    "temp": 301.335,
    "pressure": 951.08,
    "humidity": 45,
    "temp_min": 301.335,
    "temp_max": 301.335,
    "sea_level": 1025.43,
    "grnd_level": 951.08
  }
}

And I'm using the below java code to get this data.

This above json is stored in a String text.

            System.out.println(text);

        ObjectMapper mapper = new ObjectMapper();

        // read JSON from a file
        Map<String, Object> map = mapper.readValue(text, new TypeReference<Map<String, Object>>() {
        });

        System.out.println(map.get("main"));

        Map<String, Object> mapIn = mapper.readValue(map.get("main").toString(),
                new TypeReference<Map<String, Object>>() {
                });

        System.out.println(mapIn);

Here i want to print the temp value in my console. But as of now I get the below o/p with exception.

{
  "coord": {
    "lon": 106.85,
    "lat": -6.21
  },
  "weather": [{
    "id": 802,
    "main": "Clouds",
    "description": "scattered clouds",
    "icon": "03d"
  }],
  "base": "stations",
  "main": {
    "temp": 304.15,
    "pressure": 1007,
    "humidity": 62,
    "temp_min": 304.15,
    "temp_max": 304.15
  },
  "visibility": 8000,
  "wind": {
    "speed": 3.1,
    "deg": 320
  },
  "clouds": {
    "all": 40
  },
  "dt": 1478244600,
  "sys": {
    "type": 1,
    "id": 8043,
    "message": 0.0084,
    "country": "ID",
    "sunrise": 1478211943,
    "sunset": 1478256397
  },
  "id": 1642911,
  "name": "Jakarta",
  "cod": 200
} {
  temp = 304.15, pressure = 1007, humidity = 62, temp_min = 304.15, temp_max = 304.15
}
Exception in thread "main"
java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to java.lang.String
at Jackson2Example.main(Jackson2Example.java: 51)

please let me know where am I going wrong, how can I fix this and get temp value.

Thanks

why are you calling mapper.readValue again. This time you are calling it with String (not Json String). — Sachin Gupta
– Sachin Gupta, Commented Nov 4, 2016 at 8:50
@SachinGupta, this is where I'm stuck... unable to know how to get that temp from output — user3872094
– user3872094, Commented Nov 4, 2016 at 8:53

Sachin Gupta · Accepted Answer · 2016-11-04 09:00:56Z

1

You need not to call mapper.readValue again. try this:

Map<String, Object> map = mapper.readValue(text, new TypeReference<Map<String, Object>>() {
    });


Map<String, Object> mainMap = (Map<String, Object>) map.get("main");        

System.out.println(mainMap.get("temp"));

answered Nov 4, 2016 at 9:00

Sachin Gupta

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1 Comment

user3872094 Over a year ago

Haa, now I got this, this would in turn get value from the nested json. Thank you verymuch...

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