Converting JSON string to Map with custom types

Question

My JSON string is like this:

{
    "100": {
        "mode": 100,
        "enabled": true,
        "value": "someString"
    },
    "101": {
        "mode": 101,
        "enabled": false,
        "value": "someString"
    }
}

I have a class actually

class Mode {

    @JsonProperty("mode")
    long mode;

    @JsonProperty("enabled")
    boolean enabled;

    @JsonProperty("value")
    String value;

}

I tried

objectMapper.readValue(jsonString, Map.class);

But its generic map and also the numbers are converted to Integer types not Long. Using Mode in place of Map above throws exception.

How to get Long in generic Map?
And, how can I get a Map<String, Mode> out of the json string?

I have got jackson library in my projects maven.

Syed Khalid Ahmed · Accepted Answer · 2019-04-11 09:54:41Z

2

your Key is String . It will work for you .

TypeReference<HashMap<String, Mode>> typeRef = new TypeReference<HashMap<String, Mode>>() {};
Map<String,Mode> map = objectMapper.readValue(jsonString,typeRef);

Updated :

import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

public class Mode {

  @JsonProperty("mode")
  long mode;

  @JsonProperty("enabled")
  boolean enabled;

  @JsonProperty("value")
  String value;

  @Override
  public String toString() {
    return "Mode{" +
        "mode=" + mode +
        ", enabled=" + enabled +
        ", value='" + value + '\'' +
        '}';
  }

  public static void main(String[] args) throws IOException {
    String json = "{\n"
        + "    \"100\": {\n"
        + "        \"mode\": 100,\n"
        + "        \"enabled\": true,\n"
        + "        \"value\": \"someString\"\n"
        + "    },\n"
        + "    \"101\": {\n"
        + "        \"mode\": 101,\n"
        + "        \"enabled\": false,\n"
        + "        \"value\": \"someString\"\n"
        + "    }\n"
        + "}";

    ObjectMapper objectMapper = new ObjectMapper();
    TypeReference<HashMap<String, Mode>> typeRef = new TypeReference<HashMap<String, Mode>>() {
    };
    Map<String, Mode> map = objectMapper.readValue(json, typeRef);
    map.entrySet().forEach(entry-> System.out.println(entry.getKey() + " : " +entry.getValue() ));
  }
}

Output :

100 : Mode{mode=100, enabled=true, value='someString'}
101 : Mode{mode=101, enabled=false, value='someString'}

edited Apr 11, 2019 at 9:54

answered Apr 11, 2019 at 9:41

Syed Khalid Ahmed

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4 Comments

xploreraj Over a year ago

com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of "com.xyz.Mode" (although at least one Creator exists): cannot deserialize from Object value (no delegate- or property-based Creator)  at [Source: (String)"{"1001":{"mode":9223372036854775807,"enabled":true,"value":8}}"; line: 1, column: 10] (through reference chain: java.util.LinkedHashMap["1001"])

xploreraj Over a year ago

Thanks Khalid for looking. As I said, I am getting above exception.

Syed Khalid Ahmed Over a year ago

@xploreraj see Updated code. It work perfectly fine. ans i also show the output after reading Json.

xploreraj Over a year ago

Thanks Khalid. I was creating the map and then using typeref, thats why I think I got the error. Your solutions works. As regards to Integer to Long, I figured out if number is out of range for int, its automatically converted into Long by jackson.

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