Deserializing into a HashMap of custom objects with jackson

Question

I have the following class:

import org.codehaus.jackson.annotate.JsonIgnoreProperties;
import org.codehaus.jackson.annotate.JsonProperty;

import java.io.Serializable;
import java.util.HashMap;

@JsonIgnoreProperties(ignoreUnknown = true)
public class Theme implements Serializable {

    @JsonProperty
    private String themeName;

    @JsonProperty
    private boolean customized;

    @JsonProperty
    private HashMap<String, String> descriptor;

    //...getters and setters for the above properties
}

When I execute the following code:

    HashMap<String, Theme> test = new HashMap<String, Theme>();
    Theme t1 = new Theme();
    t1.setCustomized(false);
    t1.setThemeName("theme1");
    test.put("theme1", t1);

    Theme t2 = new Theme();
    t2.setCustomized(true);
    t2.setThemeName("theme2");
    t2.setDescriptor(new HashMap<String, String>());
    t2.getDescriptor().put("foo", "one");
    t2.getDescriptor().put("bar", "two");
    test.put("theme2", t2);
    String json = "";
    ObjectMapper mapper = objectMapperFactory.createObjectMapper();
    try {
        json = mapper.writeValueAsString(test);
    } catch (IOException e) {
        e.printStackTrace(); 
    }

The json string produced looks like this:

{
  "theme2": {
    "themeName": "theme2",
    "customized": true,
    "descriptor": {
      "foo": "one",
       "bar": "two"
    }
  },
  "theme1": {
    "themeName": "theme1",
    "customized": false,
    "descriptor": null
  }
}

My problem is getting the above json string to de-serizlize back into a

HashMap<String, Theme>

object.

My de-serialization code looks like this:

HashMap<String, Themes> themes =
        objectMapperFactory.createObjectMapper().readValue(json, HashMap.class);

Which de-serializes into a HashMap with the correct keys, but does not create Theme objects for the values. I don't know what to specify instead of "HashMap.class" in the readValue() method.

Any help would be appreciated.

score 100 · Accepted Answer · answered Aug 02 '13 at 10:13

100

You should create specific Map type and provide it into deserialization process:

TypeFactory typeFactory = mapper.getTypeFactory();
MapType mapType = typeFactory.constructMapType(HashMap.class, String.class, Theme.class);
HashMap<String, Theme> map = mapper.readValue(json, mapType);

answered Aug 02 '13 at 10:13

Michał Ziober

37,175
18
99
146

Ok, we're definitely heading in the right direction, as it is de-serializing using the code above. However, The hashmap is only coming in with a single key/value (theme2). It does have the correct theme associated with the key, but theme1 isn't in the hashmap? – wbj Aug 05 '13 at 14:17
Why not. For me, app prints this when I deserialize your JSON: '{theme1=Theme [themeName=theme1, customized=false, descriptor=null], theme2=Theme [themeName=theme2, customized=true, descriptor={foo=one, bar=two}]}'. – Michał Ziober Aug 05 '13 at 16:40
Found the problem - poorly formed json string in my test data. So your solution works as advertised ;) – wbj Aug 05 '13 at 16:55
1

I this also possible using Jackson annotations only? – Saiteja Parsi Jun 11 '20 at 11:10

score 31 · Answer 2 · edited Feb 19 '20 at 03:10

31

You can use TypeReference class which does the type casting for map with user defined types. More documentation at https://github.com/FasterXML/jackson-databind/

ObjectMapper mapper = new ObjectMapper();
Map<String,Theme> result =
  mapper.readValue(src, new TypeReference<Map<String,Theme>>() {});

edited Feb 19 '20 at 03:10

Maria Ines Parnisari

16,584
9
85
130

answered Sep 27 '13 at 17:35

user2824471

411
3
3

score 3 · Answer 3 · answered Jun 16 '18 at 00:00

You can make a POJO that extends a Map.

This is important for dealing with nested maps of objects.

{
  key1: { nestedKey1: { value: 'You did it!' } }
}

This can be deserialized via:

class Parent extends HashMap<String, Child> {}

class Child extends HashMap<String, MyCoolPojo> {}

class MyCoolPojo { public String value; }

Parent parent = new ObjectMapper().readValue(json, Parent.class);
parent.get("key1").get("nestedKey1").value; // "You did it!"

Deserializing into a HashMap of custom objects with jackson

3 Answers3

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