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.

Answer 1

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);