How to Deserialize a Blank JSON String Value to Null for Java.Lang.String

How to deserialize a blank JSON string value to null for java.lang.String?

Jackson will give you null for other objects, but for String it will give empty String.

But you can use a Custom JsonDeserializer to do this:

class CustomDeserializer extends JsonDeserializer<String> {

    @Override
    public String deserialize(JsonParser jsonParser, DeserializationContext context) throws IOException, JsonProcessingException {
        JsonNode node = jsonParser.readValueAsTree();
        if (node.asText().isEmpty()) {
            return null;
        }
        return node.toString();
    }

}

In class you have to use it for location field:

class EventBean {
    public Long eventId;
    public String title;

    @JsonDeserialize(using = CustomDeserializer.class)
    public String location;
}

Jackson Deserialization of all empty Strings to null in class

Define a serializer as follows:

public class EmptyStringAsNullDeserializer extends JsonDeserializer<String> {

    @Override
    public String deserialize(JsonParser jsonParser, 
                              DeserializationContext deserializationContext) 
                              throws IOException {

        String value = jsonParser.getText();
        if (value == null || value.isEmpty()) {
            return null;
        } else {
            return value;
        }
    }
}

Add it to a Module and then register the Module to your ObjectMapper:

SimpleModule module = new SimpleModule();
module.addDeserializer(String.class, new EmptyStringAsNullDeserializer());

ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(module);

Jackson: deserializing null Strings as empty Strings

You can either set it in the default constructor, or on declaration:

public class POI {
    @JsonProperty("name")
    private String name; 

    public POI() {
        name = "";
    }
}

OR

public class POI {
    @JsonProperty("name")
    private String name = "";
} 

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