How to Resolve Jackson JsonMappingException for Empty String Deserialization in Java

How can I resolve the JsonMappingException thrown by Jackson when trying to deserialize an empty string into an object?

Address address = mapper.readValue("", Address.class); // This will throw JsonMappingException

When using the Jackson library to parse JSON in Java, encountering a `JsonMappingException` due to an empty string can be frustrating. This error typically arises when the JSON structure does not match the expected object model, specifically when Jackson attempts to deserialize an empty string into a complex object like the `Address` class.

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;

@JsonIgnoreProperties(ignoreUnknown = true)
@JsonDeserialize(using = AddressDeserializer.class)
public class Address {
    private String city;
    private String stateProvinceCode;
    private String countryCode;

    // Default no-arg constructor required for Jackson to create instances
    public Address() {}

    @JsonCreator
    public Address(
        @JsonProperty("City") String city,
        @JsonProperty("StateProvinceCode") String stateProvinceCode,
        @JsonProperty("CountryCode") String countryCode) {
        this.city = city;
        this.stateProvinceCode = stateProvinceCode;
        this.countryCode = countryCode;
    }

    // Getters and Setters 
}

Causes

• The JSON input provided is an empty string instead of a valid JSON object.
• Jackson's default behavior doesn't handle empty strings for object types, expecting a valid representation of an object.

Solutions

• Use `@JsonCreator` and `@JsonProperty` annotations in your `Address` class to customize the constructor for deserialization.
• Handle empty strings by adding a custom deserializer for the `Address` class.

Mistake: Not defining a no-argument constructor in the Address class.

Solution: Always ensure that there is a public no-argument constructor in your data classes for Jackson to instantiate objects.

Mistake: Failing to handle potential empty strings in incoming JSON.

Solution: Implement custom deserializers to provide fallback logic when encountering empty strings.