I'm fetching addresses from an external API. This is the class representing the addresses:

@JsonInclude(JsonInclude.Include.NON_NULL)
public class Address implements Serializable {
    private static final long serialVersionUID = -7134571546367230214L;

    private String street;
    private int houseNumber;
    private String district;
    private String city;
    private String state;
    private String zipCode;
}

However, when the given address doesn't have a houseNumber, the API will return a string such as "NO NUMBER" on the houseNumber field, causing Jackson to throw a deserialization error, since it was expecting an integer number and got a string.

How can I tell Jackson to convert houseNumber to 0 when it finds a string value?

CodePudding user response：

You could try with a custom deserializer on the field:

 @JsonDeserialize(using = HouseNoDeserializer.class)
 private int houseNumber;

The deserializer could look like this:

 class HouseNoDeserializer extends JsonDeserializer<Integer> {
    @Override
    public Integer deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {
        //read the value as a string since you don't know whether it is a number or a string
        String v = p.readValueAs(String.class);
        try {
            //try to parse the string to an integer, if not return 0 as required (it is a non-numeric string)
            return Integer.parseInt(v);
        } catch(NumberFormatException nfe) {
            return 0;
        }
    }
}

However, I'd change houseNumber to take String anyways because right now you can't support numbers such as "1/c", "123a", etc. which are common at least in some countries.

You could then do without a custom deserializer and simply add some logic to the setter or apply it after parsing the json, i.e. replace "NO NUMBER" with another value as needed.

CodePudding user response：

You can provide custom com.fasterxml.jackson.databind.deser.DeserializationProblemHandler and handle all these kind of business values generally for all POJO classes:

import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.fasterxml.jackson.databind.deser.DeserializationProblemHandler;
import com.fasterxml.jackson.databind.json.JsonMapper;
import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

import java.io.IOException;

public class HandleErrorsApp {
    private final static JsonMapper JSON_MAPPER = JsonMapper.builder()
            .enable(SerializationFeature.INDENT_OUTPUT)
            .addModule(new JavaTimeModule())
            .addHandler(new ProjectDeserializationProblemHandler())
            .build();

    public static void main(String[] args) throws Exception {
        var json = "{\"houseNumber\":\"NO_ADDRESS\"}";
        var address = JSON_MAPPER.readValue(json, Address.class);
        System.out.println(address);
    }
}

class ProjectDeserializationProblemHandler extends DeserializationProblemHandler {
    @Override
    public Object handleWeirdStringValue(DeserializationContext ctxt, Class<?> targetType, String valueToConvert, String failureMsg) throws IOException {
        if (targetType == int.class && valueToConvert.equals("NO_ADDRESS")) {
            return 0;
        }
        return super.handleWeirdStringValue(ctxt, targetType, valueToConvert, failureMsg);
    }
}

@Data
@NoArgsConstructor
@AllArgsConstructor
class Address {

    private int houseNumber;
}

Or you can provide custom com.fasterxml.jackson.databind.util.StdConverter implementation which has a little bit simpler interface than JsonDeserializer:

import com.fasterxml.jackson.databind.SerializationFeature;
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import com.fasterxml.jackson.databind.json.JsonMapper;
import com.fasterxml.jackson.databind.util.StdConverter;
import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import org.apache.commons.lang3.math.NumberUtils;

public class HandleErrorsApp {
    private final static JsonMapper JSON_MAPPER = JsonMapper.builder()
            .enable(SerializationFeature.INDENT_OUTPUT)
            .addModule(new JavaTimeModule())
            .build();

    public static void main(String[] args) throws Exception {
        var json = "{\"houseNumber\":\"NO_ADDRESS\"}";
        var address = JSON_MAPPER.readValue(json, Address.class);
        System.out.println(address);
    }
}

class StringIntConverter extends StdConverter<String, Integer> {

    @Override
    public Integer convert(String value) {
        return NumberUtils.toInt(value, 0);
    }
}

@Data
@NoArgsConstructor
@AllArgsConstructor
class Address {

    @JsonDeserialize(converter = StringIntConverter.class)
    private int houseNumber;
}

In both cases program prints:

Address(houseNumber=0)