I'm using jackson to parse json data on a springboot application, but jackson is unable to select properly the json field to map to java field...
First of all, i'm reading data from a thirdy party library which sucks, their data model is a piece of .... and i can't ask them to fix.
their json is something like:
{ "name" : "name", "full_name" : "name", "fullName" : "name"}
they have 3 properties that map to same information in the json, but sometimes only one of these properties is non null, like
{ "name" : null, "full_name" : "", "fullName" : "name"}
Let be clear that this happens to many other properties
I'm trying to use @JsonAlias to map this weird behavior, but it doesn't work well....
@JsonProperty("name")
@JsonAlias({"full_name","fullName"})
private String name;
First that JsonAlias is taking precendence from the JsonProperty value...
second that is not ignoring null values
how can i make jackson ignore null values in a situation like this
CodePudding user response:
Multiple Setters
One of the possible options is to define a bunch of additional setters for each duplicated property, annotated with @JsonSetter
to map each setter to a corresponding property flavor.
To avoid logic duplication, every additional setter should delegate to a regular setter, which should determine if the existing value needs to be updated (if it's empty, null, etc.).
public class MyPojo {
public static final Predicate<String> NULL_OR_EMPTY =
s -> s == null || s.isEmpty(); // predicate can be reused to check multiple properties
private String name;
@JsonSetter("name")
public void setName(String name) {
if (NULL_OR_EMPTY.test(this.name)) this.name = name;
}
@JsonSetter("full_name")
public void setName1(String name) {
setName(name);
}
@JsonSetter("fullName")
public void setName2(String name) {
setName(name);
}
}
Usage example:
String json = "{ "name" : null, "full_name" : "", "fullName" : "name"}";
ObjectMapper mapper = new ObjectMapper();
MyPojo myPojo = mapper.readValue(json, MyPojo.class);
System.out.println(myPojo);
Output:
MyPojo{name='name'}
The drawbacks of this approach are the usage of "smart-setters", which might not considered to be clean (because it violates the Single responsibility principle, setters aren't meant to perform validation) and domain class gets polluted with additional setter methods. Both issues can be solved by externalizing this functionality.
Custom Converter
Another possible solution is to customize deserialization by defining a Converter for the target type.
Note: don't confuse Converter and Deserializer. Deserializer is meant to provide logic how to construct a POJO based on the information contained in the JsonParser, whilst Converter is used to transform one POJO (which is easier to deserialize) into another POJO.
So we need to create two classes: Converter and auxiliary type reflecting the data model of the incoming JSON.
Consider the following auxiliary POJO:
public record AuxiliaryPojo(
@JsonProperty("name") String name,
@JsonProperty("full_name") String name1,
@JsonProperty("fullName") String name2
) {}
And that's the Converter extending StdConverter
that bridges AuxiliaryPojo
and MyPojo
:
public class AuxiliaryPojoToMyPojo extends StdConverter<AuxiliaryPojo, MyPojo> {
public static final Predicate<String> NOT_NULL_OR_EMPTY =
s -> s != null && !s.isEmpty();
@Override
public MyPojo convert(AuxiliaryPojo v) {
return MyPojo.builder()
.name(findMatching(v.name(), v.name1(), v.name2()))
.build();
}
private String findMatching(String... args) {
return Arrays.stream(args)
.filter(NOT_NULL_OR_EMPTY)
.findFirst().orElse(null);
}
}
And here's the domain class (free from any redundant code). Note that Converter has been specified via converter
property of the @JsonDeserialize
annotation.
@Getter
@Builder
@JsonDeserialize(converter = AuxiliaryPojoToMyPojo.class)
public static class MyPojo {
private String name;
}
That would be enough to parse the sample JSON into an instance of MyPojo
:
String json = "{ "name" : null, "full_name" : "", "fullName" : "name"}";
ObjectMapper mapper = new ObjectMapper();
MyPojo myPojo = mapper.readValue(json,bMyPojo.class);
System.out.println(myPojo);
Output:
MyPojo{name='name'}
CodePudding user response:
An other solution is to ignore additionnal fields 'fullName' and 'full_name' using annotation @JsonIgnoreProperties
and a custom deserializer that throws an exception when name property is null (or equal to string "null") so that you can catch that exception in order not to create a person when name is null.
See code below:
Class Person
import java.util.ArrayList;
import java.util.List;
import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
@JsonIgnoreProperties({ "fullName", "full_name" })
public class Person {
@JsonProperty("name")
@JsonDeserialize(using = CustomNameDeserializer.class)
private String name;
public Person() {
super();
}
public String toString() {
return "name: " name;
}
public static void main(String[] args) {
String[] personArrayJson = new String[3];
personArrayJson[0]="{ \"name\" : \"nameNotNull1\", \"full_name\" : \"name\", \"fullName\" : \"name\"}";
personArrayJson[1]="{ \"name\" : \"null\", \"full_name\" : \"\", \"fullName\" : \"name\"}";
personArrayJson[2]="{ \"name\" : \"nameNotNull2\", \"full_name\" : \"name\", \"fullName\" : \"name\"}";
List<Person> persons = new ArrayList<Person>();
ObjectMapper mapper = new ObjectMapper();
Person p;
for (String personJson : personArrayJson) {
try {
p = mapper.readValue(personJson, Person.class);
persons.add(p);
} catch (JsonProcessingException e) {
//e.printStackTrace();
System.out.println("NAme is null: not deserialized");
}
}
System.out.println("Persons list contains " persons.size() " persons => " persons);
}
}
Class CustomNameDeserializer
import java.io.IOException;
import com.fasterxml.jackson.core.JacksonException;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.deser.std.StdDeserializer;
public class CustomNameDeserializer extends StdDeserializer<String> {
public CustomNameDeserializer(Class<String> s) {
super(s);
}
public CustomNameDeserializer() {
this(null);
}
@Override
public String deserialize(JsonParser p, DeserializationContext ctxt) throws IOException, JacksonException, NullPointerException{
String n = p.getValueAsString();
if(n==null || n.equals("null") || n.trim().equals(""))
throw new NullPointerException("Name is null");
return n;
}
}
Hope it helps