give a default value for an attribute if the value is null in json by jackson
Suppose i have class ie
private class Student {
private Integer x = 1000;
public Integer getX() {
return x;
}
public void setX(Integer x) {
this.x = x;
}
}
Now suppose json is "{x:12}" and doing deserialization then the x will have the value is 12 . But if the json is "{}" then the value of x = 1000 (get is from the default value of the attribute declared in the class).
Now if the json is "{x:null}" then value of x becomes null but here even in this case i want value of x to be 1000 . How to do it via jackson . Thanks in advance.
I am deserializing via below method, if it helps in anyway: objectMapper.readValue(<json string goes here>, Student.class);
You should be able to override the setter. Add the @JsonProperty(value="x") annotations to the getter and setter to let Jackson know to use them:
private class Student {
private static final Integer DEFAULT_X = 1000;
private Integer x = DEFAULT_X;
@JsonProperty(value="x")
public Integer getX() {
return x;
}
@JsonProperty(value="x")
public void setX(Integer x) {
this.x = x == null ? DEFAULT_X : x;
}
}
Consider extending JsonDeserializer
custom deserializer:
public class StudentDeserializer extends JsonDeserializer<Student> {
@Override
public Student deserialize(JsonParser p, DeserializationContext ctxt)
throws IOException, JsonProcessingException {
JsonNode node = p.getCodec().readTree(p);
// if JSON is "{}" or "{"x":null}" then create Student with default X
if (node == null || node.get("x").isNull()) {
return new Student();
}
// otherwise create Student with a parsed X value
int x = (Integer) ((IntNode) node.get("x")).numberValue();
Student student = new Student();
student.setX(x);
return student;
}
}
and it's use:
ObjectMapper mapper = new ObjectMapper();
SimpleModule module = new SimpleModule();
module.addDeserializer(Student.class, new StudentDeserializer());
mapper.registerModule(module);
Student readValue = mapper.readValue(<your json string goes here>", Student.class);
从json到object，你可以在setter中解决这个问题，并告诉Jackson不要使用Field访问，而是使用setter来解组。
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