Check the type of Json property value when converted to Java class

php editor Youzi brings you the Java Q&A topic of this article: "Checking the type of Json attribute value when converting to a Java class". During the development process, we often need to convert JSON data into Java objects, but how to effectively check and handle the type of attribute values ​​​​is an important skill in this process. This article will answer this question for you and help you better understand and use JSON data conversion technology.

Question content

Suppose I have the following json data. Here I have an id of integer type. The type of id in the java class is string.

{
  "id": 1,
  "name": "user1"
}

@lombok.data
@allargsconstructor
@noargsconstructor
class data {
    string id;
    string name;
}

I want to convert json to the class while strictly checking whether the value of the json attribute is the same type as the class field.

String json = "{\"id\":1,\"name\":\"user1\"}";
ObjectMapper objectMapper = new ObjectMapper(new JsonFactory());

Data data = objectMapper.readValue(json, Data.class);
System.out.println(data);

data(id=1, name=user1)

I hope no conversion should happen here, but it will be converted.

Solution

One way I guess is to use a custom deserializer and do a simple type check:

public class customdeserializer extends stddeserializer<string> {

  protected customdeserializer() {
    this(null);
  }

  protected customdeserializer(class<?> vc) {
    super(vc);
  }

  @override
  public string deserialize(jsonparser p, deserializationcontext ctxt) throws ioexception, jacksonexception {
    if (p.currenttoken() != jsontoken.value_string) {
      throw new invalidformatexception(p, "expected string type", p.getvalueasstring(), string.class);
    }
    return p.getvalueasstring();
  }
}

Then use this deserializer in the field you want to check:

public class Data {
  @JsonDeserialize(using = CustomDeserializer.class)
  String id;
}

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