The error message “no string-argument constructor/factory method to deserialize from string value” typically occurs when you are trying to deserialize an object from a string value, but the object does not have a suitable constructor or factory method that takes a string argument.
When deserializing an object from a string value, the deserialization process relies on a constructor or factory method to create an instance of the object using the provided string value. However, if the object does not have a constructor or factory method that accepts a string argument, the deserialization process fails and throws the mentioned error.
Here is an example to illustrate the issue:
public class Person {
private String name;
public Person() {
// Default constructor without any arguments
}
public Person(String name) {
this.name = name;
}
public String getName() {
return name;
}
}
String jsonString = "{\"name\":\"John\"}";
ObjectMapper objectMapper = new ObjectMapper();
Person person = objectMapper.readValue(jsonString, Person.class);
In the above example, the Person
class does not have a constructor or factory method that accepts a string argument. When trying to deserialize the JSON string into a Person
object using readValue(jsonString, Person.class)
, the deserialization process fails and throws the “no string-argument constructor/factory method” error.
To resolve this issue, you have a few options:
- Add a constructor or factory method to the object that accepts a string argument:
public class Person {
private String name;
public Person() {
// Default constructor without any arguments
}
public Person(String name) {
this.name = name;
}
public String getName() {
return name;
}
public static Person fromString(String jsonString) {
// Create a new Person object from the provided string value
// Parse the jsonString and set the necessary fields
return new Person(parsedName);
}
}
String jsonString = "{\"name\":\"John\"}";
ObjectMapper objectMapper = new ObjectMapper();
Person person = objectMapper.readValue(jsonString, Person.class);
public class PersonDeserializer extends StdDeserializer<Person> {
public PersonDeserializer() {
this(null);
}
public PersonDeserializer(Class<?> vc) {
super(vc);
}
@Override
public Person deserialize(JsonParser jp, DeserializationContext ctxt)
throws IOException, JsonProcessingException {
// Parse the jsonString and set the necessary fields
return new Person(parsedName);
}
}
String jsonString = "{\"name\":\"John\"}";
ObjectMapper objectMapper = new ObjectMapper();
SimpleModule module = new SimpleModule();
module.addDeserializer(Person.class, new PersonDeserializer());
objectMapper.registerModule(module);
Person person = objectMapper.readValue(jsonString, Person.class);
Both of the above options provide a way to deserialize the object from the string value by either adding a suitable constructor or factory method, or by creating a custom deserializer to handle the deserialization process.