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One solution is to create a method in the `enum` that takes a `String` and converts it to the correspondent value. Then we annotate this method with [`@JsonCreator`](https://javadoc.io/static/com.fasterxml.jackson.core/jackson-annotations/2.17.2/com/fasterxml/jackson/annotation/JsonCreator.html):

```java
import com.fasterxml.jackson.annotation.JsonCreator;

enum Bar {
    X, Y;
    
    @JsonCreator
    public static Bar fromString(String value) {
        return Bar.valueOf(value);
    }
}
```

Now only valid strings are accepted. In this case, `{"bar": "X"}` and `{"bar": "Y"}`. Any other value (such as `{"bar": "A"}` or `{"bar": 1}`) will raise an exception.

---

Another solution is to create your own deserializer:

```java
import com.fasterxml.jackson.core.JacksonException;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonToken;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonMappingException;
import java.io.IOException;

public class BarDeserializer extends JsonDeserializer<Bar> {
    @Override
    public Bar deserialize(JsonParser jp, DeserializationContext dc) throws IOException, JacksonException {
        JsonToken jsonToken = jp.getCurrentToken();
        if (jsonToken == JsonToken.VALUE_STRING) { // value is a string
            try {
                return Bar.valueOf(jp.getValueAsString());
            } catch (IllegalArgumentException | NullPointerException e) {
                throw new JsonMappingException(jp, "Invalid value for enum Bar", e);
            }
        }
        // value is not a string
        throw new JsonMappingException(jp, "Value must be a string");
    }
}
```

Then you annotate the `enum` with it:

```java
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;

@JsonDeserialize(using = BarDeserializer.class)
enum Bar {
    X, Y;
}
```