Jackson deserialize list of strings to a string

Question

Is there a simple way to deserialize a list of strings into a single string?

For example, I would have this JSON:

{
    "stringList": [
        "somethingElse"
    ],
    "simpleString": "something",
}

I would like it to be deserialized into this POJO:

@Data
@JsonIgnoreProperties(ignoreUnknown = true)
public class AClass {

    @JsonProperty("stringList")
    private String justAString;

    @JsonProperty("simpleString")
    private String someString;
}

I would like to mention that it is certain that the list has only one item and have no control over how it is generated. Is the only way to go a custom deserializer for the justAString field?

EDIT I would like to use ObjectMapper class from Jackson if it is possible

Answer 1

One way is to use alternate getter/setter methods for the property that needs conversion, i.e. move the @JsonProperty annotations from the fields to the getter methods, add an extra set of getter/setter methods, and use @JsonIgnore so the ObjectMapper doesn't use them:

class AClass {

    private String justAString;
    private String someString;

    @JsonProperty // JSON field named same as virtual property
    private List<String> getStringList() { // Getter for virtual property (private = hidden from Java callers)
        return Collections.singletonList(this.justAString);
    }

    private void setStringList(List<String> stringList) { // Setter for virtual property
        this.justAString = stringList.toString();
    }

    @JsonIgnore // This POJO property is not a JSON field
    public String getJustAString() { // Standard POJO getter
        return this.justAString;
    }

    public void setJustAString(String justAString) { // Standard POJO setter
        this.justAString = justAString;
    }

    @JsonProperty("simpleString") // JSON field named different from POJO property
    public String getSomeString() { // Standard POJO getter
        return this.someString;
    }

    public void setSomeString(String someString) { // Standard POJO setter
        this.someString = someString;
    }

}

Test

String input = "{\r\n" + 
               "    \"stringList\": [\r\n" + 
               "        \"somethingElse\"\r\n" + 
               "    ],\r\n" + 
               "    \"simpleString\": \"something\"\r\n" + 
               "}";
AClass aClass = new ObjectMapper().readValue(input, AClass.class);
System.out.println("justAString = " + aClass.getJustAString());
System.out.println("someString = " + aClass.getSomeString());

Output

justAString = [somethingElse]
someString = something

Answer 2

this :

@JsonProperty("stringList")
private String justAString;

should be a list of strings dont you think??

@JsonProperty("stringList")
private List<String> justAString;