SpringBoot achieve subclass deserialization

aims

In SpringBoot interface, we generally use @RequestBodythe class annotation need to deserialize objects, but in the case where there are a plurality of sub-classes, the deserialization routine can not meet the requirements, such as:

We have a piece of paper used to represent the class Exam:

@Data
public class Exam {

    private String name;
    private List<Question> questions;
}
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Here Questionspecial, Question itself is an abstract class that provides some common method invocation, the actual sub-class has multiple choice, multiple choice, true problem many cases

achieve

SprintBoot built serialization is used Jackson, Jackson found after inspection document provided @JsonTypeInfoand @JsonSubTypesthese two notes, with the use, may be used in an instance of a particular subclass of the specified type field value

These actual class code as follows:
abstract base class Question:

@Data
@JsonTypeInfo(
        use = JsonTypeInfo.Id.NAME,
        include = JsonTypeInfo.As.EXISTING_PROPERTY,
        property = "type",
        visible = true)
@JsonSubTypes({
        @JsonSubTypes.Type(value = SingleChoiceQuestion.class, name = Question.SINGLE_CHOICE),
        @JsonSubTypes.Type(value = MultipleChoiceQuestion.class, name = Question.MULTIPLE_CHOICE),
        @JsonSubTypes.Type(value = TrueOrFalseQuestion.class, name = Question.TRUE_OR_FALSE),
})
public abstract class Question {

    protected static final String SINGLE_CHOICE = "single_choice";
    protected static final String MULTIPLE_CHOICE = "multiple_choice";
    protected static final String TRUE_OR_FALSE = "true_or_false";

    protected String type;
    protected String content;
    protected String answer;

    protected boolean isCorrect(String answer) {
        return this.answer.equals(answer);
    }
}
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True or False TrueOrFalseQuestion:

@Data
@EqualsAndHashCode(callSuper = true)
public class TrueOrFalseQuestion extends Question {

    public TrueOrFalseQuestion() {
        this.type = TRUE_OR_FALSE;
    }
}
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Choice ChoiceQuestion:

@Data
@EqualsAndHashCode(callSuper = true)
public abstract class ChoiceQuestion extends Question {

    private List<Option> options;

    @Data
    public static class Option {
        private String code;
        private String content;
    }
}
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Multiple choice SingleChoiceQuestion:

@Data
@EqualsAndHashCode(callSuper = true)
public class SingleChoiceQuestion extends ChoiceQuestion {

    public SingleChoiceQuestion() {
        this.type = SINGLE_CHOICE;
    }
}
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Multiple choice MultipleChoiceQuestion:

@Data
@EqualsAndHashCode(callSuper = true)
public class MultipleChoiceQuestion extends ChoiceQuestion {

    public MultipleChoiceQuestion() {
        this.type = MULTIPLE_CHOICE;
    }

    @Override
    public void setAnswer(String answer) {
        this.answer = sortString(answer);
    }

    @Override
    public boolean isCorrect(String answer) {
        return this.answer.equals(sortString(answer));
    }

    private String sortString(String str) {
        char[] chars = str.toCharArray();
        Arrays.sort(chars);
        return String.valueOf(chars);
    }
}
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test

The next test
to define an interface, we can use @RequestBody pass a Exam object, and returns the analysis results:

@RequestMapping(value = "/exam", method = RequestMethod.POST)
public List<String> parseExam(@RequestBody Exam exam) {
    List<String> results = new ArrayList<>();
    results.add(String.format("Parsed an exam, name = %s", exam.getName()));
    results.add(String.format("Exam has %s questions", exam.getQuestions().size())) 
    
    List<String> types = new ArrayList<>();
    for (Question question : exam.getQuestions()) {
        types.add(question.getType());
    }
    results.add(String.format("Questions types: %s", types.toString()));
    return results;
}
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Project up and running, call interface test:

curl -X POST \
  http://127.0.0.1:8080/exam/ \
  -H 'Content-Type: application/json' \
  -d '{
	"name":"一场考试",
	"questions": [
		{
			"type": "single_choice",
			"content": "单选题",
			"options":  [
			    {
					"code":"A",
					"content": "选项A"
				},{
					"code":"B",
					"content": "选项B"
				}],
			"answer": "A"
		},{
			"type": "multiple_choice",
			"content": "多选题",
			"options":  [
				{
					"code":"A",
					"content": "选项A"
				},{
					"code":"B",
					"content": "选项B"
				}],
			"answer": "AB"
		},{
			"type": "true_or_false",
			"content": "判断题",
			"answer": "True"
		}]
}'
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Interface returns the following:

[
    "Parsed an exam, name = 一场考试",
    "Exam has 3 questions",
    "Questions types: [single_choice, multiple_choice, true_or_false]"
]
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Here the different types of question, type fields can be read correctly, show deserialization process is indeed called concrete subclasses corresponding class is instantiated.