Master Dynamic JSON in Spring Boot 3: 4 Practical Techniques

Spring Boot 3 uses Jackson for JSON handling, allowing easy serialization and deserialization. When JSON contains dynamic properties not defined in the POJO, several strategies can be applied.

1. Introduction

Jackson handles predefined JSON structures automatically, but dynamic attributes require special techniques.

2. Practical Cases

2.1 Use JsonNode property

Define a JsonNode field in the POJO to capture the dynamic part.

public class Product {
    // other properties
    private JsonNode details;
    // getters, setters
}

Test code:

ObjectMapper objectMapper = new ObjectMapper();
String json = "{ \"name\": \"SpringBoot实战案例100例\", \"category\": \"book\", \"details\": { \"price\": \"70\", \"author\": \"XGPack\" } }";
Product product = objectMapper.readValue(json, Product.class);
System.err.printf("name: %s, category: %s%n", product.getName(), product.getCategory());
System.out.println("--------------------------------");
System.err.printf("price: %s, author: %s%n",
    product.getDetails().get("price").asText(),
    product.getDetails().get("author").asText());

Output:

2.2 Use Map collection

Store dynamic attributes in a Map<String,Object> field.

public class Product_Map {
    // other properties
    private Map<String, Object> details;
    // getters, setters
}

Test code:

ObjectMapper objectMapper = ...;
String json = ...;
Product product = objectMapper.readValue(json, Product.class);
System.err.printf("name: %s, category: %s%n", product.getName(), product.getCategory());
System.out.println("--------------------------------");
System.err.printf("price: %s, author: %s%n",
    product.getDetails().get("price"),
    product.getDetails().get("author"));

2.3 Use @JsonAnySetter

Annotate a setter method to capture any unknown properties into a map.

public class Product {
    // other properties
    private Map<String, Object> details = new LinkedHashMap<>();
    @JsonAnySetter
    public void setDetail(String key, Object value) {
        details.put(key, value);
    }
    // getters, setters
}

Test code similar to previous examples; output shown below.

2.4 Custom deserializer

Implement a StdDeserializer to manually parse known and dynamic fields.

public class ProductDeserializer extends StdDeserializer<Product> {
    public ProductDeserializer() { this(null); }
    public ProductDeserializer(Class<?> vc) { super(vc); }
    @Override
    public Product deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException {
        JsonNode node = jp.getCodec().readTree(jp);
        String name = node.get("name").asText();
        String category = node.get("category").asText();
        JsonNode detailsNode = node.get("details");
        String price = detailsNode.get("price").asText();
        String author = detailsNode.get("author").asText();
        Map<String, Object> details = new HashMap<>();
        details.put("price", price);
        details.put("author", author);
        return new Product(name, category, details);
    }
}

Register the deserializer:

ObjectMapper objectMapper = new ObjectMapper();
SimpleModule module = new SimpleModule();
module.addDeserializer(Product.class, new ProductDeserializer());
objectMapper.registerModule(module);

Alternatively, annotate the POJO with @JsonDeserialize(using = ProductDeserializer.class) or use @JsonComponent in a Spring Boot application.

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