API返回JSON仅映射3个字段至Java对象转换失败求助

Hey Arun, sorry to hear your WebClient JSON conversion is giving you trouble! Let's break down the most likely issues and fix them step by step—since your API returns 100+ fields but you only care about three, the problem is almost certainly related to how Jackson handles the extra fields or how your class is structured.

1. Ensure Your ArunApi Class Has Proper Access & Annotations #

Jackson (which Spring WebClient uses under the hood) needs a way to set values on your private fields. The easiest fixes here are:

Option A: Use Lombok to Auto-Generate Getters/Setters #

If you're using Lombok, add the @Data annotation to your class—it automatically generates getters, setters, and other utility methods Jackson needs:

import lombok.Data;

@Data
public class ArunApi {
    private String data;
    private Integer size;
    private String style;
}

Option B: Manually Add Getters/Setters #

If you don't use Lombok, explicitly define getters and setters for each field:

public class ArunApi {
    private String data;
    private Integer size;
    private String style;

    // Getters
    public String getData() { return data; }
    public Integer getSize() { return size; }
    public String getStyle() { return style; }

    // Setters
    public void setData(String data) { this.data = data; }
    public void setSize(Integer size) { this.size = size; }
    public void setStyle(String style) { this.style = style; }
}

Bonus: Match JSON Field Names (If They Differ) #

If the API's JSON fields use different naming (e.g., Data instead of data, Size instead of size), use @JsonProperty to map them:

import com.fasterxml.jackson.annotation.JsonProperty;

public class ArunApi {
    @JsonProperty("Data")
    private String data;
    @JsonProperty("Size")
    private Integer size;
    @JsonProperty("Style")
    private String style;

    // Getters/Setters (or @Data if using Lombok)
}

2. Configure Jackson to Ignore Unknown Fields #

Since the API returns 100+ fields you don't care about, Jackson's default behavior is to throw an exception when it encounters fields your class doesn't define. Fix this by disabling the FAIL_ON_UNKNOWN_PROPERTIES feature in your WebClient's ObjectMapper:

import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.http.codec.json.Jackson2JsonDecoder;
import org.springframework.http.codec.json.Jackson2JsonEncoder;
import org.springframework.web.reactive.function.client.WebClient;

// Create a custom ObjectMapper that ignores unknown fields
ObjectMapper objectMapper = new ObjectMapper()
        .configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);

// Build WebClient with this custom ObjectMapper
WebClient webClient = WebClient.builder()
        .codecs(configurer -> configurer.defaultCodecs()
                .jackson2JsonDecoder(new Jackson2JsonDecoder(objectMapper))
                .jackson2JsonEncoder(new Jackson2JsonEncoder(objectMapper)))
        .build();

This tells Jackson to ignore any fields in the JSON that aren't defined in your ArunApi class.

3. Verify JSON Field Types Match Your Class #

Double-check that the API's JSON values match your field types:

• If the size field in the JSON is a string (e.g., "size": "25" instead of "size": 25), converting to Integer will fail. Fix this either by:
  • Asking the API to return a numeric size, or
  • Using @JsonDeserialize to convert the string to an integer:

    import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
    import com.fasterxml.jackson.databind.deser.std.NumberDeserializers;
    
    public class ArunApi {
        private String data;
        @JsonDeserialize(using = NumberDeserializers.IntegerDeserializer.class)
        private Integer size;
        private String style;
    
        // Getters/Setters
    }
    

4. Debug the Exact Issue #

If you're still stuck, first retrieve the raw JSON response to inspect it:

String rawJson = webClient.get()
        .uri(endPoint)
        .retrieve()
        .bodyToMono(String.class)
        .block();
System.out.println("Raw JSON Response: " + rawJson);

Then try manually converting this string to your ArunApi class to see the exact exception:

ArunApi testConversion = objectMapper.readValue(rawJson, ArunApi.class);

The exception message will tell you exactly what's wrong (e.g., missing field, type mismatch, unknown property).

内容的提问来源于stack exchange，提问作者Arun