@JsonProperty 存在但返回 null

Question

I have an annotated Java 11 class that's using Fasterxml and it's returning null for one of the properties even though I can see the data in the source JSON . 這個注釋是否有理由不再適用於jackson:2.12.0 ？

有問題的屬性在源中大寫，因此在注釋中也大寫。

來源 JSON

{
    "stringOne": "hello",
    "stringTwo": "world",
    "floatOne": 0.0,
    "NUM": 15   <-- always returns null
}

日志語句

TestJson{stringOne='hello', stringTwo='world', floatOne=0.0, NUM=null}

Class

   import com.fasterxml.jackson.annotation.JsonProperty;

import java.io.Serializable;

@JsonFormat(with = JsonFormat.Feature.ACCEPT_CASE_INSENSITIVE_PROPERTIES)
public class TestJson implements Serializable{

    protected String stringOne;
    protected String stringTwo;
    protected Float floatOne;
    protected Integer NUM;

    @JsonProperty("stringOne")
    public String getStringOne() {
        return stringOne;
    }

    public void setStringOne(String stringOne) {
        this.stringOne = stringOne;
    }

    @JsonProperty("stringTwo")
    public String getStringTwo() {
        return stringTwo;
    }

    public void setStringTwo(String stringTwo) {
        this.stringTwo = stringTwo;
    }

    @JsonProperty("floatOne")
    public Float getFloat() {
        return floatOne;
    }

    public void setFloat(Float floatOne) {
        this.floatOne = floatOne;
    }

//////// Returns null for every 'NUM' property
    @JsonProperty("NUM")
    public Integer getNum() {
        return NUM;
    }
    
    @JsonProperty("NUM")
    public void setNum(Integer NUM) {
        this.NUM= NUM;
    }

Override
    public String toString() {
        return "TestJson{" +
                "stringOne='" + stringOne + '\'' +
                ", stringTwo='" + stringTwo + '\'' +
                ", floatOne=" + floatOne +
                ", NUM=" + NUM+
                '}';
    }
   
}

編輯

將用於檢索/序列化數據的請求添加為TestJson object

        ClientResponse<TestJson> response = null;
        TestJson testJson = null;
        logger.info(encodeForLog("apiUrl.getPath: " + apiUrl.getPath()));
        logger.info("proxy:" + proxy);

        try {
            response = proxy.getData(apiUrl.getPath());

            if (response.getStatus() == Response.Status.OK.getStatusCode()) {
                testJson = response.getEntity();
                
                return testJson;
            } else {
                throw new FailedException("HTTP failure");
            }
        }
        finally {
            if (response != null) {
                response.releaseConnection();
            }
        }

Answer 1

在 setter 方法上設置 @JsonProperty。

@JsonProperty("NUM")
public Integer getNum() {
    return num;
}

@JsonProperty("NUM")
public void setNum(Integer num) {
    this.num = num;
}

可用於將非靜態方法定義為邏輯屬性（取決於其簽名）的“setter”或“getter”的標記注釋，或用作邏輯屬性的非靜態 object 字段（序列化、反序列化）財產。

https://fasterxml.github.io/jackson-annotations/javadoc/2.8/com/fasterxml/jackson/annotation/JsonProperty.ZFC35FDC70D5FC69D2698EZ83A8A8

Jackson版本無所謂：

https://fasterxml.github.io/jackson-annotations/javadoc/2.12/com/fasterxml/jackson/annotation/JsonProperty.ZFC35FDC70D5FC69D263EZ88A

用這個 class (Jackson 2.11.4) 測試：

@JsonFormat(with = JsonFormat.Feature.ACCEPT_CASE_INSENSITIVE_PROPERTIES)
public class TestJson implements Serializable {

    protected String stringOne;
    protected String stringTwo;
    protected Float floatOne;
    protected Integer num;

    @JsonProperty("stringOne")
    public String getStringOne() {
        return stringOne;
    }

    public void setStringOne(String stringOne) {
        this.stringOne = stringOne;
    }

    @JsonProperty("stringTwo")
    public String getStringTwo() {
        return stringTwo;
    }

    public void setStringTwo(String stringTwo) {
        this.stringTwo = stringTwo;
    }

    @JsonProperty("floatOne")
    public Float getFloat() {
        return floatOne;
    }

    public void setFloat(Float floatOne) {
        this.floatOne = floatOne;
    }

    //////// Returns null for every 'NUM' property
    @JsonProperty("NUM")
    public Integer getNum() {
        return num;
    }

    @JsonProperty("NUM")
    public void setNum(Integer num) {
        this.num= num;
    }

    @Override
    public String toString() {
        return "TestJson{" +
                "stringOne='" + stringOne + '\'' +
                ", stringTwo='" + stringTwo + '\'' +
                ", floatOne=" + floatOne +
                ", NUM=" + num+
                '}';
    }

}

Output：

以及 TestJson 的更好解決方案：

public class TestJson implements Serializable {

    protected String stringOne;
    protected String stringTwo;
    protected Float floatOne;
    protected Integer num;

    @JsonCreator
    public TestJson(@JsonProperty("stringOne") String stringOne
            ,@JsonProperty("stringTwo") String stringTwo
            ,@JsonProperty("floatOne") Float floatOne
            ,@JsonProperty("NUM") Integer num) {
        this.stringOne = stringOne;
        this.stringTwo = stringTwo;
        this.floatOne = floatOne;
        this.num = num;
    }

    public String getStringOne() {
        return stringOne;
    }

    public void setStringOne(String stringOne) {
        this.stringOne = stringOne;
    }

    public String getStringTwo() {
        return stringTwo;
    }

    public void setStringTwo(String stringTwo) {
        this.stringTwo = stringTwo;
    }

    public Float getFloat() {
        return floatOne;
    }

    public void setFloat(Float floatOne) {
        this.floatOne = floatOne;
    }

    public Integer getNum() {
        return num;
    }

    public void setNum(Integer num) {
        this.num= num;
    }

    @Override
    public String toString() {
        return "TestJson{" +
                "stringOne='" + stringOne + '\'' +
                ", stringTwo='" + stringTwo + '\'' +
                ", floatOne=" + floatOne +
                ", NUM=" + num+
                '}';
    }

}