使用Jackson将Java对象转换为JSON字符串时重复的JSON属性

Question

我有一个Pojo对象，它有getAsJson函数，用于返回该对象的Json字符串。 我使用JsonProperty来定义这个对象中的Json属性。 使用ObjectMapper的writeValueAsString函数写入此对象的Json字符串。

import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.annotate.JsonIgnore;
import org.codehaus.jackson.annotate.JsonIgnoreProperties;
import org.codehaus.jackson.annotate.JsonProperty;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;

@JsonIgnoreProperties(ignoreUnknown=true)
public class LogLikeArticleDetail extends BaseObject {
    private static final long serialVersionUID = -2018373118257019033L;
    @JsonProperty("LikeArticleGUId")
    private String likeArticleGUId;
    @JsonProperty("UserId")
    private String userID;
    @JsonProperty("UserName")
    private String userName;
    @JsonProperty("IP") 
    private String ip;
    @JsonProperty("OS") 
    private String os;
    @JsonProperty("UserAgent") 
    private String userAgent;
    @JsonProperty("WebsiteCode") 
    private String websiteCode;
    @JsonProperty("ArticleId") 
    private String articleID;
    @JsonProperty("ATitle") 
    private String aTitle;
    @JsonProperty("CateAlias") 
    private String cateAlias;
    @JsonProperty("LikeStatus") 
    private String likeStatus;
    @JsonProperty("TimeStamp") 
    private Date timeStamp;
        //get, set....
        //....
        @JsonIgnore
    public String getAsJSON() throws JsonGenerationException, JsonMappingException,    IOException{
        ObjectMapper mapper = new ObjectMapper();
        return mapper.writeValueAsString(this) ; 
    }
}

现在，我得到了结果

public static void main(String[] args) throws JsonGenerationException, JsonMappingException, IOException {
        Calendar calendar =  Calendar.getInstance();
        LogLikeArticleDetail logLikeArticle = new LogLikeArticleDetail("1","2","3","4","5","6","7","8","what thing \"nothing\" show","10","11",calendar.getTime());
        System.out.println(logLikeArticle.getAsJSON());
    }

但结果存在重复的属性：

{"LikeArticleGUId":"1","UserId":"2","UserName":"3","IP":"4","OS":"5","UserAgent":"6","WebsiteCode":"7","ArticleId":"8","ATitle":"what thing \"nothing\" show","CateAlias":"10","LikeStatus":"11","TimeStamp":1352256727062,"_likeArticleGUId":"1","websiteCode":"7","likeStatus":"11","userID":"2","userName":"3","ip":"4","os":"5","userAgent":"6","articleID":"8","aTitle":"what thing \"nothing\" show","cateAlias":"10","timeStamp":1352256727062}

展示给我这个问题中发生了什么？

- Sonrobby

---

我认为这可能是答案：https://dev59.com/XWw05IYBdhLWcg3wqzis - pawelzieba

Answer 1

所以我遵循：如何指定Jackson仅使用字段 - 最好是全局的

我添加了

@JsonAutoDetect(fieldVisibility = Visibility.ANY, getterVisibility = Visibility.NONE, setterVisibility = Visibility.NONE)

之前

public class LogLikeArticleDetail extends BaseObject

而我想要的结果是什么。

因此，另一个人是否能够在getAsJson()函数中解决这个问题，例如：

ObjectMapper mapper  = new ObjectMapper();
mapper.setVisibilityChecker(mapper.getSerializationConfig().getDefaultVisibilityChecker()
                .withFieldVisibility(JsonAutoDetect.Visibility.ANY)
                .withGetterVisibility(JsonAutoDetect.Visibility.NONE)
                .withSetterVisibility(JsonAutoDetect.Visibility.NONE)
                .withCreatorVisibility(JsonAutoDetect.Visibility.NONE));
return mapper.writeValueAsString(this) ;

感谢上面链接中@Sean Carpenter提出的问题和@kmb385的答案。

- Sonrobby

---

这个工作得很好，但已经被弃用了，正确的答案在这里 https://dev59.com/XWw05IYBdhLWcg3wqzis#7108530 - OscarSanhueza

Answer 2

您也可以使用注释对每个POJO进行设置。在您希望关闭自动检测的类顶部添加以下字符串：

@JsonAutoDetect(fieldVisibility=JsonAutoDetect.Visibility.ANY, getterVisibility=JsonAutoDetect.Visibility.NONE, setterVisibility=JsonAutoDetect.Visibility.NONE, creatorVisibility=JsonAutoDetect.Visibility.NONE)

例如：

@JsonAutoDetect(fieldVisibility=JsonAutoDetect.Visibility.ANY, getterVisibility=JsonAutoDetect.Visibility.NONE,
        setterVisibility=JsonAutoDetect.Visibility.NONE, creatorVisibility=JsonAutoDetect.Visibility.NONE)
class Play {
    @JsonProperty("Name")
    private String name; 

    @JsonProperty("NickName")
    private String nickName; 

    public Play(){

    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getNickName() {
        return nickName;
    }

    public void setNickName(String nickName) {
        this.nickName = nickName;
    }
}

这将返回我定义的属性，并且不会自动检测字段名称并将其添加到我的返回JSON结果中。

- mkwyche

Answer 3

我们也可以直接在getter方法上使用@JsonProperty("Name")注解来避免重复。

- Gogol

---

这可能是最简单的解决方案。当消费者必须对对象进行反序列化时，显然会调用getter方法。谢谢@Gogol - Amit Kumar

Answer 4

其实这不是问题。在这里发生的情况是，Jackson库无法自动匹配这些字段（不假定大小写一致），因此您最终会得到两倍于预期的属性。

解决此问题的简单方法是只需向getter/setter中添加注释（两者都可以）。

@JsonProperty("UserName")
public String getUserName() {
        return this.userName;
}

这个问题在Jackson Github仓库中也被提出。您可以在以下链接中找到答案。

https://github.com/FasterXML/jackson-databind/issues/1609

- Alfred Skaria