杰克逊序列化：忽略空值（或null） [英] Jackson serialization: ignore empty values (or null)

问题描述

我目前正在使用jackson 2.1.4，当我将对象转换为JSON字符串时，我在忽略字段时遇到了一些麻烦。

I'm currently using jackson 2.1.4 and I'm having some trouble ignoring fields when I'm converting an object to a JSON string.

这是我的作为要转换的对象的类：

Here's my class which acts as the object to be converted:

public class JsonOperation {

public static class Request {
    @JsonInclude(Include.NON_EMPTY)
    String requestType;
    Data data = new Data();

    public static class Data {
    @JsonInclude(Include.NON_EMPTY)
        String username;
        String email;
        String password;
        String birthday;
        String coinsPackage;
        String coins;
        String transactionId;
        boolean isLoggedIn;
    }
}

public static class Response {
    @JsonInclude(Include.NON_EMPTY)
    String requestType = null;
    Data data = new Data();

    public static class Data {
        @JsonInclude(Include.NON_EMPTY)
        enum ErrorCode { ERROR_INVALID_LOGIN, ERROR_USERNAME_ALREADY_TAKEN, ERROR_EMAIL_ALREADY_TAKEN };
        enum Status { ok, error };

        Status status;
        ErrorCode errorCode;
        String expiry;
        int coins;
        String email;
        String birthday;
        String pictureUrl;
        ArrayList <Performer> performer;
    }
}
}

以下是我如何转换它：

ObjectMapper mapper = new ObjectMapper();
mapper.setVisibility(PropertyAccessor.FIELD, Visibility.ANY);

JsonOperation subscribe = new JsonOperation();

subscribe.request.requestType = "login";

subscribe.request.data.username = "Vincent";
subscribe.request.data.password = "test";


Writer strWriter = new StringWriter();
try {
    mapper.writeValue(strWriter, subscribe.request);
} catch (JsonGenerationException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
} catch (JsonMappingException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
} catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}

Log.d("JSON", strWriter.toString())

这是输出：

{"data":{"birthday":null,"coins":null,"coinsPackage":null,"email":null,"username":"Vincent","password":"test","transactionId":null,"isLoggedIn":false},"requestType":"login"}

如何避免这些空值？我只想获取订阅目的所需的信息！

How can I avoid those null values? I only want to take required information for the "subscription" purpose!

这正是我正在寻找的输出：

Here's exactly the output that I'm looking for:

{"data":{"username":"Vincent","password":"test"},"requestType":"login"}

我也试过@JsonInclude（Include.NON_NULL）并将我的所有变量都置为null，但它也没有用！感谢您的帮助！

I also tried @JsonInclude(Include.NON_NULL) and put all my variables to null, but it didn't work either! Thanks for your help guys!

推荐答案

您的注释位置错误 - 它需要在课堂上，而不是领域。即：

You have the annotation in the wrong place - it needs to be on the class, not the field. i.e:

@JsonInclude(Include.NON_NULL) //or Include.NON_EMPTY, if that fits your use case 
public static class Request {
  // ...
}

如上所述在评论中，在版本2.x +中，此注释的语法是：

As noted in comments, in version 2.x+ the syntax for this annotation is:

@JsonSerialize(include = JsonSerialize.Inclusion.NON_NULL) // or JsonSerialize.Inclusion.NON_EMPTY

另一个选项是配置 ObjectMapper 直接，只需调用
mapper.setSerializationInclusion（Include.NON_NULL）;

The other option is to configure the ObjectMapper directly, simply by calling mapper.setSerializationInclusion(Include.NON_NULL);

（为了记录，我认为这个答案的受欢迎程度表明这个注释应该适用于逐个字段* ahem @fasterxml *）

(for the record, I think the popularity of this answer is an indication that this annotation should be applicable on a field-by-field basis *ahem @fasterxml*)

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