为 jackson 添加动态 json 属性作为 java pojo [英] Adding a dynamic json property as java pojo for jackson

问题描述

我需要从 Java pojo 创建一个像这样的 Json 负载:

I need to create a Json payload like this from Java pojo :

{ "update" : {
    "labels" : [{"add" : "A label"} ]
    }
 }

所以我创建了一个这样的 Java pojo:

so I created a Java pojo like this :

@JsonRootName(value = "update")
public class AddLabel{
  @JsonProperty("labels")
  public List<Label> labels; 
  public AddLabel(String labelName){
     this.labels = new ArrayList<>(); 
     this.labels.add(new Label(labelName); 
  }
  public static class Label{
    public String add; 
    public Label(String labelName){
       this.add = labelName; 
    }
  }
}

我喜欢将 Label 类中的add"属性设为动态，这样它也可以采用诸如remove"、set"之类的值.除了为每个人创建另一个 POJO 之外，还有其他方法可以做到这一点吗?

I like to have the "add" property in Label class as dynamic, so that it can also take values such as "remove", "set" . Is there a way to do this other than creating another POJO's for each of them?

推荐答案

您可以使用 JsonAnyGetter 注释，允许创建动态 key-value 对.下面的例子展示了我们如何为同一个 Label 类生成 3 个不同的键:

You can use JsonAnyGetter annotation which allows to create dynamic key-value pairs. Below example shows how we can generate 3 different keys for the same Label class:

import com.fasterxml.jackson.annotation.JsonAnyGetter;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonRootName;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;

public class JsonApp {

    public static void main(String[] args) throws Exception {
        AddLabel label = new AddLabel("A label");
        label.getLabels().add(AddLabel.Label.remove("Remove"));
        label.getLabels().add(AddLabel.Label.set("Set"));

        ObjectMapper mapper = new ObjectMapper();
        mapper.enable(SerializationFeature.INDENT_OUTPUT);

        System.out.println(mapper.writeValueAsString(label));
    }
}

@JsonRootName(value = "update")
class AddLabel {

    @JsonProperty("labels")
    private List<Label> labels;

    public AddLabel(String labelName) {
        this.labels = new ArrayList<>();
        this.labels.add(Label.add(labelName));
    }

    public List<Label> getLabels() {
        return labels;
    }

    public static class Label {

        private final String key;
        private final String value;

        private Label(String key, String value) {
            this.key = key;
            this.value = value;
        }

        public static Label add(String value) {
            return new Label("add", value);
        }

        public static Label remove(String value) {
            return new Label("remove", value);
        }

        public static Label set(String value) {
            return new Label("set", value);
        }

        @JsonAnyGetter
        public Map<String, String> getDynamic() {
            return Collections.singletonMap(key, value);
        }
    }
}

以上代码打印:

{
  "labels" : [ {
    "add" : "A label"
  }, {
    "remove" : "Remove"
  }, {
    "set" : "Set"
  } ]
}

另见:

• 杰克逊@JsonAnyGetter 和@JsonAnySetter 示例
• Jackson 注释示例
• 如何使用动态属性Json 对象的名称

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