你如何使用 Jackson 将 Map<Key, Value> 转换为 {"keyprop" : key, "valueprop" : value} 的数组？

Question

我正在尝试执行以下操作

给出

Map<String, String> labels = {"en_GB" : "English", "de" : "German", "it" : "Italian"}....

我想用Jackson序列化到

[{"language" : "en_GB", "label" : "English"}, {"language" : "de", "label" : "German"}, {"language" : "it", "label" : "Italian"}]

本质上将映射拆分为对象数组，键和值作为单独的属性

而不是

 {"en_GB" : "English", "de" : "German", "it" : "Italian"}

我已经搜索了整个 Jackson 文档，但我找不到这个问题的答案。我会很感激一些帮助。提前致谢！

Answer 1

方法一：定义一个中间POJO，将map转换为中间对象列表

先定义一个中间的POJO：

public class LanguageInfo {
    private String language;
    private String label;
}

将映射转换为中间 POJO 列表并将列表序列化为字符串：

Map<String, String> labels = new HashMap<>();
labels.put("en_GB", "English");
labels.put("de", "German");
labels.put("it", "Italian");

List<LanguageInfo> languageInfoList = labels.entrySet().stream()
  .map(entry -> {
      LanguageInfo info = new LanguageInfo();
      info.setLabel(entry.getValue());
      info.setLanguage(entry.getKey());
      return info;
  }).collect(Collectors.toList());
ObjectMapper mapper = new ObjectMapper();
System.out.println(mapper.writeValueAsString(languageInfoList));

输出为：

[
    {
        "language":"de",
        "label":"German"
    },
    {
        "language":"en_GB",
        "label":"English"
    },
    {
        "language":"it",
        "label":"Italian"
    }
]

方法二：定义一个JsonSerializer并用它来做序列化工作

假设你想直接序列化下面的class：

@Data
public class LanguageInfos {
    private Map<String, String> labels;
}

首先，定义一个JsonSerializer来序列化LanguageInfos:

需要中间POJO LanguageInfo定义如上：

public class LanguageInfosJsonSerializer extends JsonSerializer<LanguageInfos> {

    @Override
    public void serialize(LanguageInfos languageInfos, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {
        // LanguageInfo defined in below code
        List<LanguageInfo> languageInfoList = languageInfos.getLabels().entrySet().stream()
            .map(entry -> {
                LanguageInfo info = new LanguageInfo();
                info.setLabel(entry.getValue());
                info.setLanguage(entry.getKey());
                return info;
            }).collect(Collectors.toList());
        jsonGenerator.writeObject(languageInfoList);
    }
}

不需要中间POJO：

public class LanguageInfosJsonSerializer extends JsonSerializer<LanguageInfos> {

    @Override
    public void serialize(LanguageInfos languageInfos, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {
        jsonGenerator.writeStartArray(languageInfos.getLabels().size());
        languageInfos.getLabels().entrySet().forEach(new Consumer<Map.Entry<String, String>>() {
            @SneakyThrows
            @Override
            public void accept(Map.Entry<String, String> entry) {
                    ObjectNode node = new ObjectMapper().createObjectNode();
                    node.put("language",entry.getKey());
                    node.put("label",entry.getValue());
                    jsonGenerator.writeObject(node);
            }
        });
        jsonGenerator.writeEndArray();
    }
}

其次，将这个Serializer注册到一个ObjectMapper对象中：

SimpleModule simpleModule = new SimpleModule();
simpleModule.addSerializer(LanguageInfos.class, new LanguageInfosJsonSerializer());
ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(simpleModule);

三、直接使用ObjectMapper序列化：

Map<String, String> labels = new HashMap<>();
labels.put("en_GB", "English");
labels.put("de", "German");
labels.put("it", "Italian");

LanguageInfos languageInfos = new LanguageInfos();
languageInfos.setLabels(labels);

ObjectMapper mapper = new ObjectMapper();
SimpleModule simpleModule = new SimpleModule();
simpleModule.addSerializer(LanguageInfos.class, new LanguageInfosJsonSerializer());
mapper.registerModule(simpleModule);
System.out.println(mapper.writeValueAsString(languageInfos));

输出为：

[
    {
        "language":"de",
        "label":"German"
    },
    {
        "language":"en_GB",
        "label":"English"
    },
    {
        "language":"it",
        "label":"Italian"
    }
]

你如何使用 Jackson 将 Map<Key, Value> 转换为 {"keyprop" : key, "valueprop" : value} 的数组？

How do you convert a Map<Key, Value> into an array of {"keyprop" : key, "valueprop" : value} with Jackson?

java

serialization

json

dictionary

jackson