Jackson-Serialiser:序列化时忽略字段 [英] Jackson-Serialiser: Ignore Field at Serialisation Time

问题描述

我的情况要求更复杂的序列化.我有一个类Available(这是一个非常简化的代码段):

My situation asks for a bit more complex serialisation. I have a class Available (this is a very simplified snippet):

public class Available<T> {
  private T value;
  private boolean available;
  ...
}

所以是POJO

class Tmp {
  private Available<Integer> myInt = Available.of(123);
  private Available<Integer> otherInt = Available.clean();
  ...
}

通常会导致

{"myInt":{available:true,value:123},"otherInt":{available:false,value:null}}

但是，我希望序列化器像这样渲染相同的POJO:

However, I want a serialiser to render the same POJO like this:

{"myInt":123}

我现在所拥有的:

public class AvailableSerializer extends JsonSerializer<Available<?>> {

  @Override
  public void serialize(Available<?> available, JsonGenerator jsonGenerator, SerializerProvider provider) throws IOException, JsonProcessingException {
    if (available != null && available.isAvailable()) {
      jsonGenerator.writeObject(available.getValue());
    }

    // MISSING: nothing at all should be rendered here for the field
  }

  @Override
  public Class<Available<?>> handledType() {
    @SuppressWarnings({ "unchecked", "rawtypes" })
    Class<Available<?>> clazz = (Class) Available.class;
    return clazz;
  }

}

测试

  @Test
  public void testSerialize() throws Exception {
    SimpleModule module = new SimpleModule().addSerializer(new AvailableSerializer());
    ObjectMapper objectMapper = new ObjectMapper();
    objectMapper.registerModule(module);

    System.out.println(objectMapper.writeValueAsString(new Tmp()));
  }

输出

{"myInt":123,"otherInt"}

有人可以告诉我如何进行"MISSING"操作吗?或者，如果我做错了一切，该怎么办?

Can anyone tell me how to do the "MISSING"-stuff? Or if I'm doing it all wrong, how do I do it then?

我的限制是我不希望开发人员一直向Available类型的字段添加@Json...-批注.因此，上面的Tmp类是一个典型的使用类的外观示例. 如果可能的话...

The restriction I have is that I don't want the developers to add @Json...-annotations all the time to fields of type Available. So the Tmp-class above is an example of what a typical using class should look like. If that's possible...

推荐答案

在MichałZiober的答案之后，我不得不寻找关于Include.NON_DEFAULT和默认对象的内容，并遇到了此答案，解释了Include.NON_EMPTY Google在我的计算机中未返回首次研究(感谢Google).

After Michał Ziober's answer I had to look for something regarding Include.NON_DEFAULT and the default object and ran into this answer explaining Include.NON_EMPTY that Google didn't return in my first research (thanks Google).

现在事情变得简单了，现在:

So things become easier, it's now:

public class AvailableSerializer extends JsonSerializer<Available<?>> {

  @Override
  public void serialize(Available<?> available, JsonGenerator jsonGenerator, SerializerProvider provider) throws IOException, JsonProcessingException {
    jsonGenerator.writeObject(available.getValue());
  }

  @Override
  public Class<Available<?>> handledType() {
    @SuppressWarnings({ "unchecked", "rawtypes" })
    Class<Available<?>> clazz = (Class) Available.class;
    return clazz;
  }

  @Override
  public boolean isEmpty(SerializerProvider provider, Available<?> value) {
    return value == null || !value.isAvailable();
  }

}

通过测试

  @Test
  public void testSerialize() throws Exception {
    SimpleModule module = new SimpleModule().addSerializer(availableSerializer);
    objectMapper.registerModule(module);
    objectMapper.configOverride(Available.class).setInclude(
        // the call comes from JavaDoc of objectMapper.setSerializationInclusion(...)
        JsonInclude.Value.construct(JsonInclude.Include.NON_EMPTY, JsonInclude.Include.ALWAYS));

    Tmp tmp = new Tmp();
    assertThat(objectMapper.writeValueAsString(tmp)).isEqualTo("{\"myInt\":123}");
    tmp.otherInt.setValue(123);
    assertThat(objectMapper.writeValueAsString(tmp)).isEqualTo("{\"myInt\":123,\"otherInt\":123}");
  }

因此，如果您赞成我的回答，请也赞成MichałZiober's，因为这也可以采用一种稍有不同的方法.

So please, if you upvote my answer please also upvote Michał Ziober's as that's also working with a mildly different approach.

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