java - setSerializationInclusion(Include.NON_EMPTY) 不排除数组中的空值

Question

我已经测试了几种从输出文件 (Json) 中删除 java 对象中的 Null 值的方法。但是，似乎还有一些遗漏了。我正在使用 2.9.6

我试过以下方法:

objectMapper.setSerializationInclusion(Include.NON_NULL);
objectMapper.setSerializationInclusion(Include.NON_EMPTY);
@JsonInclude(Include.NON_NULL);

这是我的代码:

  public static String convertToJson(Hospital patient) {
    try {
      if (patient != null) {
        String json = objectMapper.writeValueAsString(patient);
        return json;
      }
    } catch (IOException e) {
      throw new RuntimeException("Error converting person to Json " + e);
    }
    return null;
  }

这些已从输出文件中删除了大约 2150 个空值。但是，结果仍然有一些以以下形式存在:

"patient" : {
    "corporateEntityCode" : "OH",
    "groupNumber" : "123ABCD",
    "patientIdentifier" : 12345678,
    "patientPreexistingDiagnosticCode" : [ null, null, null, null, null, null ],
    "patientPreexistingEffectiveDate" : [ null, null, null, null, null, null ],
    "patientSubscriptNumber" : "01",
    "subscriberNumber" : "0000000123456789"
}

这是一个存在的问题吗？还是我没有正确实现？

Answer 1

这似乎不是库中存在的问题，但令人惊讶的是，当使用 Include.NON_NULL 时，它会对 Map 产生影响，忽略value 为 null 但它对 Array 或 Collection 没有任何影响。无论如何，您可以使用自定义序列化程序很容易地实现您想要的。我创建了一个不同的模型只是为了向您展示如何去做。该示例涵盖了 Arrays 和任何扩展 Collection 的类的自定义序列化。

模型类医院:

public class Hospital {
    private List<String> patients;
    private String[] doctors;

    public List<String> getPatients() {
        return patients;
    }

    public void setPatients(List<String> patients) {
        this.patients = patients;
    }

    public String[] getDoctors() {
        return doctors;
    }

    public void setDoctors(String[] doctors) {
        this.doctors = doctors;
    }
}

自定义序列化程序忽略扩展 Collection 的类中的 null 值:

 class CollectionIgnoreNullSerializer extends StdSerializer<Collection> {
    public CollectionIgnoreNullSerializer() {
        this(null);
    }

    public CollectionIgnoreNullSerializer(Class<Collection> t) {
        super(t);
    }

    @Override
    public void serialize(Collection list, JsonGenerator jsonGenerator, SerializerProvider unused) throws IOException {
        jsonGenerator.writeStartArray();

        list.forEach(e -> {
            try {
                if (e != null) {
                    jsonGenerator.writeObject(e);
                }
            } catch (IOException e1) {
                e1.printStackTrace();
            }
        });

        jsonGenerator.writeEndArray();
    }
}

自定义序列化程序以忽略 Array 中的 null 值:

class ArrayIgnoreNullSerializer extends StdSerializer<Object[]> {
    public ArrayIgnoreNullSerializer() {
        this(null);
    }

    public ArrayIgnoreNullSerializer(Class<Object[]> t) {
        super(t);
    }

    @Override
    public void serialize(Object[] array, JsonGenerator jsonGenerator, SerializerProvider unused) throws IOException {
        jsonGenerator.writeStartArray();

        for (int i = 0; i < array.length; i++) {
            try {
                if (array[i] != null) {
                    jsonGenerator.writeObject(array[i]);
                }
            } catch (IOException e1) {
                e1.printStackTrace();
            }
        }

        jsonGenerator.writeEndArray();
    }
}

main 只是为了测试它:

public static void main(String[] args) throws IOException {
    Hospital hospital = new Hospital();

    List<String> patients = Arrays.asList(null, "Bob", "Tom", null, null);
    String[] doctors = new String[]{null, "Dr. Grimmer", "Dr. Who", null};

    hospital.setPatients(patients);
    hospital.setDoctors(doctors);

    ObjectMapper mapper = new ObjectMapper();

    SimpleModule module = new SimpleModule();
    module.addSerializer(Collection.class, new CollectionIgnoreNullSerializer());
    // You could apply the custom serialization just to Lists:
    // module.addSerializer(List.class, new CollectionIgnoreNullSerializer());

    module.addSerializer(String[].class, new ArrayIgnoreNullSerializer());
    // You could cover other type of Arrays like this:
    // module.addSerializer(Integer[].class, new ArrayIgnoreNullSerializer());
    mapper.registerModule(module);

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

这是序列化的 json:

{"patients":["Bob","Tom"],"doctors":["Dr. Grimmer","Dr. Who"]}