Jackson 将列表序列化为 xml 和 json

Question

I have a class which I want to serialize to json and XML:

@JacksonXmlRootElement(localName = "devices")
class DeviceWrapper { // <-- this class is intended to provide root xml name

    @JacksonXmlProperty(localName = "device")
    @JacksonXmlElementWrapper(useWrapping = false)
    List<Device> devices
}

Device class is just POJO:

class Device {
  String field1;
  String field2;
  ...
}

Serializing of DeviceWrapper to XML working fine:

<?xml version="1.0"?>
<devices>
  <device>
    <field1>value</field1>
    <field2>value</field2>
  </device>
  <device>
    <field1>value</field1>
    <field2>value</field2>
  </device>
  ...
</devices>

but when I try serialize DeviceWrapper to json I get:

{
  "devices": [
    {
      "field1": "val",
      "field2": "val"
    },
    {
      "field1": "val",
      "field2": "val"
    }
    ...
  ]
}

But I just want to get list of device values:

[
  {
    "field1": "val",
    "field2": "val"
  },
  {
    "field1": "val",
    "field2": "val"
  },
        ...
]

Ie I want to see devices only for xml as grouping element for list and do not want to see it in case of json. How it can be done?

Answer 1

Welcome to Stack Overflow, your problem would be solved annotating your List<Device> devices with the @JsonValue annotation, but this is not possible due to the presence of xml annotations: a way to solve is the use of the ObjectMapper#addMixIn method. If you define an interface like below :

public class DeviceWrapperModelMixIn {
    @JsonValue
    List<Device> devices;
}

You can add it to your objectmapper and obtaining the expected result without changes to the original class code:

mapper.addMixIn(DeviceWrapper.class, DeviceWrapperModelMixIn.class);
//it prints [{"field1":"val","field2":"val"},{"field1":"val","field2":"val"}]
System.out.println(mapper.writeValueAsString(wrapper));