如何编写Java类以从没有固定字段的Json获取对象？

Question

I need to have Java class to accommodate below requirement and it should be compatible for Jackson's parsing using Object Mapper.

The Json is in below format :

[
 { 
   "name" : "Snehal",
   "property1" : "value11",
   "property2" : "value12",
   "property3" : "value13",

 },
 {
   "name" : "Masne",
   "property1" : "value21",
   "property2" : "value22",
   "property3" : "value23",

},
]

In above Json, the no. of properties are not fixed, meaning there can be, say, property4, 5, 6, etc

The corresponding Java class could be thought of as below :

Class MyClass
{

  String name;

  List<String> properties;

 // getters, setters, etc

}

But this wont solve the purpose since, in this case, Json will generated something like of below format:

[ 
 {
   "name" : "Snehal",
   [
      {"property" : "value1" },
      {"property" : "value1" },
      {"property" : "value1" }
   ]
 },

 {
   .... []
 }

]

How do I implement the Java class to achieve the data in specifeid Json format ?

Answer 1

You can use @JsonAnyGetter/@JsonAnySetter annotations to mark that your class has 'extra' properties in addition to the declared fields.

Here is an example:

public class JacksonAnyGetter {

    static final String JSON = " { \n" +
            "   \"name\" : \"Snehal\",\n" +
            "   \"property1\" : \"value11\",\n" +
            "   \"property2\" : \"value12\",\n" +
            "   \"property3\" : \"value13\"\n" +
            "\n" +
            " }";

    static class Bean {
        public String name; // we always have name
        private Map<String, Object> properties = new HashMap<>();

        @JsonAnySetter
        public void add(String key, String value) {
            properties.put(key, value);
        }

        @JsonAnyGetter
        public Map<String, Object> getProperties() {
            return properties;
        }

        @Override
        public String toString() {
            return "Bean{" +
                    "name='" + name + '\'' +
                    ", properties=" + properties +
                    '}';
        }
    }

    public static void main(String[] args) throws IOException {
        final ObjectMapper mapper = new ObjectMapper();
        final Bean bean = mapper.readValue(JSON, Bean.class);
        System.out.println(bean);
        final String json = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(bean);
        System.out.println(json);
    }
}

Output:

Bean{name='Snehal', properties={property3=value13, property2=value12, property1=value11}}
{
  "name" : "Snehal",
  "property3" : "value13",
  "property2" : "value12",
  "property1" : "value11"
}