用反序列化编写Java类以表示简单的JSON文档的最简洁方法是什么？

Question

Here's the current style I've got for simple messages, using Jackson:

public class FooRequest {
    public final String foo;
    public final int bar;

    @JsonCreator
    public FooRequest(
            @JsonProperty("foo") String foo,
            @JsonProperty("bar") int bar) {
        this.foo = foo;
        this.bar = bar;
    }
}

Is there a class annotation out there that will handle the boiler plate constructor?

Answer 1

A quick Google search brought up this:

Creating a json object using jackson

Looks like you can handle the construction with JsonNodeFactory.

final JsonNodeFactory factory = JsonNodeFactory.instance;

Is that what you were looking for?

Answer 2

You can try using Jackson annotation . The Jackson annotation @JsonCreator is used to tell Jackson that the Java object has a constructor (a "creator") which can match the fields of a JSON object to the fields of the Java object.

Let's consider the following JSON object that we want to deserialize.

{
    "name":"Mr.Bond",
    "age":"30"
}

You can unmarshall the message by annotating the constructor with @JsonCreator and using the @JsonProperty

public class UserProfileCreator {
    public int age;
    public String name;

    @JsonCreator
    public UserProfileCreator(
        @JsonProperty("age") int age, 
        @JsonProperty("name") String name) {
            this.age = age;
            this.name = name;
    }
}

How will it work?

Let's write a small test program.

@Test
public void deserialize()
    throws JsonProcessingException, IOException {

    String json = "{"age":30,"name":"Mr.Bond"}";
    UserProfileCreator obj = new ObjectMapper().reader(UserProfileCreator.class).readValue(json);
    assertEquals("Mr.Bond", obj.name);
}

Answer 3

Google's gson library doesn't require you to use annotations or constructors:

import com.google.gson.Gson;
import java.util.Date;
public class Test {
    public static void main(String[] args) {
        Gson gson = new Gson();

        String toJson = gson.toJson(new Thing());
        System.out.println(toJson);
        // prints {"appleType":"granny","date":"Apr 21, 2016 10:31:17 AM","numPies":6}

        Thing fromJson = gson.fromJson(toJson, Thing.class);
        System.out.println(fromJson);
        // prints com.mycompany.mavenproject1.Thing@506c589e
    }
}
class Thing {
    String appleType = "granny";
    Date date = new Date();
    int numPies = 6;
}

Jackson may have similar features, but I don't know.