用GSON序列化java对象

Question

我想将这个对象序列化为JSON字符串

public class Person {
   public String id;
   public String name;
   public Person parent;
}

并得到如下结果：

{id: 1, name: "Joe", parent: 2}

我试着用

Person p = new Person(1, "Joe", new Person(2, "Mike"));
Gson gson = new GsonBuilder()
            .registerTypeAdapter(Persona.class, new PersonSerializer()).create();
String str = gson.toJson(p);

但不是这样，我得到了：

"1"

个性化序列化：

public class PersonSerializer implements JsonSerializer<Person> {
    public JsonElement serialize(Person src, Type typeOfSrc, ...) {
        return new JsonPrimitive(src.id);
    }
}

欢迎提出任何建议

谢谢，马里奥

Answer 1

你刚刚得到了答案。然而，我想通过使用@JsonAdapter注释的另一种方式与您分享。

像这样注释Person bean

@JsonAdapter(PersonAdatper.class)
public class Person {
    public int id;
    public String name;
    public Person parent;
}

创建自定义适配器

public  class PersonAdatper extends TypeAdapter<Person> {

    @Override
    public void write(JsonWriter writer, Person value) throws IOException {
        writer.beginObject();

        writer.name("id").value(value.getId());
        writer.name("name").value(value.getName());
        Person parent = value.getParent();
        if (parent != null) {
            writer.name("parent").value(parent.getId());
        }       
        writer.endObject();
    }

    @Override
    public Person read(JsonReader in) throws IOException {
        // do something you need
        return null;
    }

}

将对象序列化为json字符串

Person p = new Person(1, "Joe", new Person(2, "Mike"));
Gson gson = new Gson();    
String result = gson.toJson(p);

它产生如下输出：

{"id":1,"name":"Joe","parent":2}

我在使用JsonAdapter的教程GSON注释示例中找到了这种方法

Answer 2

为了获得所需的结果，您需要像这样编写序列化程序：

public static class PersonSerializer implements JsonSerializer<Person> {
    public JsonElement serialize(final Person person, final Type type, final JsonSerializationContext context) {
        JsonObject result = new JsonObject();
        result.add("id", new JsonPrimitive(person.getId()));
        result.add("name", new JsonPrimitive(person.getName()));
        Person parent = person.getParent();
        if (parent != null) {
            result.add("parent", new JsonPrimitive(parent.getId()));
        }
        return result;
    }
}

结果是

    Person p = new Person(1, "Joe", new Person(2, "Mike"));
    com.google.gson.Gson gson = new GsonBuilder().registerTypeAdapter(Person.class, new PersonSerializer())
            .create();
    System.out.println(gson.toJson(p));

将

{"id":1,"name":"Joe","parent":2}

完整代码：

import java.lang.reflect.Type;

import com.google.gson.GsonBuilder;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonPrimitive;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;

public class GsonSimpleTest {

    public static class Person {
        public int id;
        public String name;
        public Person parent;

        public Person(final int id, final String name) {
            super();
            this.id = id;
            this.name = name;
        }

        public Person(final int id, final String name, final Person parent) {
            super();
            this.id = id;
            this.name = name;
            this.parent = parent;
        }

        public int getId() {
            return id;
        }

        public void setId(final int id) {
            this.id = id;
        }

        public String getName() {
            return name;
        }

        public void setName(final String name) {
            this.name = name;
        }

        public Person getParent() {
            return parent;
        }

        public void setParent(final Person parent) {
            this.parent = parent;
        }

    }

    public static class PersonSerializer implements JsonSerializer<Person> {
        public JsonElement serialize(final Person person, final Type type, final JsonSerializationContext context) {
            JsonObject result = new JsonObject();
            result.add("id", new JsonPrimitive(person.getId()));
            result.add("name", new JsonPrimitive(person.getName()));
            Person parent = person.getParent();
            if (parent != null) {
                result.add("parent", new JsonPrimitive(parent.getId()));
            }
            return result;
        }
    }

    public static void main(final String[] args) {
        Person p = new Person(1, "Joe", new Person(2, "Mike"));
        com.google.gson.Gson gson = new GsonBuilder().registerTypeAdapter(Person.class, new PersonSerializer())
                .create();
        System.out.println(gson.toJson(p));
    }

}