Gson序列化对象如何忽略字段

Gson序列化对象如何忽略字段

Gson版本 2.8.2

附gson-2.8.2下载链接

gson-2.8.2-sources.jar

gson-2.8.2.jar

梗概

• 忽略字段。用注解@Expose(serialize = false, deserialize = false)在类的成员上以告诉Gson 跳过本字段的(反)序列化。 (反)序列化时，需要Gson gson = new GsonBuilder().excludeFieldsWithoutExposeAnnotation().create()而不是Gson gson = new Gson()
• 自定义序列化和反序列化

忽略字段

比如有下User类，我不想把nickName也输出出来，网上查了查，说只要把注解改成@Expose(serialize = false, deserialize = false)

package go.Gson;

import com.google.gson.Gson;
import com.google.gson.annotations.Expose;

public class User {

	User(String name_, String nickName_) {
		name = name_;
		nickName = nickName_;
	}

	public static void main(String[] args) {
		User u = new User("Jackey", "Jack");
		Gson gson = new Gson();
		System.out.println(gson.toJson(u));//{"name":"Jackey","nickName":"Jack"}
	}

	@Expose
	String name;

	@Expose(serialize = false, deserialize = false)
	String nickName;
}

事实是注解改了以后， 也还是会输出nickName的。

查看了下Gson-2.8.2的源码，在Expose.java中有注释，说如何使用

public class User {
  @Expose private String firstName;
  @Expose(serialize = false) private String lastName;
  @Expose (serialize = false, deserialize = false) private String emailAddress;
  private String password;
 }

If you created Gson with {@code new Gson()}, the {@code toJson()} and {@code fromJson()}

methods will use the {@code password} field along-with {@code firstName}, {@code lastName},

and {@code emailAddress} for serialization and deserialization. However, if you created Gson

with {@code Gson gson = new GsonBuilder().excludeFieldsWithoutExposeAnnotation().create()}

then the {@code toJson()} and {@code fromJson()} methods of Gson will exclude the

{@code password} field. This is because the {@code password} field is not marked with the

{@code @Expose} annotation. Gson will also exclude {@code lastName} and {@code emailAddress}

from serialization since {@code serialize} is set to {@code false}. Similarly, Gson will

exclude {@code emailAddress} from deserialization since {@code deserialize} is set to false.

即使用Gson gson = new Gson()注解不会生效，需要用Gson gson = new GsonBuilder().excludeFieldsWithoutExposeAnnotation().create()去配置Gson

代码改成如下即可

package go.Gson;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.annotations.Expose;

public class User {

	User(String name_, String nickName_) {
		name = name_;
		nickName = nickName_;
	}

	public static void main(String[] args) {
		User u = new User("Jackey", "Jack");
		Gson gson = new GsonBuilder().excludeFieldsWithoutExposeAnnotation().create();
		System.out.println(gson.toJson(u));// {"name":"Jackey"}
	}

	@Expose
	String name;

	@Expose(serialize = false, deserialize = false)
	String nickName;
}

自定义序列化过程

设想一个UserWrapper类

package go.Gson;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.annotations.Expose;

public class UserWrapper {

	UserWrapper(){
		user = new User("Jackey", "Jack");
	}

	public static void main(String[] args) {
		UserWrapper u = new UserWrapper();
		Gson gson = new GsonBuilder().excludeFieldsWithoutExposeAnnotation().create();
		System.out.println(gson.toJson(u));
	}

	@Expose
	private User user;

}

class User {

	User(String name_, String nickName_) {
		name = name_;
		nickName = nickName_;
	}

	@Expose
	String name;

	@Expose(serialize = false, deserialize = false)
	String nickName;
}

这个会输出{"user":{"name":"Jackey"}}，这很讨厌，我们想让User对象只输出name的值，要这么做：

package go.Gson;

import java.lang.reflect.Type;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonElement;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;
import com.google.gson.annotations.Expose;

public class UserWrapper {

	UserWrapper(){
		user = new User("Jackey", "Jack");
	}

	public static void main(String[] args) {
		UserWrapper u = new UserWrapper();
		Gson gson = new GsonBuilder().excludeFieldsWithoutExposeAnnotation()
				.registerTypeAdapter(User.class, new UserAdapter()).create();
		System.out.println(gson.toJson(u));
	}

	@Expose
	private User user;

}

class User {

	User(String name_, String nickName_) {
		name = name_;
		nickName = nickName_;
	}

	@Expose
	String name;

	@Expose(serialize = false, deserialize = false)
	String nickName;
}

class UserAdapter implements JsonSerializer<User> {

	@Override
	public JsonElement serialize(User src, Type typeOfSrc, JsonSerializationContext context) {
		return context.serialize(src.name);
	}

}

类似的interface 还有JsonDeserializer,TypeAdapter