Gson序列化对象自定义
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
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
