Google Gson 字段过滤：@Expose

Google Gson 使用 @Expose 注解实现字段过滤，该注解必须和 com.google.gson.GsonBuilder 类配合使用，如果使用 com.google.gson.Gson 类则不会产生任何作用。

(1) @Expose(serialize = true, deserialize = true)：序列化和反序列化时都生效，即序列化和反序列化都会处理

(2) @Expose(serialize = false, deserialize = false)：序列化和反序列化时都不生效，即序列化和反序列化都忽略，和不加 @Expose 注解效果一样

(3) @Expose(serialize = true, deserialize = false)：只有序列化时生效，即序列化时处理，反序列化时忽略

(4) @Expose(serialize = false, deserialize = true)：只有反序列化时生效，即反序列化时处理，序列化时忽略

示例

(1) POJO 类

public class User {

    @Expose(serialize = true, deserialize = true)
    private String account;

    @Expose(serialize = false, deserialize = false)
    private String password;

    @Expose(serialize = true, deserialize = false)
    private String name;

    @Expose(serialize = false, deserialize = true)
    private int age;

    public User() {}

    public User(String account, String password, String name, int age) {
        this.account = account;
        this.password = password;
        this.name = name;
        this.age = age;
    }

    public String getAccount() {
        return account;
    }

    public void setAccount(String account) {
        this.account = account;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String getName() {
        return name;
    }

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

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "User [account=" + account + ", password=" + password + ", name=" + name + ", age=" + age + "]";
    }

}

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(2) 测试代码

@Test
public void test() throws IOException {
    Gson gson = new GsonBuilder()
        .excludeFieldsWithoutExposeAnnotation()
        .create();

    User user = new User("admin", "123456", "John", 30);
    System.out.println(gson.toJson(user));

    String userStr = "{\"account\":\"normal\",\"password\":\"xyz123\",\"name\":\"Normal\",\"age\":25}";
    User normalUser = gson.fromJson(userStr, User.class);
    System.out.println(normalUser);
}

运行测试结果：