Jackson 2：仅在序列化时忽略瞬态字段

Question

我在 JAX-RS 应用程序中使用 Jackson v2，我正在尝试确定是否可能 配置“ObjectMapper”以删除带有瞬态修饰符的字段，但仅在序列化期间。

这是一个 DTO 来说明我的用例（省略了 getter 和 setter）

public class User {
    private String email;
    private transient String password;
}

考虑到上述 DTO，我想要一个对象映射器 序列化时的密码字段，反序列化时包含它。

关于瞬态，我唯一能找到的是：

MapperFeature.PROPAGATE_TRANSIENT_MARKER

但该配置与我的要求无关。

P.S - 不使用注释，因为 DTO 不与任何库耦合，另外 我不一定能控制它们。

Answer 1

不知道，看起来像transient 属性修饰符加上PROPAGATE_TRANSIENT_MARKER 就可以了。反序列化是直截了当的。不过，在序列化过程中有一些fuss with the transient marker。您需要为字段提供 getter，否则您将遇到异常“无法识别的字段...未标记为可忽略”。

针对其他要求，我添加了一个使用 jackson mixins 的版本。请注意，mixin 版本生成带有空密码字段的 json，而 PROPAGATE_TRANSIENT_MARKER 版本根本不生成任何字段。

PROPAGATE_TRANSIENT_MARKER 版本

public class SerializeDeserializeAttributes {
    private final ObjectMapper mapper = new ObjectMapper();

public <T> T fromJson(String json, Class<T> c) throws IOException {
    synchronized (mapper) {
        mapper.configure(MapperFeature.PROPAGATE_TRANSIENT_MARKER, false);
        return mapper.readValue(json, c);
    }
}

public String toJson(Object o) throws JsonProcessingException {
    synchronized (mapper) {
        mapper.configure(MapperFeature.PROPAGATE_TRANSIENT_MARKER, true);
        return mapper.writeValueAsString(o);
    }
}

    private static final String jsonFull = "{\"name\":\"A\",\"email\":\"a@a\",\"password\":\"a\",\"width\":1,\"height\":1}";
    private static final String jsonPartial = "{\"name\":\"A\",\"email\":\"a@a\",\"width\":1,\"height\":1}";
    private static final User user = new User("A", "a@a", "a", 1, 1);

    @Test
    public void serializeDeserialize() throws IOException {
        assertEquals(user, fromJson(jsonFull, User.class));
        assertEquals(jsonPartial, toJson(user));
        assertEquals(user, fromJson(jsonFull, User.class));
        assertEquals(jsonPartial, toJson(user));
    }
}

混音版

public class SerializeDeserializeAttributesMixin {

    public abstract class UserMixin {
        @JsonSerialize(using = PwdSerializer.class)
        transient String password;
    }

    static class PwdSerializer extends StdSerializer<String> {

        public PwdSerializer() {
            this(String.class);
        }

        private PwdSerializer(Class<String> t) {
            super(t);
        }

        @Override
        public void serialize(String s, JsonGenerator jg, SerializerProvider sp) throws IOException {
            jg.writeString("");
        }
    }

    private static final String jsonFull = "{\"name\":\"A\",\"email\":\"a@a\",\"password\":\"a\",\"width\":1,\"height\":1}";
    private static final String jsonPartialMixin = "{\"name\":\"A\",\"email\":\"a@a\",\"password\":\"\",\"width\":1,\"height\":1}";
    private static final User user = new User("A", "a@a", "a", 1, 1);
    private static final ObjectMapper mapperMixin = new ObjectMapper();

    static {
        mapperMixin.addMixIn(User.class, UserMixin.class);
    }


    @Test
    public void serializeDeserializeUsingMixin() throws IOException {
        assertEquals(user, mapperMixin.readValue(jsonFull, User.class));
        assertEquals(jsonPartialMixin, mapperMixin.writeValueAsString(user));
    }

}

这就是 User 类。

class User {
    private String name;
    private String email;
    private transient String password;
    private int width;
    private int height;

    public User() {
    }

    User(String name, String email, String password, int width, int height) {
        this.name = name;
        this.email = email;
        this.password = password;
        this.width = width;
        this.height = height;
    }

    public String getName() {
        return name;
    }

    public String getEmail() {
        return email;
    }

    public String getPassword() {
        return password;
    }

    public int getWidth() {
        return width;
    }

    public int getHeight() {
        return height;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        User user = (User) o;
        return Float.compare(user.width, width) == 0 &&
                Float.compare(user.height, height) == 0 &&
                Objects.equals(name, user.name) &&
                Objects.equals(email, user.email) &&
                Objects.equals(password, user.password);
    }

    @Override
    public int hashCode() {
        return Objects.hash(name, email, password, width, height);
    }

    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", email='" + email + '\'' +
                ", password='" + password + '\'' +
                ", width=" + width +
                ", height=" + height +
                '}';
    }
}