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，并且试图弄清楚是否可以配置“ObjectMapper”以删除带有瞬态修饰符的字段，但仅限于序列化期间。

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，我希望有一个对象映射器，它在序列化时删除密码字段，并在反序列化期间包含它。

我能找到的关于瞬态的唯一信息是：

MapperFeature.PROPAGATE_TRANSIENT_MARKER

但该配置与我的要求不相关。

PS - 不使用注释，因为 DTO 不耦合到任何库，而且我不一定可以控制它们。

Answer 1

不知道，看起来像transient属性修饰符加上PROPAGATE_TRANSIENT_MARKER就可以了。反序列化是直接的。不过，在序列化过程中，瞬态标记有些麻烦。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”。为了满足额外的要求，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));    }}Mixin versionpublic 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));    }}那是用户类。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 +                '}';    }}