Java 让 Jackson 使用 GSON 注释

发布于04月27日

我有一个无法更改的数据模型.

@SerializedName("first_value")
private String firstValue = null;

与杰克逊的反序列化没有按需要进行.Jackson无法匹配条目，因此该值为空.

它可以与

@JsonProperty("first_value")
private String firstValue = null;

我有没有办法让Jackson使用GSON注释，或者有没有其他解决方案不需要更改原始模型注释？

推荐答案

我研究了一下这个问题，似乎@JsonProperty注释是用JacksonAnnotationIntrospector处理的.扩展后者，使其成为句柄@SerializedName，似乎可以保持原始行为(我希望如此):

@NoArgsConstructor(access = AccessLevel.PRIVATE)
final class SerializedNameAnnotationIntrospector
        extends JacksonAnnotationIntrospector {

    @Getter
    private static final AnnotationIntrospector instance = new SerializedNameAnnotationIntrospector();

    @Override
    public PropertyName findNameForDeserialization(final Annotated annotated) {
        @Nullable
        final SerializedName serializedName = annotated.getAnnotation(SerializedName.class);
        if ( serializedName == null ) {
            return super.findNameForDeserialization(annotated);
        }
        // TODO how to handle serializedName.alternate()?
        return new PropertyName(serializedName.value());
    }

}

public final class SerializedNameAnnotationIntrospectorTest {

    private static final AnnotationIntrospector unit = SerializedNameAnnotationIntrospector.getInstance();

    @Test
    public void test()
            throws IOException {
        final ObjectMapper objectMapper = new ObjectMapper()
                .setAnnotationIntrospector(unit);
        final Model model = objectMapper.readValue("{\"first_value\":\"foo\",\"second_value\":\"bar\"}", Model.class);
        Assertions.assertEquals("foo", model.firstValue);
        Assertions.assertEquals("bar", model.secondValue);
    }

    private static final class Model {

        @SerializedName("first_value")
        private final String firstValue = null;

        // does not exist in the original model,
        // but retains here to verify whether the introspector still works fine
        @JsonProperty("second_value")
        private final String secondValue = null;

    }

}

请注意，我不确定它有多好，因为我不是杰克逊的专家.