Question

我设法将Jackson配置为序列化一个类，只需使用

就可以在类中的私有字段上没有任何getter或注释

objectMapper.setVisibility(PropertyAccessor.FIELD, JsonAutoDetect.Visibility.ANY);

但我没有设法将这个非静态类的JSON字符串设置为反序列化为没有任何参数化构造函数或setter的对象。这有可能 - 我认为它应该通过反思但我不确切地知道如何......

以下是需要通过的两项测试，以实现我的目标：

public class ObjectMapperTest {

    private ObjectMapper mapper;

    @Before
    public void init() {
        mapper = new ObjectMapper();
        mapper.setVisibility(PropertyAccessor.FIELD, JsonAutoDetect.Visibility.ANY);
    }

    @Test
    public void serialize() throws Exception {
        Payload payloadToSerialize = new Payload();
        payloadToSerialize.data = "testData";
        String serializedPayload = mapper.writeValueAsString(payloadToSerialize);
        assertThat(serializedPayload, is("{\"data\":\"testData\"}"));
        // --> OK
    }

    @Test
    public void deserialize() throws Exception {
        Payload deserializedPayload = mapper.readValue("{\"data\":\"testData\"}", Payload.class);
        assertThat(deserializedPayload.data, is("testData"));
        // com.fasterxml.jackson.databind.JsonMappingException:
        // No suitable constructor found for type [simple type, class ...ObjectMapperTest$Payload]:
        // can not instantiate from JSON object (missing default constructor or creator, or perhaps need to add/enable type information?)
        // at [Source: {"data":"testData"}; line: 1, column: 2]
    }

    public class Payload {

        private String data;

        public Payload() {
            // empty constructor for Jackson
        }
    }
}

使Payload类静态将修复测试，但静态类不是我的选项，因为我不使用项目中的内部有效负载类。任何想法如何通过对象映射器配置更改来修复它？

修改的当我在Spring MVC应用程序中使用Jackson对象映射器来序列化/反序列化时，我需要一个只改变或扩展对象映射器配置的解决方案。

Answer 1

您可以编写自己的反序列化器来解析JSON并创建Payload的实例，然后使用反射设置data值。例如：

@Before
public void init() {
    mapper = new ObjectMapper();
    mapper.setVisibility(PropertyAccessor.FIELD, JsonAutoDetect.Visibility.ANY);
    mapper.registerModule(
        new SimpleModule()
        .addDeserializer(Payload.class, new JsonDeserializer<Payload>() {
            @Override
            public Payload deserialize(JsonParser parser, DeserializationContext ctx)
                throws IOException, JsonProcessingException {
                JsonNode obj = parser.readValueAsTree(); // Read the JSON as a node

                Payload payload = new Payload();
                if (obj.isObject() && obj.has("data")) { // The node is an object and has a "data" field
                    try {
                        // Use reflection to set the value
                        Field dataField = payload.getClass().getDeclaredField("data");
                        dataField.setAccessible(true);
                        dataField.set(payload, obj.get("data").asText());
                    } catch (NoSuchFieldException | SecurityException | IllegalArgumentException | IllegalAccessException ex) {
                        throw new IOException("Reflection error", ex);
                    }
                }
                return payload;
            }
        }));
}

修改：如果您想要更多内容＆＃34; generic＆＃34;您可以尝试自己创建实例并更改所有字段的可访问性。然后你告诉Jackson使用JSON更新值。

public <T> T deserialize(final String json, final T instance) throws Exception {
    for (Field field : instance.getClass().getDeclaredFields()) {
        field.setAccessible(true);
    }
    mapper.readerForUpdating(instance).readValue(json);
    return instance;
}


@Test
public void deserializeUpdate() throws Exception {
    Payload deserializedPayload = deserialize("{\"data\":\"testData\"}", new Payload());
    assertThat(deserializedPayload.data, is("testData"));
}

我在你的Payload课上测试了这个，也许它不适用于更复杂的对象。

让杰克逊在不使用setter或构造函数的情况下反序列化为私有字段

1 个答案: