Jackson ObjectMapper使用自定義序列化器和反序列化器

Question

我有一個配置Jackson ObjectMapper的類。 它為我的對象類型添加了一些自定義序列化器和反序列化器，如下所示：

public class JsonMapperFactory {
    public static ObjectMapper createObjectMapper() {
        final SimpleModule module = new SimpleModule("customerSerializationModule", new Version(1, 0, 0, "static version"));
        addCustomDeserializersTo(module);
        addCustomSerializersTo(module);

        final ObjectMapper objectMapper = new ObjectMapper();
        objectMapper.registerModule(module);
        return objectMapper;
    }
    private static void addCustomSerializersTo(final SimpleModule module) {
        module.addSerializer(DateTime.class, new DateTimeSerializer());
    }
    private static void addCustomDeserializersTo(final SimpleModule objectMapper) {
        objectMapper.addDeserializer(DateTime.class, new DateTimeDeserializer());
    }
}

我已經在他們自己的測試類中測試了我的客戶序列化器，所以在我對這個JsonMapperFactory類的測試中，我試圖簡單地檢查創建的ObjectMapper是否具有預期的序列化器（或反序列化器）這可以通過內省ObjectMapper來實現，但它似乎沒有任何機制來做到這一點。

有誰知道測試它的好方法？

對於反序列化器，我有以下內容：

private void assertThatObjectMapperUsesCorrectDeserializer(final Class<?> typeClazz, final Class<?> deserializerClazz) throws JsonMappingException {
    final  DeserializationConfig deserializationConfig = this.objectMapper.getDeserializationConfig();
    final JsonDeserializer<Object> deserializer = this.objectMapper.getDeserializerProvider().findTypedValueDeserializer(deserializationConfig, javaTypeFor(typeClazz), null);
    assertThat(deserializer, is(instanceOf(deserializerClazz)));
}
private JavaType javaTypeFor(final Class<?> clazz) {
    return TypeFactory.type(clazz); //deprecated method :(
}

這是非常詳細的，並使用棄用的方法。

我還沒有找到一種方法來對序列化器進行類似的測試。 所以我目前使用序列化對象並檢查它是否正確序列化（基本上復制了序列化程序測試）

任何想法都非常受歡迎。

Answer 1

從這里提供的答案和評論中，我最近重新設計了類，以便為Module和ObjectMapper使用構建器。 這允許我提供模擬並檢查是否將正確的（de）序列化程序添加到模塊中，然后按預期將模塊注冊到對象映射器。

對象映射器構建器：

public class ObjectMapperBuilder {
    ObjectMapper mapper;

    public ObjectMapperBuilder configure(final ObjectMapper mapper) {
        this.mapper = mapper;
        return this;
    }

    public ObjectMapperBuilder withModule(final Module module) {
        this.mapper.registerModule(module);
        return this;
    }

    public ObjectMapper build() {
        return this.mapper;
    }
}

模塊構建器：

public class SimpleModuleBuilder {
    SimpleModule module;

    public SimpleModuleBuilder configure(final SimpleModule module) {
        this.module = module;
        return this;
    }

    public <X> SimpleModuleBuilder withSerializer(final Class<X> clazz, final JsonSerializer<X> serializer) {
        this.module.addSerializer(clazz, serializer);
        return this;
    }

    public <X> SimpleModuleBuilder withDeserializer(final Class<X> clazz, final JsonDeserializer<X> deserializer) {
        this.module.addDeserializer(clazz, deserializer);
        return this;
    }

    public SimpleModule build() {
        return this.module;
    }
}

最后，新的JsonMapperFactory：

public class JsonMapperFactory {

    public static ObjectMapper configureObjectMapper(final ObjectMapper mapper, final SimpleModule module) {
        final SimpleModuleBuilder modulebuilder = new SimpleModuleBuilder();

        final SimpleModule configuredModule = modulebuilder.configure(module)
            .withSerializer(DateTime.class, new DateTimeSerializer())
            .withDeserializer(DateTime.class, new DateTimeDeserializer())
            .build();

        final ObjectMapperBuilder objectMapperBuilder = new ObjectMapperBuilder();
        return objectMapperBuilder.configure(mapper).withModule(configuredModule).build();
    }
}

工廠方法仍在Spring配置中使用，但配置現在實例化空白Module和ObjectMapper ，然后將它們提供給工廠方法，然后再配置它們。

Answer 2

如果JsonDeserializer （和DateTimeDeserializer也是）一個接口，你可以很容易地“JMock”它，將JsonMapperFactory#createObjectMapper實例傳遞給JsonMapperFactory#createObjectMapper ，然后期望完全調用你的自定義“serialize”方法; 例如

DateTimeSerializer serializer = context.mock(DateTimeSerializer.class);
DateTimeDeserializer serializer = context.mock(DateTimeDeserializer.class);
ObjectMapper mapper = JacksonMapperFactory.createObjectMapper(deserializer, serializer);

exactly(1).of(jsonDeserializer).serialize(myDateTime,
  with(any(JsonGenerator.class),
  with(any(SerializerProvider.class)))

作為一個具體的類，你可以改為定義一個新的（測試范圍的）De / Serializer來擴展你的自定義DateTime（De）序列化程序，並簡單地計算對它的調用：

private static class DateTimeDeserializerWithCounter extends DateTimeDeserializer {
    public int counter = 0;

    @Override
    public DateTime deserialize(JsonParser jsonParser, DeserializationContext deserializationContext) throws IOException {
        counter++;
        return super.deserialize(jsonParser, deserializationContext);
    }
}

@Test
public void usageTest(){
    //init mapper with the above DateTimeDeserializerWithCounter - see below
    mapper.readValue("...", DateTime.class);
    Assert.assertEquals(1, deserializer.counter);
}

下面是一個更“以測試為導向”的工廠的快照：

//package visibility, to allow passing different De/Serializers while testing
static ObjectMapper createObjectMapper(JsonDeserializer deserializer, JsonSerializer serializer) {
    final SimpleModule module = new SimpleModule("customerSerializationModule", new Version(1, 0, 0, "static version"));
    module.addDeserializer(DateTime.class, deserializer);
    module.addSerializer(DateTime.class, serializer);

    final ObjectMapper objectMapper = new ObjectMapper();
    objectMapper.registerModule(module);
    return objectMapper;
}

//production method: no-args, as in the original version
public static ObjectMapper createObjectMapper() {
    return createObjectMapper(new DateTimeDeserializer(), new DateTimeSerializer());
}

希望有所幫助。