java spring MappingJacksonJsonView没有在mongodb ObjectId上做toString

Question

我在我的 SpringMVC 应用程序中使用 MappingJacksonJsonView 从我的控制器呈现 JSON。我希望对象中的 ObjectId 呈现为 .toString ，而是将 ObjectId 序列化为其部分。它在我的 Velocity/JSP 页面中运行良好：

Velocity:
    $thing.id
Produces:
    4f1d77bb3a13870ff0783c25


Json:
    <script type="text/javascript">
         $.ajax({
             type: 'GET',
             url: '/things/show/4f1d77bb3a13870ff0783c25',
             dataType: 'json',
             success : function(data) {
                alert(data);
             }
         });
    </script>
Produces:
    thing: {id:{time:1327331259000, new:false, machine:974358287, timeSecond:1327331259, inc:-260555739},…}
        id: {time:1327331259000, new:false, machine:974358287, timeSecond:1327331259, inc:-260555739}
            inc: -260555739
            machine: 974358287
            new: false
            time: 1327331259000
            timeSecond: 1327331259
        name: "Stack Overflow"


XML:
    <script type="text/javascript">
         $.ajax({
             type: 'GET',
             url: '/things/show/4f1d77bb3a13870ff0783c25',
             dataType: 'xml',
             success : function(data) {
                alert(data);
             }
         });
    </script>
Produces:
    <com.place.model.Thing>
        <id>
            <__time>1327331259</__time>
            <__machine>974358287</__machine>
            <__inc>-260555739</__inc>
            <__new>false</__new>
        </id>
        <name>Stack Overflow</name>
    </com.place.model.Thing>

有没有办法阻止 MappingJacksonJsonView 从 ObjectId 中获取这么多信息？我只想要 .toString() 方法，而不是所有细节。

谢谢。

添加 Spring 配置：

@Configuration
@EnableWebMvc
public class MyConfiguration {

    @Bean(name = "viewResolver")
    public ContentNegotiatingViewResolver viewResolver() {
        ContentNegotiatingViewResolver contentNegotiatingViewResolver = new ContentNegotiatingViewResolver();
        contentNegotiatingViewResolver.setOrder(1);
        contentNegotiatingViewResolver.setFavorPathExtension(true);
        contentNegotiatingViewResolver.setFavorParameter(true);
        contentNegotiatingViewResolver.setIgnoreAcceptHeader(false);
        Map<String, String> mediaTypes = new HashMap<String, String>();
        mediaTypes.put("json", "application/x-json");
        mediaTypes.put("json", "text/json");
        mediaTypes.put("json", "text/x-json");
        mediaTypes.put("json", "application/json");
        mediaTypes.put("xml", "text/xml");
        mediaTypes.put("xml", "application/xml");
        contentNegotiatingViewResolver.setMediaTypes(mediaTypes);
        List<View> defaultViews = new ArrayList<View>();
        defaultViews.add(xmlView());
        defaultViews.add(jsonView());
        contentNegotiatingViewResolver.setDefaultViews(defaultViews);
        return contentNegotiatingViewResolver;
    }

    @Bean(name = "xStreamMarshaller")
    public XStreamMarshaller xStreamMarshaller() {
        return new XStreamMarshaller();
    }

    @Bean(name = "xmlView")
    public MarshallingView xmlView() {
        MarshallingView marshallingView = new MarshallingView(xStreamMarshaller());
        marshallingView.setContentType("application/xml");
        return marshallingView;
    }

    @Bean(name = "jsonView")
    public MappingJacksonJsonView jsonView() {
        MappingJacksonJsonView mappingJacksonJsonView = new MappingJacksonJsonView();
        mappingJacksonJsonView.setContentType("application/json");
        return mappingJacksonJsonView;
    }
}

还有我的控制器：

@Controller
@RequestMapping(value = { "/things" })
public class ThingController {

    @Autowired
    private ThingRepository thingRepository;

    @RequestMapping(value = { "/show/{thingId}" }, method = RequestMethod.GET)
    public String show(@PathVariable ObjectId thingId, Model model) {
        model.addAttribute("thing", thingRepository.findOne(thingId));
        return "things/show";
    }
}

Answer 1

默认情况下，Jackson 提供接收到的对象的序列化。 ObjectId 返回 Object，因此其属性在转换为 JSON 后可见。您需要指定所需的序列化类型，这里是字符串。用于创建 ThingRepository 的 Thing 实体类将如下所示：

public class Thing {
    @Id
    @JsonSerialize(using= ToStringSerializer.class)
    ObjectId id;

    String name;
}

这里记下添加的注释@JsonSerialize(using= ToStringSerializer.class)，它指示将 ObjectID 序列化为 String。

Answer 2

我只需要让 getId() 方法返回一个字符串。这是让 Jackson 停止序列化 ObjectId 的唯一方法。

public String getId() {
    if (id != null) {
        return id.toString();
    } else {
        return null;
    }
}

public void setId(ObjectId id) {
    this.id = id;
}

setId() 仍然必须是 ObjectId，这样 Mongo（及其驱动程序）才能正确设置 ID。

Answer 3

以前的答案起到了作用，但它很丑陋并且没有经过深思熟虑 - 一个明确的解决方法来实际解决问题。

真正的问题是ObjectId 反序列化为它的组件部分。 MappingJacksonJsonView 看到 ObjectId 是什么，一个对象，然后开始处理它。在 JSON 中看到的反序列化字段是构成 ObjectId 的字段。要停止此类对象的序列化/反序列化，您必须配置一个扩展 ObjectMapper 的 CustomObjectMapper。

这里是CustomeObjectMapper：

public class CustomObjectMapper extends ObjectMapper {

    public CustomObjectMapper() {
        CustomSerializerFactory sf = new CustomSerializerFactory();
        sf.addSpecificMapping(ObjectId.class, new ObjectIdSerializer());
        this.setSerializerFactory(sf);
    }
}

这是CustomObjectMapper 使用的ObjectIdSerializer：

public class ObjectIdSerializer extends SerializerBase<ObjectId> {

    protected ObjectIdSerializer(Class<ObjectId> t) {
        super(t);
    }

    public ObjectIdSerializer() {
        this(ObjectId.class);
    }

    @Override
    public void serialize(ObjectId value, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonGenerationException {
        jgen.writeString(value.toString());
    }
}

以下是您的 @Configuration-annotated 类中需要更改的内容：

@Bean(name = "jsonView")
public MappingJacksonJsonView jsonView() {
    final MappingJacksonJsonView mappingJacksonJsonView = new MappingJacksonJsonView();
    mappingJacksonJsonView.setContentType("application/json");
    mappingJacksonJsonView.setObjectMapper(new CustomObjectMapper());
    return mappingJacksonJsonView;
}

您基本上是在告诉杰克逊如何序列化/反序列化这个特定对象。像魅力一样工作。

Answer 4

如果您在 Spring Boot 中使用自动配置映射器的自动装配实例，则只需添加此自定义程序 bean：

@Bean
public Jackson2ObjectMapperBuilderCustomizer jsonCustomizer() {
    return builder -> builder.serializerByType(ObjectId.class, ToStringSerializer.instance);
}

相关进口：

import com.fasterxml.jackson.databind.ser.std.ToStringSerializer;
import org.bson.types.ObjectId;
import org.springframework.boot.autoconfigure.jackson.Jackson2ObjectMapperBuilderCustomizer;

然后这将反映使用自动连线映射器的任何地方，例如：

@Service
public class MyService {
    private final ObjectMapper objectMapper;
    private final MongoTemplate mongoTemplate;

    @Autowired
    public MyService(ObjectMapper objectMapper) {
        this.objectMapper = objectMapper;
    }

    public String getJsonForMongoCommand(Document document) {
        return objectMapper.writeValueAsString(mongoTemplate.executeCommand(document));
    }
}

或者在这种特定情况下（未经测试，可能没有必要）：

@Bean(name = "jsonView")
public MappingJacksonJsonView jsonView(ObjectMapper objectMapper) {
    final MappingJacksonJsonView mappingJacksonJsonView = new MappingJacksonJsonView();
    mappingJacksonJsonView.setContentType("application/json");
    mappingJacksonJsonView.setObjectMapper(objectMapper);
    return mappingJacksonJsonView;
}