java - Spring MVC Rest Controller @RequestBody 解析

Question

我有一个 spring rest web 应用程序，其中包含一个如下所示的通用 rest Controller 。 GET 方法工作正常，Jackson 将对象序列化为 JSON。但是，当我尝试调用保存方法时，RequestBody 参数被转换为 LinkedHashMap 而不是 T 泛型类型定义的类型。

@RestController
public abstract class CrudAPI<T extends Object, ID extends Serializable>{

    @Transactional
    @RequestMapping(method = RequestMethod.POST, consumes = "application/json")
    public ResponseEntity<Void> save(@RequestBody T entity){
        service.save(entity);
        return new ResponseEntity(HttpStatus.CREATED);
    }

}

JSON:

{
   "id":null,
   "version":null,
   "name":"Copel",
   "disabled":false,
   "type":"P",
   "labels":[
      {
         "id":null,
         "version":null,
         "name":"unidade consumidora"
      }
   ]
}

我收到以下错误:

HTTP Status 500 - Request processing failed; nested exception is org.springframework.beans.NotReadablePropertyException: Invalid property 'version' of bean class [java.util.LinkedHashMap]: Could not find field for property during fallback access!

Spring 配置:

@Configuration
@Import(Application.class)
@EnableWebMvc
@ComponentScan(basePackages = {"br.com.doc2cloud"})
public class WebConfig extends WebMvcConfigurerAdapter implements WebApplicationInitializer {

    @Override
    public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
        configurer.enable();
    }

    private MappingJackson2HttpMessageConverter jacksonConverter() {
        ObjectMapper mapper = new ObjectMapper();
        mapper.registerModule(new Hibernate5Module());
        mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
        mapper.setDateFormat(new ISO8601DateFormat());
        mapper.setVisibility(PropertyAccessor.ALL, Visibility.NONE);
        mapper.setVisibility(PropertyAccessor.FIELD, Visibility.ANY);
        mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);

        MappingJackson2HttpMessageConverter jacksonConverter = new MappingJackson2HttpMessageConverter();
        jacksonConverter.setObjectMapper(mapper);

        return jacksonConverter;
    }

 @Override
    public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
        converters.add(jacksonConverter());
        super.configureMessageConverters(converters);
    }

    @Override
    public void onStartup(ServletContext servletContext) throws ServletException {
        servletContext.setInitParameter("javax.servlet.jsp.jstl.fmt.localizationContext", "messages");
        EnumSet<DispatcherType> dispatcherTypes = EnumSet.of(DispatcherType.REQUEST, DispatcherType.FORWARD);
        CharacterEncodingFilter characterEncodingFilter = new CharacterEncodingFilter();
        characterEncodingFilter.setEncoding("UTF-8");
        characterEncodingFilter.setForceEncoding(true);
        FilterRegistration.Dynamic characterEncoding = servletContext.addFilter("characterEncoding", characterEncodingFilter);
        characterEncoding.addMappingForUrlPatterns(dispatcherTypes, true, "/*");
    }
}

我的代码有什么问题？

Answer 1

我不认为你可以实现你想要的。 Java 泛型机制仅在编译时起作用。编译后通用类型被删除并被实际类型替换(在您的情况下为 Object )。您的 Controller 无法理解您尝试解析 JSON 数据的类型。

你得到 LinkedHashMap 的原因是 Jackson 默认将它用于“未知”类型。典型的 JSON 数据实际上是一个键值映射，Jackson 保留属性排序 - 这就是使用链接 HashMap 的原因。