Java 将Jackson Mixin与MappingJacksonHttpMessageConverter一起使用&；春季MVC

我马上就要开始真正的问题了，有没有办法访问HttpMessageConverter中控制器处理程序方法上的注释？我很确定答案是否定的（在浏览了Spring的源代码之后）

使用时是否有其他方式使用配对？我已经基于MappingJacksonHttpMessageConverter实现了我自己的HttpMessageConverter，以“升级”它以使用Jackson 2.0

控制器类

@Controller
public class Controller {

    @JsonFilter({ @JsonMixin(target=MyTargetObject.class, mixin=MyTargetMixin.class) })
    @RequestMapping(value="/my-rest/{id}/my-obj", method=RequestMethod.GET, produces="application/json")
    public @ResponseBody List<MyTargetObject> getListOfFoo(@PathVariable("id") Integer id) {
        return MyServiceImpl.getInstance().getBarObj(id).getFoos();
    }
}

public class MappingJacksonHttpMessageConverter extends AbstractHttpMessageConverter<Object> {

    ...

    @Override
    protected void writeInternal(Object object, HttpOutputMessage outputMessage) {

            //Obviously, no access to the HandlerMethod here.

    }

    ...
}

我到处寻找这个答案。到目前为止，我只看到有人在控制器的处理方法中将其对象序列化为JSON（在每个方法中都反复违反JSON）。或者直接注释它们的数据对象（没有关于如何公开对象的解耦或多个配置）

---

这可能是在HttpMessageConverter中无法完成的。还有其他选择吗？拦截器可以访问HandlerMethod，但不能访问handler方法的返回对象

这不是理想的解决方案。请参阅我的第二个答案。

我使用

modelandviewsolver

解决了这个问题。您可以直接使用

AnnotationMethodHandlerAdapter

注册这些属性，因为您知道它们总是在默认处理发生之前首先启动。因此，Spring的文档-

/**
 * Set a custom ModelAndViewResolvers to use for special method return types.
 * <p>Such a custom ModelAndViewResolver will kick in first, having a chance to resolve
 * a return value before the standard ModelAndView handling kicks in.
 */
public void setCustomModelAndViewResolver(ModelAndViewResolver customModelAndViewResolver) {
    this.customModelAndViewResolvers = new ModelAndViewResolver[] {customModelAndViewResolver};
}

看看

resolveModelAndView中所有这些有趣的参数

！我几乎可以访问Spring知道的关于该请求的所有信息。下面是我如何实现接口，使其与映射JacksonHttpMessageConverter非常相似，只是以单向方式（向外）：

这是非常棒的简单。ModelAndViewResolver将自动将返回对象转换为JSON，并应用带注释的混合插件

这其中的一个“缺点”（如果你这么说的话）是必须恢复到Spring2.5的配置方式，因为新的3.0标签不允许直接配置ModelAndViewResolver。也许他们只是忽略了这一点

我的旧配置（使用Spring 3.1样式）

我的新配置（使用Spring 2.5样式）

^^3.0+无法连接自定义ModelAndViewResolver。因此，切换回旧式

以下是自定义注释：

Json

@Target({ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
public @interface Json {

    /**
     * A list of Jackson Mixins.
     * <p>
     * {@link http://wiki.fasterxml.com/JacksonMixInAnnotations}
     */
    JsonMixin[] mixins() default {};

}

public @interface JsonMixin {
    public Class<? extends Serializable> target();
    public Class<?> mixin();
}

@Target（{ElementType.METHOD}）
@保留（RetentionPolicy.RUNTIME）
public@interface Json{
/**
*杰克逊的混血儿名单。
*
*{@linkhttp://wiki.fasterxml.com/JacksonMixInAnnotations}
*/
JsonMixin[]mixins（）默认值{}；
}

JsonMixin

@Target({ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
public @interface Json {

    /**
     * A list of Jackson Mixins.
     * <p>
     * {@link http://wiki.fasterxml.com/JacksonMixInAnnotations}
     */
    JsonMixin[] mixins() default {};

}

public @interface JsonMixin {
    public Class<? extends Serializable> target();
    public Class<?> mixin();
}

public@interface JsonMixin{
公共类mixin（）；
}

在发布了下面的答案后，我改变了我的做法。我使用了

handler方法returnvaluehandle

r。我必须创建一个编程web配置来覆盖顺序，因为自定义返回值处理程序是最后触发的。我需要在默认设置之前触发它们

@Configuration
public class WebConfig extends WebMvcConfigurationSupport {
   ...
}

希望这将引导某人朝着比我下面的答案更好的方向前进

这允许我将任何对象直接序列化为JSON。在@RequestMapping has=“application/json”中，我总是将返回值序列化为json

我对参数绑定做了同样的事情，只是使用了

HandlerMethodArgumentResolver

。只需使用您选择的注释对类进行注释（我使用JPA@Entity，因为我通常会序列化到模型中）

现在，在Spring控制器中实现了从POJO到JSON的无缝反序列化，而无需任何样板代码

另外：我的参数解析器将检查@Id标记，以确定参数的类型，如果JSON包含Id的键，则检索实体并将JSON应用于持久化对象。砰

/**
 * De-serializes JSON to a Java Object.
 * <p>
 * Also provides handling of simple data type validation.  If a {@link JsonMappingException} is thrown then it
 * is wrapped as a {@link ValidationException} and handled by the MVC/validation framework.
 *
 * @author John Strickler
 * @since 2012-08-28
 */
public class EntityArgumentResolver implements HandlerMethodArgumentResolver {

    @Autowired
    private SessionFactory sessionFactory;

    private final ObjectMapper objectMapper = new ObjectMapper();

    private static final Logger log = Logger.getLogger(EntityArgumentResolver.class);

    //whether to log the incoming JSON
    private boolean doLog = false;

    @Override
    public boolean supportsParameter(MethodParameter parameter) {
        return parameter.getParameterType().getAnnotation(Entity.class) != null;
    }

    @Override
    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {

        HttpServletRequest request = webRequest.getNativeRequest(HttpServletRequest.class);
        String requestBody = IOUtils.toString(request.getReader());
        Class<?> targetClass = parameter.getParameterType();
        Object entity = this.parse(requestBody, targetClass);
        Object entityId = getId(entity);

        if(doLog) {
            log.info(requestBody);
        }

        if(entityId != null) {
            return copyObjectToPersistedEntity(entity, getKeyValueMap(requestBody), entityId);
        } else {
            return entity;
        }
    }


    /**
     * @param rawJson a json-encoded string
     * @return a {@link Map} consisting of the key/value pairs of the JSON-encoded string
     */
    @SuppressWarnings("unchecked")
    private Map<String, Object> getKeyValueMap(String rawJson) throws JsonParseException, JsonMappingException, IOException {
        return objectMapper.readValue(rawJson, HashMap.class);
    }


    /**
     * Retrieve an existing entity and copy the new changes onto the entity.
     *
     * @param changes a recently deserialized entity object that contains the new changes
     * @param rawJson the raw json string, used to determine which keys were passed to prevent
     *                copying unset/null values over to the persisted entity
     * @return the persisted entity with the new changes copied onto it
     * @throws NoSuchMethodException
     * @throws SecurityException
     * @throws InvocationTargetException
     * @throws IllegalAccessException
     * @throws IllegalArgumentException
     */
    private Object copyObjectToPersistedEntity(Object changesObject, Map<String, Object> changesMap, Object id) throws SecurityException, NoSuchMethodException, IllegalArgumentException, IllegalAccessException, InvocationTargetException {

        Session session = sessionFactory.openSession();

        Object persistedObject =
                session.get(changesObject.getClass(), (Serializable) id);

        session.close();

        if(persistedObject == null) {
            throw new ValidationException(changesObject.getClass().getSimpleName() + " #" + id + " not found.");
        }

        Class<?> clazz = persistedObject.getClass();

        for(Method getterMethod : ReflectionUtils.getAllDeclaredMethods(clazz)) {

            Column column = getterMethod.getAnnotation(Column.class);

            //Column annotation is required
            if(column == null) {
                continue;
            }

            //Is the field allowed to be updated?
            if(!column.updatable()) {
                continue;
            }

            //Was this change a part of JSON request body?
            //(prevent fields false positive copies when certain fields weren't included in the JSON body)
            if(!changesMap.containsKey(BeanUtils.toFieldName(getterMethod))) {
                continue;
            }

            //Is the new field value different from the existing/persisted field value?
            if(ObjectUtils.equals(getterMethod.invoke(persistedObject), getterMethod.invoke(changesObject))) {
                continue;
            }

            //Copy the new field value to the persisted object
            log.info("Update " + clazz.getSimpleName() + "(" + id + ") [" + column.name() + "]");

            Object obj = getterMethod.invoke(changesObject);

            Method setter = BeanUtils.toSetter(getterMethod);

            setter.invoke(persistedObject, obj);

        }

        return persistedObject;
    }


    /**
     * Check if the recently deserialized entity object was populated with its ID field
     *
     * @param entity the object
     * @return an object value if the id exists, null if no id has been set
     */
    private Object getId(Object entity) throws IllegalArgumentException, IllegalAccessException, InvocationTargetException {

        for(Method method : ReflectionUtils.getAllDeclaredMethods(entity.getClass())) {
            if(method.getAnnotation(Id.class) != null) {
                method.setAccessible(true);
                return method.invoke(entity);
            }
        }

        return null;
    }


    private <T> T parse(String json, Class<T> clazz) throws JsonParseException, IOException {
        try {
            return objectMapper.readValue(json, clazz);
        } catch(JsonMappingException e) {
            throw new ValidationException(e);
        }
    }

    public void setDoLog(boolean doLog) {
        this.doLog = doLog;
    }

}

/**
*将JSON反序列化为Java对象。
*
*还提供了简单数据类型验证的处理。如果抛出{@link JsonMappingException}，则
*包装为{@link ValidationException}并由MVC/验证框架处理。
*
*@作者约翰·斯特里克勒
*@自2012年8月28日起
*/
公共类EntityArgumentResolver实现HandlerMethodArgumentResolver{
@自动连线
私人会话工厂会话工厂；
私有最终ObjectMapper ObjectMapper=新ObjectMapper（）；
私有静态最终记录器log=Logger.getLogger（EntityArgumentResolver.class）；
//是否记录传入的JSON
私有布尔值doLog=false；
@凌驾
公共布尔支持参数（MethodParameter）{
返回参数.getParameterType（）.getAnnotation（Entity.class）！=null；
}
@凌驾
公共对象resolveArgument（MethodParameter参数、ModelAndViewContainer mavContainer、NativeWebRequest webRequest、WebDataBinderFactory binderFactory）引发异常{
HttpServletRequest=webRequest.getNativeRequest（HttpServletRequest.class）；
String requestBody=IOUtils.toString（request.getReader（））；
Class targetClass=parameter.getParameterType（）；
Object entity=this.parse（requestBody，targetClass）；
对象entityId=getId（实体）；
if（doLog）{
日志信息（请求主体）；
}
if（entityId！=null）{
返回CopyObjectToPersistentity（实体、getKeyValueMap（requestBody）、entityId）；
}否则{
返回实体；
}
}
/**
*@param rawJson一个json编码的字符串
*@return一个{@link Map}由JSON编码字符串的键/值对组成
*/
@抑制警告（“未选中”）
私有映射getKeyValueMap（字符串rawJson）抛出JsonParseException、JsonMappingException、IOException{
返回对象映射器
public @interface JsonMixin {
    public Class<? extends Serializable> target();
    public Class<?> mixin();
}

@Configuration
public class WebConfig extends WebMvcConfigurationSupport {
   ...
}

/**
 * De-serializes JSON to a Java Object.
 * <p>
 * Also provides handling of simple data type validation.  If a {@link JsonMappingException} is thrown then it
 * is wrapped as a {@link ValidationException} and handled by the MVC/validation framework.
 *
 * @author John Strickler
 * @since 2012-08-28
 */
public class EntityArgumentResolver implements HandlerMethodArgumentResolver {

    @Autowired
    private SessionFactory sessionFactory;

    private final ObjectMapper objectMapper = new ObjectMapper();

    private static final Logger log = Logger.getLogger(EntityArgumentResolver.class);

    //whether to log the incoming JSON
    private boolean doLog = false;

    @Override
    public boolean supportsParameter(MethodParameter parameter) {
        return parameter.getParameterType().getAnnotation(Entity.class) != null;
    }

    @Override
    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {

        HttpServletRequest request = webRequest.getNativeRequest(HttpServletRequest.class);
        String requestBody = IOUtils.toString(request.getReader());
        Class<?> targetClass = parameter.getParameterType();
        Object entity = this.parse(requestBody, targetClass);
        Object entityId = getId(entity);

        if(doLog) {
            log.info(requestBody);
        }

        if(entityId != null) {
            return copyObjectToPersistedEntity(entity, getKeyValueMap(requestBody), entityId);
        } else {
            return entity;
        }
    }


    /**
     * @param rawJson a json-encoded string
     * @return a {@link Map} consisting of the key/value pairs of the JSON-encoded string
     */
    @SuppressWarnings("unchecked")
    private Map<String, Object> getKeyValueMap(String rawJson) throws JsonParseException, JsonMappingException, IOException {
        return objectMapper.readValue(rawJson, HashMap.class);
    }


    /**
     * Retrieve an existing entity and copy the new changes onto the entity.
     *
     * @param changes a recently deserialized entity object that contains the new changes
     * @param rawJson the raw json string, used to determine which keys were passed to prevent
     *                copying unset/null values over to the persisted entity
     * @return the persisted entity with the new changes copied onto it
     * @throws NoSuchMethodException
     * @throws SecurityException
     * @throws InvocationTargetException
     * @throws IllegalAccessException
     * @throws IllegalArgumentException
     */
    private Object copyObjectToPersistedEntity(Object changesObject, Map<String, Object> changesMap, Object id) throws SecurityException, NoSuchMethodException, IllegalArgumentException, IllegalAccessException, InvocationTargetException {

        Session session = sessionFactory.openSession();

        Object persistedObject =
                session.get(changesObject.getClass(), (Serializable) id);

        session.close();

        if(persistedObject == null) {
            throw new ValidationException(changesObject.getClass().getSimpleName() + " #" + id + " not found.");
        }

        Class<?> clazz = persistedObject.getClass();

        for(Method getterMethod : ReflectionUtils.getAllDeclaredMethods(clazz)) {

            Column column = getterMethod.getAnnotation(Column.class);

            //Column annotation is required
            if(column == null) {
                continue;
            }

            //Is the field allowed to be updated?
            if(!column.updatable()) {
                continue;
            }

            //Was this change a part of JSON request body?
            //(prevent fields false positive copies when certain fields weren't included in the JSON body)
            if(!changesMap.containsKey(BeanUtils.toFieldName(getterMethod))) {
                continue;
            }

            //Is the new field value different from the existing/persisted field value?
            if(ObjectUtils.equals(getterMethod.invoke(persistedObject), getterMethod.invoke(changesObject))) {
                continue;
            }

            //Copy the new field value to the persisted object
            log.info("Update " + clazz.getSimpleName() + "(" + id + ") [" + column.name() + "]");

            Object obj = getterMethod.invoke(changesObject);

            Method setter = BeanUtils.toSetter(getterMethod);

            setter.invoke(persistedObject, obj);

        }

        return persistedObject;
    }


    /**
     * Check if the recently deserialized entity object was populated with its ID field
     *
     * @param entity the object
     * @return an object value if the id exists, null if no id has been set
     */
    private Object getId(Object entity) throws IllegalArgumentException, IllegalAccessException, InvocationTargetException {

        for(Method method : ReflectionUtils.getAllDeclaredMethods(entity.getClass())) {
            if(method.getAnnotation(Id.class) != null) {
                method.setAccessible(true);
                return method.invoke(entity);
            }
        }

        return null;
    }


    private <T> T parse(String json, Class<T> clazz) throws JsonParseException, IOException {
        try {
            return objectMapper.readValue(json, clazz);
        } catch(JsonMappingException e) {
            throw new ValidationException(e);
        }
    }

    public void setDoLog(boolean doLog) {
        this.doLog = doLog;
    }

}

@EnableWebMvc
@Configuration
public class SidekickApplicationConfiguration implements WebMvcConfigurer {
    private static Logger logger = LoggerFactory.getLogger(SidekickApplicationConfiguration.class);

    @Autowired
    private RequestMappingHandlerAdapter requestHandler;

    @Bean
    RequestResponseBodyMethodProcessor registerReturnValueHandler() {
        List<HttpMessageConverter<?>> messageConverters = new ArrayList<>();
        messageConverters.add(new MappingJackson2HttpMessageConverter(PushCard.getObjectMapperForDTO()));

        logger.info("Registering RequestResponseBodyMethodProcessor with DTO ObjectMapper...");
        RequestResponseBodyMethodProcessor r = new RequestResponseBodyMethodProcessor(messageConverters);
        requestHandler.setReturnValueHandlers(Arrays.asList(r));
        return r;
    }
}