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Java 以内容类型不是application/json的websocket消息形式广播HATEOAS对象

java spring-boot websocket

Java 以内容类型不是application/json的websocket消息形式广播HATEOAS对象,java,spring-boot,websocket,jackson,spring-hateoas,Java,Spring Boot,Websocket,Jackson,Spring Hateoas,我需要在RESTController上呈现下面的类（扩展了RepresentationModel的几个类中），并将其作为广播消息呈现给websocket @Getter @JsonPropertyOrder(alphabetic=true) @Setter public class MessageWrapper extends RepresentationModel<MessageWrapper> { private Object message; private S

我需要在
RESTController
上呈现下面的类（扩展了RepresentationModel的几个类中），并将其作为广播消息呈现给websocket

@Getter
@JsonPropertyOrder(alphabetic=true)
@Setter
public class MessageWrapper extends RepresentationModel<MessageWrapper> {
    private Object message;
    private String simpleName;

    public MessageWrapper(Object message) {
        this.message = message;
        this.simpleName = message.getClass().getSimpleName();
    }
}
请注意响应的
内容类型
，以及上面的
\u链接
对象属性。我为
内容类型
创建了一个javascript处理程序，并且
\u links
属性非常重要。现在在稍后的另一个事件中，我需要向websocket广播完全相同的JSON字符串。所以我这样做了：

@Autowired
private SimpMessagingTemplate messagingTemplate;

public void broadcastToUser(StompPrincipal principal, MessageWrapper wrapper) {
    SimpMessageHeaderAccessor simpHeaderAccessor =
        SimpMessageHeaderAccessor.create(SimpMessageType.MESSAGE);

    simpHeaderAccessor.setUser(principal);
    simpHeaderAccessor.setLeaveMutable(true);

    messagingTemplate.convertAndSendToUser(
        principal.getUsername(),
        "/broadcast",
        wrapper,
        simpHeaderAccessor.getMessageHeaders());
}
它会产生以下信息：

a["MESSAGE
destination:/user/broadcast
content-type:application/json
subscription:sub-0
message-id:tluhntae-0
content-length:267

{
    "links": [
        {
            "rel": "previous",
            "href": "/thread/1044/message/86"
        },
        {
            "rel": "self",
            "href": "/thread/1044/message/87"
        }
    ],
    "message": {...},
    "simpleName": "..."
}

"]
请注意，它具有
链接
属性，而不是
\u链接
。还要注意的是，它没有像上面那样拥有一个对象值，而是拥有一个对象数组作为值。我假设对上面的
RESTController
响应使用相同的javascript回调，但是不能，因为
links
属性具有不同的结构。我可以在javascript方面对其进行分析，但我并没有尝试将其配置为按照我预期的方式呈现。我读到这是因为我将websocket消息呈现为
application/json
而不是
application/hal+json
，这就是为什么它使用
链接
而不是
\u链接
。因此，在广播之前，我将消息的
内容类型设置为HAL:


MimeType applicationJson;
        
if(RepresentationModel.class.isAssignableFrom(body.getClass())) {
    applicationJson = new MimeType("application", "hal+json");
} else {
    applicationJson = new MimeType("application", "json");
}

simpHeaderAccessor.setContentType(applicationJson);


但它会抛出以下错误：


2020-10-26 23:40:40.799 ERROR 6200 --- [nio-8080-exec-4] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.messaging.converter.MessageConversionException: Unable to convert payload with type='MessageWrapper', contentType='application/hal+json', converter=[CompositeMessageConverter[converters=[org.springframework.messaging.converter.StringMessageConverter@66389c40, org.springframework.messaging.converter.ByteArrayMessageConverter@724493b5, org.springframework.messaging.converter.MappingJackson2MessageConverter@1228bacc]]]] with root cause

org.springframework.messaging.converter.MessageConversionException: Unable to convert payload with type='MessageWrapper', contentType='application/hal+json', converter=[CompositeMessageConverter[converters=[org.springframework.messaging.converter.StringMessageConverter@66389c40, org.springframework.messaging.converter.ByteArrayMessageConverter@724493b5, org.springframework.messaging.converter.MappingJackson2MessageConverter@1228bacc]]]
    at org.springframework.messaging.core.AbstractMessageSendingTemplate.doConvert(AbstractMessageSendingTemplate.java:187) ~[spring-messaging-5.3.0-M1.jar:5.3.0-M1]
    at org.springframework.messaging.core.AbstractMessageSendingTemplate.convertAndSend(AbstractMessageSendingTemplate.java:150) ~[spring-messaging-5.3.0-M1.jar:5.3.0-M1]
    at org.springframework.messaging.simp.SimpMessagingTemplate.convertAndSendToUser(SimpMessagingTemplate.java:230) ~[spring-messaging-5.3.0-M1.jar:5.3.0-M1]
    at org.springframework.messaging.simp.SimpMessagingTemplate.convertAndSendToUser(SimpMessagingTemplate.java:211) ~[spring-messaging-5.3.0-M1.jar:5.3.0-M1]
    at dev.gideon.chatapp.service.BroadcastService.broadcastToUser(BroadcastService.java:54) ~[classes/:na]
    ...



我真的需要将websocket消息的
内容类型设置为HAL，以便按照我预期的方式对其进行封送。有没有办法实现这一点？我问这个问题是因为除了我不想做单独的javascript代码之外，我还不想做单独的javascript代码来处理带有数组值的
links
属性和带有对象值的
\u links
属性的json对象，我还认为，使用HAL
内容类型广播确实是合适的，这样，除了我自己的客户机之外，其他客户机也会这样对待它，而不仅仅是普通的JSON广播消息。
对于
内容类型的websocket广播消息，没有默认的
MessageConverter
应用程序/hal+json
。我需要为自定义MIME类型实现自己的
MessageConverter
。我创建了一个转换器，
扩展了AbstractMessageConverter
：


public class HalMessageConverter extends AbstractMessageConverter {
    public HalMessageConverter() {
        MimeType hal = new MimeType("application", "hal+json");
        this.addSupportedMimeTypes(hal);
    }

    @Override
    protected boolean supports(Class<?> clazz) {
        return RepresentationModel.class.isAssignableFrom(clazz);
    }

    @Override
    protected Object convertToInternal(
        Object payload,
        MessageHeaders headers,
        Object conversionHint) {

        TypeConstrainedMappingJackson2HttpMessageConverter converter = 
            new TypeConstrainedMappingJackson2HttpMessageConverter(RepresentationModel.class);

        Module module = new Jackson2HalModule();
        LinkRelationProvider provider = new DefaultLinkRelationProvider();

        Jackson2HalModule.HalHandlerInstantiator instantiator =
            new Jackson2HalModule.HalHandlerInstantiator(
                provider,
                CurieProvider.NONE,
                MessageResolver.DEFAULTS_ONLY);

        ObjectMapper mapper = converter.getObjectMapper();
        mapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);
        mapper.registerModule(module);
        mapper.setHandlerInstantiator(instantiator);

        try {
            String payloadJson = mapper.writeValueAsString(payload);
            byte[] bytes = payloadJson.getBytes();
            return bytes;
        } catch(JsonProcessingException exception) {
            return null;
        }
    }
}



2020-10-26 23:40:40.799 ERROR 6200 --- [nio-8080-exec-4] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.messaging.converter.MessageConversionException: Unable to convert payload with type='MessageWrapper', contentType='application/hal+json', converter=[CompositeMessageConverter[converters=[org.springframework.messaging.converter.StringMessageConverter@66389c40, org.springframework.messaging.converter.ByteArrayMessageConverter@724493b5, org.springframework.messaging.converter.MappingJackson2MessageConverter@1228bacc]]]] with root cause

org.springframework.messaging.converter.MessageConversionException: Unable to convert payload with type='MessageWrapper', contentType='application/hal+json', converter=[CompositeMessageConverter[converters=[org.springframework.messaging.converter.StringMessageConverter@66389c40, org.springframework.messaging.converter.ByteArrayMessageConverter@724493b5, org.springframework.messaging.converter.MappingJackson2MessageConverter@1228bacc]]]
    at org.springframework.messaging.core.AbstractMessageSendingTemplate.doConvert(AbstractMessageSendingTemplate.java:187) ~[spring-messaging-5.3.0-M1.jar:5.3.0-M1]
    at org.springframework.messaging.core.AbstractMessageSendingTemplate.convertAndSend(AbstractMessageSendingTemplate.java:150) ~[spring-messaging-5.3.0-M1.jar:5.3.0-M1]
    at org.springframework.messaging.simp.SimpMessagingTemplate.convertAndSendToUser(SimpMessagingTemplate.java:230) ~[spring-messaging-5.3.0-M1.jar:5.3.0-M1]
    at org.springframework.messaging.simp.SimpMessagingTemplate.convertAndSendToUser(SimpMessagingTemplate.java:211) ~[spring-messaging-5.3.0-M1.jar:5.3.0-M1]
    at dev.gideon.chatapp.service.BroadcastService.broadcastToUser(BroadcastService.java:54) ~[classes/:na]
    ...



public class HalMessageConverter extends AbstractMessageConverter {
    public HalMessageConverter() {
        MimeType hal = new MimeType("application", "hal+json");
        this.addSupportedMimeTypes(hal);
    }

    @Override
    protected boolean supports(Class<?> clazz) {
        return RepresentationModel.class.isAssignableFrom(clazz);
    }

    @Override
    protected Object convertToInternal(
        Object payload,
        MessageHeaders headers,
        Object conversionHint) {

        TypeConstrainedMappingJackson2HttpMessageConverter converter = 
            new TypeConstrainedMappingJackson2HttpMessageConverter(RepresentationModel.class);

        Module module = new Jackson2HalModule();
        LinkRelationProvider provider = new DefaultLinkRelationProvider();

        Jackson2HalModule.HalHandlerInstantiator instantiator =
            new Jackson2HalModule.HalHandlerInstantiator(
                provider,
                CurieProvider.NONE,
                MessageResolver.DEFAULTS_ONLY);

        ObjectMapper mapper = converter.getObjectMapper();
        mapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);
        mapper.registerModule(module);
        mapper.setHandlerInstantiator(instantiator);

        try {
            String payloadJson = mapper.writeValueAsString(payload);
            byte[] bytes = payloadJson.getBytes();
            return bytes;
        } catch(JsonProcessingException exception) {
            return null;
        }
    }
}



@Configuration @EnableWebSocketMessageBroker
public class WebSocketConfig implements WebSocketMessageBrokerConfigurer {
    @Override
    public boolean configureMessageConverters(List<MessageConverter> messageConverters) {
        messageConverters.add(new HalMessageConverter());
        return false;
    }
}