使用 application/json 以外的 Content-Type 将 HATEOAS 对象广播为 websocket 消息
Broadcast a HATEOAS object as a websocket message with a Content-Type other than application/json
我需要在 RESTController
上和作为到 websocket 的广播消息呈现下面的 class(在 extends RepresentationModel
的其他几个 class 中)。
@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();
}
}
我使用下面的代码将它渲染到响应主体:
@RequestMapping(
headers = {
"Content-Type=application/json",
"X-Requested-With=XMLHttpRequest"
},
method = RequestMethod.POST,
produces = "application/hal+json",
value = "/thread/{threadId}/message")
public HttpEntity<MessageWrapper> post(...) {
MessageWrapper wrapper = ...
HttpEntity<MessageWrapper> entity =
new ResponseEntity<HateoasWrapper>(wrapper, HttpStatus.OK);
return entity;
}
并生成以下截断响应:
HTTP/1.1 200
...
Content-Type: application/hal+json
{
"_links": {
"previous": {
"href": "/thread/1044/message/86"
},
"self": {
"href": "/thread/1044/message/87"
}
},
"message": {
...
},
"simpleName":"..."
}
注意响应的 Content-Type
和上面的 _links
对象属性。我为那个 Content-Type
创建了一个 javascript 处理程序并且 _links
属性很关键。现在,在稍后的某个单独事件中,我需要将完全相同的 JSON 字符串广播到 websocket。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());
}
并产生以下消息:
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 links
属性而不是 _links
。另请注意,它没有像上面那样具有对象值,而是具有一个对象数组作为值。我想对上面的 RESTController
响应使用相同的 javascript 回调,但不能,因为 links
属性具有不同的结构。我可以在 javascript 端编组它,但我宁愿不尝试配置它以按照我预期的方式呈现它。我读到这是因为我将 websocket 消息呈现为 application/json
而不是 application/hal+json
这就是它使用 links
而不是 _links
的原因。所以我在广播之前将消息的Content-Type
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);
它抛出以下错误:
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]
...
我确实需要将 websocket 消息的 Content-Type
设置为 HAL,以便按照我预期的方式对其进行编组。无论如何要实现这个?我问这个问题是因为除了我不想做单独的 javascript 代码来处理 json 对象与 links
属性与数组值和 _links
属性与对象值,我也相信用 HAL Content-Type
广播它确实是合适的,这样除了我自己的其他客户端也会这样对待它,而不仅仅是普通的 JSON 广播消息.
Content-Type
application/hal+json
的 websocket 广播消息没有默认值 MessageConverter
。我需要为我的自定义 MIME 类型实现我自己的 MessageConverter
。我创建了一个 extends AbstractMessageConverter
:
的转换器
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;
}
}
}
我需要创建一个自定义 class,因为方法 addSupportedMimeTypes
是 protected
。 convertToInternalMethod
保存转换逻辑。 Jackson2HalModule
class 是我一直在寻找的东西。这 class 就是当 Response
与 application/hal+json
的 Content-Type
一起发送时 links
变为 _links
的原因。
创建此自定义 MessageConverter
后,我将其添加到应用程序的默认转换器中:
@Configuration @EnableWebSocketMessageBroker
public class WebSocketConfig implements WebSocketMessageBrokerConfigurer {
@Override
public boolean configureMessageConverters(List<MessageConverter> messageConverters) {
messageConverters.add(new HalMessageConverter());
return false;
}
}
我需要在 RESTController
上和作为到 websocket 的广播消息呈现下面的 class(在 extends RepresentationModel
的其他几个 class 中)。
@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();
}
}
我使用下面的代码将它渲染到响应主体:
@RequestMapping(
headers = {
"Content-Type=application/json",
"X-Requested-With=XMLHttpRequest"
},
method = RequestMethod.POST,
produces = "application/hal+json",
value = "/thread/{threadId}/message")
public HttpEntity<MessageWrapper> post(...) {
MessageWrapper wrapper = ...
HttpEntity<MessageWrapper> entity =
new ResponseEntity<HateoasWrapper>(wrapper, HttpStatus.OK);
return entity;
}
并生成以下截断响应:
HTTP/1.1 200
...
Content-Type: application/hal+json
{
"_links": {
"previous": {
"href": "/thread/1044/message/86"
},
"self": {
"href": "/thread/1044/message/87"
}
},
"message": {
...
},
"simpleName":"..."
}
注意响应的 Content-Type
和上面的 _links
对象属性。我为那个 Content-Type
创建了一个 javascript 处理程序并且 _links
属性很关键。现在,在稍后的某个单独事件中,我需要将完全相同的 JSON 字符串广播到 websocket。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());
}
并产生以下消息:
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 links
属性而不是 _links
。另请注意,它没有像上面那样具有对象值,而是具有一个对象数组作为值。我想对上面的 RESTController
响应使用相同的 javascript 回调,但不能,因为 links
属性具有不同的结构。我可以在 javascript 端编组它,但我宁愿不尝试配置它以按照我预期的方式呈现它。我读到这是因为我将 websocket 消息呈现为 application/json
而不是 application/hal+json
这就是它使用 links
而不是 _links
的原因。所以我在广播之前将消息的Content-Type
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);
它抛出以下错误:
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]
...
我确实需要将 websocket 消息的 Content-Type
设置为 HAL,以便按照我预期的方式对其进行编组。无论如何要实现这个?我问这个问题是因为除了我不想做单独的 javascript 代码来处理 json 对象与 links
属性与数组值和 _links
属性与对象值,我也相信用 HAL Content-Type
广播它确实是合适的,这样除了我自己的其他客户端也会这样对待它,而不仅仅是普通的 JSON 广播消息.
Content-Type
application/hal+json
的 websocket 广播消息没有默认值 MessageConverter
。我需要为我的自定义 MIME 类型实现我自己的 MessageConverter
。我创建了一个 extends 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;
}
}
}
我需要创建一个自定义 class,因为方法 addSupportedMimeTypes
是 protected
。 convertToInternalMethod
保存转换逻辑。 Jackson2HalModule
class 是我一直在寻找的东西。这 class 就是当 Response
与 application/hal+json
的 Content-Type
一起发送时 links
变为 _links
的原因。
创建此自定义 MessageConverter
后,我将其添加到应用程序的默认转换器中:
@Configuration @EnableWebSocketMessageBroker
public class WebSocketConfig implements WebSocketMessageBrokerConfigurer {
@Override
public boolean configureMessageConverters(List<MessageConverter> messageConverters) {
messageConverters.add(new HalMessageConverter());
return false;
}
}