spring cloud gateway系列教程目錄
- spring cloud gateway系列教程1—Route Predicate
- spring cloud gateway系列教程2——GatewayFilter_上篇
- spring cloud gateway系列教程2——GatewayFilter_下篇
- spring cloud gateway系列教程3—Global Filters
- spring cloud gateway系列教程4—其他配置
Global Filters
GlobalFilter接口方法和GatewayFilter是一樣的，GlobalFilter特別之處在于它的作用是全局的。
1. Combined Global Filter and GatewayFilter Ordering
當請求到來時，Filtering Web Handler處理器會添加所有GlobalFilter實例和匹配的GatewayFilter實例到過濾器鏈中，通過對filterbean配置注解@Order，則過濾器鏈會對這些過濾器實例bean進行排序。
Spring Cloud Gateway將過濾器的邏輯按請求執行點分為”pre"和"post"的一前一后處理，如果是高優先級的過濾器，則在"pre"邏輯中最先執行，在"post"邏輯中最后執行。
ExampleConfiguration.java.
@Bean
@Order(-1)
public GlobalFilter a() {
return (exchange, chain) -> {
log.info("first pre filter");
return chain.filter(exchange).then(Mono.fromRunnable(() -> {
log.info("third post filter");
}));
};
}
@Bean
@Order(0)
public GlobalFilter b() {
return (exchange, chain) -> {
log.info("second pre filter");
return chain.filter(exchange).then(Mono.fromRunnable(() -> {
log.info("second post filter");
}));
};
}
@Bean
@Order(1)
public GlobalFilter c() {
return (exchange, chain) -> {
log.info("third pre filter");
return chain.filter(exchange).then(Mono.fromRunnable(() -> {
log.info("first post filter");
}));
};
}
上面例子陸續會打印的是：
first pre filter
second pre filter
third pre filter
first post filter
second post filter
third post filter
2. Forward Routing Filter
ForwardRoutingFilter會查看exchange的屬性ServerWebExchangeUtils.GATEWAY_REQUEST_URL_ATTR的URI內容，如果url的scheme是forward，比如：forward://localendpoint，則它會使用Spirng的DispatcherHandler來處理這個請求。
源碼實現：
@Override
public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
URI requestUrl = exchange.getRequiredAttribute(GATEWAY_REQUEST_URL_ATTR);
String scheme = requestUrl.getScheme();
if (isAlreadyRouted(exchange) || !"forward".equals(scheme)) {
return chain.filter(exchange);
}
setAlreadyRouted(exchange);
//TODO: translate url?
if (log.isTraceEnabled()) {
log.trace("Forwarding to URI: "+requestUrl);
}
return this.dispatcherHandler.handle(exchange);
}
3. LoadBalancerClient Filter
LoadBalancerClientFilter會查看exchange的屬性ServerWebExchangeUtils.GATEWAY_REQUEST_URL_ATTR的URI內容，如果url的scheme是lb，比如：lb://myservice，或者是ServerWebExchangeUtils.GATEWAY_SCHEME_PREFIX_ATTR屬性的內容是lb，則它會使用Spring Cloud的LoadBalancerClient來將host轉化為實際的host和port，并以此替換屬性ServerWebExchangeUtils.GATEWAY_REQUEST_URL_ATTR的內容，原來的URL則會被添加到ServerWebExchangeUtils.GATEWAY_ORIGINAL_REQUEST_URL_ATTR屬性的列表中。
源碼實現：
@Override
public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
URI url = exchange.getAttribute(GATEWAY_REQUEST_URL_ATTR);
String schemePrefix = exchange.getAttribute(GATEWAY_SCHEME_PREFIX_ATTR);
if (url == null || (!"lb".equals(url.getScheme()) && !"lb".equals(schemePrefix))) {
return chain.filter(exchange);
}
//preserve the original url
addOriginalRequestUrl(exchange, url);
log.trace("LoadBalancerClientFilter url before: " + url);
final ServiceInstance instance = loadBalancer.choose(url.getHost());
if (instance == null) {
throw new NotFoundException("Unable to find instance for " + url.getHost());
}
URI uri = exchange.getRequest().getURI();
// if the `lb:<scheme>` mechanism was used, use `<scheme>` as the default,
// if the loadbalancer doesn't provide one.
String overrideScheme = null;
if (schemePrefix != null) {
overrideScheme = url.getScheme();
}
URI requestUrl = loadBalancer.reconstructURI(new DelegatingServiceInstance(instance, overrideScheme), uri);
log.trace("LoadBalancerClientFilter url chosen: " + requestUrl);
exchange.getAttributes().put(GATEWAY_REQUEST_URL_ATTR, requestUrl);
return chain.filter(exchange);
}
application.yml.
spring:
cloud:
gateway:
routes:
- id: myRoute
uri: lb://service
predicates:
- Path=/service/**
默認情況下，如果LoadBalancer找不到服務實例，則會返回HTTP狀態碼503，你也可以通過修改spring.cloud.gateway.loadbalancer.use404=true配置修改為返回狀態碼404。
4. Netty Routing Filter
如果ServerWebExchangeUtils.GATEWAY_REQUEST_URL_ATTR屬性中的url的scheme是http或https，則Netty Routing Filter才會執行，并使用Netty作為http請求客戶端對下游進行代理請求。請求的響應會放在exchange的ServerWebExchangeUtils.CLIENT_RESPONSE_ATTR屬性中，以便后面的filter做進一步的處理。
5. Netty Write Response Filter
如果NettyWriteResponseFilter發現exchange的ServerWebExchangeUtils.CLIENT_RESPONSE_ATTR屬性中存在Netty的HttpClientResponse類型實例，在所有過濾器都執行完畢后，它會將響應寫回到gateway客戶端的響應中。
源碼實現:
@Override
public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
// NOTICE: nothing in "pre" filter stage as CLIENT_RESPONSE_ATTR is not added
// until the WebHandler is run
return chain.filter(exchange).then(Mono.defer(() -> {
HttpClientResponse clientResponse = exchange.getAttribute(CLIENT_RESPONSE_ATTR);
if (clientResponse == null) {
return Mono.empty();
}
log.trace("NettyWriteResponseFilter start");
ServerHttpResponse response = exchange.getResponse();
NettyDataBufferFactory factory = (NettyDataBufferFactory) response.bufferFactory();
//TODO: what if it's not netty
final Flux<NettyDataBuffer> body = clientResponse.receive()
.retain() //TODO: needed?
.map(factory::wrap);
MediaType contentType = response.getHeaders().getContentType();
return (isStreamingMediaType(contentType) ?
response.writeAndFlushWith(body.map(Flux::just)) : response.writeWith(body));
}));
}
//TODO: use framework if possible
//TODO: port to WebClientWriteResponseFilter
private boolean isStreamingMediaType(@Nullable MediaType contentType) {
return (contentType != null && this.streamingMediaTypes.stream()
.anyMatch(contentType::isCompatibleWith));
}
6. RouteToRequestUrl Filter
如果exchange的ServerWebExchangeUtils.GATEWAY_ROUTE_ATTR屬性存放了Route對象，則RouteToRequestUrlFilter會根據基于請求的URI創建新的URI，新的URI會更新到ServerWebExchangeUtils.GATEWAY_REQUEST_URL_ATTR屬性中。
如果URI有scheme前綴，比如：lb:ws://serviceid，lbscheme截取出來放到ServerWebExchangeUtils.GATEWAY_SCHEME_PREFIX_ATTR屬性中，方便后面的filter使用。
源碼實現:
@Override
public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
Route route = exchange.getAttribute(GATEWAY_ROUTE_ATTR);
if (route == null) {
return chain.filter(exchange);
}
log.trace("RouteToRequestUrlFilter start");
URI uri = exchange.getRequest().getURI();
boolean encoded = containsEncodedParts(uri);
URI routeUri = route.getUri();
if (hasAnotherScheme(routeUri)) {
// this is a special url, save scheme to special attribute
// replace routeUri with schemeSpecificPart
exchange.getAttributes().put(GATEWAY_SCHEME_PREFIX_ATTR, routeUri.getScheme());
routeUri = URI.create(routeUri.getSchemeSpecificPart());
}
URI requestUrl = UriComponentsBuilder.fromUri(uri)
.uri(routeUri)
.build(encoded)
.toUri();
exchange.getAttributes().put(GATEWAY_REQUEST_URL_ATTR, requestUrl);
return chain.filter(exchange);
}
/* for testing */ static boolean hasAnotherScheme(URI uri) {
return schemePattern.matcher(uri.getSchemeSpecificPart()).matches() && uri.getHost() == null
&& uri.getRawPath() == null;
}
7. Websocket Routing Filter
如果請求URL的scheme是ws或wss的話，那么Websocket Routing Filter就會使用Spring Web Socket底層來處理對下游的請求轉發。
如果Websocket也使用了負載均衡，則需要這樣配置：lb:ws://serviceid.
源碼實現：
@Override
public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
changeSchemeIfIsWebSocketUpgrade(exchange);
URI requestUrl = exchange.getRequiredAttribute(GATEWAY_REQUEST_URL_ATTR);
String scheme = requestUrl.getScheme();
if (isAlreadyRouted(exchange) || (!"ws".equals(scheme) && !"wss".equals(scheme))) {
return chain.filter(exchange);
}
setAlreadyRouted(exchange);
HttpHeaders headers = exchange.getRequest().getHeaders();
HttpHeaders filtered = filterRequest(getHeadersFilters(),
exchange);
List<String> protocols = headers.get(SEC_WEBSOCKET_PROTOCOL);
if (protocols != null) {
protocols = headers.get(SEC_WEBSOCKET_PROTOCOL).stream()
.flatMap(header -> Arrays.stream(commaDelimitedListToStringArray(header)))
.map(String::trim)
.collect(Collectors.toList());
}
return this.webSocketService.handleRequest(exchange,
new ProxyWebSocketHandler(requestUrl, this.webSocketClient,
filtered, protocols));
}
8. Making An Exchange As Routed
上面一些像ForwardRoutingFilter、Websocket Routing Filter的源碼中，都可以清楚看到gateway通過設置gatewayAlreadyRouted標識這個請求是否已經路由轉發出去了，無需其他filter重復路由，這樣就可以避免重復錯誤的路由操作，保證了路由的實現靈活性。
ServerWebExchangeUtils.isAlreadyRouted檢查是否已被路由，ServerWebExchangeUtils.setAlreadyRouted標記已被路由狀態。
這一章介紹了Spring Cloud Gateway官方的Global Filters使用場景，下一章講gateway其他配置的使用。
如果想查看其他spring cloud gateway的案例和使用，可以點擊查看
