Adds retry.adoc retry filter docs

Author: spencergibb

docs/modules/ROOT/pages/spring-cloud-gateway-server-mvc/filters/retry.adoc

@@ -4,22 +4,23 @@
 The `Retry` filter supports the following parameters:
 
 * `retries`: The number of retries that should be attempted.
-* `statuses`: The HTTP status codes that should be retried, represented by using `org.springframework.http.HttpStatus`.
+//TODO: implement statuses
+//* `statuses`: The HTTP status codes that should be retried, represented by using `org.springframework.http.HttpStatus`.
 * `methods`: The HTTP methods that should be retried, represented by using `org.springframework.http.HttpMethod`.
 * `series`: The series of status codes to be retried, represented by using `org.springframework.http.HttpStatus.Series`.
 * `exceptions`: A list of thrown exceptions that should be retried.
-* `backoff`: The configured exponential backoff for the retries.
-Retries are performed after a backoff interval of `firstBackoff * (factor ^ n)`, where `n` is the iteration.
-If `maxBackoff` is configured, the maximum backoff applied is limited to `maxBackoff`.
-If `basedOnPreviousValue` is true, the backoff is calculated by using `prevBackoff * factor`.
+//* `backoff`: The configured exponential backoff for the retries.
+//Retries are performed after a backoff interval of `firstBackoff * (factor ^ n)`, where `n` is the iteration.
+//If `maxBackoff` is configured, the maximum backoff applied is limited to `maxBackoff`.
+//If `basedOnPreviousValue` is true, the backoff is calculated by using `prevBackoff * factor`.
 
 The following defaults are configured for `Retry` filter, if enabled:
 
 * `retries`: Three times
 * `series`: 5XX series
 * `methods`: GET method
-* `exceptions`: `IOException` and `TimeoutException`
-* `backoff`: disabled
+* `exceptions`: `IOException`, `TimeoutException` and `RetryException`
+//* `backoff`: disabled
 
 The following listing configures a Retry  filter:
 
@@ -29,29 +30,46 @@ The following listing configures a Retry  filter:
 spring:
   cloud:
     gateway:
-      routes:
-      - id: retry_test
-        uri: http://localhost:8080/flakey
-        predicates:
-        - Host=*.retry.com
-        filters:
-        - name: Retry
-          args:
-            retries: 3
-            statuses: BAD_GATEWAY
-            methods: GET,POST
-            backoff:
-              firstBackoff: 10ms
-              maxBackoff: 50ms
-              factor: 2
-              basedOnPreviousValue: false
+      mvc:
+        routes:
+        - id: retry_test
+          uri: http://localhost:8080/flakey
+          predicates:
+          - Host=*.retry.com
+          filters:
+          - name: Retry
+            args:
+              retries: 3
+              series: SERVER_ERROR
+              methods: GET,POST
+----
+
+.GatewaySampleApplication.java
+[source,java]
+----
+import static org.springframework.cloud.gateway.server.mvc.filter.RetryFilterFunctions.retry;
+import static org.springframework.cloud.gateway.server.mvc.handler.GatewayRouterFunctions.route;
+import static org.springframework.cloud.gateway.server.mvc.handler.HandlerFunctions.http;
+import static org.springframework.cloud.gateway.server.mvc.predicate.GatewayRequestPredicates.host;
+
+@Configuration
+class RouteConfiguration {
+
+    @Bean
+    public RouterFunction<ServerResponse> gatewayRouterFunctionsAddReqHeader() {
+		return route("add_request_parameter_route")
+			.route(host("*.retry.com"), http("https://example.org"))
+				.filter(retry(config -> config.setRetries(3).setSeries(Set.of(HttpStatus.Series.SERVER_ERROR)).setMethods(Set.of(HttpMethod.GET, HttpMethod.POST))))
+			.build();
+    }
+}
 ----
 
 NOTE: When using the retry filter with a `forward:` prefixed URL, the target endpoint should be written carefully so that, in case of an error, it does not do anything that could result in a response being sent to the client and committed.
 For example, if the target endpoint is an annotated controller, the target controller method should not return `ResponseEntity` with an error status code.
 Instead, it should throw an `Exception` or signal an error (for example, through a `Mono.error(ex)` return value), which the retry filter can be configured to handle by retrying.
 
-WARNING: When using the retry filter with any HTTP method with a body, the body will be cached and the gateway will become memory constrained. The body is cached in a request attribute defined by `ServerWebExchangeUtils.CACHED_REQUEST_BODY_ATTR`. The type of the object is `org.springframework.core.io.buffer.DataBuffer`.
+// WARNING: When using the retry filter with any HTTP method with a body, the body will be cached and the gateway will become memory constrained. The body is cached in a request attribute defined by `ServerWebExchangeUtils.CACHED_REQUEST_BODY_ATTR`. The type of the object is `org.springframework.core.io.buffer.DataBuffer`.
 
 A simplified "shortcut" notation can be added with a single `status` and `method`.
 
@@ -72,15 +90,9 @@ spring:
             retries: 3
             statuses: INTERNAL_SERVER_ERROR
             methods: GET
-            backoff:
-              firstBackoff: 10ms
-              maxBackoff: 50ms
-              factor: 2
-              basedOnPreviousValue: false
-
       - id: retryshortcut_route
         uri: https://example.org
         filters:
-        - Retry=3,INTERNAL_SERVER_ERROR,GET,10ms,50ms,2,false
+        - Retry=3,INTERNAL_SERVER_ERROR,GET
 ----