Adds WeightCalculatorWebFilter.setRandomFunction()

This allows users to set a custom Function that has the ServerWebExchange available.

Default behavior is unchanged

Fixes gh-3298

spring-cloud-gateway-server/src/main/java/org/springframework/cloud/gateway/filter/WeightCalculatorWebFilter.java

@@ -25,6 +25,7 @@
 import java.util.concurrent.ThreadLocalRandom;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
+import java.util.function.Function;
 import java.util.function.Supplier;
 
 import org.apache.commons.logging.Log;
@@ -42,6 +43,7 @@
 import org.springframework.context.event.SmartApplicationListener;
 import org.springframework.core.Ordered;
 import org.springframework.core.style.ToStringCreator;
+import org.springframework.util.Assert;
 import org.springframework.web.server.ServerWebExchange;
 import org.springframework.web.server.WebFilter;
 import org.springframework.web.server.WebFilterChain;
@@ -65,7 +67,7 @@ public class WeightCalculatorWebFilter implements WebFilter, Ordered, SmartAppli
 
 	private final ConfigurationService configurationService;
 
-	private Supplier<Double> randomSupplier = null;
+	private Function<ServerWebExchange, Double> randomFunction = exchange -> ThreadLocalRandom.current().nextDouble();
 
 	private int order = WEIGHT_CALC_FILTER_ORDER;
 
@@ -101,11 +103,18 @@ public void setOrder(int order) {
 
 	@Deprecated
 	public void setRandom(Random random) {
-		this.randomSupplier = random::nextDouble;
+		Assert.notNull(random, "random may not be null");
+		this.randomFunction = exchange -> random.nextDouble();
 	}
 
 	public void setRandomSupplier(Supplier<Double> randomSupplier) {
-		this.randomSupplier = randomSupplier;
+		Assert.notNull(randomSupplier, "randomSupplier may not be null");
+		this.randomFunction = exchange -> randomSupplier.get();
+	}
+
+	public void setRandomFunction(Function<ServerWebExchange, Double> randomFunction) {
+		Assert.notNull(randomFunction, "randomFunction may not be null");
+		this.randomFunction = randomFunction;
 	}
 
 	@Override
@@ -238,17 +247,9 @@ public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
 				continue; // nothing we can do, but this is odd
 			}
 
-			/*
-			 * Usually, multiple threads accessing the same random object will have some
-			 * performance problems, so we can use ThreadLocalRandom by default
-			 */
-			double r;
-			if (this.randomSupplier != null) {
-				r = randomSupplier.get();
-			}
-			else {
-				r = ThreadLocalRandom.current().nextDouble();
-			}
+			// Usually, multiple threads accessing the same random object will have some
+			// performance problems, so we can use ThreadLocalRandom by default
+			double r = randomFunction.apply(exchange);
 
 			List<Double> ranges = config.ranges;