Update Mono.then(Supplier) deprecated calls

Reactor Core has now deprecated the `Mono.then(Supplier)`.
This is now replaced with `Mono.then(Mono.defer(Supplier))`.

spring-test/src/main/java/org/springframework/test/web/reactive/server/FluxExchangeResult.java

@@ -90,7 +90,7 @@ public class FluxExchangeResult<T> extends ExchangeResult {
 	public byte[] getResponseBodyContent() {
 		return this.body.ignoreElements()
 				.timeout(this.timeout, Mono.error(TIMEOUT_ERROR))
-				.then(() -> Mono.just(super.getResponseBodyContent()))
+				.then(Mono.defer(() -> Mono.just(super.getResponseBodyContent())))
 				.block();
 	}
 

spring-web/src/main/java/org/springframework/web/server/adapter/HttpWebHandlerAdapter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -83,7 +83,7 @@ public class HttpWebHandlerAdapter extends WebHandlerDecorator implements HttpHa
 					response.setStatusCode(HttpStatus.INTERNAL_SERVER_ERROR);
 					return Mono.empty();
 				})
-				.then(response::setComplete);
+				.then(Mono.defer(response::setComplete));
 	}
 
 	protected ServerWebExchange createExchange(ServerHttpRequest request, ServerHttpResponse response) {

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/AbstractHandlerMethodMapping.java

@@ -263,7 +263,7 @@ public abstract class AbstractHandlerMethodMapping<T> extends AbstractHandlerMap
 		try {
 			// Ensure form data is parsed for "params" conditions...
 			return exchange.getRequestParams()
-					.then(() -> {
+					.then(Mono.defer(() -> {
 						HandlerMethod handlerMethod = null;
 						try {
 							handlerMethod = lookupHandlerMethod(lookupPath, exchange);
@@ -283,7 +283,7 @@ public abstract class AbstractHandlerMethodMapping<T> extends AbstractHandlerMap
 							handlerMethod = handlerMethod.createWithResolvedBean();
 						}
 						return Mono.justOrEmpty(handlerMethod);
-					});
+					}));
 		}
 		finally {
 			this.mappingRegistry.releaseReadLock();

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/annotation/RequestMappingHandlerAdapter.java

@@ -186,10 +186,10 @@ public class RequestMappingHandlerAdapter implements HandlerAdapter, Application
 
 		return this.modelInitializer
 				.initModel(bindingContext, modelAttributeMethods, exchange)
-				.then(() -> this.methodResolver.getRequestMappingMethod(handlerMethod)
+				.then(Mono.defer(() -> this.methodResolver.getRequestMappingMethod(handlerMethod)
 						.invoke(exchange, bindingContext)
 						.doOnNext(result -> result.setExceptionHandler(exceptionHandler))
-						.onErrorResume(exceptionHandler));
+						.onErrorResume(exceptionHandler)));
 	}
 
 	private Mono<HandlerResult> handleException(Throwable ex, HandlerMethod handlerMethod,