Fix NPE when proxy exchange is not configured

Fixes gh-2075
Fixes gh-2163

spring-cloud-gateway-mvc/src/main/java/org/springframework/cloud/gateway/mvc/config/ProxyExchangeArgumentResolver.java

@@ -41,7 +41,7 @@ import static java.util.stream.Collectors.toSet;
  */
 public class ProxyExchangeArgumentResolver implements HandlerMethodArgumentResolver {
 
-	private RestTemplate rest;
+	private final RestTemplate rest;
 
 	private HttpHeaders headers;
 
@@ -77,13 +77,9 @@ public class ProxyExchangeArgumentResolver implements HandlerMethodArgumentResol
 			WebDataBinderFactory binderFactory) throws Exception {
 		ProxyExchange<?> proxy = new ProxyExchange<>(rest, webRequest, mavContainer,
 				binderFactory, type(parameter));
-		proxy.headers(headers);
-		if (this.autoForwardedHeaders.size() > 0) {
-			proxy.headers(extractAutoForwardedHeaders(webRequest));
-		}
-		if (sensitive != null) {
-			proxy.sensitive(sensitive.toArray(new String[0]));
-		}
+		configureHeaders(proxy);
+		configureAutoForwardedHeaders(proxy, webRequest);
+		configureSensitive(proxy);
 		return proxy;
 	}
 
@@ -111,4 +107,22 @@ public class ProxyExchangeArgumentResolver implements HandlerMethodArgumentResol
 		return headers;
 	}
 
+	private void configureHeaders(final ProxyExchange<?> proxy) {
+		if (headers != null) {
+			proxy.headers(headers);
+		}
+	}
+
+	private void configureAutoForwardedHeaders(final ProxyExchange<?> proxy, final NativeWebRequest webRequest) {
+		if ((autoForwardedHeaders != null) && (autoForwardedHeaders.size() > 0)) {
+			proxy.headers(extractAutoForwardedHeaders(webRequest));
+		}
+	}
+
+	private void configureSensitive(final ProxyExchange<?> proxy) {
+		if (sensitive != null) {
+			proxy.sensitive(sensitive.toArray(new String[0]));
+		}
+	}
+
 }

spring-cloud-gateway-mvc/src/test/java/org/springframework/cloud/gateway/mvc/config/ProxyExchangeArgumentResolverTest.java

@@ -0,0 +1,119 @@
+/*
+ * Copyright 2016-2019 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.cloud.gateway.mvc.config;
+
+import java.net.URI;
+import java.util.Collections;
+import java.util.List;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
+import org.springframework.boot.test.web.client.TestRestTemplate;
+import org.springframework.boot.web.client.RestTemplateBuilder;
+import org.springframework.boot.web.server.LocalServerPort;
+import org.springframework.cloud.gateway.mvc.ProxyExchange;
+import org.springframework.context.annotation.Bean;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.http.converter.ByteArrayHttpMessageConverter;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit4.SpringRunner;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RestController;
+import org.springframework.web.client.DefaultResponseErrorHandler;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+@RunWith(SpringRunner.class)
+@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
+@ContextConfiguration(classes = ProxyExchangeArgumentResolverTest.ProxyExchangeArgumentResolverTestApplication.class)
+public class ProxyExchangeArgumentResolverTest {
+
+	@Autowired
+	private TestRestTemplate rest;
+
+	@Autowired
+	private ProxyExchangeArgumentResolverTestApplication application;
+
+	@LocalServerPort
+	private int port;
+
+	@Before
+	public void setUp() throws Exception {
+		application.setHome(new URI("http://localhost:" + port));
+	}
+
+	@Test
+	public void shouldProxyRequestWhenProxyExchangeArgumentResolverIsNotConfigured() {
+		final ResponseEntity<String> response = rest.getForEntity("/proxy", String.class);
+		assertThat(response.getStatusCode()).isEqualTo(HttpStatus.OK);
+		assertThat(response.getBody()).contains("Hello World");
+	}
+
+	@SpringBootApplication
+	static class ProxyExchangeArgumentResolverTestApplication {
+
+		@Autowired
+		private ProxyController controller;
+
+		@Bean
+		public ProxyExchangeArgumentResolver proxyExchangeArgumentResolver() {
+			RestTemplateBuilder builder = new RestTemplateBuilder();
+			builder.errorHandler(new DefaultResponseErrorHandler());
+			builder.messageConverters(new ByteArrayHttpMessageConverter());
+			return new ProxyExchangeArgumentResolver(builder.build());
+		}
+
+		public void setHome(final URI home) {
+			controller.setHome(home);
+		}
+
+		@RestController
+		static class ProxyController {
+
+			private URI home;
+
+			public void setHome(URI home) {
+				this.home = home;
+			}
+
+			@GetMapping("/proxy")
+			public ResponseEntity<?> proxyFoo(ProxyExchange<?> proxy) {
+				return proxy.uri(home.toString() + "/foo").get();
+			}
+
+		}
+
+		@RestController
+		static class TestController {
+
+			@GetMapping("/foo")
+			public List<String> foo() {
+				return Collections.singletonList("Hello World");
+			}
+
+		}
+
+	}
+
+}