Nullable HttpMethod parameter only on internal doExecute delegate

Issue: SPR-15540

(cherry picked from commit f8c2d7a)

Author: jhoeller

spring-web/src/main/java/org/springframework/web/client/RestTemplate.java

@@ -653,23 +653,19 @@ public <T> ResponseEntity<T> exchange(URI url, HttpMethod method, @Nullable Http
 	public <T> ResponseEntity<T> exchange(RequestEntity<?> requestEntity, Class<T> responseType)
 			throws RestClientException {
 
-		Assert.notNull(requestEntity, "RequestEntity must not be null");
-
 		RequestCallback requestCallback = httpEntityCallback(requestEntity, responseType);
 		ResponseExtractor<ResponseEntity<T>> responseExtractor = responseEntityExtractor(responseType);
-		return nonNull(execute(requestEntity.getUrl(), requestEntity.getMethod(), requestCallback, responseExtractor));
+		return nonNull(doExecute(requestEntity.getUrl(), requestEntity.getMethod(), requestCallback, responseExtractor));
 	}
 
 	@Override
 	public <T> ResponseEntity<T> exchange(RequestEntity<?> requestEntity, ParameterizedTypeReference<T> responseType)
 			throws RestClientException {
 
-		Assert.notNull(requestEntity, "RequestEntity must not be null");
-
 		Type type = responseType.getType();
 		RequestCallback requestCallback = httpEntityCallback(requestEntity, type);
 		ResponseExtractor<ResponseEntity<T>> responseExtractor = responseEntityExtractor(type);
-		return nonNull(execute(requestEntity.getUrl(), requestEntity.getMethod(), requestCallback, responseExtractor));
+		return nonNull(doExecute(requestEntity.getUrl(), requestEntity.getMethod(), requestCallback, responseExtractor));
 	}
 
 
@@ -696,7 +692,7 @@ public <T> T execute(String url, HttpMethod method, @Nullable RequestCallback re
 
 	@Override
 	@Nullable
-	public <T> T execute(URI url, @Nullable HttpMethod method, @Nullable RequestCallback requestCallback,
+	public <T> T execute(URI url, HttpMethod method, @Nullable RequestCallback requestCallback,
 			@Nullable ResponseExtractor<T> responseExtractor) throws RestClientException {
 
 		return doExecute(url, method, requestCallback, responseExtractor);
@@ -716,8 +712,8 @@ public <T> T execute(URI url, @Nullable HttpMethod method, @Nullable RequestCall
 	protected <T> T doExecute(URI url, @Nullable HttpMethod method, @Nullable RequestCallback requestCallback,
 			@Nullable ResponseExtractor<T> responseExtractor) throws RestClientException {
 
-		Assert.notNull(url, "'url' must not be null");
-		Assert.notNull(method, "'method' must not be null");
+		Assert.notNull(url, "URI is required");
+		Assert.notNull(method, "HttpMethod is required");
 		ClientHttpResponse response = null;
 		try {
 			ClientHttpRequest request = createRequest(url, method);
@@ -726,12 +722,7 @@ protected <T> T doExecute(URI url, @Nullable HttpMethod method, @Nullable Reques
 			}
 			response = request.execute();
 			handleResponse(url, method, response);
-			if (responseExtractor != null) {
-				return responseExtractor.extractData(response);
-			}
-			else {
-				return null;
-			}
+			return (responseExtractor != null ? responseExtractor.extractData(response) : null);
 		}
 		catch (IOException ex) {
 			String resource = url.toString();
@@ -829,7 +820,7 @@ private class AcceptHeaderRequestCallback implements RequestCallback {
 		@Nullable
 		private final Type responseType;
 
-		private AcceptHeaderRequestCallback(@Nullable Type responseType) {
+		public AcceptHeaderRequestCallback(@Nullable Type responseType) {
 			this.responseType = responseType;
 		}
 
@@ -886,11 +877,11 @@ private class HttpEntityRequestCallback extends AcceptHeaderRequestCallback {
 
 		private final HttpEntity<?> requestEntity;
 
-		private HttpEntityRequestCallback(@Nullable Object requestBody) {
+		public HttpEntityRequestCallback(@Nullable Object requestBody) {
 			this(requestBody, null);
 		}
 
-		private HttpEntityRequestCallback(@Nullable Object requestBody, @Nullable Type responseType) {
+		public HttpEntityRequestCallback(@Nullable Object requestBody, @Nullable Type responseType) {
 			super(responseType);
 			if (requestBody instanceof HttpEntity) {
 				this.requestEntity = (HttpEntity<?>) requestBody;
@@ -1013,7 +1004,7 @@ public ResponseEntity<T> extractData(ClientHttpResponse response) throws IOExcep
 	private static class HeadersExtractor implements ResponseExtractor<HttpHeaders> {
 
 		@Override
-		public HttpHeaders extractData(ClientHttpResponse response) throws IOException {
+		public HttpHeaders extractData(ClientHttpResponse response) {
 			return response.getHeaders();
 		}
 	}