HTTP Outbound: Call encode() for URIs

* Encoding in `AbstractHttpRequestExecutingMessageHandler` is now done when flag is set

* Added test for URI Encoding

* Fixed checkstyle violations

**Cherry-pick to 5.1.x**

* Resolve conflicts in the `HttpRequestExecutingMessageHandlerTests`

Author: ezylot

spring-integration-http/src/main/java/org/springframework/integration/http/outbound/AbstractHttpRequestExecutingMessageHandler.java

@@ -69,6 +69,7 @@
  * @author Artem Bilan
  * @author Wallace Wadge
  * @author Shiliang Li
+ * @author Florian Schöffl
  *
  * @since 5.0
  */
@@ -303,7 +304,7 @@ private URI generateUri(Message<?> requestMessage) {
 				: UriComponentsBuilder.fromUri((URI) uri);
 		UriComponents uriComponents = uriComponentsBuilder.buildAndExpand(uriVariables);
 		try {
-			return this.encodeUri ? uriComponents.toUri() : new URI(uriComponents.toUriString());
+			return this.encodeUri ? uriComponents.encode().toUri() : new URI(uriComponents.toUriString());
 		}
 		catch (URISyntaxException e) {
 			throw new MessageHandlingException(requestMessage, "Invalid URI [" + uri + "]", e);

spring-integration-http/src/test/java/org/springframework/integration/http/outbound/HttpRequestExecutingMessageHandlerTests.java

@@ -78,6 +78,7 @@
  * @author Artem Bilan
  * @author Gary Russell
  * @author Gunnar Hillert
+ * @author Florian Schöffl
  */
 public class HttpRequestExecutingMessageHandlerTests {
 
@@ -751,6 +752,54 @@ public void testUriExpression() {
 		assertEquals(theURL, restTemplate.actualUrl.get());
 	}
 
+	@Test
+	public void testUriEncoded() {
+		SpelExpressionParser parser = new SpelExpressionParser();
+		MockRestTemplate restTemplate = new MockRestTemplate();
+
+		HttpRequestExecutingMessageHandler handler = new HttpRequestExecutingMessageHandler(
+				"http://example.com?query={query}",
+				restTemplate
+		);
+
+		// This flag is set by default to true, but for sake of clarity for the reader we explicitly set it here again
+		handler.setEncodeUri(true);
+
+		handler.setUriVariableExpressions(Collections.singletonMap("query", parser.parseExpression("payload")));
+		setBeanFactory(handler);
+		handler.afterPropertiesSet();
+		Message<?> message = new GenericMessage<>("test-äöü&%");
+		try {
+			handler.handleMessage(message);
+		}
+		catch (Exception ignored) {
+		}
+		assertEquals("http://example.com?query=test-%C3%A4%C3%B6%C3%BC%26%25", restTemplate.actualUrl.get());
+	}
+
+	@Test
+	public void testUriEncodedDisabled() {
+		SpelExpressionParser parser = new SpelExpressionParser();
+		MockRestTemplate restTemplate = new MockRestTemplate();
+
+		HttpRequestExecutingMessageHandler handler = new HttpRequestExecutingMessageHandler(
+				"http://example.com?query={query}",
+				restTemplate
+		);
+
+		handler.setEncodeUri(false);
+		handler.setUriVariableExpressions(Collections.singletonMap("query", parser.parseExpression("payload")));
+		setBeanFactory(handler);
+		handler.afterPropertiesSet();
+		Message<?> message = new GenericMessage<>("test-äöü");
+		try {
+			handler.handleMessage(message);
+		}
+		catch (Exception ignored) {
+		}
+		assertEquals("http://example.com?query=test-äöü", restTemplate.actualUrl.get());
+	}
+
 	@Test
 	public void testInt2455UriNotEncoded() {
 		MockRestTemplate restTemplate = new MockRestTemplate();