#867 - Only disable default encoders and decoders when using Spring 5.1.

Spring Framework 5.1 puts custom encoders and decoders in the wrong place, so Spring HATEOAS can't properly register with WebFlux. To make Spring HATEOS media types work requires overriding features that break other toolkits, like Spring Cloud Sleuth. However, in Spring Framework 5.2, this is no longer needed, so we need only disable the registry when Spring Framework 5.1 is on the classpath.

Related issues: #885, spring-projects/spring-framework#22612

Author: gregturn

src/main/java/org/springframework/hateoas/config/WebClientConfigurer.java

@@ -1,24 +1,23 @@
 package org.springframework.hateoas.config;
 
+import com.fasterxml.jackson.databind.ObjectMapper;
 import lombok.RequiredArgsConstructor;
-
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.List;
-
 import org.springframework.context.annotation.Configuration;
 import org.springframework.core.codec.CharSequenceEncoder;
 import org.springframework.core.codec.Decoder;
 import org.springframework.core.codec.Encoder;
 import org.springframework.core.codec.StringDecoder;
 import org.springframework.hateoas.config.EnableHypermediaSupport.HypermediaType;
+import org.springframework.hateoas.support.SpringUtilities;
 import org.springframework.http.codec.json.Jackson2JsonDecoder;
 import org.springframework.http.codec.json.Jackson2JsonEncoder;
 import org.springframework.util.MimeType;
 import org.springframework.web.reactive.function.client.ExchangeStrategies;
 import org.springframework.web.reactive.function.client.WebClient;
 
-import com.fasterxml.jackson.databind.ObjectMapper;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
 
 /**
  * Assembles {@link ExchangeStrategies} needed to wire a {@link WebClient} with hypermedia support.
@@ -52,15 +51,21 @@ public ExchangeStrategies hypermediaExchangeStrategies() {
 			decoders.add(new Jackson2JsonDecoder(objectMapper, mimeTypes));
 		});
 
-		encoders.add(CharSequenceEncoder.allMimeTypes());
-		decoders.add(StringDecoder.allMimeTypes());
+		if (SpringUtilities.isSpring5_1()) {
+			
+			encoders.add(CharSequenceEncoder.allMimeTypes());
+			decoders.add(StringDecoder.allMimeTypes());
+		}
 
 		return ExchangeStrategies.builder().codecs(clientCodecConfigurer -> {
 
 			encoders.forEach(encoder -> clientCodecConfigurer.customCodecs().encoder(encoder));
 			decoders.forEach(decoder -> clientCodecConfigurer.customCodecs().decoder(decoder));
 
-			clientCodecConfigurer.registerDefaults(false);
+			if (SpringUtilities.isSpring5_1()) {
+				clientCodecConfigurer.registerDefaults(false);
+			}
+
 		}).build();
 	}
 

src/main/java/org/springframework/hateoas/support/SpringUtilities.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright 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
+ *
+ *      http://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.hateoas.support;
+
+import lombok.experimental.UtilityClass;
+
+import org.springframework.context.ApplicationContext;
+
+/**
+ * Utility for Spring-specific functions.
+ * 
+ * @author Greg Turnquist
+ */
+@UtilityClass
+public class SpringUtilities {
+
+	/**
+	 * @return boolean indicating this is Spring Framework 5.1
+	 */
+	public boolean isSpring5_1() {
+
+		String versionOfSpringFramework = ApplicationContext.class.getPackage().getImplementationVersion();
+
+		String[] parts = versionOfSpringFramework.split("\\.");
+		int majorVersion = Integer.parseInt(parts[0]);
+		int minorVersion = Integer.parseInt(parts[1]);
+
+		return majorVersion == 5 && minorVersion == 1;
+	}
+
+}