#1019 - Improvements to I18N optimizations.

We now properly look for resource bundles by scanning for a resource bundle *pattern* instead of a plain file named rest-messages. Added integration tests to make sure that resource bundles are not skipped even if they existed.

Added the ability to define common messages in a rest-default-messages.properties, as Spring Data REST requires that and it would be too cumbersome for Spring Data REST to additionally deploy them in its own configuration.

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

@@ -15,14 +15,26 @@
  */
 package org.springframework.hateoas.config;
 
-import org.springframework.context.MessageSource;
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+import java.util.Properties;
+import java.util.stream.Collectors;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.beans.factory.config.PropertiesFactoryBean;
+import org.springframework.context.ApplicationContext;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Import;
 import org.springframework.context.annotation.Primary;
+import org.springframework.context.support.AbstractMessageSource;
 import org.springframework.context.support.AbstractResourceBasedMessageSource;
 import org.springframework.context.support.ReloadableResourceBundleMessageSource;
-import org.springframework.core.io.ClassPathResource;
+import org.springframework.core.io.Resource;
 import org.springframework.hateoas.client.LinkDiscoverer;
 import org.springframework.hateoas.client.LinkDiscoverers;
 import org.springframework.hateoas.mediatype.MessageResolver;
@@ -50,7 +62,9 @@ import org.springframework.util.ClassUtils;
 @Configuration
 @Import(EntityLinksConfiguration.class)
 @EnablePluginRegistries({ LinkDiscoverer.class })
-class HateoasConfiguration {
+public class HateoasConfiguration {
+
+	private @Autowired ApplicationContext context;
 
 	@Bean
 	public MessageResolver messageResolver() {
@@ -104,17 +118,53 @@ class HateoasConfiguration {
 	 * @return will never be {@literal null}.
 	 */
 	@Nullable
-	private static final MessageSource lookupMessageSource() {
+	private final AbstractMessageSource lookupMessageSource() {
 
-		ClassPathResource resource = new ClassPathResource("rest-messages");
+		List<Resource> candidates = loadProperties("rest-default-messages", false);
 
-		if (!resource.exists()) {
+		if (candidates.isEmpty() && loadProperties("rest-messages", true).isEmpty()) {
 			return null;
 		}
 
 		AbstractResourceBasedMessageSource messageSource = new ReloadableResourceBundleMessageSource();
 		messageSource.setBasename("classpath:rest-messages");
+		messageSource.setDefaultEncoding(StandardCharsets.UTF_8.toString());
+
+		if (!candidates.isEmpty()) {
+			messageSource.setCommonMessages(loadProperties(candidates));
+		}
 
 		return messageSource;
 	}
+
+	@Nullable
+	private final Properties loadProperties(Collection<Resource> sources) {
+
+		Resource[] resources = loadProperties("rest-default-messages", false).stream().toArray(Resource[]::new);
+
+		PropertiesFactoryBean factory = new PropertiesFactoryBean();
+		factory.setLocations(resources);
+
+		try {
+
+			factory.afterPropertiesSet();
+			return factory.getObject();
+
+		} catch (IOException o_O) {
+			throw new IllegalStateException("Could not load default properties from resources!", o_O);
+		}
+	}
+
+	private final List<Resource> loadProperties(String baseName, boolean withWildcard) {
+
+		try {
+			return Arrays //
+					.stream(context.getResources(String.format("classpath:%s%s.properties", baseName, withWildcard ? "*" : ""))) //
+					.filter(Resource::exists) //
+					.collect(Collectors.toList());
+
+		} catch (IOException e) {
+			return Collections.emptyList();
+		}
+	}
 }

src/main/java/org/springframework/hateoas/mediatype/DefaultOnlyMessageResolver.java

@@ -18,7 +18,12 @@ package org.springframework.hateoas.mediatype;
 import org.springframework.context.MessageSourceResolvable;
 import org.springframework.lang.Nullable;
 
-enum NoMessageResolver implements MessageResolver {
+/**
+ * {@link MessageResolver} to always resort to the {@link MessageSourceResolvable}'s default message.
+ *
+ * @author Oliver Drotbohm
+ */
+enum DefaultOnlyMessageResolver implements MessageResolver {
 
 	INSTANCE;
 
@@ -29,6 +34,6 @@ enum NoMessageResolver implements MessageResolver {
 	@Nullable
 	@Override
 	public String resolve(MessageSourceResolvable resolvable) {
-		return null;
+		return resolvable.getDefaultMessage();
 	}
 }

src/main/java/org/springframework/hateoas/mediatype/MessageResolver.java

@@ -28,7 +28,7 @@ import org.springframework.lang.Nullable;
  */
 public interface MessageResolver {
 
-	public static final MessageResolver NONE = NoMessageResolver.INSTANCE;
+	public static final MessageResolver DEFAULTS_ONLY = DefaultOnlyMessageResolver.INSTANCE;
 
 	/**
 	 * Resolve the given {@link MessageSourceResolvable}. Return {@literal null} if no message was found.
@@ -46,6 +46,9 @@ public interface MessageResolver {
 	 * @return will never be {@literal null}.
 	 */
 	public static MessageResolver of(@Nullable MessageSource messageSource) {
-		return messageSource == null ? NoMessageResolver.INSTANCE : new MessageSourceResolver(messageSource);
+
+		return messageSource == null //
+				? DefaultOnlyMessageResolver.INSTANCE //
+				: new MessageSourceResolver(messageSource);
 	}
 }

src/main/java/org/springframework/hateoas/mediatype/hal/HalMediaTypeConfiguration.java

@@ -18,6 +18,7 @@ package org.springframework.hateoas.mediatype.hal;
 import java.util.List;
 
 import org.springframework.beans.factory.ObjectProvider;
+import org.springframework.beans.factory.annotation.Qualifier;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.hateoas.client.LinkDiscoverer;
@@ -42,7 +43,7 @@ public class HalMediaTypeConfiguration implements HypermediaMappingInformation {
 	private final LinkRelationProvider relProvider;
 	private final ObjectProvider<CurieProvider> curieProvider;
 	private final ObjectProvider<HalConfiguration> halConfiguration;
-	private final MessageResolver resolver;
+	private final @Qualifier("messageResolver") MessageResolver resolver;
 
 	/**
 	 * @param relProvider

src/main/java/org/springframework/hateoas/mediatype/hal/Jackson2HalModule.java

@@ -121,14 +121,19 @@ public class Jackson2HalModule extends SimpleModule {
 		}
 
 		public HalLinkListSerializer(@Nullable BeanProperty property, CurieProvider curieProvider, EmbeddedMapper mapper,
-				MessageResolver accessor, HalConfiguration halConfiguration) {
+				MessageResolver resolver, HalConfiguration halConfiguration) {
 
 			super(TypeFactory.defaultInstance().constructType(Links.class));
 
+			Assert.notNull(curieProvider, "CurieProvider must not be null!");
+			Assert.notNull(mapper, "EmbeddedMapper must not be null!");
+			Assert.notNull(resolver, "MessageResolver must not be null!");
+			Assert.notNull(halConfiguration, "HalConfiguration must not be null!");
+
 			this.property = property;
 			this.curieProvider = curieProvider;
 			this.mapper = mapper;
-			this.resolver = accessor;
+			this.resolver = resolver;
 			this.halConfiguration = halConfiguration;
 		}