DATAREDIS-1032 - Improve cache key converter registration.

Original pull request: #475.

Author: christophstrobl

src/main/java/org/springframework/data/redis/cache/RedisCache.java

@@ -309,7 +309,7 @@ protected String convertKey(Object key) {
 		}
 
 		throw new IllegalStateException(String.format(
-				"Cannot convert cache key %s to String. Please provide a suitable Converter via 'RedisCacheConfiguration.withConversionService(...)' or override '%s.toString()'.",
+				"Cannot convert cache key %s to String. Please register a suitable Converter via 'RedisCacheConfiguration.configureKeyConverters(...)' or override '%s.toString()'.",
 				source, key != null ? key.getClass().getSimpleName() : "Object"));
 	}
 

src/main/java/org/springframework/data/redis/cache/RedisCacheConfiguration.java

@@ -18,10 +18,12 @@
 import java.nio.charset.StandardCharsets;
 import java.time.Duration;
 import java.util.Optional;
+import java.util.function.Consumer;
 
 import org.springframework.cache.Cache;
 import org.springframework.cache.interceptor.SimpleKey;
 import org.springframework.core.convert.ConversionService;
+import org.springframework.core.convert.converter.Converter;
 import org.springframework.core.convert.converter.ConverterRegistry;
 import org.springframework.data.redis.serializer.RedisSerializationContext.SerializationPair;
 import org.springframework.data.redis.serializer.RedisSerializer;
@@ -303,6 +305,37 @@ public ConversionService getConversionService() {
 		return conversionService;
 	}
 
+	/**
+	 * Add a {@link Converter} for extracting the {@link String} representation of a cache key if no suitable
+	 * {@link Object#toString()} method is present.
+	 *
+	 * @param cacheKeyConverter
+	 * @throws IllegalStateException if {@link #getConversionService()} does not allow converter registration.
+	 * @since 2.2
+	 */
+	public void addCacheKeyConverter(Converter<?, String> cacheKeyConverter) {
+		configureKeyConverters(it -> it.addConverter(cacheKeyConverter));
+	}
+
+	/**
+	 * Configure the underlying conversion system used to extract the cache key.
+	 *
+	 * @param registryConsumer never {@literal null}.
+	 * @throws IllegalStateException if {@link #getConversionService()} does not allow converter registration.
+	 * @since 2.2
+	 */
+	public void configureKeyConverters(Consumer<ConverterRegistry> registryConsumer) {
+
+		if (!(getConversionService() instanceof ConverterRegistry)) {
+			throw new IllegalStateException(String.format(
+					"'%s' returned by getConversionService() does not allow converter registration." //
+							+ " Please make sure to provide a ConversionService that implements ConverterRegistry.",
+					getConversionService().getClass().getSimpleName()));
+		}
+
+		registryConsumer.accept((ConverterRegistry) getConversionService());
+	}
+
 	/**
 	 * Registers default cache key converters. The following converters get registered:
 	 * <ul>

src/test/java/org/springframework/data/redis/cache/RedisCacheConfigurationUnitTests.java

@@ -19,7 +19,9 @@
 
 import org.junit.Test;
 import org.springframework.beans.DirectFieldAccessor;
+import org.springframework.core.convert.converter.Converter;
 import org.springframework.instrument.classloading.ShadowingClassLoader;
+import org.springframework.lang.Nullable;
 
 /**
  * Unit tests for {@link RedisCacheConfiguration}.
@@ -43,4 +45,26 @@ public void shouldSetClassLoader() {
 
 		assertThat(usedClassLoader).isSameAs(classLoader);
 	}
+
+	@Test // DATAREDIS-1032
+	public void shouldAllowConverterRegistration() {
+
+		RedisCacheConfiguration config = RedisCacheConfiguration.defaultCacheConfig();
+		config.configureKeyConverters(registry -> registry.addConverter(new DomainTypeConverter()));
+
+		assertThat(config.getConversionService().canConvert(DomainType.class, String.class)).isTrue();
+	}
+
+	private static class DomainType {
+
+	}
+
+	static class DomainTypeConverter implements Converter<DomainType, String> {
+
+		@Nullable
+		@Override
+		public String convert(DomainType source) {
+			return null;
+		}
+	}
 }