Move identityConverter to Converters.

Move the no op identity converter to Converters and reuse those across the connection package.
Fix nullables and minor code format issues along the way.

See: #1951
Original Pull Request: #1960

Author: christophstrobl

src/main/java/org/springframework/data/redis/connection/DefaultStringRedisConnection.java

@@ -76,6 +76,17 @@ abstract public class Converters {
 	private static final byte[] ZERO = new byte[] { '0' };
 	private static final String CLUSTER_NODES_LINE_SEPARATOR = "\n";
 
+	/**
+	 * Returns a {@link Converter} that always returns its input argument.
+	 *
+	 * @param <T> the type of the input and output objects to the function
+	 * @return a function that always returns its input argument
+	 * @since 2.5
+	 */
+	public static <T> Converter<T, T> identityConverter() {
+		return t -> t;
+	}
+
 	public static Boolean stringToBoolean(String source) {
 		return ObjectUtils.nullSafeEquals("OK", source);
 	}

src/main/java/org/springframework/data/redis/connection/convert/Converters.java

@@ -21,7 +21,6 @@
 import java.util.stream.Collectors;
 
 import org.springframework.core.convert.converter.Converter;
-import org.springframework.lang.NonNull;
 import org.springframework.util.Assert;
 
 /**
@@ -50,7 +49,6 @@ public SetConverter(Converter<S, T> itemConverter) {
 	 * @see org.springframework.core.convert.converter.Converter#convert(Object)
 	 */
 	@Override
-	@NonNull
 	public Set<T> convert(Set<S> source) {
 
 		return source.stream().map(itemConverter::convert)

src/main/java/org/springframework/data/redis/connection/convert/SetConverter.java

@@ -21,7 +21,6 @@
 import org.springframework.core.convert.converter.Converter;
 import org.springframework.data.redis.core.types.RedisClientInfo;
 import org.springframework.data.redis.core.types.RedisClientInfo.RedisClientInfoBuilder;
-import org.springframework.lang.NonNull;
 
 /**
  * {@link Converter} implementation to create one {@link RedisClientInfo} per line entry in given {@link String} array.
@@ -43,7 +42,6 @@ public class StringToRedisClientInfoConverter implements Converter<String[], Lis
 	 * @see org.springframework.core.convert.converter.Converter#convert(Object)
 	 */
 	@Override
-	@NonNull
 	public List<RedisClientInfo> convert(String[] lines) {
 
 		List<RedisClientInfo> clientInfoList = new ArrayList<>(lines.length);

src/main/java/org/springframework/data/redis/connection/convert/StringToRedisClientInfoConverter.java

@@ -79,7 +79,6 @@ public class JedisConnection extends AbstractRedisConnection {
 			nullDefault) -> doInvoke(true, directFunction, pipelineFunction, converter, nullDefault));
 
 	private final @Nullable Pool<Jedis> pool;
-	private final int dbIndex;
 	private final String clientName;
 
 	private List<JedisResult> pipelinedResults = new ArrayList<>();
@@ -124,7 +123,6 @@ protected JedisConnection(Jedis jedis, @Nullable Pool<Jedis> pool, int dbIndex,
 
 		this.jedis = jedis;
 		this.pool = pool;
-		this.dbIndex = dbIndex;
 		this.clientName = clientName;
 
 		// select the db

src/main/java/org/springframework/data/redis/connection/jedis/JedisConnection.java

@@ -29,6 +29,7 @@
 import java.util.function.Supplier;
 
 import org.springframework.core.convert.converter.Converter;
+import org.springframework.data.redis.connection.convert.Converters;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
@@ -65,16 +66,6 @@ class JedisInvoker {
 		this.synchronizer = synchronizer;
 	}
 
-	/**
-	 * Returns a {@link Converter} that always returns its input argument.
-	 *
-	 * @param <T> the type of the input and output objects to the function
-	 * @return a function that always returns its input argument
-	 */
-	static <T> Converter<T, T> identityConverter() {
-		return t -> t;
-	}
-
 	/**
 	 * Invoke the {@link ConnectionFunction0} and return its result.
 	 *
@@ -87,7 +78,7 @@ <R> R just(ConnectionFunction0<R> function) {
 
 		return synchronizer.invoke(function::apply, it -> {
 			throw new UnsupportedOperationException("Operation not supported in pipelining/transaction mode");
-		}, identityConverter(), () -> null);
+		}, Converters.identityConverter(), () -> null);
 	}
 
 	/**
@@ -102,7 +93,7 @@ <R> R just(ConnectionFunction0<R> function, PipelineFunction0<R> pipelineFunctio
 		Assert.notNull(function, "ConnectionFunction must not be null!");
 		Assert.notNull(pipelineFunction, "PipelineFunction must not be null!");
 
-		return synchronizer.invoke(function::apply, pipelineFunction::apply, identityConverter(), () -> null);
+		return synchronizer.invoke(function::apply, pipelineFunction::apply, Converters.identityConverter(), () -> null);
 	}
 
 	/**
@@ -568,7 +559,7 @@ interface ManyInvocationSpec<S> {
 		 * @return the result as {@link List}.
 		 */
 		default List<S> toList() {
-			return toList(identityConverter());
+			return toList(Converters.identityConverter());
 		}
 
 		/**
@@ -587,7 +578,7 @@ default List<S> toList() {
 		 * @return the result as {@link Set}.
 		 */
 		default Set<S> toSet() {
-			return toSet(identityConverter());
+			return toSet(Converters.identityConverter());
 		}
 
 		/**
@@ -915,8 +906,9 @@ static class DefaultSingleInvocationSpec<S> implements SingleInvocationSpec<S> {
 		private final Function<MultiKeyPipelineBase, Response<S>> parentPipelineFunction;
 		private final Synchronizer synchronizer;
 
-		public DefaultSingleInvocationSpec(Function<Jedis, S> parentFunction,
+		DefaultSingleInvocationSpec(Function<Jedis, S> parentFunction,
 				Function<MultiKeyPipelineBase, Response<S>> parentPipelineFunction, Synchronizer synchronizer) {
+
 			this.parentFunction = parentFunction;
 			this.parentPipelineFunction = parentPipelineFunction;
 			this.synchronizer = synchronizer;
@@ -946,7 +938,7 @@ static class DefaultManyInvocationSpec<S> implements ManyInvocationSpec<S> {
 		private final Function<MultiKeyPipelineBase, Response<Collection<S>>> parentPipelineFunction;
 		private final Synchronizer synchronizer;
 
-		public DefaultManyInvocationSpec(Function<Jedis, ? extends Collection<S>> parentFunction,
+		DefaultManyInvocationSpec(Function<Jedis, ? extends Collection<S>> parentFunction,
 				Function<MultiKeyPipelineBase, Response<? extends Collection<S>>> parentPipelineFunction,
 				Synchronizer synchronizer) {
 
@@ -1008,7 +1000,7 @@ interface Synchronizer {
 		@SuppressWarnings({ "unchecked", "rawtypes" })
 		default <I, T> T invoke(Function<Jedis, I> callFunction,
 				Function<MultiKeyPipelineBase, Response<I>> pipelineFunction) {
-			return (T) doInvoke((Function) callFunction, (Function) pipelineFunction, identityConverter(), () -> null);
+			return (T) doInvoke((Function) callFunction, (Function) pipelineFunction, Converters.identityConverter(), () -> null);
 		}
 
 		@Nullable

src/main/java/org/springframework/data/redis/connection/jedis/JedisInvoker.java

@@ -176,9 +176,6 @@ protected ScanIteration<byte[]> doScan(long cursorId, ScanOptions options) {
 			protected void doClose() {
 				JedisKeyCommands.this.connection.close();
 			}
-
-			;
-
 		}.open();
 	}
 

src/main/java/org/springframework/data/redis/connection/jedis/JedisKeyCommands.java

@@ -27,6 +27,7 @@
 import java.util.function.Supplier;
 
 import org.springframework.core.convert.converter.Converter;
+import org.springframework.data.redis.connection.convert.Converters;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
@@ -66,16 +67,6 @@ class LettuceInvoker {
 		this.synchronizer = synchronizer;
 	}
 
-	/**
-	 * Returns a {@link Converter} that always returns its input argument.
-	 *
-	 * @param <T> the type of the input and output objects to the function
-	 * @return a function that always returns its input argument
-	 */
-	static <T> Converter<T, T> identityConverter() {
-		return t -> t;
-	}
-
 	/**
 	 * Invoke the {@link ConnectionFunction0} and return its result.
 	 *
@@ -86,7 +77,7 @@ <R> R just(ConnectionFunction0<R> function) {
 
 		Assert.notNull(function, "ConnectionFunction must not be null!");
 
-		return synchronizer.invoke(() -> function.apply(connection), identityConverter(), () -> null);
+		return synchronizer.invoke(() -> function.apply(connection), Converters.identityConverter(), () -> null);
 	}
 
 	/**
@@ -421,7 +412,7 @@ interface ManyInvocationSpec<S> {
 		 * @return the result as {@link List}.
 		 */
 		default List<S> toList() {
-			return toList(identityConverter());
+			return toList(Converters.identityConverter());
 		}
 
 		/**
@@ -440,7 +431,7 @@ default List<S> toList() {
 		 * @return the result as {@link Set}.
 		 */
 		default Set<S> toSet() {
-			return toSet(identityConverter());
+			return toSet(Converters.identityConverter());
 		}
 
 		/**
@@ -665,12 +656,13 @@ public <T> Set<T> toSet(Converter<S, T> converter) {
 	/**
 	 * Interface to define a synchronization function to evaluate {@link RedisFuture}.
 	 */
+	@FunctionalInterface
 	interface Synchronizer {
 
 		@Nullable
 		@SuppressWarnings({ "unchecked", "rawtypes" })
 		default <I, T> T invoke(Supplier<RedisFuture<I>> futureSupplier) {
-			return (T) doInvoke((Supplier) futureSupplier, identityConverter(), () -> null);
+			return (T) doInvoke((Supplier) futureSupplier, Converters.identityConverter(), () -> null);
 		}
 
 		@Nullable

src/main/java/org/springframework/data/redis/connection/lettuce/LettuceInvoker.java

@@ -26,6 +26,7 @@
 import java.util.Set;
 
 import org.springframework.data.redis.connection.RedisZSetCommands;
+import org.springframework.data.redis.connection.convert.Converters;
 import org.springframework.data.redis.core.Cursor;
 import org.springframework.data.redis.core.KeyBoundCursor;
 import org.springframework.data.redis.core.ScanIteration;
@@ -185,7 +186,7 @@ public Set<byte[]> zRevRange(byte[] key, long start, long end) {
 		Assert.notNull(key, "Key must not be null!");
 
 		return connection.invoke().fromMany(RedisSortedSetAsyncCommands::zrevrange, key, start, end)
-				.toSet(LettuceInvoker.identityConverter());
+				.toSet(Converters.identityConverter());
 	}
 
 	/*