Clean up LettuceConverters.

Use lambdas where possible. Deprecate unused methods. Favor LettuceInvoker conversion methods over List to List/List to Set converters.

See #1797
Original Pull Request #1948

Author: mp911de

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

@@ -25,6 +25,8 @@
  */
 public class LongToBooleanConverter implements Converter<Long, Boolean> {
 
+	public static final LongToBooleanConverter INSTANCE = new LongToBooleanConverter();
+
 	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.core.convert.converter.Converter#convert(Object)

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

@@ -35,6 +35,8 @@
  */
 public class StringToRedisClientInfoConverter implements Converter<String[], List<RedisClientInfo>> {
 
+	public static final StringToRedisClientInfoConverter INSTANCE = new StringToRedisClientInfoConverter();
+
 	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.core.convert.converter.Converter#convert(Object)

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

@@ -598,21 +598,23 @@ public List<Object> exec() {
 		isMulti = false;
 
 		try {
+			Converter<Exception, DataAccessException> exceptionConverter = this::convertLettuceAccessException;
+
 			if (isPipelined()) {
 				RedisFuture<TransactionResult> exec = getAsyncDedicatedRedisCommands().exec();
 
 				LettuceTransactionResultConverter resultConverter = new LettuceTransactionResultConverter(
-						new LinkedList<>(txResults), LettuceConverters.exceptionConverter());
+						new LinkedList<>(txResults), exceptionConverter);
 
 				pipeline(newLettuceResult(exec, source -> resultConverter
-						.convert(LettuceConverters.transactionResultUnwrapper().convert((TransactionResult) source))));
+						.convert(LettuceConverters.transactionResultUnwrapper().convert(source))));
 				return null;
 			}
 
-			TransactionResult transactionResult = (getDedicatedRedisCommands()).exec();
+			TransactionResult transactionResult = getDedicatedRedisCommands().exec();
 			List<Object> results = LettuceConverters.transactionResultUnwrapper().convert(transactionResult);
 			return convertPipelineAndTxResults
-					? new LettuceTransactionResultConverter(txResults, LettuceConverters.exceptionConverter()).convert(results)
+					? new LettuceTransactionResultConverter(txResults, exceptionConverter).convert(results)
 					: results;
 		} catch (Exception ex) {
 			throw convertLettuceAccessException(ex);