Fix new Sonar smells

* Use method chain in the `AggregatorSpec.processor()`
* Add JavaDoc to the `AvroHeaders.PREFIX`

spring-integration-core/src/main/java/org/springframework/integration/dsl/AggregatorSpec.java

@@ -66,10 +66,10 @@ public class AggregatorSpec extends CorrelationHandlerSpec<AggregatorSpec, Aggre
 	 * @return the handler spec.
 	 */
 	public AggregatorSpec processor(Object target, String methodName) {
-		super.processor(target);
-		return outputProcessor(methodName != null
-				? new MethodInvokingMessageGroupProcessor(target, methodName)
-				: new MethodInvokingMessageGroupProcessor(target));
+		return super.processor(target)
+				.outputProcessor(methodName != null
+						? new MethodInvokingMessageGroupProcessor(target, methodName)
+						: new MethodInvokingMessageGroupProcessor(target));
 	}
 
 	/**

spring-integration-core/src/main/java/org/springframework/integration/transformer/SimpleFromAvroTransformer.java

@@ -39,6 +39,8 @@ import org.springframework.util.ClassUtils;
  * from {@code byte[]}.
  *
  * @author Gary Russell
+ * @author Artem Bilan
+ *
  * @since 5.2
  *
  */
@@ -48,8 +50,8 @@ public class SimpleFromAvroTransformer extends AbstractTransformer implements Be
 
 	private final DecoderFactory decoderFactory = new DecoderFactory();
 
-	private Expression typeIdExpression = new FunctionExpression<Message<?>>(
-			msg -> msg.getHeaders().get(AvroHeaders.TYPE));
+	private Expression typeIdExpression =
+			new FunctionExpression<Message<?>>((message) -> message.getHeaders().get(AvroHeaders.TYPE));
 
 	private EvaluationContext evaluationContext;
 
@@ -76,11 +78,15 @@ public class SimpleFromAvroTransformer extends AbstractTransformer implements Be
 	 * @return the transformer
 	 */
 	public SimpleFromAvroTransformer typeExpression(Expression expression) {
-		Assert.notNull(expression, "'expression' must not be null");
+		assertExpressionNotNull(expression);
 		this.typeIdExpression = expression;
 		return this;
 	}
 
+	private void assertExpressionNotNull(Object expression) {
+		Assert.notNull(expression, "'expression' must not be null");
+	}
+
 	/**
 	 * Set the expression to evaluate against the message to determine the type id.
 	 * Default {@code headers['avro_type']}.
@@ -88,7 +94,7 @@ public class SimpleFromAvroTransformer extends AbstractTransformer implements Be
 	 * @return the transformer
 	 */
 	public SimpleFromAvroTransformer typeExpression(String expression) {
-		Assert.notNull(expression, "'expression' must not be null");
+		assertExpressionNotNull(expression);
 		this.typeIdExpression = EXPRESSION_PARSER.parseExpression(expression);
 		return this;
 	}
@@ -99,7 +105,7 @@ public class SimpleFromAvroTransformer extends AbstractTransformer implements Be
 	 * @param expression the expression.
 	 */
 	public void setTypeExpression(Expression expression) {
-		Assert.notNull(expression, "'expression' must not be null");
+		assertExpressionNotNull(expression);
 		this.typeIdExpression = expression;
 	}
 
@@ -109,7 +115,7 @@ public class SimpleFromAvroTransformer extends AbstractTransformer implements Be
 	 * @param expression the expression.
 	 */
 	public void setTypeExpression(String expression) {
-		Assert.notNull(expression, "'expression' must not be null");
+		assertExpressionNotNull(expression);
 		this.typeIdExpression = EXPRESSION_PARSER.parseExpression(expression);
 	}
 
@@ -147,5 +153,4 @@ public class SimpleFromAvroTransformer extends AbstractTransformer implements Be
 		}
 	}
 
-
 }

spring-integration-core/src/main/java/org/springframework/integration/transformer/support/AvroHeaders.java

@@ -20,6 +20,8 @@ package org.springframework.integration.transformer.support;
  * Pre-defined names and prefixes for Apache Avro related headers.
  *
  * @author Gary Russell
+ * @author Artem Bilan
+ *
  * @since 5.2
  */
 public final class AvroHeaders {
@@ -28,11 +30,14 @@ public final class AvroHeaders {
 		super();
 	}
 
-	public static final String PREFIX = "avro";
+	/**
+	 * The prefix for Apache Avro specific message headers.
+	 */
+	public static final String PREFIX = "avro_";
 
 	/**
 	 * The {@code SpecificRecord} type.
 	 */
-	public static final String TYPE = PREFIX + "_type";
+	public static final String TYPE = PREFIX + "type";
 
 }

spring-integration-rsocket/src/main/java/org/springframework/integration/rsocket/AbstractRSocketConnector.java

@@ -27,7 +27,6 @@ import org.springframework.core.codec.CharSequenceEncoder;
 import org.springframework.core.codec.StringDecoder;
 import org.springframework.core.io.buffer.DefaultDataBufferFactory;
 import org.springframework.messaging.rsocket.RSocketStrategies;
-import org.springframework.messaging.rsocket.annotation.support.DefaultMetadataExtractor;
 import org.springframework.messaging.rsocket.annotation.support.MetadataExtractor;
 import org.springframework.util.Assert;
 import org.springframework.util.MimeType;
@@ -126,8 +125,9 @@ public abstract class AbstractRSocketConnector
 	/**
 	 * Configure a {@link MetadataExtractor} to extract the route and possibly
 	 * other metadata from the first payload of incoming requests.
-	 * <p>By default this is a {@link DefaultMetadataExtractor} with the
-	 * configured {@link RSocketStrategies} (and decoders), extracting a route
+	 * <p>By default this is a
+	 * {@link org.springframework.messaging.rsocket.annotation.support.DefaultMetadataExtractor}
+	 * with the configured {@link RSocketStrategies} (and decoders), extracting a route
 	 * from {@code "message/x.rsocket.routing.v0"} or {@code "text/plain"}
 	 * metadata entries.
 	 * @param extractor the extractor to use