Fix Sonar smells for XML module

Author: artembilan

spring-integration-xml/src/main/java/org/springframework/integration/xml/DefaultXmlPayloadConverter.java

@@ -71,12 +71,7 @@ else if (object instanceof Node) {
 			}
 			else if (object instanceof DOMSource) {
 				Node node = ((DOMSource) object).getNode();
-				if (node instanceof Document) {
-					return (Document) node;
-				}
-				else {
-					return nodeToDocument(node);
-				}
+				return nodeToDocument(node);
 			}
 			else if (object instanceof Source) {
 				InputSource inputSource = sourceToInputSource((Source) object);
@@ -111,6 +106,9 @@ private static InputSource sourceToInputSource(Source source) {
 	}
 
 	protected Document nodeToDocument(Node node) {
+		if (node instanceof Document) {
+			return (Document) node;
+		}
 		Document document = getDocumentBuilder().newDocument();
 		document.appendChild(document.importNode(node, true));
 		return document;

spring-integration-xml/src/main/java/org/springframework/integration/xml/transformer/UnmarshallingTransformer.java

@@ -19,6 +19,7 @@
 import java.io.ByteArrayInputStream;
 import java.io.File;
 import java.io.IOException;
+import java.io.UncheckedIOException;
 
 import javax.xml.transform.Source;
 import javax.xml.transform.dom.DOMSource;
@@ -29,7 +30,6 @@
 import org.springframework.integration.transformer.AbstractPayloadTransformer;
 import org.springframework.integration.xml.source.DomSourceFactory;
 import org.springframework.integration.xml.source.SourceFactory;
-import org.springframework.messaging.MessagingException;
 import org.springframework.oxm.Unmarshaller;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
@@ -96,8 +96,7 @@ public String getComponentType() {
 
 	@Override
 	public Object transformPayload(Object payload) {
-		Source source = null;
-
+		Source source;
 		try {
 			if (this.mimeMessageUnmarshallerHelper != null) {
 				Object result = this.mimeMessageUnmarshallerHelper.maybeUnmarshalMimeMessage(payload);
@@ -127,15 +126,14 @@ else if (payload instanceof Source) {
 			else {
 				source = this.sourceFactory.createSource(payload);
 			}
-			if (source == null) {
-				throw new MessagingException(
-						"failed to transform message, payload not assignable from " + Source.class.getName()
-								+ "and no conversion possible");
-			}
+			Assert.state(source != null, () ->
+					"failed to transform message, payload not assignable from " + Source.class.getName()
+							+ "and no conversion possible");
+
 			return this.unmarshaller.unmarshal(source);
 		}
 		catch (IOException e) {
-			throw new MessagingException("failed to unmarshal payload", e);
+			throw new UncheckedIOException("failed to unmarshal payload", e);
 		}
 	}
 

spring-integration-xml/src/main/java/org/springframework/integration/xml/transformer/XsltPayloadTransformer.java

@@ -156,9 +156,9 @@ public XsltPayloadTransformer(Resource xslResource, ResultTransformer resultTran
 			String transformerFactoryClassName) {
 
 		Assert.notNull(xslResource, "'xslResource' must not be null.");
-		Assert.isTrue(xslResource instanceof ClassPathResource || // NOSONAR boolean complexity
+		Assert.isTrue(xslResource instanceof ClassPathResource ||
 						xslResource instanceof FileSystemResource ||
-						xslResource instanceof VfsResource ||
+						xslResource instanceof VfsResource || // NOSONAR boolean complexity
 						(SERVLET_CONTEXT_RESOURCE_CLASS != null
 								&& SERVLET_CONTEXT_RESOURCE_CLASS.isInstance(xslResource)),
 				"Only 'ClassPathResource', 'FileSystemResource', 'ServletContextResource' or 'VfsResource'" +