diff --git a/Backend/xslt-rest/pom.xml b/Backend/xslt-rest/pom.xml
index db97ca3..4f593b2 100644
--- a/Backend/xslt-rest/pom.xml
+++ b/Backend/xslt-rest/pom.xml
@@ -14,6 +14,7 @@
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     <jackson.version>2.14.1</jackson.version>
     <slf4j.version>2.0.6</slf4j.version>
+    <log4j.version>2.19.0</log4j.version>
   </properties>
 
   <build>
@@ -77,7 +78,7 @@
     <dependency>
       <groupId>com.sparkjava</groupId>
       <artifactId>spark-core</artifactId>
-      <version>2.9.3</version>
+      <version>2.9.4</version>
     </dependency>
 
     <!--    JSON    -->
@@ -133,8 +134,15 @@
     <dependency>
       <groupId>org.apache.logging.log4j</groupId>
       <artifactId>log4j-core</artifactId>
-      <version>2.19.0</version>
+      <version>${log4j.version}</version>
     </dependency>
 
+    <dependency>
+      <groupId>org.apache.logging.log4j</groupId>
+      <artifactId>log4j-api</artifactId>
+      <version>${log4j.version}</version>
+    </dependency>
+
+
   </dependencies>
 </project>
\ No newline at end of file
diff --git a/Backend/xslt-rest/src/main/java/com/r11/tools/xslt/SparkInitializer.java b/Backend/xslt-rest/src/main/java/com/r11/tools/xslt/SparkInitializer.java
index 8464c6f..e17ad41 100644
--- a/Backend/xslt-rest/src/main/java/com/r11/tools/xslt/SparkInitializer.java
+++ b/Backend/xslt-rest/src/main/java/com/r11/tools/xslt/SparkInitializer.java
@@ -4,6 +4,8 @@ import com.fasterxml.jackson.databind.JsonMappingException;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.r11.tools.xslt.processors.Saxon;
 import com.r11.tools.xslt.processors.Xalan;
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
 import spark.*;
 
 import java.util.HashMap;
@@ -14,6 +16,9 @@ import java.util.Map;
  * @author Wojciech Czop
  */
 public class SparkInitializer {
+
+    private static final Logger LOG = LogManager.getLogger(SparkInitializer.class);
+
     /**
      * Initializes spark framework
      */
@@ -32,17 +37,19 @@ public class SparkInitializer {
         Spark.post("/xpathpost", xpathHandler);
         Spark.post("/xsdpost", xsdHandler);
         Spark.get("/procinfo", procinfoHandler);
-        System.out.println("Server is online");
+
+        LOG.info("Server is online at port: " + Spark.port());
     }
 
     /**
      * Handler that returns processor version
      */
-    private static Route procinfoHandler = (Request req, Response resp) -> {
+    private static final Route procinfoHandler = (Request req, Response resp) -> {
         try {
             resp.header("processor", "Saxon " + Saxon.getVersion() + " over s9api");
             return Saxon.getVersion();
         } catch (Exception ex) {
+            LOG.error("Error on retrieving engine version. " + ex);
             return ex.getMessage();
         }
     };
@@ -51,11 +58,10 @@ public class SparkInitializer {
      * Handler that returns info if document is valid
      * Also provides info about request time and processor
      */
-    private static Route xsdHandler = (Request req, Response resp) -> {
+    private static final Route xsdHandler = (Request req, Response resp) -> {
         String body = req.body();
-        System.out.println("Request: " + body);
         ObjectMapper mapper = new ObjectMapper();
-        Map<String, String> requestMap = null;
+        Map<String, String> requestMap = new HashMap<>();
         Map<String, String> responseMap = new HashMap<>();
         try {
             requestMap = mapper.readValue(body, Map.class);
@@ -65,8 +71,6 @@ public class SparkInitializer {
 
         String data = requestMap.get("data");
         String xsd = requestMap.get("process");
-        String processor = requestMap.get("processor");
-        String version = requestMap.get("version");
 
         resp.header("processor", Xalan.getVersion());
         long timeStart = System.currentTimeMillis();
@@ -76,12 +80,13 @@ public class SparkInitializer {
             responseMap.put("result", tmp);
             responseMap.put("status", "OK");
         } catch (Exception ex) {
-            System.out.println("Exception: "+ex.getMessage());
+            LOG.error("Error on validation against XSD using Xalan. " + ex);
             responseMap.put("result", ex.getMessage());
             responseMap.put("status", "ERR");
             resp.status(400);
         }
         long duration = System.currentTimeMillis() - timeStart;
+        LOG.info("Request: " + body + " processed in " + duration + " ms.");
         responseMap.put("processor", Xalan.getVersion());
         responseMap.put("time", "" + duration);
         resp.body(mapper.writeValueAsString(responseMap));
@@ -91,17 +96,15 @@ public class SparkInitializer {
     /**
      * Handler that returns output of xpath query and processor data
      */
-    private static Route xpathHandler = (Request req, Response resp) -> {
-
+    private static final Route xpathHandler = (Request req, Response resp) -> {
         String body = req.body();
-        System.out.println("Request: " + body);
         ObjectMapper mapper = new ObjectMapper();
-        Map<String, String> requestMap = null;
+        Map<String, String> requestMap = new HashMap<>();
         Map<String, String> responseMap = new HashMap<>();
         try {
             requestMap = mapper.readValue(body, Map.class);
         } catch (JsonMappingException ex) {
-            ex.printStackTrace();
+            LOG.error("JSON mapping error. " + ex);
         }
 
         String data = requestMap.get("data");
@@ -109,6 +112,7 @@ public class SparkInitializer {
         String processor = requestMap.get("processor");
         String version = requestMap.get("version");
 
+
         String tmp = "";
         long timeStart;
         long duration;
@@ -116,70 +120,66 @@ public class SparkInitializer {
         if (processor == null) {
             return "saxon, xalan";
         }
-        try {
-            switch (processor) {
-                case "saxon":
-                    resp.header("processor", "Saxon " + Saxon.getVersion() + " " + version + " over s9api");
-                    System.out.print("Processing start...");
-                    timeStart = System.currentTimeMillis();
-                    try {
-                        tmp = Saxon.processXPath(data, query, version).trim();
-                        responseMap.put("result", tmp);
-                        responseMap.put("status", "OK");
-                    } catch (Exception ex) {
-                        responseMap.put("result", ex.getMessage());
-                        responseMap.put("status", "ERR");
-                        resp.status(400);
-                    }
-                    duration = System.currentTimeMillis() - timeStart;
-                    System.out.println("end(" + duration + ")");
-                    responseMap.put("processor", "Saxon " + Saxon.getVersion() + " " + version + " over s9api");
-                    responseMap.put("time", "" + duration);
-                    resp.body(mapper.writeValueAsString(responseMap));
-                    return resp;
 
-                case "xalan":
-                    resp.header("processor", Xalan.getVersion());
-                    timeStart = System.currentTimeMillis();
-                    try {
-                        tmp = Xalan.processXPath(data, query).trim();
-                        responseMap.put("result", tmp);
-                        responseMap.put("status", "OK");
-                    } catch (Exception ex) {
-                        responseMap.put("result", ex.getMessage());
-                        responseMap.put("status", "ERR");
-                        resp.status(400);
-                    }
-                    duration = System.currentTimeMillis() - timeStart;
-                    responseMap.put("processor", Xalan.getVersion());
+        switch (processor) {
+            case "saxon":
+                resp.header("processor", "Saxon " + Saxon.getVersion() + " " + version + " over s9api");
+                timeStart = System.currentTimeMillis();
+                try {
+                    tmp = Saxon.processXPath(data, query, version).trim();
                     responseMap.put("result", tmp);
-                    responseMap.put("time", Long.toString(duration));
-                    resp.body(mapper.writeValueAsString(responseMap));
-                    return resp;
+                    responseMap.put("status", "OK");
+                } catch (Exception ex) {
+                    LOG.error("Error on processing XPath using Saxon. " + ex);
+                    responseMap.put("result", ex.getMessage());
+                    responseMap.put("status", "ERR");
+                    resp.status(400);
+                }
+                duration = System.currentTimeMillis() - timeStart;
+                LOG.info("Request" + body + " processed in " + duration + " ms.");
+                responseMap.put("processor", "Saxon " + Saxon.getVersion() + " " + version + " over s9api");
+                responseMap.put("time", "" + duration);
+                resp.body(mapper.writeValueAsString(responseMap));
+                return resp;
 
-                default:
-                    return "saxon, xalan";
-            }
+            case "xalan":
+                resp.header("processor", Xalan.getVersion());
+                timeStart = System.currentTimeMillis();
+                try {
+                    tmp = Xalan.processXPath(data, query).trim();
+                    responseMap.put("result", tmp);
+                    responseMap.put("status", "OK");
+                } catch (Exception ex) {
+                    LOG.error("Error on processing XPath using Xalan. " + ex);
+                    responseMap.put("result", ex.getMessage());
+                    responseMap.put("status", "ERR");
+                    resp.status(400);
+                }
+                duration = System.currentTimeMillis() - timeStart;
+                LOG.info("Request: " + body + " processed in " + duration + " ms.");
+                responseMap.put("processor", Xalan.getVersion());
+                responseMap.put("result", tmp);
+                responseMap.put("time", Long.toString(duration));
+                resp.body(mapper.writeValueAsString(responseMap));
+                return resp;
 
-        } catch (Exception ex) {
-            ex.printStackTrace();
-            return ex.getMessage();
+            default:
+                return "saxon, xalan";
         }
     };
 
     /**
      * Handler that returns outcome of xslt transformation and processor data
      */
-    private static Route xsltHandler = (Request req, Response resp) -> {
+    private static final Route xsltHandler = (Request req, Response resp) -> {
         String body = req.body();
         ObjectMapper mapper = new ObjectMapper();
-        Map<String, String> jsonMap = null;
+        Map<String, String> jsonMap = new HashMap<>();
         Map<String, String> responseMap = new HashMap<>();
         try {
             jsonMap = mapper.readValue(body, Map.class);
-            System.out.println(jsonMap);
         } catch (JsonMappingException ex) {
-            ex.printStackTrace();
+            LOG.error("JSON mapping error. " + ex);
         }
         String data = jsonMap.get("data");
         String query = jsonMap.get("process");
@@ -189,52 +189,51 @@ public class SparkInitializer {
         if (processor == null) {
             return "saxon, xalan";
         }
-        try {
-            String tmp;
-            long timeStart;
-            long duration;
-            switch (processor) {
-                case "saxon":
-                    timeStart = System.currentTimeMillis();
-                    try {
-                        tmp = Saxon.processXSLT(data, query);
-                        responseMap.put("result", tmp);
-                        responseMap.put("status", "OK");
-                    } catch (Exception ex) {
-                        responseMap.put("result", ex.getMessage());
-                        responseMap.put("status", "ERR");
-                        resp.status(400);
-                    }
 
+        String tmp;
+        long timeStart;
+        long duration;
+        switch (processor) {
+            case "saxon":
+                timeStart = System.currentTimeMillis();
+                try {
+                    tmp = Saxon.processXSLT(data, query);
+                    responseMap.put("result", tmp);
+                    responseMap.put("status", "OK");
+                } catch (Exception ex) {
+                    LOG.error("Error on processing XSLT using Saxon. " + ex);
+                    responseMap.put("result", ex.getMessage());
+                    responseMap.put("status", "ERR");
+                    resp.status(400);
+                }
+                duration = System.currentTimeMillis() - timeStart;
+                LOG.info("Request: " + body + " processed in " + duration + " ms.");
+                responseMap.put("processor", "Saxon " + Saxon.getVersion() + " " + version);
+                responseMap.put("time", Long.toString(duration));
+                resp.body(mapper.writeValueAsString(responseMap));
+                return resp;
 
-                    duration = System.currentTimeMillis() - timeStart;
-                    responseMap.put("processor", "Saxon " + Saxon.getVersion() + " " + version);
-                    responseMap.put("time", Long.toString(duration));
-                    resp.body(mapper.writeValueAsString(responseMap));
-                    return resp;
+            case "xalan":
+                timeStart = System.currentTimeMillis();
+                try {
+                    tmp = Xalan.processXSLT(data, query);
+                    responseMap.put("result", tmp);
+                    responseMap.put("status", "OK");
+                } catch (Exception ex) {
+                    LOG.error("Error on processing XSLT using Xalan. " + ex);
+                    responseMap.put("result", ex.getMessage());
+                    responseMap.put("status", "ERR");
+                    resp.status(400);
+                }
+                duration = System.currentTimeMillis() - timeStart;
+                LOG.info("Request: " + body + " processed in " + duration + " ms.");
+                responseMap.put("processor", Xalan.getVersion());
+                responseMap.put("time", Long.toString(duration));
+                resp.body(mapper.writeValueAsString(responseMap));
+                return resp;
 
-                case "xalan":
-                    timeStart = System.currentTimeMillis();
-                    try {
-                        tmp = Xalan.processXSLT(data, query);
-                        responseMap.put("result", tmp);
-                        responseMap.put("status", "OK");
-                    } catch (Exception ex) {
-                        responseMap.put("result", ex.getMessage());
-                        responseMap.put("status", "ERR");
-                        resp.status(400);
-                    }
-                    duration = System.currentTimeMillis() - timeStart;
-                    responseMap.put("processor", Xalan.getVersion());
-                    responseMap.put("time", Long.toString(duration));
-                    resp.body(mapper.writeValueAsString(responseMap));
-                    return resp;
-
-                default:
-                    return "saxon, xalan";
-            }
-        } catch (Exception ex) {
-            return ex.getMessage();
+            default:
+                return "saxon, xalan";
         }
     };
 }
diff --git a/Backend/xslt-rest/src/main/java/com/r11/tools/xslt/processors/NewNamespaceResolver.java b/Backend/xslt-rest/src/main/java/com/r11/tools/xslt/processors/NewNamespaceResolver.java
index f89da0b..ba8a439 100644
--- a/Backend/xslt-rest/src/main/java/com/r11/tools/xslt/processors/NewNamespaceResolver.java
+++ b/Backend/xslt-rest/src/main/java/com/r11/tools/xslt/processors/NewNamespaceResolver.java
@@ -1,11 +1,10 @@
 package com.r11.tools.xslt.processors;
 
-import net.sf.saxon.om.NamespaceBinding;
 import net.sf.saxon.om.NamespaceMap;
 import net.sf.saxon.s9api.XPathCompiler;
 import net.sf.saxon.s9api.XdmNode;
-
-import java.util.Iterator;
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
 
 /**
  * Handler for saxon namespace scan engine.
@@ -13,6 +12,7 @@ import java.util.Iterator;
  * @author Wojciech Czop
  */
 public class NewNamespaceResolver {
+    private static final Logger LOG = LogManager.getLogger("NewNamespaceResolver");
 
     private NamespaceMap namespaceMap;
 
@@ -21,12 +21,13 @@ public class NewNamespaceResolver {
      * @param doc dom structure object
      * @return map of namespaces
      */
+
+    // TODO: Closer inspection. Return value is never used according to IntelliJ
+    //
     public NamespaceMap process(XdmNode doc) {
         namespaceMap = NamespaceMap.emptyMap();
-        Iterator<XdmNode> it = doc.children().iterator();
-//        TODO: remove
-        while (it.hasNext()) {
-            XdmNode tmp = it.next();
+        //        TODO: remove
+        for (XdmNode tmp : doc.children()) {
             extractNamespace(tmp);
         }
 //        end
@@ -38,12 +39,6 @@ public class NewNamespaceResolver {
      * @param compiler compiler used to compile xpath statements
      */
     public void exportNamespaces(XPathCompiler compiler){
-        Iterator<NamespaceBinding> it = namespaceMap.iterator();
-//        TODO: remove
-        while(it.hasNext()){
-            System.out.println(it.next());
-        }
-//        end
         namespaceMap.forEach(namespaceBinding -> compiler.declareNamespace(namespaceBinding.getPrefix(), namespaceBinding.getURI()));
     }
 
@@ -58,17 +53,11 @@ public class NewNamespaceResolver {
         }
         if (node.children().iterator().hasNext()) {
 
-            Iterator<XdmNode> it = node.children().iterator();
-            while (it.hasNext()) {
-                XdmNode rNode = it.next();
-//                TODO: remove
-                if(rNode.getUnderlyingNode().getPrefix().isEmpty() && !rNode.getParent().getUnderlyingNode().getPrefix().isEmpty()){
-
-                    System.out.println("prefix missing, parent has "+rNode.getParent().getUnderlyingNode().getPrefix() + ", but child has none");
-
-                    System.out.println();
+            for (XdmNode rNode : node.children()) {
+                if (rNode.getUnderlyingNode().getPrefix().isEmpty() && !rNode.getParent().getUnderlyingNode().getPrefix().isEmpty()) {
+                    LOG.warn("Missing prefix. Parent has " + rNode.getParent().getUnderlyingNode().getPrefix() + ", but child has none");
                 }
-//                end
+
                 extractNamespace(rNode);
             }
         }
diff --git a/Backend/xslt-rest/src/main/java/com/r11/tools/xslt/processors/Saxon.java b/Backend/xslt-rest/src/main/java/com/r11/tools/xslt/processors/Saxon.java
index 34ee6a4..f4f10fe 100644
--- a/Backend/xslt-rest/src/main/java/com/r11/tools/xslt/processors/Saxon.java
+++ b/Backend/xslt-rest/src/main/java/com/r11/tools/xslt/processors/Saxon.java
@@ -1,6 +1,9 @@
 package com.r11.tools.xslt.processors;
 
 import net.sf.saxon.s9api.*;
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+
 import javax.xml.transform.stream.StreamSource;
 import java.io.StringReader;
 import java.io.StringWriter;
diff --git a/Backend/xslt-rest/src/main/java/com/r11/tools/xslt/processors/Xalan.java b/Backend/xslt-rest/src/main/java/com/r11/tools/xslt/processors/Xalan.java
index b85a089..42db619 100644
--- a/Backend/xslt-rest/src/main/java/com/r11/tools/xslt/processors/Xalan.java
+++ b/Backend/xslt-rest/src/main/java/com/r11/tools/xslt/processors/Xalan.java
@@ -1,5 +1,7 @@
 package com.r11.tools.xslt.processors;
 
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
 import org.w3c.dom.Document;
 import org.xml.sax.InputSource;
 
@@ -25,6 +27,7 @@ import java.io.StringWriter;
  * @author Wojciech Czop
  */
 public class Xalan {
+
     /**
      * Transforms string containing xml document via xslt
      * @param data xml to be transformed
diff --git a/Backend/xslt-rest/src/main/resources/log4j2.xml b/Backend/xslt-rest/src/main/resources/log4j2.xml
new file mode 100644
index 0000000..f0933e3
--- /dev/null
+++ b/Backend/xslt-rest/src/main/resources/log4j2.xml
@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<Configuration status="WARN">
+	<Appenders>
+		<Console name="Console" target="SYSTEM_OUT">
+			<PatternLayout pattern="%d{HH:mm:ss.SSS} [%c] %-5level - %msg%n"/>
+		</Console>
+		<File name="File" fileName="/tmp/xml_tools_java_backend.log" append="true">
+			<PatternLayout>
+				<Pattern>%d{HH:mm:ss.SSS} [%c] %-5level - %msg%n</Pattern>
+			</PatternLayout>
+		</File>
+	</Appenders>
+	<Loggers>
+		<Logger name="com.r11.tools.xslt.SparkInitializer" level="info" additivity="true">
+			<AppenderRef ref="Console"/>
+		</Logger>
+		<Root level="info">
+			<AppenderRef ref="File"/>
+		</Root>
+	</Loggers>
+</Configuration>
\ No newline at end of file