diff --git a/src/main/java/me/steffenjacobs/jsonmatcher/service/MessageApplicationService.java b/src/main/java/me/steffenjacobs/jsonmatcher/service/MessageApplicationService.java
new file mode 100644
index 0000000..b1610ad
--- /dev/null
+++ b/src/main/java/me/steffenjacobs/jsonmatcher/service/MessageApplicationService.java
@@ -0,0 +1,55 @@
+package me.steffenjacobs.jsonmatcher.service;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Set;
+
+import org.json.JSONObject;
+
+import me.steffenjacobs.jsonmatcher.domain.MappingDTO;
+
+/** @author Steffen Jacobs */
+public class MessageApplicationService {
+
+	/***
+	 * applies the model to a given source object and performs e.g. unit
+	 * transformation
+	 */
+	public String applyModelToJson(String source, Set<MappingDTO<?, ?>> model) {
+
+		final Map<String, MappingDTO<?, ?>> modelBySourceKey = new HashMap<>();
+		for (MappingDTO<?, ?> dto : model) {
+			modelBySourceKey.put(dto.getKeySource(), dto);
+		}
+
+		final JSONObject json = new JSONObject(source);
+
+		final StringBuilder sb = new StringBuilder();
+		sb.append("{");
+		int count = 0;
+		for (String key : json.keySet()) {
+			@SuppressWarnings("rawtypes")
+			MappingDTO m = modelBySourceKey.get(key);
+			Object value = json.get(key);
+			@SuppressWarnings("unchecked")
+			Object result = m.getValueTransformation().apply(value);
+			sb.append("\"");
+			sb.append(m.getKeyTarget());
+			sb.append("\": ");
+			if (result instanceof String) {
+				sb.append("\"");
+				sb.append(result);
+				sb.append("\"");
+			} else {
+				sb.append(result);
+			}
+			count++;
+			if (count < json.length()) {
+				sb.append(", ");
+			}
+
+		}
+		sb.append("}");
+		return sb.toString();
+	}
+}
diff --git a/src/main/java/me/steffenjacobs/jsonmatcher/service/matcher/ValueMatcher.java b/src/main/java/me/steffenjacobs/jsonmatcher/service/matcher/ValueMatcher.java
index d4b54e5..9437cae 100644
--- a/src/main/java/me/steffenjacobs/jsonmatcher/service/matcher/ValueMatcher.java
+++ b/src/main/java/me/steffenjacobs/jsonmatcher/service/matcher/ValueMatcher.java
@@ -15,8 +15,6 @@ public class ValueMatcher {
 
 	public Function<Object, Object> matchValues(Object source, Object target) {
 
-		// TODO handle unit in string and do conversion
-
 		// same types
 		if (source.getClass() == target.getClass()) {
 
diff --git a/src/test/java/me/steffenjacobs/jsonmatcher/TestMapperWithBigList.java b/src/test/java/me/steffenjacobs/jsonmatcher/TestMapperWithBigList.java
index dde3dc9..3ffd1ce 100644
--- a/src/test/java/me/steffenjacobs/jsonmatcher/TestMapperWithBigList.java
+++ b/src/test/java/me/steffenjacobs/jsonmatcher/TestMapperWithBigList.java
@@ -71,7 +71,7 @@ public void testMapperWithBigList() throws IOException, URISyntaxException {
 		testForList(new TestDataGenerator().generateSampled());
 	}
 
-	private boolean isMappingAllowed(MappingDTO<Object, Object> mapping) {
+	private boolean isMappingAllowed(MappingDTO<Object, Object> mapping) throws NullPointerException{
 		return allowedMappings.get(mapping.getKeySource()).contains(mapping.getKeyTarget());
 	}
 
@@ -100,7 +100,7 @@ public void testForList(List<String> lines) {
 					println(printingService.mappingToString(line, line2, mapping, SHOW_JSON));
 					try {
 						assertTrue(isMappingAllowed(mapping));
-					} catch (AssertionError error) {
+					} catch (AssertionError  | NullPointerException error) {
 						countErrors++;
 						if (PRINT_ERRORS) {
 							System.out.println("Bad mapping: " + mapping.getKeySource() + " -> " + mapping.getKeyTarget());
diff --git a/src/test/java/me/steffenjacobs/jsonmatcher/TestMessageApplicationService.java b/src/test/java/me/steffenjacobs/jsonmatcher/TestMessageApplicationService.java
new file mode 100644
index 0000000..a7fecea
--- /dev/null
+++ b/src/test/java/me/steffenjacobs/jsonmatcher/TestMessageApplicationService.java
@@ -0,0 +1,55 @@
+package me.steffenjacobs.jsonmatcher;
+
+import java.util.HashSet;
+import java.util.Set;
+import java.util.function.Function;
+
+import org.json.JSONObject;
+import org.junit.Assert;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import me.steffenjacobs.jsonmatcher.domain.MappingDTO;
+import me.steffenjacobs.jsonmatcher.service.MessageApplicationService;
+import me.steffenjacobs.jsonmatcher.service.matcher.ValueMatcher;
+
+/** @author Steffen Jacobs */
+public class TestMessageApplicationService {
+
+	private static MessageApplicationService messageApplicationService;
+	private static ValueMatcher valueMatcher;
+
+	@BeforeClass
+	public static void setup() {
+		messageApplicationService = new MessageApplicationService();
+		valueMatcher = new ValueMatcher();
+	}
+
+	@Test
+	public void testApplyModelToJson() {
+
+		final String exemplaryJsonSource = "{\"t\": \"23.3°C\", \"hum\": 22}";
+		// expected: "{\"temperature\": \"73.94°F\", \"humidity\": \"22%\"}";
+
+		// celsius to fahrenheit conversion formula
+		final Function<Double, Double> convertCelsiusToFahrenheit = t -> t * 1.8 + 32;
+
+		// create mappings
+		final MappingDTO<String, String> mapTemperature = new MappingDTO<>("t", "temperature",
+				t -> convertCelsiusToFahrenheit.apply(valueMatcher.findNumberWithUnit(t).getA()) + "°F", 1);
+		final MappingDTO<Integer, String> mapHumidity = new MappingDTO<>("hum", "humidity", h -> h + "%", 1);
+
+		final Set<MappingDTO<? extends Object, ? extends Object>> mappings = new HashSet<>();
+		mappings.add(mapTemperature);
+		mappings.add(mapHumidity);
+
+		// execute mapping
+		String result = messageApplicationService.applyModelToJson(exemplaryJsonSource, mappings);
+
+		// check if mapping is correct
+		JSONObject jsonResult = new JSONObject(result);
+		Assert.assertEquals(2, jsonResult.length());
+		Assert.assertEquals("73.94°F", jsonResult.get("temperature"));
+		Assert.assertEquals("22%", jsonResult.get("humidity"));
+	}
+}