Add layers where exceptions get thrown for more user code stack trace lines

src/main/java/org/springframework/samples/petclinic/loggers/VetLogger.java

@@ -0,0 +1,13 @@
+package org.springframework.samples.petclinic.loggers;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.samples.petclinic.vet.Vet;
+
+public class VetLogger {
+	private static final Logger logger = LoggerFactory.getLogger(VetLogger.class);
+
+	public static void LogSpecialty(Vet vet){
+		logger.info("Vet Speciality='{}'", vet.getSpecialties().get(0).getName());
+	}
+}

src/main/java/org/springframework/samples/petclinic/owner/OwnerController.java

@@ -25,6 +25,7 @@
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.PageRequest;
 import org.springframework.data.domain.Pageable;
+import org.springframework.samples.petclinic.validation.ControllerValidation;
 import org.springframework.stereotype.Controller;
 import org.springframework.ui.Model;
 import org.springframework.validation.BindingResult;
@@ -136,10 +137,7 @@ private String addPaginationModel(int page, Model model, Page<Owner> paginated)
 	}
 
 	private Page<Owner> findPaginatedForOwnersLastName(int page, String lastname) {
-		if(page < 1){
-			// defensive programming
-			throw new IllegalArgumentException("Page must be greater than 0");
-		}
+		ControllerValidation.ValidatePageNumber(page);
 
 		int pageSize = 5;
 		Pageable pageable = PageRequest.of(page - 1, pageSize);

src/main/java/org/springframework/samples/petclinic/owner/PetController.java

@@ -18,6 +18,7 @@
 import java.time.LocalDate;
 import java.util.Collection;
 
+import org.springframework.samples.petclinic.validation.ControllerValidation;
 import org.springframework.stereotype.Controller;
 import org.springframework.ui.ModelMap;
 import org.springframework.util.StringUtils;
@@ -124,13 +125,10 @@ public String processCreationForm(Owner owner, @Valid Pet pet, BindingResult res
 	@GetMapping("/pets/{petId}/edit")
 	public String initUpdateForm(Owner owner, @PathVariable("petId") int petId, ModelMap model,
 			RedirectAttributes redirectAttributes) {
-		if(owner == null){
-			throw new IllegalArgumentException("Owner not found!");
-		}
+		ControllerValidation.ValidateNotNull(owner, "Owner");
 		Pet pet = owner.getPet(petId);
-		if(pet == null){
-			throw new IllegalArgumentException("Pet not found!");
-		}
+
+		ControllerValidation.ValidateNotNull(pet, "Pet");
 		model.put("pet", pet);
 		return VIEWS_PETS_CREATE_OR_UPDATE_FORM;
 	}

src/main/java/org/springframework/samples/petclinic/validation/BaseValidation.java

@@ -0,0 +1,9 @@
+package org.springframework.samples.petclinic.validation;
+
+public class BaseValidation {
+	public static void IntegerMustBeGreaterThan(Integer a, Integer b, String label) {
+		if(a < b){
+			throw new IllegalArgumentException(label + " must be greater than " + b);
+		}
+	}
+}

src/main/java/org/springframework/samples/petclinic/validation/ControllerValidation.java

@@ -0,0 +1,13 @@
+package org.springframework.samples.petclinic.validation;
+
+public class ControllerValidation {
+	public static void ValidatePageNumber(int pageNumber) throws IllegalArgumentException {
+		BaseValidation.IntegerMustBeGreaterThan(pageNumber, 0, "Page Number");
+	}
+
+	public static void ValidateNotNull(Object object, String name) throws IllegalArgumentException {
+		if (object == null) {
+			throw new IllegalArgumentException(name + " cannot be null");
+		}
+	}
+}

src/main/java/org/springframework/samples/petclinic/vet/VetController.java

@@ -20,6 +20,8 @@
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.PageRequest;
 import org.springframework.data.domain.Pageable;
+import org.springframework.samples.petclinic.loggers.VetLogger;
+import org.springframework.samples.petclinic.validation.ControllerValidation;
 import org.springframework.stereotype.Controller;
 import org.springframework.ui.Model;
 import org.springframework.web.bind.annotation.GetMapping;
@@ -69,10 +71,8 @@ private String addPaginationModel(int page, Page<Vet> paginated, Model model) {
 	}
 
 	private Page<Vet> findPaginated(int page) {
-		if(page < 1) {
-			// defensive programming
-			throw new IllegalArgumentException("Page must be greater than 0");
-		}
+		ControllerValidation.ValidatePageNumber(page);
+
 		int pageSize = 5;
 		Pageable pageable = PageRequest.of(page - 1, pageSize);
 		return vetRepository.findAll(pageable);
@@ -96,7 +96,7 @@ private Page<Vet> findPaginated(int page) {
 		Vets vets = new Vets();
 		Collection<Vet> vetList = this.vetRepository.findByLastName(lastName);
 		for (Vet vet : vetList) {
-			logger.info("Vet Speciality='{}'", vet.getSpecialties().get(0).getName());
+			VetLogger.LogSpecialty(vet);
 		}
 		vets.getVetList().addAll(vetList);
 		return vets;