Create Navigation class to avoid "magic strings" and code duplication

src/main/java/ru/ulstu/grant/controller/GrantController.java

@@ -20,6 +20,10 @@ import java.util.List;
 import java.util.stream.Collectors;
 
 import static org.springframework.util.StringUtils.isEmpty;
+import static ru.ulstu.grant.controller.Navigation.GRANTS_PAGE;
+import static ru.ulstu.grant.controller.Navigation.GRANT_PAGE;
+import static ru.ulstu.grant.controller.Navigation.REDIRECT_TO;
+import static ru.ulstu.grant.controller.Navigation.hasErrors;
 
 
 @Controller()
@@ -56,36 +60,30 @@ public class GrantController {
         if (grantDto.getDeadlines().isEmpty()) {
             errors.rejectValue("deadlines", "errorCode", "Не может быть пустым");
         }
-        if (errors.hasErrors()) {
-            return "/grants/grant";
-        }
+        hasErrors(errors, GRANT_PAGE);
         grantService.save(grantDto);
-        return "redirect:/grants/grants";
+        return String.format(REDIRECT_TO, GRANTS_PAGE);
     }
 
     @PostMapping(value = "/grant", params = "addDeadline")
     public String addDeadline(@Valid GrantDto grantDto, Errors errors) {
         filterEmptyDeadlines(grantDto);
-        if (errors.hasErrors()) {
-            return "/grants/grant";
-        }
+        hasErrors(errors, GRANT_PAGE);
         grantDto.getDeadlines().add(new DeadlineDto());
-        return "/grants/grant";
+        return GRANT_PAGE;
     }
 
     @PostMapping(value = "/grant", params = "createProject")
     public String createProject(@Valid GrantDto grantDto, Errors errors) {
-        if (errors.hasErrors()) {
-            return "/grants/grant";
-        }
+        hasErrors(errors, GRANT_PAGE);
         grantService.createProject(grantDto);
-        return "/grants/grant";
+        return GRANT_PAGE;
     }
 
     @GetMapping("/delete/{grant-id}")
     public String delete(@PathVariable("grant-id") Integer grantId) throws IOException {
         grantService.delete(grantId);
-        return "redirect:/grants/grants";
+        return String.format(REDIRECT_TO, GRANTS_PAGE);
     }
 
     @ModelAttribute("allStatuses")

src/main/java/ru/ulstu/grant/controller/Navigation.java

@@ -0,0 +1,16 @@
+package ru.ulstu.grant.controller;
+
+import org.springframework.validation.Errors;
+
+public class Navigation {
+    public static final String REDIRECT_TO = "redirect:%s";
+    public static final String GRANTS_PAGE = "/grants/grants";
+    public static final String GRANT_PAGE = "/grants/grant";
+
+    public static String hasErrors(Errors errors, String page) {
+        if (errors.hasErrors()) {
+            return page;
+        }
+        return null;
+    }
+}