src/main/java/net/javahippie/fitpub/FitPubApplication.java

@@ -10,6 +10,7 @@ import org.apache.hc.client5.http.io.HttpClientConnectionManager;
 import org.apache.hc.core5.util.Timeout;
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.boot.context.properties.ConfigurationPropertiesScan;
 import org.springframework.context.annotation.Bean;
 import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
 import org.springframework.scheduling.annotation.EnableAsync;
@@ -22,6 +23,7 @@ import org.springframework.web.client.RestTemplate;
  * through the ActivityPub protocol.
  */
 @SpringBootApplication
+@ConfigurationPropertiesScan
 @EnableAsync
 @EnableScheduling
 @Slf4j

src/main/java/net/javahippie/fitpub/config/FitPubTextLimitsProperties.java

@@ -0,0 +1,41 @@
+package net.javahippie.fitpub.config;
+
+import lombok.Data;
+import org.springframework.boot.context.properties.ConfigurationProperties;
+
+/**
+ * Configurable max-length limits for user and activity text fields.
+ */
+@Data
+@ConfigurationProperties(prefix = "fitpub")
+public class FitPubTextLimitsProperties {
+
+    private User user = new User();
+    private Activity activity = new Activity();
+
+    @Data
+    public static class User {
+        private Bio bio = new Bio();
+    }
+
+    @Data
+    public static class Bio {
+        private int maxLength = 500;
+    }
+
+    @Data
+    public static class Activity {
+        private Title title = new Title();
+        private Description description = new Description();
+    }
+
+    @Data
+    public static class Title {
+        private int maxLength = 200;
+    }
+
+    @Data
+    public static class Description {
+        private int maxLength = 5000;
+    }
+}

src/main/java/net/javahippie/fitpub/controller/ActivitiesViewController.java

@@ -1,5 +1,8 @@
 package net.javahippie.fitpub.controller;
 
+import lombok.RequiredArgsConstructor;
+import net.javahippie.fitpub.service.TextValidationService;
+import org.springframework.ui.Model;
 import org.springframework.stereotype.Controller;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.PathVariable;
@@ -10,8 +13,11 @@ import org.springframework.web.bind.annotation.RequestMapping;
  */
 @Controller
 @RequestMapping("/activities")
+@RequiredArgsConstructor
 public class ActivitiesViewController {
 
+    private final TextValidationService textValidationService;
+
     /**
      * Show activities list page
      */
@@ -24,7 +30,9 @@ public class ActivitiesViewController {
      * Show activity upload page
      */
     @GetMapping("/upload")
-    public String uploadActivity() {
+    public String uploadActivity(Model model) {
+        model.addAttribute("activityTitleMaxLength", textValidationService.getActivityTitleMaxLength());
+        model.addAttribute("activityDescriptionMaxLength", textValidationService.getActivityDescriptionMaxLength());
         return "activities/upload";
     }
 
@@ -41,8 +49,10 @@ public class ActivitiesViewController {
      * Show activity edit page
      */
     @GetMapping("/{id}/edit")
-    public String editActivity(@PathVariable String id) {
+    public String editActivity(@PathVariable String id, Model model) {
         // The activity data will be loaded via JavaScript API calls
+        model.addAttribute("activityTitleMaxLength", textValidationService.getActivityTitleMaxLength());
+        model.addAttribute("activityDescriptionMaxLength", textValidationService.getActivityDescriptionMaxLength());
         return "activities/edit";
     }
 }

src/main/java/net/javahippie/fitpub/controller/ActivityController.java

@@ -21,6 +21,7 @@ import net.javahippie.fitpub.service.WeatherService;
 import net.javahippie.fitpub.service.FitFileService;
 import net.javahippie.fitpub.service.PrivacyZoneService;
 import net.javahippie.fitpub.service.ReactionEnricher;
+import net.javahippie.fitpub.service.TextValidationService;
 import net.javahippie.fitpub.service.TrackPrivacyFilter;
 import org.springframework.beans.factory.annotation.Value;
 import org.springframework.http.HttpStatus;
@@ -48,6 +49,7 @@ import java.util.UUID;
 @Slf4j
 public class ActivityController {
 
+    private final TextValidationService textValidationService;
     private final ActivityFileService activityFileService;
     private final FitFileService fitFileService;
     private final UserRepository userRepository;
@@ -153,6 +155,9 @@ public class ActivityController {
     ) {
         log.info("User {} uploading activity file: {}", userDetails.getUsername(), file.getOriginalFilename());
 
+        textValidationService.validateActivityTitle(request.getTitle());
+        textValidationService.validateActivityDescription(request.getDescription());
+
         User user = userRepository.findByUsername(userDetails.getUsername())
             .orElseThrow(() -> new UsernameNotFoundException("User not found"));
 
@@ -311,6 +316,9 @@ public class ActivityController {
 
         UUID userId = getUserId(userDetails);
 
+        textValidationService.validateActivityTitle(request.getTitle());
+        textValidationService.validateActivityDescription(request.getDescription());
+
         try {
             Activity updated = fitFileService.updateActivity(
                 id,

src/main/java/net/javahippie/fitpub/controller/ApiExceptionHandler.java

@@ -0,0 +1,19 @@
+package net.javahippie.fitpub.controller;
+
+import net.javahippie.fitpub.exception.ApiValidationException;
+import net.javahippie.fitpub.model.dto.ApiError;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.ExceptionHandler;
+import org.springframework.web.bind.annotation.RestControllerAdvice;
+
+/**
+ * Central exception mapping for REST APIs.
+ */
+@RestControllerAdvice
+public class ApiExceptionHandler {
+
+    @ExceptionHandler(ApiValidationException.class)
+    public ResponseEntity<ApiError> handleApiValidation(ApiValidationException e) {
+        return ResponseEntity.badRequest().body(new ApiError("BAD_REQUEST", e.getMessage()));
+    }
+}

src/main/java/net/javahippie/fitpub/controller/ProfileViewController.java

@@ -1,5 +1,7 @@
 package net.javahippie.fitpub.controller;
 
+import lombok.RequiredArgsConstructor;
+import net.javahippie.fitpub.service.TextValidationService;
 import org.springframework.stereotype.Controller;
 import org.springframework.ui.Model;
 import org.springframework.web.bind.annotation.GetMapping;
@@ -9,8 +11,11 @@ import org.springframework.web.bind.annotation.PathVariable;
  * Controller for user profile view pages.
  */
 @Controller
+@RequiredArgsConstructor
 public class ProfileViewController {
 
+    private final TextValidationService textValidationService;
+
     /**
      * Current user's profile page.
      * Shows own profile with edit capabilities.
@@ -34,6 +39,7 @@ public class ProfileViewController {
     @GetMapping("/profile/edit")
     public String editProfile(Model model) {
         model.addAttribute("pageTitle", "Edit Profile");
+        model.addAttribute("bioMaxLength", textValidationService.getUserBioMaxLength());
         return "profile/edit";
     }
 

src/main/java/net/javahippie/fitpub/controller/UserController.java

@@ -14,6 +14,7 @@ import net.javahippie.fitpub.repository.FollowRepository;
 import net.javahippie.fitpub.repository.RemoteActorRepository;
 import net.javahippie.fitpub.repository.UserRepository;
 import net.javahippie.fitpub.service.FederationService;
+import net.javahippie.fitpub.service.TextValidationService;
 import net.javahippie.fitpub.service.WebFingerClient;
 import net.javahippie.fitpub.service.UserService;
 import org.springframework.beans.factory.annotation.Value;
@@ -47,6 +48,7 @@ public class UserController {
     private final WebFingerClient webFingerClient;
     private final FederationService federationService;
     private final UserService userService;
+    private final TextValidationService textValidationService;
     private final net.javahippie.fitpub.repository.ActivityPeakRepository activityPeakRepository;
 
     @Value("${fitpub.base-url}")
@@ -101,6 +103,8 @@ public class UserController {
     ) {
         log.info("User {} updating profile", userDetails.getUsername());
 
+        textValidationService.validateUserBio(request.getBio());
+
         User user = userRepository.findByUsername(userDetails.getUsername())
             .orElseThrow(() -> new UsernameNotFoundException("User not found"));
 

src/main/java/net/javahippie/fitpub/exception/ApiValidationException.java

@@ -0,0 +1,11 @@
+package net.javahippie.fitpub.exception;
+
+/**
+ * Exception for API request validation that depends on runtime configuration.
+ */
+public class ApiValidationException extends RuntimeException {
+
+    public ApiValidationException(String message) {
+        super(message);
+    }
+}

src/main/java/net/javahippie/fitpub/model/dto/ActivityUpdateRequest.java

@@ -1,7 +1,6 @@
 package net.javahippie.fitpub.model.dto;
 
 import jakarta.validation.constraints.NotNull;
-import jakarta.validation.constraints.Size;
 import lombok.AllArgsConstructor;
 import lombok.Builder;
 import lombok.Data;
@@ -18,10 +17,8 @@ import net.javahippie.fitpub.model.entity.Activity;
 public class ActivityUpdateRequest {
 
     @NotNull(message = "Title is required")
-    @Size(min = 1, max = 200, message = "Title must be between 1 and 200 characters")
     private String title;
 
-    @Size(max = 5000, message = "Description must not exceed 5000 characters")
     private String description;
 
     @NotNull(message = "Visibility is required")

src/main/java/net/javahippie/fitpub/model/dto/ActivityUploadRequest.java

@@ -1,6 +1,4 @@
 package net.javahippie.fitpub.model.dto;
-
-import jakarta.validation.constraints.Size;
 import lombok.AllArgsConstructor;
 import lombok.Builder;
 import lombok.Data;
@@ -17,10 +15,8 @@ import net.javahippie.fitpub.model.entity.Activity;
 @AllArgsConstructor
 public class ActivityUploadRequest {
 
-    @Size(max = 200, message = "Title must not exceed 200 characters")
     private String title;
 
-    @Size(max = 5000, message = "Description must not exceed 5000 characters")
     private String description;
 
     private Activity.Visibility visibility;

src/main/java/net/javahippie/fitpub/model/dto/ApiError.java

@@ -0,0 +1,13 @@
+package net.javahippie.fitpub.model.dto;
+
+import lombok.Value;
+
+/**
+ * Standard error payload for API responses.
+ */
+@Value
+public class ApiError {
+
+    String code;
+    String message;
+}

src/main/java/net/javahippie/fitpub/model/dto/UserUpdateRequest.java

@@ -21,7 +21,6 @@ public class UserUpdateRequest {
     @Size(max = 100, message = "Display name must not exceed 100 characters")
     private String displayName;
 
-    @Size(max = 500, message = "Bio must not exceed 500 characters")
     private String bio;
 
     @URL(message = "Avatar URL must be a valid URL")

src/main/java/net/javahippie/fitpub/service/TextValidationService.java

@@ -0,0 +1,46 @@
+package net.javahippie.fitpub.service;
+
+import lombok.RequiredArgsConstructor;
+import net.javahippie.fitpub.config.FitPubTextLimitsProperties;
+import net.javahippie.fitpub.exception.ApiValidationException;
+import org.springframework.stereotype.Service;
+
+/**
+ * Central validation policy for configurable text fields.
+ */
+@Service
+@RequiredArgsConstructor
+public class TextValidationService {
+
+    private final FitPubTextLimitsProperties textLimitsProperties;
+
+    public int getUserBioMaxLength() {
+        return textLimitsProperties.getUser().getBio().getMaxLength();
+    }
+
+    public int getActivityTitleMaxLength() {
+        return textLimitsProperties.getActivity().getTitle().getMaxLength();
+    }
+
+    public int getActivityDescriptionMaxLength() {
+        return textLimitsProperties.getActivity().getDescription().getMaxLength();
+    }
+
+    public void validateUserBio(String bio) {
+        validateMaxLength(bio, getUserBioMaxLength(), "Bio");
+    }
+
+    public void validateActivityTitle(String title) {
+        validateMaxLength(title, getActivityTitleMaxLength(), "Title");
+    }
+
+    public void validateActivityDescription(String description) {
+        validateMaxLength(description, getActivityDescriptionMaxLength(), "Description");
+    }
+
+    private void validateMaxLength(String value, int maxLength, String fieldName) {
+        if (value != null && value.length() > maxLength) {
+            throw new ApiValidationException(fieldName + " must not exceed " + maxLength + " characters");
+        }
+    }
+}

src/main/resources/application.yml

@@ -84,6 +84,18 @@ fitpub:
     # Leave empty to allow open registration
     password: ${REGISTRATION_PASSWORD:}
 
+# User settings
+  user:
+    bio:
+      max-length: ${FITPUB_USER_BIO_MAX_LENGTH:500}
+
+# Activity settings
+  activity:
+    title:
+      max-length: ${FITPUB_ACTIVITY_TITLE_MAX_LENGTH:200}
+    description:
+      max-length: ${FITPUB_ACTIVITY_DESCRIPTION_MAX_LENGTH:5000}
+
   # Storage settings
   storage:
     fit-files:

src/main/resources/templates/activities/edit.html

@@ -51,7 +51,7 @@
                                        id="title"
                                        name="title"
                                        placeholder="e.g., Morning Run"
-                                       maxlength="200"
+                                       th:attr="maxlength=${activityTitleMaxLength}"
                                        required>
                                 <div class="invalid-feedback">
                                     Please provide a title for your activity.
@@ -83,9 +83,9 @@
                                           name="description"
                                           rows="4"
                                           placeholder="Share details about your activity..."
-                                          maxlength="5000"></textarea>
+                                          th:attr="maxlength=${activityDescriptionMaxLength}"></textarea>
                                 <div class="form-text">
-                                    <span id="descCharCount">0</span>/5000 characters
+                                    <span id="descCharCount">0</span>/<span th:text="${activityDescriptionMaxLength}">5000</span> characters
                                 </div>
                             </div>
 

src/main/resources/templates/activities/upload.html

@@ -83,7 +83,7 @@
                                            id="title"
                                            name="title"
                                            placeholder="e.g., Morning Run"
-                                           maxlength="200">
+                                           th:attr="maxlength=${activityTitleMaxLength}">
                                     <div class="invalid-feedback">
                                         Please provide a title for your activity.
                                     </div>
@@ -126,9 +126,9 @@
                                               name="description"
                                               rows="4"
                                               placeholder="Share details about your activity..."
-                                              maxlength="5000"></textarea>
+                                              th:attr="maxlength=${activityDescriptionMaxLength}"></textarea>
                                     <div class="form-text">
-                                        <span id="descCharCount">0</span>/5000 characters
+                                        <span id="descCharCount">0</span>/<span th:text="${activityDescriptionMaxLength}">5000</span> characters
                                     </div>
                                 </div>
 

src/main/resources/templates/profile/edit.html

@@ -39,9 +39,10 @@
                             <!-- Bio -->
                             <div class="mb-3">
                                 <label for="bio" class="form-label">Bio</label>
-                                <textarea class="form-control" id="bio" name="bio" rows="4" maxlength="500"></textarea>
+                                <textarea class="form-control" id="bio" name="bio" rows="4"
+                                          th:attr="maxlength=${bioMaxLength}"></textarea>
                                 <div class="form-text">
-                                    <span id="bioCharCount">0</span>/500 characters
+                                    <span id="bioCharCount">0</span>/<span th:text="${bioMaxLength}">500</span> characters
                                 </div>
                             </div>
 

src/test/java/net/javahippie/fitpub/service/TextValidationServiceTest.java

@@ -0,0 +1,69 @@
+package net.javahippie.fitpub.service;
+
+import net.javahippie.fitpub.config.FitPubTextLimitsProperties;
+import net.javahippie.fitpub.exception.ApiValidationException;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+@DisplayName("TextValidationService Tests")
+class TextValidationServiceTest {
+
+    @Test
+    @DisplayName("Should allow user bio up to configured max length")
+    void shouldAllowUserBioUpToConfiguredMaxLength() {
+        TextValidationService service = new TextValidationService(properties(12, 20, 30));
+
+        assertDoesNotThrow(() -> service.validateUserBio("123456789012"));
+    }
+
+    @Test
+    @DisplayName("Should reject user bio longer than configured max length")
+    void shouldRejectUserBioLongerThanConfiguredMaxLength() {
+        TextValidationService service = new TextValidationService(properties(12, 20, 30));
+
+        assertThrows(ApiValidationException.class, () -> service.validateUserBio("1234567890123"));
+    }
+
+    @Test
+    @DisplayName("Should allow activity title up to configured max length")
+    void shouldAllowActivityTitleUpToConfiguredMaxLength() {
+        TextValidationService service = new TextValidationService(properties(12, 10, 30));
+
+        assertDoesNotThrow(() -> service.validateActivityTitle("1234567890"));
+    }
+
+    @Test
+    @DisplayName("Should reject activity title longer than configured max length")
+    void shouldRejectActivityTitleLongerThanConfiguredMaxLength() {
+        TextValidationService service = new TextValidationService(properties(12, 10, 30));
+
+        assertThrows(ApiValidationException.class, () -> service.validateActivityTitle("12345678901"));
+    }
+
+    @Test
+    @DisplayName("Should allow activity description up to configured max length")
+    void shouldAllowActivityDescriptionUpToConfiguredMaxLength() {
+        TextValidationService service = new TextValidationService(properties(12, 10, 20));
+
+        assertDoesNotThrow(() -> service.validateActivityDescription("12345678901234567890"));
+    }
+
+    @Test
+    @DisplayName("Should reject activity description longer than configured max length")
+    void shouldRejectActivityDescriptionLongerThanConfiguredMaxLength() {
+        TextValidationService service = new TextValidationService(properties(12, 10, 20));
+
+        assertThrows(ApiValidationException.class, () -> service.validateActivityDescription("123456789012345678901"));
+    }
+
+    private FitPubTextLimitsProperties properties(int bioMaxLength, int titleMaxLength, int descriptionMaxLength) {
+        FitPubTextLimitsProperties properties = new FitPubTextLimitsProperties();
+        properties.getUser().getBio().setMaxLength(bioMaxLength);
+        properties.getActivity().getTitle().setMaxLength(titleMaxLength);
+        properties.getActivity().getDescription().setMaxLength(descriptionMaxLength);
+        return properties;
+    }
+}