updates on docs

common/src/main/java/stirling/software/common/util/ExceptionUtils.java

@@ -104,7 +104,7 @@ public class ExceptionUtils {
      */
     public static IOException createIOException(
             String messageKey, String defaultMessage, Exception cause, Object... args) {
-        String message = String.format(defaultMessage, args);
+        String message = messageKey != null ? defaultMessage : String.format(defaultMessage, args);
         return new IOException(message, cause);
     }
 
@@ -119,7 +119,7 @@ public class ExceptionUtils {
      */
     public static RuntimeException createRuntimeException(
             String messageKey, String defaultMessage, Exception cause, Object... args) {
-        String message = String.format(defaultMessage, args);
+        String message = messageKey != null ? defaultMessage : String.format(defaultMessage, args);
         return new RuntimeException(message, cause);
     }
 
@@ -133,7 +133,8 @@ public class ExceptionUtils {
      */
     public static IllegalArgumentException createIllegalArgumentException(
             String messageKey, String defaultMessage, Object... args) {
-        String message = String.format(defaultMessage, args);
+        // Only format if no translation key provided (for backwards compatibility)
+        String message = messageKey != null ? defaultMessage : String.format(defaultMessage, args);
         return new TranslatableException(message, messageKey, args);
     }
 

devGuide/EXCEPTION_HANDLING_GUIDE.md

@@ -1,14 +1,23 @@
 # Exception Handling Guide
 
-This guide shows how to use the new centralized exception handling utilities for consistent, internationalized error messages.
+This guide shows how to use the centralized exception handling utilities for consistent error messages with frontend translation support.
+
+## Architecture Overview
+
+The system uses a **backend-frontend translation split**:
+- **Backend**: Creates structured JSON error responses with translation keys and English fallbacks
+- **Frontend**: Translates error messages to user's language using JavaScript
 
 ## New Utilities
 
-### 1. I18nUtils
+### 1. ExceptionUtils  
-Provides centralized access to Spring MessageSource for internationalized messages.
+Creates `TranslatableException` instances with structured translation data for frontend.
 
-### 2. ExceptionUtils
+### 2. GlobalExceptionHandler
-Handles exceptions with internationalized error messages and appropriate logging.
+Converts exceptions to structured JSON responses with translation information.
+
+### 3. MessageFormatter.js
+Frontend utility for translating error messages with placeholder replacement.
 
 ## Usage Examples
 
@@ -58,17 +67,35 @@ throw ExceptionUtils.createFileProcessingException("merge", originalException);
 throw ExceptionUtils.createIOException("error.customKey", "Default message", originalException, arg1, arg2);
 ```
 
-### Using I18nUtils Directly
+### JSON Error Response Format
 
-```java
+The system returns structured JSON error responses with translation support:
-// Get message with current locale
-String message = I18nUtils.getMessage("error.pdfCorrupted");
 
-// Get message with arguments
+```json
-String message = I18nUtils.getMessage("error.pdfCorruptedDuring", "during merge");
+{
+  "error": "Bad Request",
+  "message": "DPI value 500 exceeds maximum safe limit of 300. High DPI values can cause memory issues and crashes. Please use a lower DPI value.",
+  "trace": "java.lang.IllegalArgumentException: ...",
+  "translationKey": "error.dpiExceedsLimit", 
+  "translationArgs": ["500", "300"]
+}
+```
 
-// Get message with fallback
+**Key Features:**
-String message = I18nUtils.getMessage("error.customKey", "Default message", arg1, arg2);
+- `message`: English fallback for API consumers that ignore translation
+- `translationKey`: Frontend translation key 
+- `translationArgs`: Arguments for placeholder replacement
+- API consumers can rely on `message` for backwards compatibility
+
+### Frontend Translation with MessageFormatter
+
+```javascript
+// Translate error messages with placeholder replacement
+const displayMessage = window.MessageFormatter.translate(
+    json.translationKey,
+    json.translationArgs, 
+    json.message // fallback to original message
+);
 ```
 
 ## Controller Pattern