implement API error model and 404 contract test for missing transaction

Author: JaskRendix

support_portal_backend/src/main/java/com/support/controller/TransactionController.java

@@ -1,5 +1,6 @@
 package com.support.controller;
 
+import com.support.exception.ResourceNotFoundException;
 import com.support.model.Transaction;
 import com.support.repository.TransactionRepository;
 import org.springframework.web.bind.annotation.*;
@@ -26,4 +27,10 @@ public List<Transaction> getAllTransactions() {
     public List<Transaction> getTransactionsByStatus(@PathVariable String status) {
         return repository.findByStatus(status);
     }
+
+    @GetMapping("/transactions/{id}")
+    public Transaction getTransactionById(@PathVariable Long id) {
+        return repository.findById(id)
+                .orElseThrow(() -> new ResourceNotFoundException("Transaction not found with ID: " + id));
+    }
 }

support_portal_backend/src/main/java/com/support/exception/GlobalExceptionHandler.java

@@ -0,0 +1,38 @@
+package com.support.exception;
+
+import com.support.model.ApiError;
+import jakarta.servlet.http.HttpServletRequest;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.ControllerAdvice;
+import org.springframework.web.bind.annotation.ExceptionHandler;
+
+import java.time.LocalDateTime;
+
+@ControllerAdvice
+public class GlobalExceptionHandler {
+
+    @ExceptionHandler(ResourceNotFoundException.class)
+    public ResponseEntity<ApiError> handleNotFound(ResourceNotFoundException ex, HttpServletRequest request) {
+        ApiError error = new ApiError(
+                LocalDateTime.now(),
+                HttpStatus.NOT_FOUND.value(),
+                "Resource Not Found",
+                ex.getMessage(),
+                request.getRequestURI()
+        );
+        return new ResponseEntity<>(error, HttpStatus.NOT_FOUND);
+    }
+
+    @ExceptionHandler(Exception.class)
+    public ResponseEntity<ApiError> handleGlobal(Exception ex, HttpServletRequest request) {
+        ApiError error = new ApiError(
+                LocalDateTime.now(),
+                HttpStatus.INTERNAL_SERVER_ERROR.value(),
+                "Internal Server Error",
+                "An unexpected error occurred", // Don't leak raw stack traces in Payments!
+                request.getRequestURI()
+        );
+        return new ResponseEntity<>(error, HttpStatus.INTERNAL_SERVER_ERROR);
+    }
+}

support_portal_backend/src/main/java/com/support/exception/ResourceNotFoundException.java

@@ -0,0 +1,7 @@
+package com.support.exception;
+
+public class ResourceNotFoundException extends RuntimeException {
+    public ResourceNotFoundException(String message) {
+        super(message);
+    }
+}

support_portal_backend/src/main/java/com/support/model/ApiError.java

@@ -0,0 +1,15 @@
+package com.support.model;
+
+import lombok.AllArgsConstructor;
+import lombok.Data;
+import java.time.LocalDateTime;
+
+@Data
+@AllArgsConstructor
+public class ApiError {
+    private LocalDateTime timestamp;
+    private int status;
+    private String error;
+    private String message;
+    private String path;
+}

support_portal_backend/src/test/java/com/support/controller/TransactionControllerTest.java

@@ -69,4 +69,14 @@ public void shouldReturnEmptyListWhenNoTransactionsFound() throws Exception {
                 .andExpect(status().isOk())
                 .andExpect(content().json("[]"));
     }
+
+    @Test
+    public void shouldReturn404WhenTransactionNotFound() throws Exception {
+        when(repository.findById(99L)).thenReturn(java.util.Optional.empty());
+
+        mockMvc.perform(get("/api/support/transactions/99"))
+                .andExpect(status().isNotFound())
+                .andExpect(jsonPath("$.error").value("Resource Not Found"))
+                .andExpect(jsonPath("$.message").contains("ID: 99"));
+    }
 }