fix: detect incompatible Jackson version at startup (#24009)

Vaadin requires Jackson 3.1+ but Spring Boot 4.0.3 and earlier ship
Jackson 3.0 which has incompatible API changes. This caused a cryptic
NoSuchMethodError at runtime. Adding an early check in
VaadinService.init() surfaces a clear error message with remediation
steps instead.

Author: Artur-

flow-server/src/main/java/com/vaadin/flow/internal/JacksonUtils.java

@@ -85,6 +85,40 @@ public static ObjectMapper getMapper() {
         return objectMapper;
     }
 
+    /**
+     * Checks that the Jackson version on the classpath is compatible with this
+     * version of Vaadin by verifying that expected API methods are available.
+     *
+     * @throws IllegalStateException
+     *             if the Jackson version is not compatible
+     */
+    public static void checkJacksonCompatibility() {
+        try {
+            ObjectMapper.class.getMethod("treeToValue", JsonNode.class,
+                    Class.class);
+        } catch (NoSuchMethodException e) {
+            String jacksonVersion = "unknown";
+            try {
+                jacksonVersion = ObjectMapper.class.getPackage()
+                        .getImplementationVersion();
+            } catch (Exception ignored) {
+                // ignore, we'll report "unknown"
+            }
+            throw new IllegalStateException(
+                    "The Jackson version on the classpath (" + jacksonVersion
+                            + ") is not compatible with this version of"
+                            + " Vaadin. If you are using Spring Boot, make"
+                            + " sure it is version 4.0.4 or newer (using"
+                            + " Jackson 3.1). If you have a Jackson 3.0"
+                            + " dependency, upgrade it to 3.1. If you have"
+                            + " a Jackson 2 dependency, upgrade it to 2.21"
+                            + " or later. In other cases, check"
+                            + " https://github.com/vaadin/platform/"
+                            + "releases/tag/25.1.0 for more details.",
+                    e);
+        }
+    }
+
     /**
      * Create a new ObjectNode.
      *

flow-server/src/main/java/com/vaadin/flow/server/VaadinService.java

@@ -231,6 +231,7 @@ protected VaadinService() {
      *             if a problem occurs when creating the service
      */
     public void init() throws ServiceException {
+        JacksonUtils.checkJacksonCompatibility();
         doSetClassLoader();
         instantiator = createInstantiator();
 

flow-server/src/test/java/com/vaadin/flow/internal/JacksonUtilsTest.java

@@ -40,6 +40,7 @@
 import tools.jackson.databind.node.ObjectNode;
 
 import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertThrows;
@@ -507,4 +508,9 @@ public void writeValue_nullReturnsNullNode() {
         assertEquals(mapper.nullNode(), result);
     }
 
+    @Test
+    public void checkJacksonCompatibility_compatibleVersion_noException() {
+        assertDoesNotThrow(JacksonUtils::checkJacksonCompatibility);
+    }
+
 }