fix: report Lookup instance absence with ISE and meaningful message (#…

…11240) (#11272)

fixes #11219

Co-authored-by: Denis <denis@vaadin.com>

flow-server/src/main/java/com/vaadin/flow/server/startup/ApplicationConfiguration.java

@@ -48,6 +48,16 @@ public interface ApplicationConfiguration extends AbstractConfiguration {
     static ApplicationConfiguration get(VaadinContext context) {
         return context.getAttribute(ApplicationConfiguration.class, () -> {
             Lookup lookup = context.getAttribute(Lookup.class);
+            if (lookup == null) {
+                throw new IllegalStateException("The application "
+                        + Lookup.class.getSimpleName()
+                        + " instance is not found in the " + VaadinContext.class
+                        + " instance. It means that "
+                        + "the container has not executed "
+                        + Lookup.class.getSimpleName()
+                        + " initialization code: so either the container is not Servlet 3.0 compatible"
+                        + " or project configuration is broken.");
+            }
             ApplicationConfigurationFactory factory = lookup
                     .lookup(ApplicationConfigurationFactory.class);
             return factory.create(context);

flow-server/src/test/java/com/vaadin/flow/server/startup/ApplicationConfigurationTest.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2000-2021 Vaadin Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+package com.vaadin.flow.server.startup;
+
+import java.util.function.Supplier;
+
+import org.junit.Test;
+import org.mockito.Mockito;
+
+import com.vaadin.flow.di.Lookup;
+import com.vaadin.flow.server.VaadinContext;
+
+public class ApplicationConfigurationTest {
+
+    @Test(expected = IllegalStateException.class)
+    public void get_contextHasNoLookup_iseIsThrown() {
+        VaadinContext context = Mockito.spy(VaadinContext.class);
+        Mockito.when(context.getAttribute(Lookup.class)).thenReturn(null);
+        Mockito.doAnswer(
+                invocation -> invocation.getArgument(1, Supplier.class).get())
+                .when(context).getAttribute(Mockito.any(), Mockito.any());
+        ApplicationConfiguration.get(context);
+    }
+
+}