Fix NPE with missing configurer

- Throw BeanDefinitionStoreException in favor of NPE if
  @EnableStateMachine or @EnableStateMachineFactory is used
  without a configurer meaning user is missing proper config
  adapter like EnumStateMachineConfigurerAdapter.
- Polish StateMachineConfiguration and StateMachineFactoryConfiguration
  by removing wrong typed refs to Enum.
- Fixes #119

spring-statemachine-core/src/main/java/org/springframework/statemachine/config/configuration/StateMachineConfiguration.java

@@ -19,6 +19,7 @@ import java.lang.annotation.Annotation;
 import java.util.ArrayList;
 import java.util.List;
 
+import org.springframework.beans.factory.BeanDefinitionStoreException;
 import org.springframework.beans.factory.BeanNameAware;
 import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.beans.factory.support.BeanDefinitionBuilder;
@@ -30,6 +31,7 @@ import org.springframework.statemachine.StateMachine;
 import org.springframework.statemachine.config.EnableStateMachine;
 import org.springframework.statemachine.config.ObjectStateMachineFactory;
 import org.springframework.statemachine.config.StateMachineConfig;
+import org.springframework.statemachine.config.StateMachineConfigurerAdapter;
 import org.springframework.statemachine.config.builders.StateMachineConfigBuilder;
 import org.springframework.statemachine.config.builders.StateMachineConfigurationConfig;
 import org.springframework.statemachine.config.builders.StateMachineStates;
@@ -38,8 +40,18 @@ import org.springframework.statemachine.config.common.annotation.AbstractImporti
 import org.springframework.statemachine.config.common.annotation.AnnotationConfigurer;
 import org.springframework.util.ClassUtils;
 
+/**
+ * {@link Configuration} which gets imported from {@link EnableStateMachine} and registers
+ * a {@link StateMachine} build from a {@link StateMachineConfigurerAdapter} via
+ * a {@link BeanDefinition}.
+ *
+ * @author Janne Valkealahti
+ *
+ * @param <S> the type of state
+ * @param <E> the type of event
+ */
 @Configuration
-public class StateMachineConfiguration<S extends Enum<S>, E extends Enum<E>> extends
+public class StateMachineConfiguration<S, E> extends
 		AbstractImportingAnnotationConfiguration<StateMachineConfigBuilder<S, E>, StateMachineConfig<S, E>> {
 
 	private final StateMachineConfigBuilder<S, E> builder = new StateMachineConfigBuilder<S, E>();
@@ -67,7 +79,7 @@ public class StateMachineConfiguration<S extends Enum<S>, E extends Enum<E>> ext
 		return types;
 	}
 
-	private static class StateMachineDelegatingFactoryBean<S extends Enum<S>, E extends Enum<E>>
+	private static class StateMachineDelegatingFactoryBean<S, E>
 		extends BeanDelegatingFactoryBean<StateMachine<S, E>,StateMachineConfigBuilder<S, E>,StateMachineConfig<S, E>>
 		implements SmartLifecycle, BeanNameAware {
 
@@ -82,7 +94,7 @@ public class StateMachineConfiguration<S extends Enum<S>, E extends Enum<E>> ext
 			this.clazzName = clazzName;
 			this.contextEvents = contextEvents;
 		}
-		
+
 		@Override
 		public void setBeanName(String name) {
 			this.beanName = name;
@@ -90,6 +102,12 @@ public class StateMachineConfiguration<S extends Enum<S>, E extends Enum<E>> ext
 
 		@Override
 		public void afterPropertiesSet() throws Exception {
+			// do not continue without configurers, it would not work
+			if (getConfigurers() == null || getConfigurers().size() == 0) {
+				throw new BeanDefinitionStoreException(
+						"Cannot configure state machine due to missing configurers. Did you remember to use " +
+						"@EnableStateMachine with a StateMachineConfigurerAdapter.");
+			}
 			for (AnnotationConfigurer<StateMachineConfig<S, E>, StateMachineConfigBuilder<S, E>> configurer : getConfigurers()) {
 				Class<?> clazz = configurer.getClass();
 				if (ClassUtils.getUserClass(clazz).getName().equals(clazzName)) {

spring-statemachine-core/src/main/java/org/springframework/statemachine/config/configuration/StateMachineFactoryConfiguration.java

@@ -20,6 +20,7 @@ import java.util.ArrayList;
 import java.util.List;
 
 import org.springframework.beans.BeansException;
+import org.springframework.beans.factory.BeanDefinitionStoreException;
 import org.springframework.beans.factory.BeanFactory;
 import org.springframework.beans.factory.BeanFactoryAware;
 import org.springframework.beans.factory.FactoryBean;
@@ -33,6 +34,7 @@ import org.springframework.core.type.AnnotationMetadata;
 import org.springframework.statemachine.config.EnableStateMachineFactory;
 import org.springframework.statemachine.config.ObjectStateMachineFactory;
 import org.springframework.statemachine.config.StateMachineConfig;
+import org.springframework.statemachine.config.StateMachineConfigurerAdapter;
 import org.springframework.statemachine.config.StateMachineFactory;
 import org.springframework.statemachine.config.builders.StateMachineConfigBuilder;
 import org.springframework.statemachine.config.builders.StateMachineConfigurationConfig;
@@ -42,8 +44,18 @@ import org.springframework.statemachine.config.common.annotation.AbstractImporti
 import org.springframework.statemachine.config.common.annotation.AnnotationConfigurer;
 import org.springframework.util.ClassUtils;
 
+/**
+ * {@link Configuration} which gets imported from {@link EnableStateMachineFactory} and registers
+ * a {@link StateMachineFactory} build from a {@link StateMachineConfigurerAdapter} via
+ * a {@link BeanDefinition}.
+ *
+ * @author Janne Valkealahti
+ *
+ * @param <S> the type of state
+ * @param <E> the type of event
+ */
 @Configuration
-public class StateMachineFactoryConfiguration<S extends Enum<S>, E extends Enum<E>> extends
+public class StateMachineFactoryConfiguration<S, E> extends
 		AbstractImportingAnnotationConfiguration<StateMachineConfigBuilder<S, E>, StateMachineConfig<S, E>> {
 
 	private final StateMachineConfigBuilder<S, E> builder = new StateMachineConfigBuilder<S, E>();
@@ -70,7 +82,7 @@ public class StateMachineFactoryConfiguration<S extends Enum<S>, E extends Enum<
 		return types;
 	}
 
-	private static class StateMachineFactoryDelegatingFactoryBean<S extends Enum<S>, E extends Enum<E>> implements
+	private static class StateMachineFactoryDelegatingFactoryBean<S, E> implements
 			FactoryBean<StateMachineFactory<S, E>>, BeanFactoryAware, InitializingBean {
 
 		private final StateMachineConfigBuilder<S, E> builder;
@@ -104,6 +116,12 @@ public class StateMachineFactoryConfiguration<S extends Enum<S>, E extends Enum<
 
 		@Override
 		public void afterPropertiesSet() throws Exception {
+			// do not continue without configurers, it would not work
+			if (configurers == null || configurers.size() == 0) {
+				throw new BeanDefinitionStoreException(
+						"Cannot configure state machine due to missing configurers. Did you remember to use " +
+						"@EnableStateMachineFactory with a StateMachineConfigurerAdapter.");
+			}
 			for (AnnotationConfigurer<StateMachineConfig<S, E>, StateMachineConfigBuilder<S, E>> configurer : configurers) {
 				Class<?> clazz = configurer.getClass();
 				if (ClassUtils.getUserClass(clazz).getName().equals(clazzName)) {

spring-statemachine-core/src/test/java/org/springframework/statemachine/config/ConfigurationTests.java

@@ -15,8 +15,8 @@
  */
 package org.springframework.statemachine.config;
 
-import static org.hamcrest.Matchers.notNullValue;
 import static org.hamcrest.Matchers.is;
+import static org.hamcrest.Matchers.notNullValue;
 import static org.junit.Assert.assertThat;
 import static org.junit.Assert.assertTrue;
 
@@ -27,6 +27,7 @@ import java.util.EnumSet;
 import java.util.List;
 
 import org.junit.Test;
+import org.springframework.beans.factory.BeanCreationException;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
@@ -149,6 +150,18 @@ public class ConfigurationTests extends AbstractStateMachineTests {
 		assertThat(((List<?>)o3).size(), is(2));
 	}
 
+	@Test(expected = BeanCreationException.class)
+	public void testEnableStateMachineNoAdapter() {
+		context.register(Config12.class);
+		context.refresh();
+	}
+
+	@Test(expected = BeanCreationException.class)
+	public void testEnableStateMachineFactoryNoAdapter() {
+		context.register(Config13.class);
+		context.refresh();
+	}
+
 	@Configuration
 	@EnableStateMachine
 	public static class Config1 extends EnumStateMachineConfigurerAdapter<TestStates, TestEvents> {
@@ -534,4 +547,14 @@ public class ConfigurationTests extends AbstractStateMachineTests {
 
 	}
 
+	@Configuration
+	@EnableStateMachine
+	public static class Config12 {
+	}
+
+	@Configuration
+	@EnableStateMachineFactory
+	public static class Config13 {
+	}
+
 }