chore(spring-boot): add application context classloader switch option

in case of an initialized restarter which is part of the Spring Developer
tools

Related to CAM-9043

spring-boot-starter/starter/pom.xml

@@ -92,6 +92,13 @@
       <optional>true</optional>
     </dependency>
 
+    <dependency>
+      <groupId>org.springframework.boot</groupId>
+      <artifactId>spring-boot-devtools</artifactId>
+      <scope>provided</scope>
+      <optional>true</optional>
+    </dependency>
+
     <dependency>
       <groupId>org.apache.commons</groupId>
       <artifactId>commons-lang3</artifactId>

spring-boot-starter/starter/src/main/java/org/camunda/bpm/spring/boot/starter/CamundaBpmPluginConfiguration.java

@@ -19,7 +19,9 @@
 import com.fasterxml.jackson.datatype.jdk8.Jdk8Module;
 import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
 import com.fasterxml.jackson.module.paramnames.ParameterNamesModule;
+
 import org.camunda.bpm.engine.impl.cfg.ProcessEnginePlugin;
+import org.camunda.bpm.spring.boot.starter.plugin.ApplicationContextClassloaderSwitchPlugin;
 import org.camunda.bpm.spring.boot.starter.spin.CamundaJacksonFormatConfiguratorJSR310;
 import org.camunda.bpm.spring.boot.starter.spin.CamundaJacksonFormatConfiguratorJdk8;
 import org.camunda.bpm.spring.boot.starter.spin.CamundaJacksonFormatConfiguratorParameterNames;
@@ -30,6 +32,7 @@
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingClass;
+import org.springframework.boot.devtools.restart.ConditionalOnInitializedRestarter;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 
@@ -105,4 +108,23 @@ public static ProcessEnginePlugin connectProcessEnginePlugin() {
       return new ConnectProcessEnginePlugin();
     }
   }
+
+
+  /*
+    Provide option to apply application context classloader switch when Spring
+    Spring Developer tools are enabled
+    For more details: https://jira.camunda.com/browse/CAM-9043
+   */
+  @ConditionalOnInitializedRestarter
+  @Configuration
+  static class InitializedRestarterConfiguration {
+
+    @Bean
+    @ConditionalOnMissingBean(name = "applicationContextClassloaderSwitchPlugin")
+    public ApplicationContextClassloaderSwitchPlugin applicationContextClassloaderSwitchPlugin() {
+      return new ApplicationContextClassloaderSwitchPlugin();
+    }
+  }
+
+
 }

spring-boot-starter/starter/src/main/java/org/camunda/bpm/spring/boot/starter/plugin/ApplicationContextClassloaderSwitchPlugin.java

@@ -0,0 +1,53 @@
+/*
+ * Copyright Camunda Services GmbH and/or licensed to Camunda Services GmbH
+ * under one or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information regarding copyright
+ * ownership. Camunda licenses this file to you under the Apache License,
+ * Version 2.0; 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 org.camunda.bpm.spring.boot.starter.plugin;
+
+import org.camunda.bpm.engine.ProcessEngine;
+import org.camunda.bpm.engine.impl.cfg.ProcessEngineConfigurationImpl;
+import org.camunda.bpm.engine.impl.cfg.ProcessEnginePlugin;
+import org.springframework.beans.BeansException;
+import org.springframework.context.ApplicationContext;
+import org.springframework.context.ApplicationContextAware;
+
+public class ApplicationContextClassloaderSwitchPlugin implements ProcessEnginePlugin, ApplicationContextAware {
+
+  protected ClassLoader applicationContextClassloader;
+
+  @Override
+  public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
+    applicationContextClassloader = applicationContext.getClassLoader();
+  }
+
+  @Override
+  public void preInit(ProcessEngineConfigurationImpl processEngineConfiguration) {
+    processEngineConfiguration.setClassLoader(applicationContextClassloader);
+  }
+
+  @Override
+  public void postInit(ProcessEngineConfigurationImpl processEngineConfiguration) {
+  }
+
+  @Override
+  public void postProcessEngineBuild(ProcessEngine processEngine) {
+  }
+
+  @Override
+  public String toString() {
+    return getClass().getSimpleName();
+  }
+
+}