activiti整合springboot问题总结

因项目需求，将cloud项目的工作流模块迁移到springboot项目中。将中途遇到的一些问题整合到此处。

已处理部分

activiti依赖spring与项目spring不兼容。

解决

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-parent</artifactId>
            <version>${spring-boot-starter.version}</version>
            <scope>import</scope>
            <type>pom</type>
        </dependency>
    </dependencies>
</dependencyManagement>

MyBatis依赖冲突

启动报错：

***************************
APPLICATION FAILED TO START
***************************

Description:

An attempt was made to call a method that does not exist. The attempt was made from the following location:

    org.mybatis.spring.SqlSessionFactoryBean.buildSqlSessionFactory(SqlSessionFactoryBean.java:564)

The following method did not exist:

    org.apache.ibatis.session.Configuration.setDefaultEnumTypeHandler(Ljava/lang/Class;)V

The method's class, org.apache.ibatis.session.Configuration, is available from the following locations:

    jar:file:/D:/Program%20Files/maven/.m2/repository/org/mybatis/mybatis/3.4.2/mybatis-3.4.2.jar!/org/apache/ibatis/session/Configuration.class

It was loaded from the following location:

    file:/D:/Program%20Files/maven/.m2/repository/org/mybatis/mybatis/3.4.2/mybatis-3.4.2.jar


Action:

Correct the classpath of your application so that it contains a single, compatible version of org.apache.ibatis.session.Configuration

Disconnected from the target VM, address: '127.0.0.1:64349', transport: 'socket'

Process finished with exit code 1

解决

引入activiti时排除MyBatis

<dependency>
    <groupId>org.activiti</groupId>
    <artifactId>activiti-spring-boot-starter</artifactId>
    <exclusions>
        <exclusion>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
        </exclusion>
    </exclusions>
</dependency>

activiti 的bean与项目中的bean重名。

注：已配置 spring.main.allow-bean-definition-overriding: true 允许项目存在重名bean。

通过注解创建的bean默认使用org.springframework.context.annotation.AnnotationBeanNameGenerator#generateBeanName生成beanName。如果没有指定名字，则默认使用首字母小写的类名或者方法名。
通过beanFactory将activiti的TaskService、HistoryService等服务注入spring容器中。项目本身也有同名的service时，同名的只有一个service被创建。

    // activiti Service创建：
    @Bean
    public ProcessEngineConfiguration processEngineConfiguration(DataSource dataSource, PlatformTransactionManager transactionManager) {
        SpringProcessEngineConfiguration processEngineConfiguration = new SpringProcessEngineConfiguration();
        processEngineConfiguration.setDataSource(dataSource);
        processEngineConfiguration.setDatabaseType("mysql");
        processEngineConfiguration.setTransactionManager(transactionManager);
        return processEngineConfiguration;
    }

    /**
     * 流程引擎，与spring整合使用factoryBean
     */
    @Bean
    public ProcessEngineFactoryBean processEngine(ProcessEngineConfiguration processEngineConfiguration) {
        ProcessEngineFactoryBean processEngineFactoryBean = new ProcessEngineFactoryBean();
        processEngineFactoryBean.setProcessEngineConfiguration((ProcessEngineConfigurationImpl) processEngineConfiguration);
        return processEngineFactoryBean;
    }

    @Bean
    public RepositoryService repositoryService(ProcessEngine processEngine) {
        return processEngine.getRepositoryService();
    }

    @Bean
    public RuntimeService runtimeService(ProcessEngine processEngine) {
        return processEngine.getRuntimeService();
    }

    @Bean
    public TaskService taskService(ProcessEngine processEngine) {
        return processEngine.getTaskService();
    }

    @Bean
    public HistoryService historyService(ProcessEngine processEngine) {
        return processEngine.getHistoryService();
    }

问题排查

spring默认的重名处理方法为org.springframework.beans.factory.support.DefaultListableBeanFactory#registerBeanDefinition，直接覆盖先前的bean。
监控 org.springframework.context.annotation.ClassPathBeanDefinitionScanner#doScan
发现,通过ComponentScan扫描的bean最先被创建，而所以导致通过@Service创建的bean被覆盖，@Autowrite无法注入。虽然可以通过修改类名或者指定bean名称解决，但是闲着也是闲着，不如折腾一下。
既然因为重名导致被覆盖，又不想手动改名字，那就修改生成beanName的规则。
继承AnnotationBeanNameGenerator 重写generateBeanName方法,使用类的完整路径作为bean名称。

项目使用springboot2.2.13 需要通过@ComponentScan( basePackages = {"xxx"},nameGenerator = UniqueNameGenerator.class)配置生效。
此处又有几个小知识点：
@SpringBootApplication默认扫描同级目录下的包。
@ComponentScan会覆盖@SpringBootApplication中配置的路径，而@ComponentScans不会。先前画蛇添足使用了@ComponentScans，程序会把两种扫包规则都执行一遍，而@ComponentScans使用的是自定义的命名规则@SpringBootApplication使用的是默认的命名规则，导致部分包下的bean会被创建两遍。
报错：

implementations of CachingConfigurer were found when only 1 was expected. Refactor the configuration such that CachingConfigurer is implemented only once or not at all.

解决

使用自定义beanName生成规则，并通过ComponentScan配置

public class UniqueNameGenerator extends AnnotationBeanNameGenerator {
    @Override
    @NonNull
    public String generateBeanName(@NonNull BeanDefinition definition,@NonNull BeanDefinitionRegistry registry) {
        if (definition instanceof AnnotatedBeanDefinition) {
            //获取指定beanName
            String beanName = determineBeanNameFromAnnotation((AnnotatedBeanDefinition) definition);
            if (StringUtils.hasText(beanName)) {
                return beanName;
            }
        }
        return Objects.requireNonNull(definition.getBeanClassName());
    }
}

@ComponentScan(basePackages = {"com.xxx", "org.activiti.engine.impl"}, nameGenerator = UniqueNameGenerator.class)
@SpringBootApplication(exclude = {DataSourceAutoConfiguration.class})
public class Application{

调用接口报错，两个类加载器中有两个不同的对象

Handler dispatch failed;  nested exception is java.lang.LinkageError: loader constraint violation:  when resolving interface method \"org.activiti.engine.RepositoryService.createModelQuery()Lorg/activiti/engine/repository/ModelQuery;\" the class loader (instance of org/springframework/boot/devtools/restart/classloader/RestartClassLoader) of the current class, com/pms/workflow/service/ModelService, and the class loader (instance of sun/misc/Launcher$AppClassLoader) for the method's defining class, org/activiti/engine/RepositoryService,  have different Class objects for the type org/activiti/engine/repository/ModelQuery used in the signature

错误内容大意是：调用RepositoryService.createModelQuery()Lorg时发现两个类加载器RestartClassLoader和AppClassLoader中存在不同的class对象

AppClassLoader是JVM的应用类加载器，RestartClassLoader 是个啥？
点进去一看路径org.springframework.boot.devtools.restart.classloader.RestartClassLoader，
水平有限搞不懂问题的根源，删掉spring-boot-devtools依赖就完事。

未处理部分

Spring

springboot多模块项目,新建的子模块内容无法引入

估计是IDE问题，删除后新建就好了

参考

《聊Spring的bean覆盖（存在同名name/id问题），介绍Spring名称生成策略接口BeanNameGenerator》
《SprintBoot devtools导致同一个类出现两个不同的Class类》