解决提取Mybatis多数据源公共组件“At least one base package must be specified”的问题
在一个微服务项目中，需要把数据库配置部分做成一个公共组件给需要的子服务依赖，这个数据库公共组件包含所有的数据源配置，但是子服务可以自行选择使用部分数据源，而且要自行维护mapper，所以每个数据源上的basePackages在不同的子服务里是不同的，这就需要把basePackages的值通过占位符配置在配置文件中读取。
上面这些就是实现思路，但是这里有个问题，@MapperScan注解功能的实现类MapperScannerRegistrar实现的是ImportBeanDefinitionRegistrar。在对@Configuration注解标记的类配置时，实现占位符功能的PropertyPlaceholderAutoConfiguration还没有开始加载，所以为了动态读取配置文件信息，需要引入Environment，实现EnvironmentAware接口。
所以接下来我就自定义了@MapperScan和MapperScannerRegister，主要是修改MapperScannerRegister中读取@MapperScan中basePackages的逻辑，代码如下：
for (String pkg : annoAttrs.getStringArray("basePackages")) { if (StringUtils.hasText(pkg)) { String value = parsePlaceHolder(pkg); if (StringUtils.hasText(value)) { List<String> values = Arrays.asList(value.split(",")); for (String base : values) { basePackages.add(base); } } } } private String parsePlaceHolder(String pro) { if (StringUtils.hasText(pro) && pro.contains(PropertySourcesPlaceholderConfigurer.DEFAULT_PLACEHOLDER_PREFIX)) { String value = environment.getProperty(pro.substring(2, pro.length() - 1)); if (null == value) { LOGGER.warn("The value of property '{}' is null", pro); } return value; } return pro; }
数据源上的配置：
@Configuration @MapperScan(basePackages = {"${mybatis.mapperScan.basePackages.order}"}, sqlSessionTemplateRef = "orderSqlSessionTemplate") public class OrderDataSourceConfig {...}
下游子服务使用，在application.yml中增加配置：
mybatis:
mapperScan:
basePackages:
order: com.abc.bc.order.mapper.order
然后启动子服务，很无情的失败了：
[2020-12-28 00:03:38,450][ERROR][main][org.springframework.boot.SpringApplication:821]Application run failed java.lang.IllegalArgumentException: At least one base package must be specified at org.springframework.util.Assert.notEmpty(Assert.java:372) at org.springframework.context.annotation.ClassPathBeanDefinitionScanner.doScan(ClassPathBeanDefinitionScanner.java:272) at org.mybatis.spring.mapper.ClassPathMapperScanner.doScan(ClassPathMapperScanner.java:181) at org.springframework.context.annotation.ClassPathBeanDefinitionScanner.scan(ClassPathBeanDefinitionScanner.java:253) at org.mybatis.spring.mapper.MapperScannerConfigurer.postProcessBeanDefinitionRegistry(MapperScannerConfigurer.java:356) at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanDefinitionRegistryPostProcessors(PostProcessorRegistrationDelegate.java:275) at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:125) at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:705) at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:531) at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:140) at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:742) at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:389) at org.springframework.boot.SpringApplication.run(SpringApplication.java:311) at org.springframework.boot.SpringApplication.run(SpringApplication.java:1213) at org.springframework.boot.SpringApplication.run(SpringApplication.java:1202)
这是Spring的ClassPathBeanDefinitionScanner扫描器在扫码basePackages包并注册beanDefinitions时报错了，因为我们虽然不使用所有的数据源配置，但是其他的数据源配置上也指定了basePackages，我们没有配置其值，导致doScan(String... basePackages)时参数非空校验不通过。问题找到了，这明显是要子服务把所有的数据源配置上basePackages啊，这不符合要求啊，有可能这个项目有很多个数据源，而这个子服务刚好只需要使用其中一个，它就只需要配置自己需要的那些mapper。所以最终的设想就是即使子服务引入了全部的数据源，但是对于不需要使用的就不让Spring去扫描其配置的basePackages，这也是这个数据库公共组件应该支持的。接着改之前的MapperScannerRegister，如果basePackages为空，就不交给Spring管理了。代码如下：
/** * 如果没有配置basePackages，就不注册bean */ if (basePackages.isEmpty()) { return; }
重新打包启动，一切正常。
下面是MapperScannerRegister的完整代码：
import org.mybatis.spring.mapper.MapperFactoryBean; import org.mybatis.spring.mapper.MapperScannerConfigurer; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.springframework.beans.BeanUtils; import org.springframework.beans.factory.support.BeanDefinitionBuilder; import org.springframework.beans.factory.support.BeanDefinitionRegistry; import org.springframework.beans.factory.support.BeanNameGenerator; import org.springframework.context.EnvironmentAware; import org.springframework.context.ResourceLoaderAware; import org.springframework.context.annotation.ImportBeanDefinitionRegistrar; import org.springframework.context.support.PropertySourcesPlaceholderConfigurer; import org.springframework.core.annotation.AnnotationAttributes; import org.springframework.core.env.Environment; import org.springframework.core.io.ResourceLoader; import org.springframework.core.type.AnnotationMetadata; import org.springframework.util.ClassUtils; import org.springframework.util.StringUtils; import java.lang.annotation.Annotation; import java.util.ArrayList; import java.util.Arrays; import java.util.List; import java.util.stream.Collectors; public class MapperScannerRegistrar implements ImportBeanDefinitionRegistrar, ResourceLoaderAware, EnvironmentAware { private static final Logger LOGGER = LoggerFactory.getLogger(MapperScannerRegistrar.class); private Environment environment; @Override public void setResourceLoader(ResourceLoader resourceLoader) { // NOP } @Override public void setEnvironment(Environment environment) { this.environment = environment; } @Override public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) { AnnotationAttributes mapperScanAttrs = AnnotationAttributes .fromMap(importingClassMetadata.getAnnotationAttributes(MapperScan.class.getName())); if (mapperScanAttrs != null) { registerBeanDefinitions(mapperScanAttrs, registry, generateBaseBeanName(importingClassMetadata, 0)); } } void registerBeanDefinitions(AnnotationAttributes annoAttrs, BeanDefinitionRegistry registry, String beanName) { BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(MapperScannerConfigurer.class); builder.addPropertyValue("processPropertyPlaceHolders", true); Class<? extends Annotation> annotationClass = annoAttrs.getClass("annotationClass"); if (!Annotation.class.equals(annotationClass)) { builder.addPropertyValue("annotationClass", annotationClass); } Class<?> markerInterface = annoAttrs.getClass("markerInterface"); if (!Class.class.equals(markerInterface)) { builder.addPropertyValue("markerInterface", markerInterface); } Class<? extends BeanNameGenerator> generatorClass = annoAttrs.getClass("nameGenerator"); if (!BeanNameGenerator.class.equals(generatorClass)) { builder.addPropertyValue("nameGenerator", BeanUtils.instantiateClass(generatorClass)); } Class<? extends MapperFactoryBean> mapperFactoryBeanClass = annoAttrs.getClass("factoryBean"); if (!MapperFactoryBean.class.equals(mapperFactoryBeanClass)) { builder.addPropertyValue("mapperFactoryBeanClass", mapperFactoryBeanClass); } String sqlSessionTemplateRef = annoAttrs.getString("sqlSessionTemplateRef"); if (StringUtils.hasText(sqlSessionTemplateRef)) { builder.addPropertyValue("sqlSessionTemplateBeanName", annoAttrs.getString("sqlSessionTemplateRef")); } String sqlSessionFactoryRef = annoAttrs.getString("sqlSessionFactoryRef"); if (StringUtils.hasText(sqlSessionFactoryRef)) { builder.addPropertyValue("sqlSessionFactoryBeanName", annoAttrs.getString("sqlSessionFactoryRef")); } List<String> basePackages = new ArrayList<>(); basePackages.addAll( Arrays.stream(annoAttrs.getStringArray("value")).filter(StringUtils::hasText).collect(Collectors.toList())); /** * 修改点 */ for (String pkg : annoAttrs.getStringArray("basePackages")) { if (StringUtils.hasText(pkg)) { String value = parsePlaceHolder(pkg); if (StringUtils.hasText(value)) { List<String> values = Arrays.asList(value.split(",")); for (String base : values) { basePackages.add(base); } } } } basePackages.addAll(Arrays.stream(annoAttrs.getClassArray("basePackageClasses")).map(ClassUtils::getPackageName) .collect(Collectors.toList())); /** * 如果没有配置basePackages，就不注册bean */ if (basePackages.isEmpty()) { return; } String lazyInitialization = annoAttrs.getString("lazyInitialization"); if (StringUtils.hasText(lazyInitialization)) { builder.addPropertyValue("lazyInitialization", lazyInitialization); } builder.addPropertyValue("basePackage", StringUtils.collectionToCommaDelimitedString(basePackages)); registry.registerBeanDefinition(beanName, builder.getBeanDefinition()); } private static String generateBaseBeanName(AnnotationMetadata importingClassMetadata, int index) { return importingClassMetadata.getClassName() + "#" + org.mybatis.spring.annotation.MapperScannerRegistrar.class.getSimpleName() + "#" + index; } private String parsePlaceHolder(String pro) { if (StringUtils.hasText(pro) && pro.contains(PropertySourcesPlaceholderConfigurer.DEFAULT_PLACEHOLDER_PREFIX)) { String value = environment.getProperty(pro.substring(2, pro.length() - 1)); if (null == value) { LOGGER.warn("The value of property '{}' is null", pro); } return value; } return pro; } }
