Understanding SpringBoot MyBatis Integration: @MapperScan, @Import, and Bean Definition Processing

The author, a senior architect, introduces the topic of using SpringBoot with MyBatis and the need to configure dependencies and annotations.

Configuration snippet shows MyBatis settings: mybatis: mapper-locations: classpath:mapper/*.xml type-aliases-package: com.coco.pojo and mentions adding an annotation on the startup class.

The @MapperScan("com.coco.mapper") annotation is highlighted as the entry point that tells Spring to scan the specified package for mapper interfaces.

The article then explains the role of @Import({MapperScannerRegistrar.class}), noting that this annotation registers a class that will be instantiated during SpringBoot startup.

MapperScannerRegistrar implements ImportBeanDefinitionRegistrar, allowing Spring to process the @MapperScan annotation, create a ClassPathMapperScanner, and register each mapper interface as a BeanDefinition.

Debug mode code snippet demonstrates the registerBeanDefinitions method: @Override public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) { // Get MapperScan annotation attributes AnnotationAttributes annoAttrs = AnnotationAttributes.fromMap(importingClassMetadata.getAnnotationAttributes(MapperScan.class.getName())); ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry); // Extract basePackages from annotation for (String pkg : annoAttrs.getStringArray("basePackages")) { if (StringUtils.hasText(pkg)) { basePackages.add(pkg); } } // Scan the packages for mapper interfaces scanner.doScan(StringUtils.toStringArray(basePackages)); }

The processing of BeanDefinitions is described: after scanning, a collection of BeanDefinitionHolder objects is returned, each representing a mapper interface bean whose beanClass is later changed to MapperFactoryBean.

This transformation enables Spring to create proxy instances via MyBatis's MapperProxy, which uses JDK dynamic proxies to delegate method calls to the appropriate SQL statements defined in XML mapper files.

The overall flow is summarized: Spring scans mapper interfaces, registers BeanDefinitions, modifies them, creates proxy beans, and finally invokes the corresponding SQL when a mapper method is called.

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