mybatis-spring @MapperScan走读分析

接上一篇文章：https://blog.csdn.net/qq_26437925/article/details/145100531， 本文注解分析mybatis-spring中的@MapperScan注解，则将容易许多。

@MapperScan注解定义

@MapperScan注解加入了@Import(MapperScannerRegistrar.class)， 所以可以知晓

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import(MapperScannerRegistrar.class)
public @interface MapperScan {/*** Alias for the {@link #basePackages()} attribute. Allows for more concise* annotation declarations e.g.:* {@code @EnableMyBatisMapperScanner("org.my.pkg")} instead of {@code* @EnableMyBatisMapperScanner(basePackages= "org.my.pkg"})}.*/String[] value() default {};/*** Base packages to scan for MyBatis interfaces. Note that only interfaces* with at least one method will be registered; concrete classes will be* ignored.*/String[] basePackages() default {};/*** Type-safe alternative to {@link #basePackages()} for specifying the packages* to scan for annotated components. The package of each class specified will be scanned.* <p>Consider creating a special no-op marker class or interface in each package* that serves no purpose other than being referenced by this attribute.*/Class<?>[] basePackageClasses() default {};/*** The {@link BeanNameGenerator} class to be used for naming detected components* within the Spring container.*/Class<? extends BeanNameGenerator> nameGenerator() default BeanNameGenerator.class;/*** This property specifies the annotation that the scanner will search for.* <p>* The scanner will register all interfaces in the base package that also have* the specified annotation.* <p>* Note this can be combined with markerInterface.*/Class<? extends Annotation> annotationClass() default Annotation.class;/*** This property specifies the parent that the scanner will search for.* <p>* The scanner will register all interfaces in the base package that also have* the specified interface class as a parent.* <p>* Note this can be combined with annotationClass.*/Class<?> markerInterface() default Class.class;/*** Specifies which {@code SqlSessionTemplate} to use in the case that there is* more than one in the spring context. Usually this is only needed when you* have more than one datasource.*/String sqlSessionTemplateRef() default "";/*** Specifies which {@code SqlSessionFactory} to use in the case that there is* more than one in the spring context. Usually this is only needed when you* have more than one datasource.*/String sqlSessionFactoryRef() default "";/*** Specifies a custom MapperFactoryBean to return a mybatis proxy as spring bean.**/Class<? extends MapperFactoryBean> factoryBean() default MapperFactoryBean.class;}

ConfigurationClassPostProcessor扫描注册beanDefinition

mybatis-spring中自定义了org.mybatis.spring.annotation.MapperScannerRegistrar实现了ImportBeanDefinitionRegistrar接口，所以能被处理

mybatis-spring也实现了自己的Scanner能够扫描出所有的@Mapper的interface, 然后定义出BeanDefinition

继续debug可以看到对BeanDefinisiton 会设置BeanClass为FactoryBean类

即自定义的org.mybatis.spring.mapper.MapperFactoryBean

org.mybatis.spring.mapper.MapperFactoryBean

仍然是重点关注getObject方法

@Override
public T getObject() throws Exception {return getSqlSession().getMapper(this.mapperInterface);
}

数据库操作也封装为SqlSession接口，有多个实现类可选择

最后也会发现是java 动态代理

org.apache.ibatis.binding.MapperProxy

代理的具体实现则在mybatis依赖的MapperProxy类中

@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {try {if (Object.class.equals(method.getDeclaringClass())) {return method.invoke(this, args);} else if (isDefaultMethod(method)) {return invokeDefaultMethod(proxy, method, args);}} catch (Throwable t) {throw ExceptionUtil.unwrapThrowable(t);}final MapperMethod mapperMethod = cachedMapperMethod(method);return mapperMethod.execute(sqlSession, args);
}

sql执行

public Object execute(SqlSession sqlSession, Object[] args) {Object result;switch (command.getType()) {case INSERT: {Object param = method.convertArgsToSqlCommandParam(args);result = rowCountResult(sqlSession.insert(command.getName(), param));break;}case UPDATE: {Object param = method.convertArgsToSqlCommandParam(args);result = rowCountResult(sqlSession.update(command.getName(), param));break;}case DELETE: {Object param = method.convertArgsToSqlCommandParam(args);result = rowCountResult(sqlSession.delete(command.getName(), param));break;}case SELECT:if (method.returnsVoid() && method.hasResultHandler()) {executeWithResultHandler(sqlSession, args);result = null;} else if (method.returnsMany()) {result = executeForMany(sqlSession, args);} else if (method.returnsMap()) {result = executeForMap(sqlSession, args);} else if (method.returnsCursor()) {result = executeForCursor(sqlSession, args);} else {Object param = method.convertArgsToSqlCommandParam(args);result = sqlSession.selectOne(command.getName(), param);}break;case FLUSH:result = sqlSession.flushStatements();break;default:throw new BindingException("Unknown execution method for: " + command.getName());}if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) {throw new BindingException("Mapper method '" + command.getName() + " attempted to return null from a method with a primitive return type (" + method.getReturnType() + ").");}return result;
}

org.apache.ibatis.executor.SimpleExecutor#doUpdate

继续深入找一个简单的sql执行实现类，可以看到类似jdbc的处理流程

总结

最后还是回到了上一篇博文：https://blog.csdn.net/qq_26437925/article/details/145100531。只不过mybatis-spring要丰富一些，原理仍然是动态代理，BeanFactoryPostProcessor ，FactoryBean，BeanPostProcessor这些基础知识。