在SpringBoot中针对MyBatis中的配置如下

# mybatis配置
mybatis.mapper-locations=classpath*:sqlMapper/**/*.xml
mybatis.type-aliases-package=com.example.durid.demo.entity

那么在对应类org.mybatis.spring.boot.autoconfigure.MybatisProperties中获取配置参数的地方打上断点，不如如下位置：

  public String[] getMapperLocations() {return this.mapperLocations;}public void setMapperLocations(String[] mapperLocations) {this.mapperLocations = mapperLocations;}

以debug模式启动Spring Boot程序：

拷贝出来的调用栈信息如下：

setMapperLocations:118, MybatisProperties (org.mybatis.spring.boot.autoconfigure)
invoke0:-1, NativeMethodAccessorImpl (sun.reflect)
invoke:62, NativeMethodAccessorImpl (sun.reflect)
invoke:43, DelegatingMethodAccessorImpl (sun.reflect)
invoke:498, Method (java.lang.reflect)
setValue:346, JavaBeanBinder$BeanProperty (org.springframework.boot.context.properties.bind)
bind:96, JavaBeanBinder (org.springframework.boot.context.properties.bind)
bind:79, JavaBeanBinder (org.springframework.boot.context.properties.bind)
bind:56, JavaBeanBinder (org.springframework.boot.context.properties.bind)
lambda$bindDataObject$5:452, Binder (org.springframework.boot.context.properties.bind)
get:-1, 1371495133 (org.springframework.boot.context.properties.bind.Binder$$Lambda$100)
withIncreasedDepth:572, Binder$Context (org.springframework.boot.context.properties.bind)
withDataObject:558, Binder$Context (org.springframework.boot.context.properties.bind)
access$400:513, Binder$Context (org.springframework.boot.context.properties.bind)
bindDataObject:450, Binder (org.springframework.boot.context.properties.bind)
bindObject:391, Binder (org.springframework.boot.context.properties.bind)
bind:320, Binder (org.springframework.boot.context.properties.bind)
bind:308, Binder (org.springframework.boot.context.properties.bind)
bind:238, Binder (org.springframework.boot.context.properties.bind)
bind:225, Binder (org.springframework.boot.context.properties.bind)
bind:89, ConfigurationPropertiesBinder (org.springframework.boot.context.properties)
bind:107, ConfigurationPropertiesBindingPostProcessor (org.springframework.boot.context.properties)
postProcessBeforeInitialization:96, ConfigurationPropertiesBindingPostProcessor (org.springframework.boot.context.properties)
applyBeanPostProcessorsBeforeInitialization:416, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
initializeBean:1788, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
doCreateBean:595, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
createBean:517, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
lambda$doGetBean$0:323, AbstractBeanFactory (org.springframework.beans.factory.support)
getObject:-1, 697508322 (org.springframework.beans.factory.support.AbstractBeanFactory$$Lambda$154)
getSingleton:222, DefaultSingletonBeanRegistry (org.springframework.beans.factory.support)
doGetBean:321, AbstractBeanFactory (org.springframework.beans.factory.support)
getBean:202, AbstractBeanFactory (org.springframework.beans.factory.support)
resolveCandidate:276, DependencyDescriptor (org.springframework.beans.factory.config)
doResolveDependency:1287, DefaultListableBeanFactory (org.springframework.beans.factory.support)
resolveDependency:1207, DefaultListableBeanFactory (org.springframework.beans.factory.support)
resolveAutowiredArgument:885, ConstructorResolver (org.springframework.beans.factory.support)
createArgumentArray:789, ConstructorResolver (org.springframework.beans.factory.support)
autowireConstructor:228, ConstructorResolver (org.springframework.beans.factory.support)
autowireConstructor:1358, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
createBeanInstance:1204, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
doCreateBean:557, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
createBean:517, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
lambda$doGetBean$0:323, AbstractBeanFactory (org.springframework.beans.factory.support)
getObject:-1, 697508322 (org.springframework.beans.factory.support.AbstractBeanFactory$$Lambda$154)
getSingleton:222, DefaultSingletonBeanRegistry (org.springframework.beans.factory.support)
doGetBean:321, AbstractBeanFactory (org.springframework.beans.factory.support)
getBean:202, AbstractBeanFactory (org.springframework.beans.factory.support)
instantiateUsingFactoryMethod:409, ConstructorResolver (org.springframework.beans.factory.support)
instantiateUsingFactoryMethod:1338, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
createBeanInstance:1177, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
doCreateBean:557, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
createBean:517, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
lambda$doGetBean$0:323, AbstractBeanFactory (org.springframework.beans.factory.support)
getObject:-1, 697508322 (org.springframework.beans.factory.support.AbstractBeanFactory$$Lambda$154)
getSingleton:222, DefaultSingletonBeanRegistry (org.springframework.beans.factory.support)
doGetBean:321, AbstractBeanFactory (org.springframework.beans.factory.support)
getBean:202, AbstractBeanFactory (org.springframework.beans.factory.support)
resolveCandidate:276, DependencyDescriptor (org.springframework.beans.factory.config)
doResolveDependency:1287, DefaultListableBeanFactory (org.springframework.beans.factory.support)
resolveDependency:1207, DefaultListableBeanFactory (org.springframework.beans.factory.support)
autowireByType:1511, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
populateBean:1406, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
doCreateBean:594, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
createBean:517, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
lambda$doGetBean$0:323, AbstractBeanFactory (org.springframework.beans.factory.support)
getObject:-1, 697508322 (org.springframework.beans.factory.support.AbstractBeanFactory$$Lambda$154)
getSingleton:222, DefaultSingletonBeanRegistry (org.springframework.beans.factory.support)
doGetBean:321, AbstractBeanFactory (org.springframework.beans.factory.support)
getBean:202, AbstractBeanFactory (org.springframework.beans.factory.support)
resolveCandidate:276, DependencyDescriptor (org.springframework.beans.factory.config)
doResolveDependency:1287, DefaultListableBeanFactory (org.springframework.beans.factory.support)
resolveDependency:1207, DefaultListableBeanFactory (org.springframework.beans.factory.support)
inject:640, AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement (org.springframework.beans.factory.annotation)
inject:130, InjectionMetadata (org.springframework.beans.factory.annotation)
postProcessProperties:399, AutowiredAnnotationBeanPostProcessor (org.springframework.beans.factory.annotation)
populateBean:1422, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
doCreateBean:594, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
createBean:517, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
lambda$doGetBean$0:323, AbstractBeanFactory (org.springframework.beans.factory.support)
getObject:-1, 697508322 (org.springframework.beans.factory.support.AbstractBeanFactory$$Lambda$154)
getSingleton:222, DefaultSingletonBeanRegistry (org.springframework.beans.factory.support)
doGetBean:321, AbstractBeanFactory (org.springframework.beans.factory.support)
getBean:202, AbstractBeanFactory (org.springframework.beans.factory.support)
resolveCandidate:276, DependencyDescriptor (org.springframework.beans.factory.config)
doResolveDependency:1287, DefaultListableBeanFactory (org.springframework.beans.factory.support)
resolveDependency:1207, DefaultListableBeanFactory (org.springframework.beans.factory.support)
inject:640, AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement (org.springframework.beans.factory.annotation)
inject:130, InjectionMetadata (org.springframework.beans.factory.annotation)
postProcessProperties:399, AutowiredAnnotationBeanPostProcessor (org.springframework.beans.factory.annotation)
populateBean:1422, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
doCreateBean:594, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
createBean:517, AbstractAutowireCapableBeanFactory (org.springframework.beans.factory.support)
lambda$doGetBean$0:323, AbstractBeanFactory (org.springframework.beans.factory.support)
getObject:-1, 697508322 (org.springframework.beans.factory.support.AbstractBeanFactory$$Lambda$154)
getSingleton:222, DefaultSingletonBeanRegistry (org.springframework.beans.factory.support)
doGetBean:321, AbstractBeanFactory (org.springframework.beans.factory.support)
getBean:202, AbstractBeanFactory (org.springframework.beans.factory.support)
preInstantiateSingletons:879, DefaultListableBeanFactory (org.springframework.beans.factory.support)
finishBeanFactoryInitialization:878, AbstractApplicationContext (org.springframework.context.support)
refresh:550, AbstractApplicationContext (org.springframework.context.support)
refresh:141, ServletWebServerApplicationContext (org.springframework.boot.web.servlet.context)
refresh:747, SpringApplication (org.springframework.boot)
refreshContext:397, SpringApplication (org.springframework.boot)
run:315, SpringApplication (org.springframework.boot)
run:1226, SpringApplication (org.springframework.boot)
run:1215, SpringApplication (org.springframework.boot)
main:10, DemoApplication (com.example.durid.demo)

从调用栈底部开始分析 会发现这个配置真正开始读取是在完成Bean工厂实例化的时候

获取一个名称为userController的bean

查看一下UserController的定义

package com.example.durid.demo.controller;import com.example.durid.demo.entity.User;
import com.example.durid.demo.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;import java.util.List;@RestController
@RequestMapping("/user")
public class UserController {@Autowiredprivate UserService userService;// http://localhost:8083/user/list@RequestMapping("/list")public List<User> list() {return userService.list();}// http://localhost:8083/user/get/2@RequestMapping("/get/{id}")public User get(@PathVariable("id") Integer id) {return userService.findById(id);}// http://localhost:8083/user/delete/2@PostMapping("/delete/{id}")public boolean delete(@PathVariable("id") Integer id) {return userService.deleteById(id);}// http://localhost:8083/user/add@PostMapping("/add")public boolean add(@RequestBody User user) {return userService.add(user);}
}

UserController依赖UserService类型的Bean，猜测后面应该会引起UserService类型Bean的初始化


再分析一下UserService类

package com.example.durid.demo.service.impl;import com.example.durid.demo.entity.User;
import com.example.durid.demo.mapper.UserMapper;
import com.example.durid.demo.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;import java.util.List;@Service
public class UserServiceImpl implements UserService {@Autowiredprivate UserMapper userMapper;@Overridepublic boolean add(User user) {return userMapper.insert(user) == 1;}@Overridepublic List<User> list() {return userMapper.selectAll();}@Overridepublic boolean deleteById(Integer id) {return userMapper.deleteByPrimaryKey(id) == 1;}@Overridepublic User findById(Integer id) {return userMapper.selectByPrimaryKey(id);}
}

UserService依赖于UserMapper类型的Bean，因此后面会导致UserMapper类型Bean的初始化


而UserMapper是一个接口，通过动态代理生成一个MapperFactoryBean类型的实现，这个逻辑属于MyBatis的范畴，此处略去不表。

分析一下MapperFactoryBean类的定义

/*** Copyright 2010-2019 the original author or authors.** Licensed under the Apache License, Version 2.0 (the "License");* 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.mybatis.spring.mapper;import static org.springframework.util.Assert.notNull;import org.apache.ibatis.executor.ErrorContext;
import org.apache.ibatis.session.Configuration;
import org.mybatis.spring.SqlSessionTemplate;
import org.mybatis.spring.support.SqlSessionDaoSupport;
import org.springframework.beans.factory.FactoryBean;/*** BeanFactory that enables injection of MyBatis mapper interfaces. It can be set up with a SqlSessionFactory or a* pre-configured SqlSessionTemplate.* <p>* Sample configuration:** <pre class="code">* {@code*   <bean id="baseMapper" class="org.mybatis.spring.mapper.MapperFactoryBean" abstract="true" lazy-init="true">*     <property name="sqlSessionFactory" ref="sqlSessionFactory" />*   </bean>**   <bean id="oneMapper" parent="baseMapper">*     <property name="mapperInterface" value="my.package.MyMapperInterface" />*   </bean>**   <bean id="anotherMapper" parent="baseMapper">*     <property name="mapperInterface" value="my.package.MyAnotherMapperInterface" />*   </bean>* }* </pre>* <p>* Note that this factory can only inject <em>interfaces</em>, not concrete classes.** @author Eduardo Macarron** @see SqlSessionTemplate*/
public class MapperFactoryBean<T> extends SqlSessionDaoSupport implements FactoryBean<T> {private Class<T> mapperInterface;private boolean addToConfig = true;public MapperFactoryBean() {// intentionally empty}public MapperFactoryBean(Class<T> mapperInterface) {this.mapperInterface = mapperInterface;}/*** {@inheritDoc}*/@Overrideprotected void checkDaoConfig() {super.checkDaoConfig();notNull(this.mapperInterface, "Property 'mapperInterface' is required");Configuration configuration = getSqlSession().getConfiguration();if (this.addToConfig && !configuration.hasMapper(this.mapperInterface)) {try {configuration.addMapper(this.mapperInterface);} catch (Exception e) {logger.error("Error while adding the mapper '" + this.mapperInterface + "' to configuration.", e);throw new IllegalArgumentException(e);} finally {ErrorContext.instance().reset();}}}/*** {@inheritDoc}*/@Overridepublic T getObject() throws Exception {return getSqlSession().getMapper(this.mapperInterface);}/*** {@inheritDoc}*/@Overridepublic Class<T> getObjectType() {return this.mapperInterface;}/*** {@inheritDoc}*/@Overridepublic boolean isSingleton() {return true;}// ------------- mutators --------------/*** Sets the mapper interface of the MyBatis mapper** @param mapperInterface*          class of the interface*/public void setMapperInterface(Class<T> mapperInterface) {this.mapperInterface = mapperInterface;}/*** Return the mapper interface of the MyBatis mapper** @return class of the interface*/public Class<T> getMapperInterface() {return mapperInterface;}/*** If addToConfig is false the mapper will not be added to MyBatis. This means it must have been included in* mybatis-config.xml.* <p>* If it is true, the mapper will be added to MyBatis in the case it is not already registered.* <p>* By default addToConfig is true.** @param addToConfig*          a flag that whether add mapper to MyBatis or not*/public void setAddToConfig(boolean addToConfig) {this.addToConfig = addToConfig;}/*** Return the flag for addition into MyBatis config.** @return true if the mapper will be added to MyBatis in the case it is not already registered.*/public boolean isAddToConfig() {return addToConfig;}
}

该类又继承了SqlSessionDaoSupport

/*** Copyright 2010-2019 the original author or authors.** Licensed under the Apache License, Version 2.0 (the "License");* 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.mybatis.spring.support;import static org.springframework.util.Assert.notNull;import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.mybatis.spring.SqlSessionTemplate;
import org.springframework.dao.support.DaoSupport;/*** Convenient super class for MyBatis SqlSession data access objects. It gives you access to the template which can then* be used to execute SQL methods.* <p>* This class needs a SqlSessionTemplate or a SqlSessionFactory. If both are set the SqlSessionFactory will be ignored.* <p>* * @author Putthiphong Boonphong* @author Eduardo Macarron** @see #setSqlSessionFactory* @see #setSqlSessionTemplate* @see SqlSessionTemplate*/
public abstract class SqlSessionDaoSupport extends DaoSupport {private SqlSessionTemplate sqlSessionTemplate;/*** Set MyBatis SqlSessionFactory to be used by this DAO. Will automatically create SqlSessionTemplate for the given* SqlSessionFactory.** @param sqlSessionFactory*          a factory of SqlSession*/public void setSqlSessionFactory(SqlSessionFactory sqlSessionFactory) {if (this.sqlSessionTemplate == null || sqlSessionFactory != this.sqlSessionTemplate.getSqlSessionFactory()) {this.sqlSessionTemplate = createSqlSessionTemplate(sqlSessionFactory);}}/*** Create a SqlSessionTemplate for the given SqlSessionFactory. Only invoked if populating the DAO with a* SqlSessionFactory reference!* <p>* Can be overridden in subclasses to provide a SqlSessionTemplate instance with different configuration, or a custom* SqlSessionTemplate subclass.* * @param sqlSessionFactory*          the MyBatis SqlSessionFactory to create a SqlSessionTemplate for* @return the new SqlSessionTemplate instance* @see #setSqlSessionFactory*/@SuppressWarnings("WeakerAccess")protected SqlSessionTemplate createSqlSessionTemplate(SqlSessionFactory sqlSessionFactory) {return new SqlSessionTemplate(sqlSessionFactory);}/*** Return the MyBatis SqlSessionFactory used by this DAO.** @return a factory of SqlSession*/public final SqlSessionFactory getSqlSessionFactory() {return (this.sqlSessionTemplate != null ? this.sqlSessionTemplate.getSqlSessionFactory() : null);}/*** Set the SqlSessionTemplate for this DAO explicitly, as an alternative to specifying a SqlSessionFactory.** @param sqlSessionTemplate*          a template of SqlSession* @see #setSqlSessionFactory*/public void setSqlSessionTemplate(SqlSessionTemplate sqlSessionTemplate) {this.sqlSessionTemplate = sqlSessionTemplate;}/*** Users should use this method to get a SqlSession to call its statement methods This is SqlSession is managed by* spring. Users should not commit/rollback/close it because it will be automatically done.** @return Spring managed thread safe SqlSession*/public SqlSession getSqlSession() {return this.sqlSessionTemplate;}/*** Return the SqlSessionTemplate for this DAO, pre-initialized with the SessionFactory or set explicitly.* <p>* <b>Note: The returned SqlSessionTemplate is a shared instance.</b> You may introspect its configuration, but not* modify the configuration (other than from within an {@link #initDao} implementation). Consider creating a custom* SqlSessionTemplate instance via {@code new SqlSessionTemplate(getSqlSessionFactory())}, in which case you're* allowed to customize the settings on the resulting instance.** @return a template of SqlSession*/public SqlSessionTemplate getSqlSessionTemplate() {return this.sqlSessionTemplate;}/*** {@inheritDoc}*/@Overrideprotected void checkDaoConfig() {notNull(this.sqlSessionTemplate, "Property 'sqlSessionFactory' or 'sqlSessionTemplate' are required");}}

该类有setSqlSessionFactory和setSqlSessionTemplate，会触发SqlSessionFactory类型Bean的注入

然后开始SqlSessionFactory类型Bean的解析

-- 查看sqlSessionFactory的mbd定义信息：
Root bean: class [null]; scope=singleton; abstract=false; lazyInit=null; autowireMode=3; dependencyCheck=0; autowireCandidate=true; primary=false; factoryBeanName=org.mybatis.spring.boot.autoconfigure.MybatisAutoConfiguration; factoryMethodName=sqlSessionFactory; initMethodName=null; destroyMethodName=(inferred); defined in class path resource [org/mybatis/spring/boot/autoconfigure/MybatisAutoConfiguration.class]

从mbd信息可知：该类的定义在MybatisAutoConfiguration类中的sqlSessionFactory方法中：

  @Bean@ConditionalOnMissingBeanpublic SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception {SqlSessionFactoryBean factory = new SqlSessionFactoryBean();factory.setDataSource(dataSource);factory.setVfs(SpringBootVFS.class);if (StringUtils.hasText(this.properties.getConfigLocation())) {factory.setConfigLocation(this.resourceLoader.getResource(this.properties.getConfigLocation()));}applyConfiguration(factory);if (this.properties.getConfigurationProperties() != null) {factory.setConfigurationProperties(this.properties.getConfigurationProperties());}if (!ObjectUtils.isEmpty(this.interceptors)) {factory.setPlugins(this.interceptors);}if (this.databaseIdProvider != null) {factory.setDatabaseIdProvider(this.databaseIdProvider);}if (StringUtils.hasLength(this.properties.getTypeAliasesPackage())) {factory.setTypeAliasesPackage(this.properties.getTypeAliasesPackage());}if (this.properties.getTypeAliasesSuperType() != null) {factory.setTypeAliasesSuperType(this.properties.getTypeAliasesSuperType());}if (StringUtils.hasLength(this.properties.getTypeHandlersPackage())) {factory.setTypeHandlersPackage(this.properties.getTypeHandlersPackage());}if (!ObjectUtils.isEmpty(this.typeHandlers)) {factory.setTypeHandlers(this.typeHandlers);}if (!ObjectUtils.isEmpty(this.properties.resolveMapperLocations())) {factory.setMapperLocations(this.properties.resolveMapperLocations());}Set<String> factoryPropertyNames = Stream.of(new BeanWrapperImpl(SqlSessionFactoryBean.class).getPropertyDescriptors()).map(PropertyDescriptor::getName).collect(Collectors.toSet());Class<? extends LanguageDriver> defaultLanguageDriver = this.properties.getDefaultScriptingLanguageDriver();if (factoryPropertyNames.contains("scriptingLanguageDrivers") && !ObjectUtils.isEmpty(this.languageDrivers)) {// Need to mybatis-spring 2.0.2+factory.setScriptingLanguageDrivers(this.languageDrivers);if (defaultLanguageDriver == null && this.languageDrivers.length == 1) {defaultLanguageDriver = this.languageDrivers[0].getClass();}}if (factoryPropertyNames.contains("defaultScriptingLanguageDriver")) {// Need to mybatis-spring 2.0.2+factory.setDefaultScriptingLanguageDriver(defaultLanguageDriver);}return factory.getObject();}

@org.springframework.context.annotation.Configuration
@ConditionalOnClass({ SqlSessionFactory.class, SqlSessionFactoryBean.class })
@ConditionalOnSingleCandidate(DataSource.class)
@EnableConfigurationProperties(MybatisProperties.class)
@AutoConfigureAfter({ DataSourceAutoConfiguration.class, MybatisLanguageDriverAutoConfiguration.class })
public class MybatisAutoConfiguration implements InitializingBean

查看该类的构造方法

  public MybatisAutoConfiguration(MybatisProperties properties, ObjectProvider<Interceptor[]> interceptorsProvider,ObjectProvider<TypeHandler[]> typeHandlersProvider, ObjectProvider<LanguageDriver[]> languageDriversProvider,ResourceLoader resourceLoader, ObjectProvider<DatabaseIdProvider> databaseIdProvider,ObjectProvider<List<ConfigurationCustomizer>> configurationCustomizersProvider) {this.properties = properties;this.interceptors = interceptorsProvider.getIfAvailable();this.typeHandlers = typeHandlersProvider.getIfAvailable();this.languageDrivers = languageDriversProvider.getIfAvailable();this.resourceLoader = resourceLoader;this.databaseIdProvider = databaseIdProvider.getIfAvailable();this.configurationCustomizers = configurationCustomizersProvider.getIfAvailable();}

此时会触发MybatisProperties类型Bean的初始化化操作

MybatisProperties类有默认构造函数，而且不依赖其他类型的Bean，但此处在初始化这种类型Bean的时候是需要注入配置参数到Bean属性中的，而这个操作是由ConfigurationPropertiesBindingPostProcessor来进行的。

ConfigurationPropertiesBindingPostProcessor进行参数的注入操作


查看该类的方法

	@Overridepublic Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {bind(ConfigurationPropertiesBean.get(this.applicationContext, bean, beanName));return bean;}

添加一个条件断点，再次debug

在进行配置类后置处理之前会通过ConfigurationPropertiesBean包装一下

查看该类的注释：

Provides access to @ConfigurationProperties bean details, regardless of if the annotation was used directly or on a @Bean factory method. This class can be used to access all configuration properties beans in an ApplicationContext, or individual beans on a case-by-case basis (for example, in a BeanPostProcessor).

提供对@ConfigurationProperties Bean详细信息的访问，无论注释是直接使用还是在@Bean工厂方法上使用。 可以使用此类访问ApplicationContext中的所有配置属性Bean，也可以视情况访问单个Bean（例如，在BeanPostProcessor中）。

其中提供了获取所有配置属性Bean的方法如下：

	public static Map<String, ConfigurationPropertiesBean> getAll(ApplicationContext applicationContext) {Assert.notNull(applicationContext, "ApplicationContext must not be null");if (applicationContext instanceof ConfigurableApplicationContext) {return getAll((ConfigurableApplicationContext) applicationContext);}Map<String, ConfigurationPropertiesBean> propertiesBeans = new LinkedHashMap<>();applicationContext.getBeansWithAnnotation(ConfigurationProperties.class).forEach((beanName, bean) -> propertiesBeans.put(beanName, get(applicationContext, bean, beanName)));return propertiesBeans;}

获取单个Bean

	public static ConfigurationPropertiesBean get(ApplicationContext applicationContext, Object bean, String beanName) {Method factoryMethod = findFactoryMethod(applicationContext, beanName);return create(beanName, bean, bean.getClass(), factoryMethod);}

此处是通过第二个方法获取，该方法注解为：

Return a @ConfigurationPropertiesBean instance for the given bean details or null if the bean is not a @ConfigurationProperties object. Annotations are considered both on the bean itself, as well as any factory method (for example a @Bean method).

返回给定bean详细信息的@ConfigurationPropertiesBean实例；如果该bean不是@ConfigurationProperties对象，则返回null。 注释在bean本身以及任何工厂方法（例如@Bean方法）上均被考虑。

此处也会考虑加在工厂方法上的@ConfigurationPropertie注解

但是当前类中不存在工厂方法


通过传入的参数创建对象

	private static ConfigurationPropertiesBean create(String name, Object instance, Class<?> type, Method factory) {// 查找实例或工厂方法上是否存在ConfigurationProperties注解ConfigurationProperties annotation = findAnnotation(instance, type, factory, ConfigurationProperties.class);if (annotation == null) {return null;}// 查找Validated注解 此处会返回nullValidated validated = findAnnotation(instance, type, factory, Validated.class);Annotation[] annotations = (validated != null) ? new Annotation[] { annotation, validated }: new Annotation[] { annotation };// 解析ResolvableType信息ResolvableType bindType = (factory != null) ? ResolvableType.forMethodReturnType(factory): ResolvableType.forClass(type);// 解析bindTarget信息Bindable<Object> bindTarget = Bindable.of(bindType).withAnnotations(annotations);if (instance != null) {bindTarget = bindTarget.withExistingValue(instance);}// 构造一个ConfigurationPropertiesBean对象return new ConfigurationPropertiesBean(name, instance, annotation, bindTarget);}

返回ConfigurationPropertiesBindingPostProcessor类中进行bind操作

	private void bind(ConfigurationPropertiesBean bean) {if (bean == null || hasBoundValueObject(bean.getName())) {return;}Assert.state(bean.getBindMethod() == BindMethod.JAVA_BEAN, "Cannot bind @ConfigurationProperties for bean '"+ bean.getName() + "'. Ensure that @ConstructorBinding has not been applied to regular bean");try {this.binder.bind(bean);}catch (Exception ex) {throw new ConfigurationPropertiesBindException(bean, ex);}}

然后通过ConfigurationPropertiesBinder进行值的绑定

	private void bind(ConfigurationPropertiesBean bean) {if (bean == null || hasBoundValueObject(bean.getName())) {return;}Assert.state(bean.getBindMethod() == BindMethod.JAVA_BEAN, "Cannot bind @ConfigurationProperties for bean '"+ bean.getName() + "'. Ensure that @ConstructorBinding has not been applied to regular bean");try {this.binder.bind(bean);}catch (Exception ex) {throw new ConfigurationPropertiesBindException(bean, ex);}}

ConfigurationPropertiesBinder类注释如下：

Internal class used by the ConfigurationPropertiesBindingPostProcessor to handle the actual @ConfigurationProperties binding.

ConfigurationPropertiesBindingPostProcessor使用的内部类来处理实际的@ConfigurationProperties绑定。

BindResult<?> bind(ConfigurationPropertiesBean propertiesBean) {// 获取bindTarget对象Bindable<?> target = propertiesBean.asBindTarget();// 获取注解ConfigurationProperties annotation = propertiesBean.getAnnotation();// 根据目标类型和注解获取一个BindHandler处理器  Callback interface that can be used to    // handle additional logic during element binding. BindHandler bindHandler = getBindHandler(target, annotation);return getBinder().bind(annotation.prefix(), target, bindHandler);
}

target=[Bindable@1e4c6583 type = org.mybatis.spring.boot.autoconfigure.MybatisProperties, value = 'provided', annotations = array<Annotation>[@org.springframework.boot.context.properties.ConfigurationProperties(ignoreInvalidFields=false, ignoreUnknownFields=true, prefix=mybatis, value=mybatis)]]annotation=@org.springframework.boot.context.properties.ConfigurationProperties(ignoreInvalidFields=false, ignoreUnknownFields=true, prefix=mybatis, value=mybatis)bindHandler=

	private <T> BindHandler getBindHandler(Bindable<T> target, ConfigurationProperties annotation) {List<Validator> validators = getValidators(target);BindHandler handler = new IgnoreTopLevelConverterNotFoundBindHandler();if (annotation.ignoreInvalidFields()) {handler = new IgnoreErrorsBindHandler(handler);}if (!annotation.ignoreUnknownFields()) {UnboundElementsSourceFilter filter = new UnboundElementsSourceFilter();handler = new NoUnboundElementsBindHandler(handler, filter);}if (!validators.isEmpty()) {handler = new ValidationBindHandler(handler, validators.toArray(new Validator[0]));}// 此处没有配置ConfigurationPropertiesBindHandlerAdvisor 此处不会进行处理for (ConfigurationPropertiesBindHandlerAdvisor advisor : getBindHandlerAdvisors()) {handler = advisor.apply(handler);}return handler;}

private List<ConfigurationPropertiesBindHandlerAdvisor> getBindHandlerAdvisors() {return this.applicationContext.getBeanProvider(ConfigurationPropertiesBindHandlerAdvisor.class).orderedStream().collect(Collectors.toList());
}