在上章节中讲述了SpringBoot整合Mybatis的过程，以及一些配置说明，这节主要讲解一下整合的源码。
废话不多说，直接进入今天的主题。
阅读过我之前写的文章的童靴，肯定知道SpringBoot整合第三方技术的时候，都会有一个xxxAutoConfiguration的自动配置类，咱们来一起找找看。其实在项目整合Mybatis的时候，需要依赖mybatis-spring-boot-starter包：
org.mybatis.spring.boot
mybatis-spring-boot-starter
${mybatis.springboot.version}
依赖情况如下：
springboot整合mybatis的starter包.png
在mybatis-spring-boot-autoconfigure-xxx.jar包中可以找到META-INF/spring.factories的文件，打开后可以看到里面的自动配置类：
# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.mybatis.spring.boot.autoconfigure.MybatisAutoConfiguration
因此进入MybatisAutoConfiguration配置类中：
@org.springframework.context.annotation.Configuration
@ConditionalOnClass({ SqlSessionFactory.class, SqlSessionFactoryBean.class })
@ConditionalOnBean(DataSource.class)
@EnableConfigurationProperties(MybatisProperties.class)
@AutoConfigureAfter(DataSourceAutoConfiguration.class)
public class MybatisAutoConfiguration {
private static final Logger logger = LoggerFactory.getLogger(MybatisAutoConfiguration.class);
private final MybatisProperties properties;
private final Interceptor[] interceptors;
private final ResourceLoader resourceLoader;
private final DatabaseIdProvider databaseIdProvider;
private final List configurationCustomizers;
public MybatisAutoConfiguration(MybatisProperties properties,
ObjectProvider interceptorsProvider,
ResourceLoader resourceLoader,
ObjectProvider databaseIdProvider,
ObjectProvider> configurationCustomizersProvider) {
this.properties = properties;
this.interceptors = interceptorsProvider.getIfAvailable();
this.resourceLoader = resourceLoader;
this.databaseIdProvider = databaseIdProvider.getIfAvailable();
this.configurationCustomizers = configurationCustomizersProvider.getIfAvailable();
}
@PostConstruct
//在构造函数之后，初始化之前，加载mybatis的配置文件
public void checkConfigFileExists() {
if (this.properties.isCheckConfigLocation() && StringUtils.hasText(this.properties.getConfigLocation())) {
Resource resource = this.resourceLoader.getResource(this.properties.getConfigLocation());
Assert.state(resource.exists(), "Cannot find config location: " + resource
+ " (please add config file or check your Mybatis configuration)");
}
}
@Bean
@ConditionalOnMissingBean
public 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()));
}
Configuration configuration = this.properties.getConfiguration();
if (configuration == null && !StringUtils.hasText(this.properties.getConfigLocation())) {
configuration = new Configuration();
}
if (configuration != null && !CollectionUtils.isEmpty(this.configurationCustomizers)) {
for (ConfigurationCustomizer customizer : this.configurationCustomizers) {
customizer.customize(configuration);
}
}
factory.setConfiguration(configuration);
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 (StringUtils.hasLength(this.properties.getTypeHandlersPackage())) {
factory.setTypeHandlersPackage(this.properties.getTypeHandlersPackage());
}
if (!ObjectUtils.isEmpty(this.properties.resolveMapperLocations())) {
factory.setMapperLocations(this.properties.resolveMapperLocations());
}
return factory.getObject();
}
@Bean
@ConditionalOnMissingBean
public SqlSessionTemplate sqlSessionTemplate(SqlSessionFactory sqlSessionFactory) {
ExecutorType executorType = this.properties.getExecutorType();
if (executorType != null) {
return new SqlSessionTemplate(sqlSessionFactory, executorType);
} else {
return new SqlSessionTemplate(sqlSessionFactory);
}
}
//other code...
}
在自动配置的时候会导入一个Properties配置类MybatisProperties，咱们来看一下，
@ConfigurationProperties(prefix = MybatisProperties.MYBATIS_PREFIX)
public class MybatisProperties {
public static final String MYBATIS_PREFIX = "mybatis";
/**
* Location of MyBatis xml config file.
*/
private String configLocation;
/**
* Locations of MyBatis mapper files.
*/
private String[] mapperLocations;
/**
* Packages to search type aliases. (Package delimiters are ",; \t\n")
*/
private String typeAliasesPackage;
/**
* Packages to search for type handlers. (Package delimiters are ",; \t\n")
*/
private String typeHandlersPackage;
/**
* Indicates whether perform presence check of the MyBatis xml config file.
*/
private boolean checkConfigLocation = false;
/**
* Execution mode for {@link org.mybatis.spring.SqlSessionTemplate}.
*/
private ExecutorType executorType;
/**
* Externalized properties for MyBatis configuration.
*/
private Properties configurationProperties;
/**
* A Configuration object for customize default settings. If {@link #configLocation}
* is specified, this property is not used.
*/
@NestedConfigurationProperty
private Configuration configuration;
//other code...
}
该Properties配置类作用主要用于与yml/properties中以mybatis开头的属性进行一一对应，略过。
在MybatisAutoConfiguration自动配置类中，SpringBoot默认自动配置了两个Bean，分别是SqlSessionFactory和SqlSessionTemplate。SqlSessionFactory主要是将Properties配置类中的属性赋值到SqlSessionFactoryBean中，类似以前xml中配置的SqlSessionFactory:
在创建SqlSessionFactory的Bean中，有段代码：
if (configuration != null && !CollectionUtils.isEmpty(this.configurationCustomizers)) {
for (ConfigurationCustomizer customizer : this.configurationCustomizers) {
customizer.customize(configuration);
}
}
在【Spring Boot】（23）、Spring Boot整合Mybatis的章节中也讲述了，通过实现Mybatis中的ConfigurationCustomizer接口，重写customize方法，达到==覆盖Mybatis中的默认配置项==的功能。
public interface ConfigurationCustomizer {
void customize(Configuration configuration);
}
参数Configuration即为Mybatis的配置项：
public class Configuration {
protected Environment environment;
protected boolean safeRowBoundsEnabled;
protected boolean safeResultHandlerEnabled = true;
protected boolean mapUnderscoreToCamelCase;
protected boolean aggressiveLazyLoading;
protected boolean multipleResultSetsEnabled = true;
protected boolean useGeneratedKeys;
protected boolean useColumnLabel = true;
protected boolean cacheEnabled = true;
protected boolean callSettersOnNulls;
protected boolean useActualParamName = true;
protected boolean returnInstanceForEmptyRow;
protected String logPrefix;
protected Class logImpl;
protected Class vfsImpl;
protected LocalCacheScope localCacheScope = LocalCacheScope.SESSION;
protected JdbcType jdbcTypeForNull = JdbcType.OTHER;
protected Set lazyLoadTriggerMethods = new HashSet(Arrays.asList(new String[] { "equals", "clone", "hashCode", "toString" }));
protected Integer defaultStatementTimeout;
protected Integer defaultFetchSize;
protected ExecutorType defaultExecutorType = ExecutorType.SIMPLE;
protected AutoMappingBehavior autoMappingBehavior = AutoMappingBehavior.PARTIAL;
protected AutoMappingUnknownColumnBehavior autoMappingUnknownColumnBehavior = AutoMappingUnknownColumnBehavior.NONE;
protected Properties variables = new Properties();
protected ReflectorFactory reflectorFactory = new DefaultReflectorFactory();
protected ObjectFactory objectFactory = new DefaultObjectFactory();
protected ObjectWrapperFactory objectWrapperFactory = new DefaultObjectWrapperFactory();
protected boolean lazyLoadingEnabled = false;
protected ProxyFactory proxyFactory = new JavassistProxyFactory(); // #224 Using internal Javassist instead of OGNL
protected String databaseId;
/**
* Configuration factory class.
* Used to create Configuration for loading deserialized unread properties.
*
* @see Issue 300 (google code)
*/
protected Class configurationFactory;
protected final MapperRegistry mapperRegistry = new MapperRegistry(this);
protected final InterceptorChain interceptorChain = new InterceptorChain();
protected final TypeHandlerRegistry typeHandlerRegistry = new TypeHandlerRegistry();
protected final TypeAliasRegistry typeAliasRegistry = new TypeAliasRegistry();
protected final LanguageDriverRegistry languageRegistry = new LanguageDriverRegistry();
protected final Map mappedStatements = new StrictMap("Mapped Statements collection");
protected final Map caches = new StrictMap("Caches collection");
protected final Map resultMaps = new StrictMap("Result Maps collection");
protected final Map parameterMaps = new StrictMap("Parameter Maps collection");
protected final Map keyGenerators = new StrictMap("Key Generators collection");
protected final Set loadedResources = new HashSet();
protected final Map sqlFragments = new StrictMap("XML fragments parsed from previous mappers");
protected final Collection incompleteStatements = new LinkedList();
protected final Collection incompleteCacheRefs = new LinkedList();
protected final Collection incompleteResultMaps = new LinkedList();
protected final Collection incompleteMethods = new LinkedList();
//other code...
}
具体可以看看【Spring Boot】（23）、Spring Boot整合Mybatis中的使用方式，在此就不在讲解了。
另外一个Bean为SqlSessionTemplate，通过SqlSessionFactory来生成SqlSession代理类：
public class SqlSessionTemplate implements SqlSession, DisposableBean {
private final SqlSessionFactory sqlSessionFactory;
private final ExecutorType executorType;
private final SqlSession sqlSessionProxy;
private final PersistenceExceptionTranslator exceptionTranslator;
//other code...
public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType,
PersistenceExceptionTranslator exceptionTranslator) {
notNull(sqlSessionFactory, "Property 'sqlSessionFactory' is required");
notNull(executorType, "Property 'executorType' is required");
this.sqlSessionFactory = sqlSessionFactory;
this.executorType = executorType;
this.exceptionTranslator = exceptionTranslator;
//生成SqlSessioin代理类
this.sqlSessionProxy = (SqlSession) newProxyInstance(
SqlSessionFactory.class.getClassLoader(),
new Class[] { SqlSession.class },
new SqlSessionInterceptor());
}
}
在MybatisAutoConfiguration自动配置类中，有个静态内部类 AutoConfiguredMapperScannerRegistrar
public static class AutoConfiguredMapperScannerRegistrar
implements BeanFactoryAware, ImportBeanDefinitionRegistrar, ResourceLoaderAware {
private BeanFactory beanFactory;
private ResourceLoader resourceLoader;
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
logger.debug("Searching for mappers annotated with @Mapper");
ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
try {
if (this.resourceLoader != null) {
scanner.setResourceLoader(this.resourceLoader);
}
List packages = AutoConfigurationPackages.get(this.beanFactory);
if (logger.isDebugEnabled()) {
for (String pkg : packages) {
logger.debug("Using auto-configuration base package '{}'", pkg);
}
}
//添加@Mapper注解
scanner.setAnnotationClass(Mapper.class);
scanner.registerFilters();
//进行包扫描，加载添加@Mapper注解的类
scanner.doScan(StringUtils.toStringArray(packages));
} catch (IllegalStateException ex) {
logger.debug("Could not determine auto-configuration package, automatic mapper scanning disabled.", ex);
}
}
@Override
public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
this.beanFactory = beanFactory;
}
@Override
public void setResourceLoader(ResourceLoader resourceLoader) {
this.resourceLoader = resourceLoader;
}
}
@org.springframework.context.annotation.Configuration
@Import({ AutoConfiguredMapperScannerRegistrar.class })
@ConditionalOnMissingBean(MapperFactoryBean.class)
public static class MapperScannerRegistrarNotFoundConfiguration {
@PostConstruct
public void afterPropertiesSet() {
logger.debug("No {} found.", MapperFactoryBean.class.getName());
}
}
它主要用于扫描带有@Mapper注解的mapper接口，暂时先不讲这个内部类，后面再讲。
咱们先来讲下Mybatis的MapperScannerRegistrar，它的功能同上述功能刚好相反。学过SpringBoot整合Mybatis的童靴，肯定知道一个注解@MapperScan，来看看它的签名：
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import(MapperScannerRegistrar.class)
public @interface MapperScan {
//other code...
}
可以看到，如果使用了@MapperScan注解，则项目会导入MapperScannerRegistrar：
public class MapperScannerRegistrar implements ImportBeanDefinitionRegistrar, ResourceLoaderAware {
private ResourceLoader resourceLoader;
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
AnnotationAttributes annoAttrs = AnnotationAttributes.fromMap(importingClassMetadata.getAnnotationAttributes(MapperScan.class.getName()));
ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
// this check is needed in Spring 3.1
if (resourceLoader != null) {
scanner.setResourceLoader(resourceLoader);
}
Class annotationClass = annoAttrs.getClass("annotationClass");
if (!Annotation.class.equals(annotationClass)) {
scanner.setAnnotationClass(annotationClass);
}
Class markerInterface = annoAttrs.getClass("markerInterface");
if (!Class.class.equals(markerInterface)) {
scanner.setMarkerInterface(markerInterface);
}
Class generatorClass = annoAttrs.getClass("nameGenerator");
if (!BeanNameGenerator.class.equals(generatorClass)) {
scanner.setBeanNameGenerator(BeanUtils.instantiateClass(generatorClass));
}
Class mapperFactoryBeanClass = annoAttrs.getClass("factoryBean");
if (!MapperFactoryBean.class.equals(mapperFactoryBeanClass)) {
scanner.setMapperFactoryBean(BeanUtils.instantiateClass(mapperFactoryBeanClass));
}
scanner.setSqlSessionTemplateBeanName(annoAttrs.getString("sqlSessionTemplateRef"));
scanner.setSqlSessionFactoryBeanName(annoAttrs.getString("sqlSessionFactoryRef"));
List basePackages = new ArrayList();
//解析@MapperScan的属性
for (String pkg : annoAttrs.getStringArray("value")) {
if (StringUtils.hasText(pkg)) {
basePackages.add(pkg);
}
}
for (String pkg : annoAttrs.getStringArray("basePackages")) {
if (StringUtils.hasText(pkg)) {
basePackages.add(pkg);
}
}
for (Class clazz : annoAttrs.getClassArray("basePackageClasses")) {
basePackages.add(ClassUtils.getPackageName(clazz));
}
scanner.registerFilters();
//进行包扫描
scanner.doScan(StringUtils.toStringArray(basePackages));
}
@Override
public void setResourceLoader(ResourceLoader resourceLoader) {
this.resourceLoader = resourceLoader;
}
}
一旦使用@MapperScan注解，则回在MapperScannerRegistrar#registerBeanDefinitions方法中会解析@MapperScan注解的属性，加载basePackages，并进行包扫描，调用==doScan==方法。
public class ClassPathMapperScanner extends ClassPathBeanDefinitionScanner {
//other code...
private MapperFactoryBean mapperFactoryBean = new MapperFactoryBean==重点代码：==
definition.setBeanClass(this.mapperFactoryBean.getClass());
==从这句代码可以看到，在MapperScannerRegistrar中，把@MapperScan包扫描进来的Mapper接口的class设置成来MapperFactoryBean的class，所以使用@MapperScan注解的话，在容器中就存在MapperFactoryBean这个类型的Bean，从而导致MapperScannerRegistrarNotFoundConfiguration配置类不生效，原因就是类签名上有个注解@ConditionalOnMissingBean(MapperFactoryBean.class)。==
既然如果使用了@MapperScan注解会导致AutoConfiguredMapperScannerRegistrar(MapperScannerRegistrarNotFoundConfiguration)不生效，那么只要去掉@MapperScan注解，自然就会进入AutoConfiguredMapperScannerRegistrar这个导入类了，重点来了：
//默认为Application主类所在的包及其子包
List packages = AutoConfigurationPackages.get(this.beanFactory);
//设置扫描器的扫描类类型，带有@Mapper注解的类
scanner.setAnnotationClass(Mapper.class);
scanner.registerFilters();
//进行包扫描
scanner.doScan(StringUtils.toStringArray(packages));
最后Mybatis的CRUD操作都是通过SqlSessionTemplate这个代理实例进行操作。