1 前言
当你把 Spring、SpringBoot、Mybatis 或者 Mybatis-Plus 的源码都看过后，那有没有想过比如 Mybatis 如何整合到 Spring 或者 SpringBoot 的呢？就是思考框架跟框架之间的融合，那么这节我们就来看看单纯的 Mybatis 是如何融合到 SpringBoot 的。融合 Spring 的就不看了，毕竟大家现在用的少，比较老的了，就不写了哈，主要看融合 SpringBoot 的。
SpringBoot 的一大特点就是自动装配，就是 Starter。那么 Mybatis 的融合也是基于此。
2 环境准备
首先我们新建个工程，然后引入 Mybatis，这里我直接截图，就不罗嗦了哈：
SpringBoot :2.3.7.RELEASE
<dependency>
<groupId>org.mybatis.spring.boot</groupId>
<artifactId>mybatis-spring-boot-starter</artifactId>
<version>2.2.0</version>
</dependency>
<dependency>
<groupId>org.postgresql</groupId>
<artifactId>postgresql</artifactId>
<version>42.2.7</version>
</dependency>
配置信息：
# 服务端口 server.port = 9900 # 驱动 spring.datasource.driver-class-name = org.postgresql.Driver spring.datasource.hikari.connection-test-query=SELECT 1 # 数据库信息 spring.datasource.url = jdbc:postgresql://localhost:5432/test spring.datasource.username = postgres spring.datasource.password = sql626.. # 扫描 Mapper xml mybatis.mapper-locations=classpath*:mapper/*.xml # SQL日志 mybatis.configuration.log-impl = org.apache.ibatis.logging.stdout.StdOutImpl
启动类以及文件结构：
效果：
3 源码分析
好了，环境准备好了，我们就看看 Mybatis 是如何结合的，从哪里看起呢？我们是不是引入了一个 Starter，自动装配就从 Starter 看起：
3.1 MybatisAutoConfiguration 配置
可以看到 META-INF 下的 spring.factories：
Mybatis 最重要的几个类 Configuration、SqlSessionFactory就都在这里边了：
@Configuration
@ConditionalOnClass({SqlSessionFactory.class, SqlSessionFactoryBean.class})
@ConditionalOnSingleCandidate(DataSource.class)
@EnableConfigurationProperties({MybatisProperties.class})
@AutoConfigureAfter({DataSourceAutoConfiguration.class, MybatisLanguageDriverAutoConfiguration.class})
public class MybatisAutoConfiguration implements InitializingBean {
private static final Logger logger = LoggerFactory.getLogger(MybatisAutoConfiguration.class);
private final MybatisProperties properties;
private final Interceptor[] interceptors;
private final TypeHandler[] typeHandlers;
private final LanguageDriver[] languageDrivers;
private final ResourceLoader resourceLoader;
private final DatabaseIdProvider databaseIdProvider;
private final List<ConfigurationCustomizer> configurationCustomizers;
...
}
3.2 MybatisProperties 属性
mybatis 前缀的属性都会封装进该对象：
@ConfigurationProperties(
prefix = "mybatis"
)
public class MybatisProperties {
public static final String MYBATIS_PREFIX = "mybatis";
...
@NestedConfigurationProperty
private Configuration configuration;
}
那么该对象是什么时候生成的呢？谁引进的呢？细心的会发现刚才在第一步里 MybatisAutoConfiguration 的构造函数里，依靠 Spring 的依赖注入（构造器注入）来创建的。
小细节：@NestedConfigurationProperty 属性嵌套，构造 Configuration
3.3 SqlSessionFactoryBean
我们再看一个重要的 SqlSessionFactoryBean，看后缀就能知道它是 FactoryBean 形式创建的：
@Bean
@ConditionalOnMissingBean
public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception {
SqlSessionFactoryBean factory = new SqlSessionFactoryBean();
// 数据源
factory.setDataSource(dataSource);
factory.setVfs(SpringBootVFS.class);
if (StringUtils.hasText(this.properties.getConfigLocation())) {
factory.setConfigLocation(this.resourceLoader.getResource(this.properties.getConfigLocation()));
}
// configuration 配置对象（上一步的 MybatisProperties 中有的话就用它的，没有的话就创新一个新的）
this.applyConfiguration(factory);
if (this.properties.getConfigurationProperties() != null) {
factory.setConfigurationProperties(this.properties.getConfigurationProperties());
}
// 插件集合
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 = (Set)Stream.of((new BeanWrapperImpl(SqlSessionFactoryBean.class)).getPropertyDescriptors()).map(FeatureDescriptor::getName).collect(Co
Class<? extends LanguageDriver> defaultLanguageDriver = this.properties.getDefaultScriptingLanguageDriver();
if (factoryPropertyNames.contains("scriptingLanguageDrivers") && !ObjectUtils.isEmpty(this.languageDrivers)) {
factory.setScriptingLanguageDrivers(this.languageDrivers);
if (defaultLanguageDriver == null && this.languageDrivers.length == 1) {
defaultLanguageDriver = this.languageDrivers[0].getClass();
}
}
if (factoryPropertyNames.contains("defaultScriptingLanguageDriver")) {
factory.setDefaultScriptingLanguageDriver(defaultLanguageDriver);
}
// getObject
return factory.getObject();
}
private void applyConfiguration(SqlSessionFactoryBean factory) {
// 先从 MybatisProperties 中拿
org.apache.ibatis.session.Configuration configuration = this.properties.getConfiguration();
// 发现没有或者也没配置的话 就创建一个新的
if (configuration == null && !StringUtils.hasText(this.properties.getConfigLocation())) {
configuration = new org.apache.ibatis.session.Configuration();
}
if (configuration != null && !CollectionUtils.isEmpty(this.configurationCustomizers)) {
Iterator var3 = this.configurationCustomizers.iterator();
while(var3.hasNext()) {
ConfigurationCustomizer customizer = (ConfigurationCustomizer)var3.next();
customizer.customize(configuration);
}
}
factory.setConfiguration(configuration);
}
然后继续看 getObject() 方法：
public SqlSessionFactory getObject() throws Exception {
// afterPropertiesSet 进行创建
if (this.sqlSessionFactory == null) {
this.afterPropertiesSet();
}
return this.sqlSessionFactory;
}
public void afterPropertiesSet() throws Exception {
// 必须校验
Assert.notNull(this.dataSource, "Property 'dataSource' is required");
Assert.notNull(this.sqlSessionFactoryBuilder, "Property 'sqlSessionFactoryBuilder' is required");
Assert.state(this.configuration == null && this.configLocation == null || this.configuration == null || this.configLocation == null, "Property 'configuration' and 'configLocation' can not specified with together");
// 创建
this.sqlSessionFactory = this.buildSqlSessionFactory();
}
继续进入 buildSqlSessionFactory 开始创建：
protected SqlSessionFactory buildSqlSessionFactory() throws Exception {
XMLConfigBuilder xmlConfigBuilder = null;
Configuration targetConfiguration;
Optional var10000;
if (this.configuration != null) {
targetConfiguration = this.configuration;
if (targetConfiguration.getVariables() == null) {
targetConfiguration.setVariables(this.configurationProperties);
} else if (this.configurationProperties != null) {
targetConfiguration.getVariables().putAll(this.configurationProperties);
}
} else if (this.configLocation != null) {
xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), (String)null, this.configurationProperties);
targetConfiguration = xmlConfigBuilder.getConfiguration();
} else {
LOGGER.debug(() -> {
return "Property 'configuration' or 'configLocation' not specified, using default MyBatis Configuration";
});
targetConfiguration = new Configuration();
var10000 = Optional.ofNullable(this.configurationProperties);
Objects.requireNonNull(targetConfiguration);
var10000.ifPresent(targetConfiguration::setVariables);
}
var10000 = Optional.ofNullable(this.objectFactory);
Objects.requireNonNull(targetConfiguration);
var10000.ifPresent(targetConfiguration::setObjectFactory);
var10000 = Optional.ofNullable(this.objectWrapperFactory);
Objects.requireNonNull(targetConfiguration);
var10000.ifPresent(targetConfiguration::setObjectWrapperFactory);
var10000 = Optional.ofNullable(this.vfs);
Objects.requireNonNull(targetConfiguration);
var10000.ifPresent(targetConfiguration::setVfsImpl);
Stream var24;
if (StringUtils.hasLength(this.typeAliasesPackage)) {
var24 = this.scanClasses(this.typeAliasesPackage, this.typeAliasesSuperType).stream().filter((clazz) -> {
return !clazz.isAnonymousClass();
}).filter((clazz) -> {
return !clazz.isInterface();
}).filter((clazz) -> {
return !clazz.isMemberClass();
});
TypeAliasRegistry var10001 = targetConfiguration.getTypeAliasRegistry();
Objects.requireNonNull(var10001);
var24.forEach(var10001::registerAlias);
}
if (!ObjectUtils.isEmpty(this.typeAliases)) {
Stream.of(this.typeAliases).forEach((typeAlias) -> {
targetConfiguration.getTypeAliasRegistry().registerAlias(typeAlias);
LOGGER.debug(() -> {
return "Registered type alias: '" + typeAlias + "'";
});
});
}
if (!ObjectUtils.isEmpty(this.plugins)) {
Stream.of(this.plugins).forEach((plugin) -> {
targetConfiguration.addInterceptor(plugin);
LOGGER.debug(() -> {
return "Registered plugin: '" + plugin + "'";
});
});
}
if (StringUtils.hasLength(this.typeHandlersPackage)) {
var24 = this.scanClasses(this.typeHandlersPackage, TypeHandler.class).stream().filter((clazz) -> {
return !clazz.isAnonymousClass();
}).filter((clazz) -> {
return !clazz.isInterface();
}).filter((clazz) -> {
return !Modifier.isAbstract(clazz.getModifiers());
});
TypeHandlerRegistry var25 = targetConfiguration.getTypeHandlerRegistry();
Objects.requireNonNull(var25);
var24.forEach(var25::register);
}
if (!ObjectUtils.isEmpty(this.typeHandlers)) {
Stream.of(this.typeHandlers).forEach((typeHandler) -> {
targetConfiguration.getTypeHandlerRegistry().register(typeHandler);
LOGGER.debug(() -> {
return "Registered type handler: '" + typeHandler + "'";
});
});
}
targetConfiguration.setDefaultEnumTypeHandler(this.defaultEnumTypeHandler);
if (!ObjectUtils.isEmpty(this.scriptingLanguageDrivers)) {
Stream.of(this.scriptingLanguageDrivers).forEach((languageDriver) -> {
targetConfiguration.getLanguageRegistry().register(languageDriver);
LOGGER.debug(() -> {
return "Registered scripting language driver: '" + languageDriver + "'";
});
});
}
var10000 = Optional.ofNullable(this.defaultScriptingLanguageDriver);
Objects.requireNonNull(targetConfiguration);
var10000.ifPresent(targetConfiguration::setDefaultScriptingLanguage);
if (this.databaseIdProvider != null) {
try {
targetConfiguration.setDatabaseId(this.databaseIdProvider.getDatabaseId(this.dataSource));
} catch (SQLException var23) {
throw new NestedIOException("Failed getting a databaseId", var23);
}
}
var10000 = Optional.ofNullable(this.cache);
Objects.requireNonNull(targetConfiguration);
var10000.ifPresent(targetConfiguration::addCache);
if (xmlConfigBuilder != null) {
try {
xmlConfigBuilder.parse();
LOGGER.debug(() -> {
return "Parsed configuration file: '" + this.configLocation + "'";
});
} catch (Exception var21) {
throw new NestedIOException("Failed to parse config resource: " + this.configLocation, var21);
} finally {
ErrorContext.instance().reset();
}
}
// 这里对以后理解 Mybatis 和 Spring 的事务两者结合帮助很大
targetConfiguration.setEnvironment(new Environment(this.environment, (TransactionFactory)(this.transactionFactory == null ? new SpringManagedTransactionFactory() : this.transactionFactory), this.dataSource));
// 扫描我们的 Mapper.xml
if (this.mapperLocations != null) {
if (this.mapperLocations.length == 0) {
LOGGER.warn(() -> {
return "Property 'mapperLocations' was specified but matching resources are not found.";
});
} else {
Resource[] var3 = this.mapperLocations;
int var4 = var3.length;
for(int var5 = 0; var5 < var4; ++var5) {
Resource mapperLocation = var3[var5];
if (mapperLocation != null) {
try {
XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(), targetConfiguration, mapperLocation.toString(), targetConfiguration.getSqlFragments());
xmlMapperBuilder.parse();
} catch (Exception var19) {
throw new NestedIOException("Failed to parse mapping resource: '" + mapperLocation + "'", var19);
} finally {
ErrorContext.instance().reset();
}
LOGGER.debug(() -> {
return "Parsed mapper file: '" + mapperLocation + "'";
});
}
}
}
} else {
LOGGER.debug(() -> {
return "Property 'mapperLocations' was not specified.";
});
}
return this.sqlSessionFactoryBuilder.build(targetConfiguration);
}
两个重要的：
（1）Environment 里的 TransactionFactory （SpringManagedTransactionFactory 对 Mybatis 和 Spring 事务的结合衔接）
（2）扫描 Mapper.xml 进行解析注入（这个就不细看了哈，之前看过了 xml 的解析，可以看我之前的哈）
3.4 AutoConfiguredMapperScannerRegistrar
看到这里，我们还差什么？是不是就差 Mapper 接口没看到了？
可以看到我的启动类上 @MapperScan 用于扫描我们的 Mapper 接口，但是当我把这个去掉，程序还是能正常运行，这是为什么呢？这就是 MybatisAutoConfiguration.AutoConfiguredMapperScannerRegistrar 发挥作用了：
并且它跟 @MapperScan 不冲突，当存在 @MapperScan的时候，那就交给 MapperScannerRegistrar 来处理了，没有的话，就交给 MybatisAutoConfiguration.AutoConfiguredMapperScannerRegistrar 来处理，他会通过 @Mapper 标记来进行处理哈。
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE})
@Documented
@Import({MapperScannerRegistrar.class})
@Repeatable(MapperScans.class)
public @interface MapperScan {
String[] value() default {};
}
具体如何创建代理（JDK 的代理噢），就不看了哈（之前看过了哈）可以参考这篇【Mapper 接口都是怎么注入到 Spring容器中的？https://www.cnblogs.com/kukuxjx/p/17505609.html】。
4 小结
好啦，看到这里就差不多了哈，画个图来简单小结下：
