前言：入职新公司，SpringBoot和Mybatis都被封装了一次，光用而不知道原理实在受不了，于是开始恶补源码，由于刚开始比较浅，存属娱乐，大神勿喷。
就如网上的流传的SpringBoot与Mybatis整合两种方式
一.使用 pom文件使用:org.mybatis.spring.boot 依赖
坐标：
<groupId>org.mybatis.spring.boot</groupId>
<artifactId>mybatis-spring-boot-starter</artifactId>
<version>xxxxx</version> 通过pom.xml能够看到该依赖的其他依赖文件
注意这个org.mybatis.spring....autoconfigure包，找到这个包，点开META-INF目录下，找到spring.factories文件 这是自动配置mybatis注解，mapper存放位置等的地方。
这里如果EnableAutoConfigurationImportSelector不懂的可以看 https://www.jianshu.com/p/464d04c36fb1
，这里不在详细解释，只要知道是Spring的一个自动配置的注解，通过它会自动加载类。
进入 MybatisAutoConfiguration
@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<ConfigurationCustomizer>configurationCustomizers;
MybatisProperties 类是接受Mybatis配置文件的类
@ConfigurationProperties(
prefix = "mybatis"
)
public class MybatisProperties {
public static final String MYBATIS_PREFIX = "mybatis";
private String configLocation;
private String[] mapperLocations;
private String typeAliasesPackage;
private String typeHandlersPackage;
private boolean checkConfigLocation = false;
private ExecutorType executorType;
private Properties configurationProperties;
@NestedConfigurationProperty
private Configuration configuration;
config-location Location of MyBatis xml config file.
check-config-location Indicates whether perform presence check of the MyBatis xml config file.
mapper-locations Locations of Mapper xml config file.
type-aliases-package Packages to search for type aliases. (Package delimiters are ",; \t\n")
type-handlers-package Packages to search for type handlers. (Package delimiters are ",; \t\n")
executor-type Executor type: SIMPLE, REUSE, BATCH.
configuration-properties Externalized properties for MyBatis configuration. Specified properties can be used as placeholder on MyBatis config file and Mapper file. For detail see the MyBatis reference page
configuration A MyBatis Configuration bean. About available properties see the MyBatis reference page. NOTE This property cannot be used at the same time with the config-location.
@PostConstruct 在初始化的时候执行：加载配置文件
@PostConstruct
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)");
} @Bea@ConditionalOnMissingBean 自动创建 sqlSessionFactory和SqlSessionTemplate
下面的静态内部类 AutoConfiguredMapperScannerRegistrar 会在运行期间@Mapper注解，使用过@Mapper的Mapper接口
自动的生成动态代理mapper接口
public static class AutoConfiguredMapperScannerRegistrar implements BeanFactoryAware, ImportBeanDefinitionRegistrar, ResourceLoaderAware {
private BeanFactory beanFactory;
private ResourceLoader resourceLoader;
public AutoConfiguredMapperScannerRegistrar() {
}
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
MybatisAutoConfiguration.logger.debug("Searching for mappers annotated with @Mapper");
ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
try {
if (this.resourceLoader != null) {
scanner.setResourceLoader(this.resourceLoader);
}
List<String> packages = AutoConfigurationPackages.get(this.beanFactory);
if (MybatisAutoConfiguration.logger.isDebugEnabled()) {
Iterator var5 = packages.iterator();
while(var5.hasNext()) {
String pkg = (String)var5.next();
MybatisAutoConfiguration.logger.debug("Using auto-configuration base package '{}'", pkg);
}
}
//注册注解
scanner.setAnnotationClass(Mapper.class);
scanner.registerFilters();
scanner.doScan(StringUtils.toStringArray(packages));
} catch (IllegalStateException var7) {
MybatisAutoConfiguration.logger.debug("Could not determine auto-configuration package, automatic mapper scanning disabled.", var7);
}
}
public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
this.beanFactory = beanFactory;
}
public void setResourceLoader(ResourceLoader resourceLoader) {
this.resourceLoader = resourceLoader;
}
}
注意：要是此时在SpringBoot启动类上使用了@MapperScan()注解，那么此时将进入@Import 导入的类，进行注册
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE})
@Documented
@Import({MapperScannerRegistrar.class})
public @interface MapperScan {
String[] value() default {}; String[] basePackages() default {}; Class<?>[] basePackageClasses() default {}; Class<? extends BeanNameGenerator> nameGenerator() default BeanNameGenerator.class; Class<? extends Annotation> annotationClass() default Annotation.class; Class<?> markerInterface() default Class.class; String sqlSessionTemplateRef() default ""; String sqlSessionFactoryRef() default ""; Class<? extends MapperFactoryBean> factoryBean() default MapperFactoryBean.class;
}
在 MapperScannerRegistrar的 registerBeanDefinitions 方法用ClassPathMapperScanner进行注册，使用doScan扫描包
此时注册的注解需要annotationClass的值，
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
AnnotationAttributes annoAttrs = AnnotationAttributes.fromMap(importingClassMetadata.getAnnotationAttributes(MapperScan.class.getName()));
ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
if (this.resourceLoader != null) {
scanner.setResourceLoader(this.resourceLoader);
}
Class<? extends Annotation> 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<? extends BeanNameGenerator> generatorClass = annoAttrs.getClass("nameGenerator");
if (!BeanNameGenerator.class.equals(generatorClass)) {
scanner.setBeanNameGenerator((BeanNameGenerator)BeanUtils.instantiateClass(generatorClass));
}
Class<? extends MapperFactoryBean> mapperFactoryBeanClass = annoAttrs.getClass("factoryBean");
if (!MapperFactoryBean.class.equals(mapperFactoryBeanClass)) {
scanner.setMapperFactoryBean((MapperFactoryBean)BeanUtils.instantiateClass(mapperFactoryBeanClass));
}
scanner.setSqlSessionTemplateBeanName(annoAttrs.getString("sqlSessionTemplateRef"));
scanner.setSqlSessionFactoryBeanName(annoAttrs.getString("sqlSessionFactoryRef"));
List<String> basePackages = new ArrayList();
String[] var10 = annoAttrs.getStringArray("value");
int var11 = var10.length;
int var12;
String pkg;
for(var12 = 0; var12 < var11; ++var12) {
pkg = var10[var12];
if (StringUtils.hasText(pkg)) {
basePackages.add(pkg);
}
}
var10 = annoAttrs.getStringArray("basePackages");
var11 = var10.length;
for(var12 = 0; var12 < var11; ++var12) {
pkg = var10[var12];
if (StringUtils.hasText(pkg)) {
basePackages.add(pkg);
}
}
Class[] var14 = annoAttrs.getClassArray("basePackageClasses");
var11 = var14.length;
for(var12 = 0; var12 < var11; ++var12) {
Class<?> clazz = var14[var12];
basePackages.add(ClassUtils.getPackageName(clazz));
}
scanner.registerFilters();
scanner.doScan(StringUtils.toStringArray(basePackages));
}
若既不使用@MapperScan 注解 也不使用@Mapper注解，则Mapper类不能生成代理对象，则在@Autowire注入时，会报错
nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException
二 使用Mybatis-Spring整合
该整合jar包含的类
spring.handlers中内容找到处理器org.mybatis.spring.config.NamespaceHandler
http\://mybatis.org/schema/mybatis-spring=org.mybatis.spring.config.NamespaceHandler
处理器中会有解析器MapperScannerBeanDefinitionParser来解析这个xml
public void init() {
this.registerBeanDefinitionParser("scan", new MapperScannerBeanDefinitionParser());
}
在 MapperScannerBeanDefinitionParser进行注册
public synchronized BeanDefinition parse(Element element, ParserContext parserContext) {
ClassPathMapperScanner scanner = new ClassPathMapperScanner(parserContext.getRegistry());
ClassLoader classLoader = scanner.getResourceLoader().getClassLoader();
XmlReaderContext readerContext = parserContext.getReaderContext();
scanner.setResourceLoader(readerContext.getResourceLoader());
String annotationClassName;
String markerInterfaceClassName;
String nameGeneratorClassName;
try {
annotationClassName = element.getAttribute("annotation");
if (StringUtils.hasText(annotationClassName)) {
Class<? extends Annotation> markerInterface = classLoader.loadClass(annotationClassName);
scanner.setAnnotationClass(markerInterface);
}
markerInterfaceClassName = element.getAttribute("marker-interface");
if (StringUtils.hasText(markerInterfaceClassName)) {
Class<?> markerInterface = classLoader.loadClass(markerInterfaceClassName);
scanner.setMarkerInterface(markerInterface);
}
nameGeneratorClassName = element.getAttribute("name-generator");
if (StringUtils.hasText(nameGeneratorClassName)) {
Class<?> nameGeneratorClass = classLoader.loadClass(nameGeneratorClassName);
BeanNameGenerator nameGenerator = (BeanNameGenerator)BeanUtils.instantiateClass(nameGeneratorClass, BeanNameGenerator.class);
scanner.setBeanNameGenerator(nameGenerator);
}
} catch (Exception var11) {
readerContext.error(var11.getMessage(), readerContext.extractSource(element), var11.getCause());
}
annotationClassName = element.getAttribute("template-ref");
scanner.setSqlSessionTemplateBeanName(annotationClassName);
markerInterfaceClassName = element.getAttribute("factory-ref");
scanner.setSqlSessionFactoryBeanName(markerInterfaceClassName);
scanner.registerFilters();
nameGeneratorClassName = element.getAttribute("base-package");
scanner.scan(StringUtils.tokenizeToStringArray(nameGeneratorClassName, ",; \t\n"));
return null;
}
也可以使用@MapperScanner注解 在 MapperScannerConfigurer进行注册
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
if (this.processPropertyPlaceHolders) {
this.processPropertyPlaceHolders();
}
ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
scanner.setAddToConfig(this.addToConfig);
scanner.setAnnotationClass(this.annotationClass);
scanner.setMarkerInterface(this.markerInterface);
scanner.setSqlSessionFactory(this.sqlSessionFactory);
scanner.setSqlSessionTemplate(this.sqlSessionTemplate);
scanner.setSqlSessionFactoryBeanName(this.sqlSessionFactoryBeanName);
scanner.setSqlSessionTemplateBeanName(this.sqlSessionTemplateBeanName);
scanner.setResourceLoader(this.applicationContext);
scanner.setBeanNameGenerator(this.nameGenerator);
scanner.registerFilters();
scanner.scan(StringUtils.tokenizeToStringArray(this.basePackage, ",; \t\n"));
}
还可以在 xml文档里注册 MapperScannerConfigurer自动管理（同上，一个xml一个注解）
<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
<property name="basePackage" value="org.mybatis.spring.sample.mapper" />
<property name="sqlSessionFactoryBeanName" value="sqlSessionFactory"/>
</bean>
注意： org-mybatis-spring.boot为： 1.3.0 mybatis-spring:1.3.1 ,mybatis:3.4.4