Spring 3.x+版本支援使用@Configuration和@Bean注解來提供基于 Java 的配置。
如果使用基于java的配置,可以使用@MapperScan注解來掃描映射Mapper接口類。
@MapperScan(value = "org.springframework.orm.mapper", sqlSessionFactoryRef = "sqlSessionFactoryBean")
// 通過Bean注解注入自定義建構的SqlSessionFactoryBean對象
@Bean
public SqlSessionFactoryBean sqlSessionFactoryBean() throws Exception {
SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
sqlSessionFactoryBean.setDataSource(dataSource());
sqlSessionFactoryBean.setMapperLocations(new PathMatchingResourcePatternResolver()
.getResources("T1Mapper.xml"));
sqlSessionFactoryBean.setTypeAliasesPackage("org.springframework.orm.entity");
return sqlSessionFactoryBean;
}
value:指定mapper接口類包路徑
sqlSessionFactoryRef:指定SqlSessionFactoryBean對象名
MapperScan進一步解析
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
// 通過spring import注解方式加載
@Import(MapperScannerRegistrar.class)
public @interface MapperScan {
@Import 是被用來整合所有在@Configuration注解中定義的bean配置
這裡MapperScannerRegistrar實作了ImportBeanDefinitionRegistrar接口注入bean,再通過import注解導入加載。
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
// 擷取注解
AnnotationAttributes annoAttrs = AnnotationAttributes.fromMap(importingClassMetadata.getAnnotationAttributes(MapperScan.class.getName()));
// 擴充spring中ClassPathBeanDefinitionScanner類将類掃面成BeanDefinition
ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
// 掃描包路徑集
List<String> basePackages = new ArrayList<String>();
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));
}
// 注冊相關filter
scanner.registerFilters();
// 掃描
scanner.doScan(StringUtils.toStringArray(basePackages));
scanner.doScan中将實作mapper掃描映射
// 通過spring提供的方法将mapper接口類掃描轉換成BeanDefinitionHolder集合
Set<BeanDefinitionHolder> beanDefinitions = super.doScan(basePackages);
if (beanDefinitions.isEmpty()) {
logger.warn("No MyBatis mapper was found in '" + Arrays.toString(basePackages) + "' package. Please check your configuration.");
} else {
// 再根據BeanDefinitionHolder做相關處理
processBeanDefinitions(beanDefinitions);
}
return beanDefinitions;
processBeanDefinitions方法中會設定mapper注入對應實作的bean等配置
private MapperFactoryBean<?> mapperFactoryBean = new MapperFactoryBean<Object>();
// 配置構造函數中參數值
definition.getConstructorArgumentValues().addGenericArgumentValue(definition.getBeanClassName()); // issue #59
// 設定BeanClass為MapperFactoryBean類
definition.setBeanClass(this.mapperFactoryBean.getClass());
// 設定屬性值
definition.getPropertyValues().add("addToConfig", this.addToConfig);
definition.setBeanClass(this.mapperFactoryBean.getClass())此處設定mapper接口對應的實作類為MapperFactoryBean類。
MapperFactoryBean類實作了FactoryBean功能,最後實際執行的bean對象是通過getObject方法擷取。
public T getObject() throws Exception {
// 此處使用了動态代理
return getSqlSession().getMapper(this.mapperInterface);
}
protected T newInstance(MapperProxy<T> mapperProxy) {
// 通過MapperProxy生成mapper接口執行的代理對象
return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
}
public T newInstance(SqlSession sqlSession) {
// MapperProxy就是實際的目标對象,也就是代理對象
final MapperProxy<T> mapperProxy = new MapperProxy<>(sqlSession, mapperInterface, methodCache);
return newInstance(mapperProxy);
}
到此處為止,可以看到mybatis加載的mapper接口對應的實作目标類都是MapperProxy對象。
SqlSessionTemplate類中執行具體操作是再次使用了一次代理
this.sqlSessionFactory = sqlSessionFactory;
this.executorType = executorType;
this.exceptionTranslator = exceptionTranslator;
this.sqlSessionProxy = (SqlSession) newProxyInstance(
SqlSessionFactory.class.getClassLoader(),
new Class[] { SqlSession.class },
new SqlSessionInterceptor());
sqlSessionProxy代理對象是在SqlSessionTemplate對象構造方法時指定的
......
public void select(String statement, ResultHandler handler) {
this.sqlSessionProxy.select(statement, handler);
}
public void select(String statement, Object parameter, ResultHandler handler) {
this.sqlSessionProxy.select(statement, parameter, handler);
}
......
SqlSessionInterceptor代理類
private class SqlSessionInterceptor implements InvocationHandler {
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
SqlSession sqlSession = getSqlSession(
SqlSessionTemplate.this.sqlSessionFactory,
SqlSessionTemplate.this.executorType,
SqlSessionTemplate.this.exceptionTranslator);
try {
Object result = method.invoke(sqlSession, args);
if (!isSqlSessionTransactional(sqlSession, SqlSessionTemplate.this.sqlSessionFactory)) {
// force commit even on non-dirty sessions because some databases require
// a commit/rollback before calling close()
sqlSession.commit(true);
}
return result;
} catch (Throwable t) {
Throwable unwrapped = unwrapThrowable(t);
if (SqlSessionTemplate.this.exceptionTranslator != null && unwrapped instanceof PersistenceException) {
// release the connection to avoid a deadlock if the translator is no loaded. See issue #22
closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
sqlSession = null;
Throwable translated = SqlSessionTemplate.this.exceptionTranslator.translateExceptionIfPossible((PersistenceException) unwrapped);
if (translated != null) {
unwrapped = translated;
}
}
throw unwrapped;
} finally {
if (sqlSession != null) {
closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
}
}
}
}