在現在的JavaEE開發過程中,我們經常會使用到Spring+SpringMVC+Mybatis這個組合。那麼Mybatis是如何集成到Spring中的呢?
本文只講@MapperScan註解方式的整個過程。其他方式類似。
Mapper集成到Spring使用大概分爲如下幾個步驟:
- 使用Import方式引入註冊類MapperScannerRegistrar
- MapperScannerRegistrar獲取配置參數。
- 使用ClassPathMapperScanner進行掃描。比如掃描basePackages下面的類。然後對掃描的bean定義處理,比如替換beanClass爲MapperFactoryBean.class
- Sping進行註冊bean,調用到MapperFactoryBean的getObject()。返回一個代理對象MapperProxy
- 使用代理對象進行增刪改查,接口方法會被代理到MapperMethod,最終用sqlSession進行增刪改查。
一、使用Import方式引入註冊類MapperScannerRegistrar
先看@MapperScan代碼
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import(MapperScannerRegistrar.class)
public @interface MapperScan{
這個註解中有一個@Import(MapperScannerRegistrar.class)。
這個@Import在Spring解析中會先去實例化一個MapperScannerRegistrar.class的單例bean到Spring中。
二、MapperScannerRegistrar
MapperScannerRegistrar實現了ImportBeanDefinitionRegistrar接口。ImportBeanDefinitionRegistrar會返回@Import中定義參數,然後我們使用
ClassPathMapperScanner掃描。
@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<? 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(BeanUtils.instantiateClass(generatorClass));
}
Class<? extends MapperFactoryBean> 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<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));
}
scanner.registerFilters();
scanner.doScan(StringUtils.toStringArray(basePackages));
}
三、 使用ClassPathMapperScanner進行掃描
ClassPathMapperScanner繼承了ClassPathBeanDefinitionScanner,可以掃描我們需要的bean定義。比如我們經常配置的basePackages。他就會給我掃描下面所有的類,然後對掃描的Mapper bean定義進行處理。後面Spring對掃描的beanDefintion進行初始化等操作。
下面是ClassPathMapperScanner中處理bean定義的方法
private void processBeanDefinitions(Set<BeanDefinitionHolder> beanDefinitions) {
GenericBeanDefinition definition;
//遍歷bean定義
for (BeanDefinitionHolder holder : beanDefinitions) {
//BeanDefinitionHolder會包裝一個BeanDefinition
definition = (GenericBeanDefinition) holder.getBeanDefinition();
if (logger.isDebugEnabled()) {
logger.debug("Creating MapperFactoryBean with name '" + holder.getBeanName()
+ "' and '" + definition.getBeanClassName() + "' mapperInterface");
}
// the mapper interface is the original class of the bean
// but, the actual class of the bean is MapperFactoryBean
//此處把bean定義的構造方法中加一個參數
//其實後面調用的MapperFactoryBean的這個構造方法,這個構造方法需要一個class。這個class就是掃描出來的Mapper的class
//public MapperFactoryBean(Class<T> mapperInterface) {
// this.mapperInterface = mapperInterface;
// }
definition.getConstructorArgumentValues().addGenericArgumentValue(definition.getBeanClassName()); // issue #59
// 此處會把 beanClass替換爲MapperFactoryBean.class,後續spring進行初始化的時候就會通過MapperFactoryBean.class進行反射
definition.setBeanClass(this.mapperFactoryBean.getClass());
//添加參數
definition.getPropertyValues().add("addToConfig", this.addToConfig);
//下面的if沒有設置一般都不會進入
boolean explicitFactoryUsed = false;
if (StringUtils.hasText(this.sqlSessionFactoryBeanName)) {
definition.getPropertyValues().add("sqlSessionFactory", new RuntimeBeanReference(this.sqlSessionFactoryBeanName));
explicitFactoryUsed = true;
} else if (this.sqlSessionFactory != null) {
definition.getPropertyValues().add("sqlSessionFactory", this.sqlSessionFactory);
explicitFactoryUsed = true;
}
if (StringUtils.hasText(this.sqlSessionTemplateBeanName)) {
if (explicitFactoryUsed) {
logger.warn("Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
}
definition.getPropertyValues().add("sqlSessionTemplate", new RuntimeBeanReference(this.sqlSessionTemplateBeanName));
explicitFactoryUsed = true;
} else if (this.sqlSessionTemplate != null) {
if (explicitFactoryUsed) {
logger.warn("Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
}
definition.getPropertyValues().add("sqlSessionTemplate", this.sqlSessionTemplate);
explicitFactoryUsed = true;
}
if (!explicitFactoryUsed) {
if (logger.isDebugEnabled()) {
logger.debug("Enabling autowire by type for MapperFactoryBean with name '" + holder.getBeanName() + "'.");
}
//設置@autowire的方式爲class
definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
}
}
}
四、 Sping進行註冊MapperFactoryBean
在Spring中有一個比較特殊的bean較FactoryBean。這個bean爲使用者提供了一種靈活初始化bean的方式,Spring在構造FactoryBean類型的bean的時候會調用FactoryBean.getObject()進行初始化bean。
下面是MapperFactoryBean初始化bean的方法
@Override
public T getObject() throws Exception {
//會返回一個MapperProxy的類,Spring就會把MapperProxy註冊到容器中,當使用Mapper的類型獲取bean的時候其實spring返回的是一個MapperProxy代理對象。
return getSqlSession().getMapper(this.mapperInterface);
}
返回MapperProxy的方法是通過MapperRegistry.getMapper返回的
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
if (mapperProxyFactory == null) {
throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
}
try {
return mapperProxyFactory.newInstance(sqlSession);
} catch (Exception e) {
throw new BindingException("Error getting mapper instance. Cause: " + e, e);
}
}
進入MapperProxyFactory類
public class MapperProxyFactory<T> {
//mapper接口的class
private final Class<T> mapperInterface;
//MapperMethod緩存
private final Map<Method, MapperMethod> methodCache = new ConcurrentHashMap<Method, MapperMethod>();
public MapperProxyFactory(Class<T> mapperInterface) {
this.mapperInterface = mapperInterface;
}
public Class<T> getMapperInterface() {
return mapperInterface;
}
public Map<Method, MapperMethod> getMethodCache() {
return methodCache;
}
@SuppressWarnings("unchecked")
protected T newInstance(MapperProxy<T> mapperProxy) {
//使用JDK動態代理爲mapperInterface創建一個mapperProxy的動態代理,後續調用mapperInterface方法的時候會進入mapperProxy的invoke方法。invoke會代理mapperInterface的方法調用。
return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
}
public T newInstance(SqlSession sqlSession) {
//new一個MapperProxy代理對象
final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache);
return newInstance(mapperProxy);
}
}
五. 使用代理對象進行增刪改查
MapperProxy其實就是一個InvocationHandler,MapperProxy代理所有的Mapper方法調用。
public class MapperProxy<T> implements InvocationHandler, Serializable {
private static final long serialVersionUID = -6424540398559729838L;
private final SqlSession sqlSession;
private final Class<T> mapperInterface;
private final Map<Method, MapperMethod> methodCache;
public MapperProxy(SqlSession sqlSession, Class<T> mapperInterface, Map<Method, MapperMethod> methodCache) {
this.sqlSession = sqlSession;
this.mapperInterface = mapperInterface;
this.methodCache = methodCache;
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
try {
//代理的對象是否爲實體類
if (Object.class.equals(method.getDeclaringClass())) {
return method.invoke(this, args);
} else if (isDefaultMethod(method)) {//是否爲接口的default方法
return invokeDefaultMethod(proxy, method, args);
}
} catch (Throwable t) {
throw ExceptionUtil.unwrapThrowable(t);
}
//接口Mapper一般都是進入這裏,這邊會用一個MapperMethod進行調用,裏面其實就是一個sqlSeesion的調用。
final MapperMethod mapperMethod = cachedMapperMethod(method);
return mapperMethod.execute(sqlSession, args);
}
到這裏mybatis中Mapper如何集成到Spring的大概就完了。
那麼sqlSession如何集成到Spring的呢?
其實很簡單,sqlSession其實需要我們自己手動配置,mybatis-spring中爲我們提供了一個SqlSessionFactoryBean,這個也是一個FactoryBean。SqlSessionFactoryBean會返回一個SqlSessionFactory。SqlSessionFactory註冊到Spring中。在使用sqlSession的地方直接通過SqlSessionFactory返回即可。