MyBatis创建代理流程
1. 通过注解扫描 basePackages
@MapperScan("com.demo.*")
@SpringBootApplication
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
}
2. @MapperScan注解@Import(MapperScannerRegistrar.class)
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import(MapperScannerRegistrar.class)
@Repeatable(MapperScans.class)
public @interface MapperScan {
...
}
3. 动态注册MapperScannerConfigurer的beanDefinition
MapperScannerRegistrar 实现了ImportBeanDefinitionRegistrar 接口，ImportBeanDefinitionRegistrar是spring对外提供动态注册beanDefinition的接口，在refresh#invokeBeanFactoryPostProcessors(beanFactory); 会调用所有实现了ImportBeanDefinitionRegistrar 接口的bean。
spring在初始化的时候，会回调registerBeanDefinitions方法，将MapperScannerConfigurer的bean definition注入spring容器。
void registerBeanDefinitions(AnnotationAttributes annoAttrs, BeanDefinitionRegistry registry, String beanName) {
BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(MapperScannerConfigurer.class);
builder.addPropertyValue("processPropertyPlaceHolders", true);
...
...
...
builder.addPropertyValue("basePackage", StringUtils.collectionToCommaDelimitedString(basePackages));
registry.registerBeanDefinition(beanName, builder.getBeanDefinition());
}
4.执行MapperScannerConfigurer的postProcessBeanDefinitionRegistry
MapperScannerConfigurer 实现了BeanDefinitionRegistryPostProcessor 接口，在refresh#invokeBeanFactoryPostProcessors(beanFactory); 会回调postProcessBeanDefinitionRegistry 方法。
说明：postProcessBeanDefinitionRegistry方法可以修改在BeanDefinitionRegistry接口实现类中注册的任意BeanDefinition，也可以增加和删除BeanDefinition。原因是这个方法执行前所有常规的BeanDefinition已经被加载到BeanDefinitionRegistry接口实现类中，但还没有bean被实例化。
@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
if (this.processPropertyPlaceHolders) {
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.setMapperFactoryBeanClass(this.mapperFactoryBeanClass);
if (StringUtils.hasText(lazyInitialization)) {
scanner.setLazyInitialization(Boolean.valueOf(lazyInitialization));
}
scanner.registerFilters();
scanner.scan(
StringUtils.tokenizeToStringArray(this.basePackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS));
}
在这里会将@MapperScan("com.demo.*") 包进行扫描
5. 将基础包下的类扫描加载为BeanDefinition，将mapper接口BeanClass设置为MapperFactoryBean
@Override
public Set<BeanDefinitionHolder> doScan(String... basePackages) {
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 {
processBeanDefinitions(beanDefinitions);
}
return beanDefinitions;
}
private void processBeanDefinitions(Set<BeanDefinitionHolder> beanDefinitions) {
GenericBeanDefinition definition;
for (BeanDefinitionHolder holder : beanDefinitions) {
definition = (GenericBeanDefinition) holder.getBeanDefinition();
String beanClassName = definition.getBeanClassName();
LOGGER.debug(() -> "Creating MapperFactoryBean with name '" + holder.getBeanName() + "' and '" + beanClassName
+ "' mapperInterface");
// the mapper interface is the original class of the bean
// but, the actual class of the bean is MapperFactoryBean
definition.getConstructorArgumentValues().addGenericArgumentValue(beanClassName); // issue #59
//在这里将BeanClass设置为MapperFactoryBean
definition.setBeanClass(this.mapperFactoryBeanClass);
...
...
...
}
6. MapperFactoryBean 生成Mapper的代理类MapperProxy
public class MapperFactoryBean<T> extends SqlSessionDaoSupport implements FactoryBean<T> {
...
@Override
public T getObject() throws Exception {
return getSqlSession().getMapper(this.mapperInterface);
}
...
}
public class DefaultSqlSession implements SqlSession {
...
@Override
public <T> T getMapper(Class<T> type) {
return configuration.<T>getMapper(type, this);
}
...
}
public class Configuration {
...
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
return mapperRegistry.getMapper(type, sqlSession);
}
...
}
public class MapperRegistry {
...
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);
}
}
...
}
public class MapperProxyFactory<T> {
...
protected T newInstance(MapperProxy<T> mapperProxy) {
return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
}
public T newInstance(SqlSession sqlSession) {
final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache);
return newInstance(mapperProxy);
}
}
7. 生成Proxy的class示例
public final class $Proxy1 extends Proxy implements Producer3 {
private static Method m1;
private static Method m2;
private static Method m3;
private static Method m0;
public $Proxy1(InvocationHandler var1) throws {
super(var1);
}
public final boolean equals(Object var1) throws {
try {
return (Boolean)super.h.invoke(this, m1, new Object[]{var1});
} catch (RuntimeException | Error var3) {
throw var3;
} catch (Throwable var4) {
throw new UndeclaredThrowableException(var4);
}
}
public final String toString() throws {
try {
return (String)super.h.invoke(this, m2, (Object[])null);
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
public final void sell() throws {
try {
super.h.invoke(this, m3, (Object[])null);
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
public final int hashCode() throws {
try {
return (Integer)super.h.invoke(this, m0, (Object[])null);
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
static {
try {
m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object"));
m2 = Class.forName("java.lang.Object").getMethod("toString");
m3 = Class.forName("com.demo.proxy.dynamic.Producer3").getMethod("sell");
m0 = Class.forName("java.lang.Object").getMethod("hashCode");
} catch (NoSuchMethodException var2) {
throw new NoSuchMethodError(var2.getMessage());
} catch (ClassNotFoundException var3) {
throw new NoClassDefFoundError(var3.getMessage());
}
}
}
