在使用原生mybatis的过程中，会有如下代码使用
UserMapper userMapper=sqlSession.getMapper(UserMapper.class);
那么底层实际上使用的是jdk的动态代理来为UserMapper接口生成代理对象。
public class DefaultSqlSession implements SqlSession {
//mybatis 核心对象
private final Configuration configuration;
private final Executor executor;
//构造器
public DefaultSqlSession(Configuration configuration, Executor executor, boolean autoCommit) {
this.configuration = configuration;
this.executor = executor;
this.dirty = false;
this.autoCommit = autoCommit;
}
//构造器
public DefaultSqlSession(Configuration configuration, Executor executor) {
this(configuration, executor, false);
}
//实际调用的是configuration的getMapper方法
@Override
public <T> T getMapper(Class<T> type) {
return configuration.<T>getMapper(type, this);
}
}
在configuration对象中调用的是MapperRegistry的getMapper方法
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
return mapperRegistry.getMapper(type, sqlSession);
}
public class MapperRegistry {
private final Configuration config;
private final Map<Class<?>, MapperProxyFactory<?>> knownMappers = new HashMap<Class<?>, MapperProxyFactory<?>>();
public MapperRegistry(Configuration config) {
this.config = config;
}
@SuppressWarnings("unchecked")
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 {
//生成mapper的动态代理对象
return mapperProxyFactory.newInstance(sqlSession);
} catch (Exception e) {
throw new BindingException("Error getting mapper instance. Cause: " + e, e);
}
}
}
public class MapperProxyFactory<T> {
private final Class<T> mapperInterface;
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;
}
//最后生成动态代理对象的方法，调用接口的方法，最后都会去调用MapperProxy的invoke方法
@SuppressWarnings("unchecked")
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);
}
}
MapperProxy是动态代理中的InvocationHandler
public class MapperProxy implements InvocationHandler
上面是mybatis中为mapper接口生成动态代理对象的过程。
思考的问题是：生成的mapper对象是如何被spring管理起来的。也就是说为什么可以通过 @autowired的注解进行自动注入？
