1.项目结构

2. 源码分析

2.1 获取Session DefaultSqlSessionFactory#openSession

private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {Transaction tx = null;try {final Environment environment = configuration.getEnvironment();final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);final Executor executor = configuration.newExecutor(tx, execType);return new DefaultSqlSession(configuration, executor, autoCommit);} catch (Exception e) {closeTransaction(tx); // may have fetched a connection so lets call close()throw ExceptionFactory.wrapException("Error opening session.  Cause: " + e, e);} finally {ErrorContext.instance().reset();}}

1. 从配置中获取环境信息
2. 获取事务工厂，通过事务工厂创建事务
3. 创建执行器，这里会对执行器进行了JDK动态代理
4. 将这些信息封装到DefaultSqlSession对象里面

2.2 获取Mapper DefaultSqlSession#getMapper

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> {private final Class<T> mapperInterface;private final Map<Method, MapperMethodInvoker> methodCache = new ConcurrentHashMap<>();public MapperProxyFactory(Class<T> mapperInterface) {this.mapperInterface = mapperInterface;}public Class<T> getMapperInterface() {return mapperInterface;}public Map<Method, MapperMethodInvoker> getMethodCache() {return methodCache;}@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<>(sqlSession, mapperInterface, methodCache);return newInstance(mapperProxy);}}

1. 从Configuration.mapperRegistry.knownMappers获取到MapperProxyFactory
2. 通过MapperProxyFactory创建MapperProxy对象
3. 创建代理对象，MapperProxy 代理Mapper接口