Spring集成Mybatis源码剖析
Spring集成Mybatis时定义了一个SqlSessionFactoryBean实例
<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean"> <property name="dataSource" ref="dataSource" /> //mybatis配置文件 <property name="configLocation" value="XXX.xml"></property> //mapper文件 <property name="mapperLocations" value="classpath:XXX.xml"></property> </bean>
进入SqlSessionFactoryBean可以看出,由buildSqlSessionFactory()加载配置信息
protected SqlSessionFactory buildSqlSessionFactory() throws IOException { Configuration configuration; XMLConfigBuilder xmlConfigBuilder = null; if (this.configuration != null) { configuration = this.configuration; if (configuration.getVariables() == null) { configuration.setVariables(this.configurationProperties); } else if (this.configurationProperties != null) { configuration.getVariables().putAll(this.configurationProperties); } } else if (this.configLocation != null) { //根据mybatis配置文件生成配置信息 xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties); configuration = xmlConfigBuilder.getConfiguration(); } else { if (LOGGER.isDebugEnabled()) { LOGGER.debug("Property `configuration` or 'configLocation' not specified, using default MyBatis Configuration"); } configuration = new Configuration(); configuration.setVariables(this.configurationProperties); } if (this.objectFactory != null) { configuration.setObjectFactory(this.objectFactory); } if (this.objectWrapperFactory != null) { configuration.setObjectWrapperFactory(this.objectWrapperFactory); } if (this.vfs != null) { configuration.setVfsImpl(this.vfs); } if (hasLength(this.typeAliasesPackage)) { String[] typeAliasPackageArray = tokenizeToStringArray(this.typeAliasesPackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS); for (String packageToScan : typeAliasPackageArray) { configuration.getTypeAliasRegistry().registerAliases(packageToScan, typeAliasesSuperType == null ? Object.class : typeAliasesSuperType); if (LOGGER.isDebugEnabled()) { LOGGER.debug("Scanned package: '" + packageToScan + "' for aliases"); } } } if (!isEmpty(this.typeAliases)) { for (Class<?> typeAlias : this.typeAliases) { configuration.getTypeAliasRegistry().registerAlias(typeAlias); if (LOGGER.isDebugEnabled()) { LOGGER.debug("Registered type alias: '" + typeAlias + "'"); } } } if (!isEmpty(this.plugins)) { for (Interceptor plugin : this.plugins) { configuration.addInterceptor(plugin); if (LOGGER.isDebugEnabled()) { LOGGER.debug("Registered plugin: '" + plugin + "'"); } } } if (hasLength(this.typeHandlersPackage)) { String[] typeHandlersPackageArray = tokenizeToStringArray(this.typeHandlersPackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS); for (String packageToScan : typeHandlersPackageArray) { configuration.getTypeHandlerRegistry().register(packageToScan); if (LOGGER.isDebugEnabled()) { LOGGER.debug("Scanned package: '" + packageToScan + "' for type handlers"); } } } if (!isEmpty(this.typeHandlers)) { for (TypeHandler<?> typeHandler : this.typeHandlers) { configuration.getTypeHandlerRegistry().register(typeHandler); if (LOGGER.isDebugEnabled()) { LOGGER.debug("Registered type handler: '" + typeHandler + "'"); } } } if (this.databaseIdProvider != null) {//fix #64 set databaseId before parse mapper xmls try { configuration.setDatabaseId(this.databaseIdProvider.getDatabaseId(this.dataSource)); } catch (SQLException e) { throw new NestedIOException("Failed getting a databaseId", e); } } if (this.cache != null) { configuration.addCache(this.cache); } if (xmlConfigBuilder != null) { try { xmlConfigBuilder.parse(); if (LOGGER.isDebugEnabled()) { LOGGER.debug("Parsed configuration file: '" + this.configLocation + "'"); } } catch (Exception ex) { throw new NestedIOException("Failed to parse config resource: " + this.configLocation, ex); } finally { ErrorContext.instance().reset(); } } if (this.transactionFactory == null) { this.transactionFactory = new SpringManagedTransactionFactory(); } configuration.setEnvironment(new Environment(this.environment, this.transactionFactory, this.dataSource)); if (!isEmpty(this.mapperLocations)) { for (Resource mapperLocation : this.mapperLocations) { if (mapperLocation == null) { continue; } try { XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(), configuration, mapperLocation.toString(), configuration.getSqlFragments()); xmlMapperBuilder.parse(); } catch (Exception e) { throw new NestedIOException("Failed to parse mapping resource: '" + mapperLocation + "'", e); } finally { ErrorContext.instance().reset(); } if (LOGGER.isDebugEnabled()) { LOGGER.debug("Parsed mapper file: '" + mapperLocation + "'"); } } } else { if (LOGGER.isDebugEnabled()) { LOGGER.debug("Property 'mapperLocations' was not specified or no matching resources found"); } } //根据配置信息生成SqlSessionFactory实例 return this.sqlSessionFactoryBuilder.build(configuration); }
进入SqlSessionFactoryBuilder,可以发现里面的build()方法根据配置文件生成SqlSessionFactory
//自己读取配置文件生成SqlSessionFactory public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) { try { XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties); return build(parser.parse()); } catch (Exception e) { throw ExceptionFactory.wrapException("Error building SqlSession.", e); } finally { ErrorContext.instance().reset(); try { inputStream.close(); } catch (IOException e) { // Intentionally ignore. Prefer previous error. } } } //默认生成DefaultSqlSessionFactory实例 public SqlSessionFactory build(Configuration config) { return new DefaultSqlSessionFactory(config); }
以一次通过ID获取实体为例
dao层调用SqlSessionTemplate的selectOne()方法
@Override public <T> T selectOne(String statement, Object parameter) { return this.sqlSessionProxy.<T> selectOne(statement, parameter); }
SqlSessionTemplate里面有个内部类SqlSessionInterceptor ,通过代理模式执行数据库操作
private class SqlSessionInterceptor implements InvocationHandler { @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { //通过SqlSessionUtils获取sqlSession 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); } } } }
SqlSessionUtils.getSqlSession()
public static SqlSession getSqlSession(SqlSessionFactory sessionFactory, ExecutorType executorType, PersistenceExceptionTranslator exceptionTranslator) { notNull(sessionFactory, NO_SQL_SESSION_FACTORY_SPECIFIED); notNull(executorType, NO_EXECUTOR_TYPE_SPECIFIED); SqlSessionHolder holder = (SqlSessionHolder) TransactionSynchronizationManager.getResource(sessionFactory); SqlSession session = sessionHolder(executorType, holder); if (session != null) { return session; } if (LOGGER.isDebugEnabled()) { LOGGER.debug("Creating a new SqlSession"); }
//开启session会话 session = sessionFactory.openSession(executorType); registerSessionHolder(sessionFactory, executorType, exceptionTranslator, session); return session; }
开启session会话的操作由SqlSessionFactory.openSessionFromDataSource()方法完成
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(); } }
执行DefaultSqlSession.selectOne()方法
public <T> T selectOne(String statement, Object parameter) { // Popular vote was to return null on 0 results and throw exception on too many. List<T> list = this.<T>selectList(statement, parameter); if (list.size() == 1) { return list.get(0); } else if (list.size() > 1) { throw new TooManyResultsException("Expected one result (or null) to be returned by selectOne(), but found: " + list.size()); } else { return null; } }
执行selectList()
public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) { try { MappedStatement ms = configuration.getMappedStatement(statement); return executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER); } catch (Exception e) { throw ExceptionFactory.wrapException("Error querying database. Cause: " + e, e); } finally { ErrorContext.instance().reset(); } }
这里用到了执行器Executor,相关文章请看Mybatis缓存机制,然后将结果输出