Spring创建iBatis的SqlMapClient实例

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SqlMapClient是iBatis 2.x操作数据库的主要类，相当于hibernate的Session。
Spring创建iBatis的SqlMapClient实例是通过SqlMapClientFactoryBean.afterPropertiesSet方法创建的，由于SqlMapClientFactoryBean实现InitializingBean接口，IoC容器会在依赖注入完成后回调InitializingBean接口的afterPropertiesSet。
applicationContext.xml配置sqlMapClient

<bean id="sqlMapClient" class="org.springframework.orm.ibatis.SqlMapClientFactoryBean">
   <property name="dataSource" ref="dataSource" />
   <property name="configLocation">
     <value>classpath:sqlMapConfig.xml</value>
   </property>
</bean>

SqlMapClientFactoryBean通过的getObject()返回sqlMapClient，跟其他的FactoryBean一样。
生成的过程afterPropertiesSet方法

public void afterPropertiesSet() throws Exception {
	/*设置自定义的lobHandler，LobHandler为操作二进制字段和大文本字段提供统一接口访问，如Oracle LOB*/
	if (this.lobHandler != null) {
		/*当前线程绑定Ibatis blob/clob等大字段数据处理器资源  */
		configTimeLobHandlerHolder.set(this.lobHandler);
	}

	try {
		/*创建iBatis的sqlMapClient相当于hibernate的Session，是iBatis操作数据库的主要类*/		this.sqlMapClient = buildSqlMapClient(this.configLocations, this.mappingLocations, this.sqlMapClientProperties);

		// Tell the SqlMapClient to use the given DataSource, if any.
		/*设置dataSource数据源*/
		if (this.dataSource != null) {
			TransactionConfig transactionConfig = (TransactionConfig) this.transactionConfigClass.newInstance();
			DataSource dataSourceToUse = this.dataSource;
			if (this.useTransactionAwareDataSource && !(this.dataSource instanceof TransactionAwareDataSourceProxy)) {
				/*生成事务数据源的动态代理*/
				dataSourceToUse = new TransactionAwareDataSourceProxy(this.dataSource);
			}
			//为事务配置对象设置数据源
			transactionConfig.setDataSource(dataSourceToUse);
			//为事务配置对象设置属性
			transactionConfig.initialize(this.transactionConfigProperties);
			applyTransactionConfig(this.sqlMapClient, transactionConfig);
		}
	}

	finally {
		if (this.lobHandler != null) {
			// Reset LobHandler holder.
			configTimeLobHandlerHolder.remove();
		}
	}
}

具体sqlMapClient创建的过程

/*根据iBatis的配置文档sqlMapConfig.xml、映射文档如User.xml和属性文档生成sqlMapClient
 * */
protected SqlMapClient buildSqlMapClient(
		Resource[] configLocations, Resource[] mappingLocations, Properties properties)
		throws IOException {
	/*判断配置文档是否为空*/
	if (ObjectUtils.isEmpty(configLocations)) {
		throw new IllegalArgumentException("At least 1 'configLocation' entry is required");
	}

	SqlMapClient client = null;
	/*生成配置文档解析器*/
	SqlMapConfigParser configParser = new SqlMapConfigParser();
	for (Resource configLocation : configLocations) {
		/*获取配置文档的输入流*/
		InputStream is = configLocation.getInputStream();
		try {
			/*生成sqlMapClient*/
			client = configParser.parse(is, properties);
		}
		catch (RuntimeException ex) {
			throw new NestedIOException("Failed to parse config resource: " + configLocation, ex.getCause());
		}
	}

	if (mappingLocations != null) {
		/*创建映射文档的解析器，自己可以在createSqlMapParser中做一些自定义处理，如通过反射方式设置缓冲配置*/			
		SqlMapParser mapParser = SqlMapParserFactory.createSqlMapParser(configParser);
		for (Resource mappingLocation : mappingLocations) {
			try {
				mapParser.parse(mappingLocation.getInputStream());
			}
			catch (NodeletException ex) {
				throw new NestedIOException("Failed to parse mapping resource: " + mappingLocation, ex);
			}
		}
	}

	return client;
}

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