背景：调试模式下，单步运行一个查询订单协议操作，记录了ibatis框架的执行动作，侧面剖析其原理。
一、简介：
1. dal 层的dao接口实现类通常会继承SqlMapClientDaoSupport。spring容器在初始化一个dao bean实例时，通常会注入两块信息DataSource（数据源）和sqlMapClient（主要是sql语句），这两块信息会封装到SqlMapClientTemplate
2. 其中数据源的实例通常采用apache的开源项目dbcp
代码配置如下：
<beanid="dataSource"class="org.apache.commons.dbcp.BasicDataSource"destroy-method="close">
<propertyname="driverClassName"value="com.mysql.jdbc.Driver"/>
<propertyname="url"value="xxxx"/>
<propertyname="username"><value>xxxx</value></property>
<propertyname="password"><value>xxxxx</value></property>
<propertyname="maxActive"><value>20</value></property>
<propertyname="initialSize"><value>1</value></property>
<propertyname="maxWait"><value>60000</value></property>
<propertyname="maxIdle"><value>20</value></property>
<propertyname="minIdle"><value>3</value></property>
<propertyname="removeAbandoned"><value>true</value></property>
<propertyname="removeAbandonedTimeout"><value>180</value></property>
<propertyname="connectionProperties"><value>clientEncoding=GBK</value></property>
</bean>
各配置参数的具体含义可参照：dbcp基本配置和重连配置
3. sqlMapClient
<beanid="sqlMapClient"class="org.springframework.orm.ibatis.SqlMapClientFactoryBean">
<propertyname="configLocation">
<value>classpath:sqlmap.xml</value>
</property>
</bean>
<beanid="sqlMapClientTddl"class="org.springframework.orm.ibatis.SqlMapClientFactoryBean">
<propertyname="dataSource"ref="tGroupDataSource"/>
<propertyname="configLocation"value="classpath:sqlmap.xml"/>
</bean>
sqlMapClient，主要是借助于实现FactoryBean和InitializingBean两个接口，加载sql.xml文件资源信息，得到sqlMapClient组件
注：上面的sqlMapClient默认不配置数据源，后面的SqlMapClientTemplate优先从全局变量中取，如果没有再从sqlMapClient中查找。
public DataSource getDataSource() {
DataSource ds = super.getDataSource();
return (ds != null ? ds : this.sqlMapClient.getDataSource());
}
构造sqlMapClient组件的代码块。
public void afterPropertiesSet() throws Exception {
if (this.lobHandler != null) {
// Make given LobHandler available for SqlMapClient configuration.
// Do early because because mapping resource might refer to custom types.
configTimeLobHandlerHolder.set(this.lobHandler);
}
try {
this.sqlMapClient = buildSqlMapClient(this.configLocations, this.mappingLocations, this.sqlMapClientProperties);
// Tell the SqlMapClient to use the given DataSource, if any.
if (this.dataSource != null) {
TransactionConfig transactionConfig = (TransactionConfig) this.transactionConfigClass.newInstance();
DataSource dataSourceToUse = this.dataSource;
if (this.useTransactionAwareDataSource && !(this.dataSource instanceof TransactionAwareDataSourceProxy)) {
dataSourceToUse = new TransactionAwareDataSourceProxy(this.dataSource);
}
transactionConfig.setDataSource(dataSourceToUse);
transactionConfig.initialize(this.transactionConfigProperties);
applyTransactionConfig(this.sqlMapClient, transactionConfig);
}
}
finally {
if (this.lobHandler != null) {
// Reset LobHandler holder.
configTimeLobHandlerHolder.set(null);
}
}
}
4. SqlMapExecutor
该接口是对SQL操作行为的抽象，提供了SQL单条执行和批处理涉及的所有操作方法
5. SqlMapTransactionManager
该接口是对事务行为的抽象，提供了事务执行过程中涉及的所有方法。
6. SqlMapClient
该接口定位是SQL执行客户端，是线程安全的，用于处理多个线程的sql执行。它继承了上面两个接口，这意味着该接口具有SQL执行和事务处理的能力，该接口的核心实现类是SqlMapClientImpl。
7. SqlMapSession
该接口在继承关系上和SqlMapClient一致，但它的定位是保存单线程sql执行过程的session信息。该接口的核心实现类是SqlMapSessionImpl
8. MappedStatement
该接口定位是单条SQL执行时的上下文环境信息，如SQL标识、SQL、参数信息、返回结果、操作行为等。
9. ParameterMap/ResultMap
该接口用于在SQL执行的前后提供参数准备和执行结果集的处理。
整体类图：
二、具体调用
接下来就到了数据持久层的代码调用，所有的数据库DML操作（增、删、改、查）都是借助于SqlMapClientTemplate来实现的。
public OrderEnsureProtocolDO getOrderEnsureProtocolByOrderId(Long orderId) {
if (orderId == null) {
return null;
}
return (OrderEnsureProtocolDO) this.getSqlMapClientTemplate().queryForObject("MS-FIND-ORDERENSUREPROTOCOL-BY-ORDERID",
orderId);
}
如果一次执行的sql较多，我们会采用批处理的形式
public void batchDeleteOfferSaleRecord(final List<Long> orderEntryIds) throws Exception {
if (orderEntryIds == null || orderEntryIds.size() <1 || orderEntryIds.size() > 50) {
return;
}
this.getSqlMapClientTemplate().execute(new SqlMapClientCallback() {
@Override
public Object doInSqlMapClient(SqlMapExecutor executor) throws SQLException {
executor.startBatch();
for (Long entryId : orderEntryIds) {
executor.insert(MS\_DELETE\_SALE_RECORD, entryId);
}
return executor.executeBatch();
}
});
}
不管采用上面哪种方式，查看源代码会发现，最后都是在调用execute(SqlMapClientCallback action)方法
public Object queryForObject(final String statementName, final Object parameterObject)
throws DataAccessException {
return execute(new SqlMapClientCallback() {
public Object doInSqlMapClient(SqlMapExecutor executor) throws SQLException {
return executor.queryForObject(statementName, parameterObject);
}
});
}
public Object execute(SqlMapClientCallback action) throws DataAccessException {
Assert.notNull(action, "Callback object must not be null");
Assert.notNull(this.sqlMapClient, "No SqlMapClient specified");
//获取session信息(SqlMapSessionImpl实例)
SqlMapSession session = this.sqlMapClient.openSession();
if (logger.isDebugEnabled()) {
logger.debug("Opened SqlMapSession \[" + session + "\] for iBATIS operation");
}
Connection ibatisCon = null;
try {
Connection springCon = null;//数据库连接
DataSource dataSource = getDataSource();
boolean transactionAware = (dataSource instanceof TransactionAwareDataSourceProxy);
try {
//获取数据获连接
ibatisCon = session.getCurrentConnection();
if (ibatisCon == null) {
springCon = (transactionAware ?
dataSource.getConnection() : DataSourceUtils.doGetConnection(dataSource));
//将数据源set到session会话中
session.setUserConnection(springCon);
if (logger.isDebugEnabled()) {
logger.debug("Obtained JDBC Connection \[" + springCon + "\] for iBATIS operation");
}
}
else {
if (logger.isDebugEnabled()) {
logger.debug("Reusing JDBC Connection \[" + ibatisCon + "\] for iBATIS operation");
}
}
}
catch (SQLException ex) {
throw new CannotGetJdbcConnectionException("Could not get JDBC Connection", ex);
}
try {
//执行SQL
return action.doInSqlMapClient(session);
}
catch (SQLException ex) {
throw getExceptionTranslator().translate("SqlMapClient operation", null, ex);
}
finally {
省略。。。一系列的关闭工作
}
}
SqlMapSessionImpl().queryForObject()的方法很简单，直接交给代理对象SqlMapExecutorDelegate处理（里面注入了很多功能对象，负责具体的sql执行）
public Object queryForObject(String id, Object paramObject) throws SQLException {
return delegate.queryForObject(session, id, paramObject);
}
经过N层重载，最后调用内部的通用方法
入参：
id=MS-FIND-ORDERENSUREPROTOCOL-BY-ORDERID
paramObject=26749329
public Object queryForObject(SessionScope session, String id, Object paramObject, Object resultObject) throws SQLException {
Object object = null;
//MappedStatement对象集是上文中提及的初始化方法SqlMapClientFactoryBean.afterPropertiesSet()中，由配置文件构建而成
//调试中的ms为SelectStatement，具体的执行器
MappedStatement ms = getMappedStatement(id);
// 用于事务执行
Transaction trans = getTransaction(session);
boolean autoStart = trans == null;
try {
trans = autoStartTransaction(session, autoStart, trans);
// 从RequestScope池中获取该次sql执行中的上下文环境RequestScope
RequestScope request = popRequest(session, ms);
try {
// 执行sql
object = ms.executeQueryForObject(request, trans, paramObject, resultObject);
} finally {
pushRequest(request); //归还RequestScope
}
autoCommitTransaction(session, autoStart);
} finally {
autoEndTransaction(session, autoStart);
}
return object;
}
接下来由MappedStatement.executeQueryForObject()来执行
public Object executeQueryForObject(RequestScope request, Transaction trans, Object parameterObject, Object resultObject)
throws SQLException {
try {
Object object = null;
DefaultRowHandler rowHandler = new DefaultRowHandler();
//执行sql语句
executeQueryWithCallback(request, trans.getConnection(), parameterObject, resultObject, rowHandler, SqlExecutor.NO\_SKIPPED\_RESULTS, SqlExecutor.NO\_MAXIMUM\_RESULTS);
//结果处理，返回结果
List list = rowHandler.getList();
if (list.size() > 1) {
throw new SQLException("Error: executeQueryForObject returned too many results.");
} else if (list.size() > 0) {
object = list.get(0);
}
。。。。。。。。。
}
MappedStatement.executeQueryWithCallback()方法包含了参数值映射、sql准备和sql执行等关键过程
protected void executeQueryWithCallback(RequestScope request, Connection conn, Object parameterObject, Object resultObject, RowHandler rowHandler, int skipResults, int maxResults)
throws SQLException {
//预先封装错误信息，如果报错时便于排查问题
ErrorContext errorContext = request.getErrorContext();
errorContext.setActivity("preparing the mapped statement for execution");
errorContext.setObjectId(this.getId());
errorContext.setResource(this.getResource());
try {
//验证入参
parameterObject = validateParameter(parameterObject);
//获取SQL对象
Sql sql = getSql();
errorContext.setMoreInfo("Check the parameter map.");
// 入参映射
ParameterMap parameterMap = sql.getParameterMap(request, parameterObject);
errorContext.setMoreInfo("Check the result map.");
//获取结果
ResultMap resultMap = sql.getResultMap(request, parameterObject);
request.setResultMap(resultMap);
request.setParameterMap(parameterMap);
errorContext.setMoreInfo("Check the parameter map.");
//获取参数值
Object\[\] parameters = parameterMap.getParameterObjectValues(request, parameterObject);
errorContext.setMoreInfo("Check the SQL statement.");
//获取拼装后的sql语句
String sqlString = sql.getSql(request, parameterObject);
errorContext.setActivity("executing mapped statement");
errorContext.setMoreInfo("Check the SQL statement or the result map.");
RowHandlerCallback callback = new RowHandlerCallback(resultMap, resultObject, rowHandler);
//sql执行
sqlExecuteQuery(request, conn, sqlString, parameters, skipResults, maxResults, callback);
....省略
}
最后调用com.ibatis.sqlmap.engine.execution.SqlExecutor.executeQuery(RequestScope, Connection, String, Object[], int, int, RowHandlerCallback)
public void executeQuery(RequestScope request, Connection conn, String sql, Object\[\] parameters, int skipResults, int maxResults, RowHandlerCallback callback) throws SQLException {
...省略
PreparedStatement ps = null;
ResultSet rs = null;
setupResultObjectFactory(request);
try {
errorContext.setMoreInfo("Check the SQL Statement (preparation failed).");
Integer rsType = request.getStatement().getResultSetType();
//初始化PreparedStatement，设置sql、参数值等
if (rsType != null) {
ps = prepareStatement(request.getSession(), conn, sql, rsType);
} else {
ps = prepareStatement(request.getSession(), conn, sql);
}
setStatementTimeout(request.getStatement(), ps);
Integer fetchSize = request.getStatement().getFetchSize();
if (fetchSize != null) {
ps.setFetchSize(fetchSize.intValue());
}
errorContext.setMoreInfo("Check the parameters (set parameters failed).");
request.getParameterMap().setParameters(request, ps, parameters);
errorContext.setMoreInfo("Check the statement (query failed).");
//执行
ps.execute();
errorContext.setMoreInfo("Check the results (failed to retrieve results).");
//结果集处理
rs = handleMultipleResults(ps, request, skipResults, maxResults, callback);
。。。省略
}