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SPRING技术内幕-笔记(十二)spring驱动ibatis的设计与实现

12.1设计原理
对ibatis的使用相对来说比较简单,在spring的封装中,有几个基本过程,首先需要创建sqlmapclient,这个sqlmapclient类似于在hibernate中的session,对于它的创建,在spring中设计sqlmapclientfactorybean,通过这个factorybean;哎读取sqlmapclient的配置和具体创建。在配置和创建好sqlmapclient之后,在spring中同样为sqlmapclient的使用封装了sqlmapclienttemplate,他同样作为一个模板,封装了通过sqlmapclient完成的主要操作。

12.2创建sqlmapclient
在springIOC容器中,ibatis实例通常通过sqlmapclientfactorybean来设置,在sqlmapfactorybean中完成sqlmapclient的创建,sqlmapclient是用户使用ibatis操作数据库的主要类,这个创建过程包括一些对sqlmapclient的配置过程(比如对数据源打他source的配置),以及对参数的配置,宰割创建过程是在afterpropertiesset中完成,他在依赖注入完成以后被ioc容器回调。
IOC调用回顾:

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protected void invokeInitMethods(String beanName, final Object bean, RootBeanDefinition mbd)
throws Throwable {

boolean isInitializingBean = (bean instanceof InitializingBean);
if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {
if (logger.isDebugEnabled()) {
logger.debug("Invoking afterPropertiesSet() on bean with name '" + beanName + "'");
}
if (System.getSecurityManager() != null) {
try {
AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
public Object run() throws Exception {
((InitializingBean) bean).afterPropertiesSet();
return null;
}
}, getAccessControlContext());
}
catch (PrivilegedActionException pae) {
throw pae.getException();
}
}
else {
//对bean注入之后进行初始化
((InitializingBean) bean).afterPropertiesSet();
}
}

if (mbd != null) {
String initMethodName = mbd.getInitMethodName();
if (initMethodName != null && !(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
!mbd.isExternallyManagedInitMethod(initMethodName)) {
invokeCustomInitMethod(beanName, bean, mbd);
}
}
}

SqlMapClientFactoryBean的getObject以及afterPropertiesSet方法:
public SqlMapClient getObject() {
return this.sqlMapClient;
}

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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 {
//开始创建sqlMapClient
this.sqlMapClient = buildSqlMapClient(this.configLocations, this.mappingLocations, this.sqlMapClientProperties);

// Tell the SqlMapClient to use the given DataSource, if any.
//为sqlMapClient 设置数据源
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.remove();
}
}
}

buildSqlMapClient方法的实现:

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	protected SqlMapClient buildSqlMapClient(
Resource[] configLocations, Resource[] mappingLocations, Properties properties)
throws IOException {

if (ObjectUtils.isEmpty(configLocations)) {
throw new IllegalArgumentException("At least 1 'configLocation' entry is required");
}

SqlMapClient client = null;
//对应对数据源以及数据源附属参数的设置
SqlMapConfigParser configParser = new SqlMapConfigParser();
for (Resource configLocation : configLocations) {
InputStream is = configLocation.getInputStream();
try {
client = configParser.parse(is, properties);
}
catch (RuntimeException ex) {
throw new NestedIOException("Failed to parse config resource: " + configLocation, ex.getCause());
}
}
//对映射文件的初始化。
if (mappingLocations != null) {
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;
}

12.3 sqlmapclienttemplate的实现

sqlmapclienttemplate封装了对ibatis的操作,其继承关系如下:
这里写图片描述

sqlmapclienttemplate是一个核心,这个类持有一个sqlmapclient,这个类是ibatis的类,是直接使用ibatis时调用的,它提供了使用ibatis的API,类似于hibernate的session,同时,sqlmapclientdaosupport中持有一个salmapclienttemplate,尽管对ibatis的操作是由sqlmapclienttemplate来完成,但应用可以通过扩展sqlmapclientdaosupport来对ibatis进行操作。spring封装ibatis操作基本上封装在sqlmapclienttemplate的设计和实现中。其设计时序图:
这里写图片描述

在这个时序过程中,template会从sqlmapclient中得到session和datasource,并进行一系列的初始化过程,然后回调sqlmapclientcallback的doinsqlmapclient方法执行具体的动作,最后释放数据库连接和关闭session。
代码实现:

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/**
* Execute the given data access action on a SqlMapExecutor.
* @param action callback object that specifies the data access action
* @return a result object returned by the action, or <code>null</code>
* @throws DataAccessException in case of SQL Maps errors
*/
//使用SqlMapExecutor完成数据的操作
public <T> T execute(SqlMapClientCallback<T> action) throws DataAccessException {
Assert.notNull(action, "Callback object must not be null");
Assert.notNull(this.sqlMapClient, "No SqlMapClient specified");

// We always need to use a SqlMapSession, as we need to pass a Spring-managed
// Connection (potentially transactional) in. This shouldn't be necessary if
// we run against a TransactionAwareDataSourceProxy underneath, but unfortunately
// we still need it to make iBATIS batch execution work properly: If iBATIS
// doesn't recognize an existing transaction, it automatically executes the
// batch for every single statement...
//通过sqlMapClient完成sqlmapsession
SqlMapSession session = this.sqlMapClient.openSession();
if (logger.isDebugEnabled()) {
logger.debug("Opened SqlMapSession [" + session + "] for iBATIS operation");
}
Connection ibatisCon = null;
//得到数据源
try {
Connection springCon = null;
DataSource dataSource = getDataSource();
boolean transactionAware = (dataSource instanceof TransactionAwareDataSourceProxy);

// Obtain JDBC Connection to operate on...
try {
ibatisCon = session.getCurrentConnection();
if (ibatisCon == null) {
//此处将要获取connection,如果已经在spring的事物管理之下,数据源直接拿过来使用,否则就是用
//DataSourceUtils生成一个connection,并将得到的connnection放在spring的事物管理之下。
springCon = (transactionAware ?
dataSource.getConnection() : DataSourceUtils.doGetConnection(dataSource));
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);
}

// Execute given callback...
try {
//执行SqlMapClientCallback的回调函数
return action.doInSqlMapClient(session);
}
catch (SQLException ex) {
throw getExceptionTranslator().translate("SqlMapClient operation", null, ex);
}
finally {
try {
if (springCon != null) {
if (transactionAware) {
springCon.close();
}
else {
DataSourceUtils.doReleaseConnection(springCon, dataSource);
}
}
}
catch (Throwable ex) {
logger.debug("Could not close JDBC Connection", ex);
}
}

// Processing finished - potentially session still to be closed.
}
//释放datasource
finally {
// Only close SqlMapSession if we know we've actually opened it
// at the present level.
if (ibatisCon == null) {
session.close();
}
}
}

sqlmapclienttemplate的其他方法也是调用exector方法提供回调函数实现的。
比如:

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public Object queryForObject(final String statementName, final Object parameterObject)
throws DataAccessException {

return execute(new SqlMapClientCallback<Object>() {
public Object doInSqlMapClient(SqlMapExecutor executor) throws SQLException {
return executor.queryForObject(statementName, parameterObject);
}
});
}

关于datasource的关闭以及事物的绑定都已经做好了封装。