《Spring技术内幕》学习笔记13——SqlMapClientTemplate对Ibatis的封装

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1. SqlMapClientFactoryBean：

Spring中通过SqlMapClientTemplate提供对Ibatis的支持，与Spring对Hibernate的支持类似，Spring中SqlMapClientFactoryBean就是管理Ibatis的IoC容器，我们首先分析SqlMapClientFactoryBean的源码：

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//Spring管理Ibatis的IoC容器
public class SqlMapClientFactoryBean implements FactoryBean<SqlMapClient>, InitializingBean {
//当前线程绑定Ibatis blob/clob等大字段数据处理器资源
private static final ThreadLocal<LobHandler> configTimeLobHandlerHolder = new ThreadLocal<LobHandler>();
public static LobHandler getConfigTimeLobHandler() {
return configTimeLobHandlerHolder.get();
}
//Ibatis配置文件路径
private Resource[] configLocations;
//Ibatis映射文件路径
private Resource[] mappingLocations;
//Ibatis sqlMapClient属性
private Properties sqlMapClientProperties;
//数据源
private DataSource dataSource;
//使用Spring事务包装数据源
private boolean useTransactionAwareDataSource = true;
//事务配置类
private Class transactionConfigClass = ExternalTransactionConfig.class;
//事务配置属性
private Properties transactionConfigProperties;
//blob/clob等lob类型处理器
private LobHandler lobHandler;
//Ibatis sqlMapClient
private SqlMapClient sqlMapClient;
public SqlMapClientFactoryBean() {
this.transactionConfigProperties = new Properties();
//不允许事务自动提交
this.transactionConfigProperties.setProperty("SetAutoCommitAllowed", "false");
}
//指定Ibatis sqlMapClient配置文件路径
public void setConfigLocation(Resource configLocation) {
this.configLocations = (configLocation != null ? new Resource[] {configLocation} : null);
}
//指定多个sqlMapClient配置文件路径，这些配置文件在运行时合并
public void setConfigLocations(Resource[] configLocations) {
this.configLocations = configLocations;
}
//指定Ibatis映射文件路径，这些映射文件在运行时被合并到SqlMapClient的配置中
public void setMappingLocations(Resource[] mappingLocations) {
this.mappingLocations = mappingLocations;
}
//指定Ibatis SqlMapClient可选的属性，即在SqlMapClient配置文件中通过属性
//文件设置的属性
public void setSqlMapClientProperties(Properties sqlMapClientProperties) {
this.sqlMapClientProperties = sqlMapClientProperties;
}
//设置Ibatis使用的数据源
public void setDataSource(DataSource dataSource) {
this.dataSource = dataSource;
}
//设置数据源是否使用事务包装
public void setUseTransactionAwareDataSource(boolean useTransactionAwareDataSource) {
this.useTransactionAwareDataSource = useTransactionAwareDataSource;
}
//设置Ibatis使用的事务配置类，默认是//com.ibatis.sqlmap.engine.transaction.external.ExternalTransactionConfig
public void setTransactionConfigClass(Class transactionConfigClass) {
if (transactionConfigClass == null || !TransactionConfig.class.isAssignableFrom(transactionConfigClass)) {
throw new IllegalArgumentException("Invalid transactionConfigClass: does not implement " +
"com.ibatis.sqlmap.engine.transaction.TransactionConfig");
}
this.transactionConfigClass = transactionConfigClass;
}
//设置Ibatis事务配置类属性
public void setTransactionConfigProperties(Properties transactionConfigProperties) {
this.transactionConfigProperties = transactionConfigProperties;
}
//设置Ibatis使用的处理clob/blob等大字段的处理器
public void setLobHandler(LobHandler lobHandler) {
this.lobHandler = lobHandler;
}
//IoC容器初始化完成之后的回调方法，是InitializingBean接口的实现方法
public void afterPropertiesSet() throws Exception {
//配置lob处理器
if (this.lobHandler != null) {
configTimeLobHandlerHolder.set(this.lobHandler);
}
//创建Ibatis的SqlMapClient
try {
this.sqlMapClient = buildSqlMapClient(this.configLocations, this.mappingLocations, this.sqlMapClientProperties);
//为创建的SqlMapClient设置数据源
if (this.dataSource != null) {
//创建事务配置实例
TransactionConfig transactionConfig = (TransactionConfig) this.transactionConfigClass.newInstance();
//获取数据源
DataSource dataSourceToUse = this.dataSource;
//如果Ibatis配置指定使用事务包装的数据源，并且当前获取到的数据源
//不是事务包装数据源代理类型
if (this.useTransactionAwareDataSource && !(this.dataSource instanceof TransactionAwareDataSourceProxy)) {
//为指定数据源创建事务包装代理
dataSourceToUse = new TransactionAwareDataSourceProxy(this.dataSource);
}
//事务配置对象设置数据源
transactionConfig.setDataSource(dataSourceToUse);
//初始化事务配置对象 transactionConfig.initialize(this.transactionConfigProperties);
applyTransactionConfig(this.sqlMapClient, transactionConfig);
}
}
//创建SqlMapClient成功后，清除当前线程绑定的Lob处理器资源
finally {
if (this.lobHandler != null) {
configTimeLobHandlerHolder.remove();
}
}
}
//具体创建SqlMapClient的方法，根据给定的Ibatis配置文件、Ibatis映射文件
//和Ibatis配置中的属性文件创建SqlMapClient
protected SqlMapClient buildSqlMapClient(
Resource[] configLocations, Resource[] mappingLocations, Properties properties)
throws IOException {
//如果给定Ibatis配置文件路径为空
if (ObjectUtils.isEmpty(configLocations)) {
throw new IllegalArgumentException("At least 1 'configLocation' entry is required");
}
SqlMapClient client = null;
//创建Ibatis配置文件解析器
SqlMapConfigParser configParser = new SqlMapConfigParser();
//遍历所有的Ibatis配置文件
for (Resource configLocation : configLocations) {
//获取Ibatis配置文件输入流
InputStream is = configLocation.getInputStream();
try {
//创建Ibatis SqlMapClient
client = configParser.parse(is, properties);
}
catch (RuntimeException ex) {
throw new NestedIOException("Failed to parse config resource: " + configLocation, ex.getCause());
}
}
//如果Ibatis映射文件不为null
if (mappingLocations != null) {
//根据Ibatis配置文件解析器创建Ibatis映射文件解析器
SqlMapParser mapParser = SqlMapParserFactory.createSqlMapParser(configParser);
//遍历所给定的Ibatis映射文件
for (Resource mappingLocation : mappingLocations) {
try {
//解析Ibatis映射文件
mapParser.parse(mappingLocation.getInputStream());
}
catch (NodeletException ex) {
throw new NestedIOException("Failed to parse mapping resource: " + mappingLocation, ex);
}
}
}
//返回创建的SqlMapClient对象
return client;
}
//将Ibatis配置中指定的事务配置应用到SqlMapClient上
protected void applyTransactionConfig(SqlMapClient sqlMapClient, TransactionConfig transactionConfig) {
//如果SqlMapClient不是ExtendedSqlMapClient类型，则无法将Ibatis配置//中指定的事务配置应用到SqlMapClient对象
if (!(sqlMapClient instanceof ExtendedSqlMapClient)) {
throw new IllegalArgumentException(
"Cannot set TransactionConfig with DataSource for SqlMapClient if not of type " +
"ExtendedSqlMapClient: " + sqlMapClient);
}
ExtendedSqlMapClient extendedClient = (ExtendedSqlMapClient) sqlMapClient;
//设置最大并发Ibatis事务数量 transactionConfig.setMaximumConcurrentTransactions(extendedClient.getDelegate().getMaxTransactions());
//为SqlMapClient设置事务处理器
extendedClient.getDelegate().setTxManager(new TransactionManager(transactionConfig));
}
//Spring IoC容器中对应用提供的一个获取被管理对象的方法，应该通过此方法获
//取被Spring IoC容器管理的Ibatis SqlMapClient对象
public SqlMapClient getObject() {
return this.sqlMapClient;
}
//获取SqlMapClient的类型
public Class<? extends SqlMapClient> getObjectType() {
return (this.sqlMapClient != null ? this.sqlMapClient.getClass() : SqlMapClient.class);
}
//默认Spring IoC容器中管理的对象是单态模式的
public boolean isSingleton() {
return true;
}
//Ibatis映射解析器工厂，内部类
private static class SqlMapParserFactory {
//创建Ibatis映射解析器
public static SqlMapParser createSqlMapParser(SqlMapConfigParser configParser) {
XmlParserState state = null;
try {
//使用JDK反射机制获取SqlMapConfigParser类中的state字段
Field stateField = SqlMapConfigParser.class.getDeclaredField("state");
//使用JDK反射机制使state字段可以被访问，主要解决private、//protect和默认访问权限没有提供get方法的情况
stateField.setAccessible(true);
//使用Ibatis配置解析器获取指定字段的值
state = (XmlParserState) stateField.get(configParser);
}
catch (Exception ex) {
throw new IllegalStateException("iBATIS 2.3.2 'state' field not found in SqlMapConfigParser class - " +
"please upgrade to IBATIS 2.3.2 or higher in order to use the new 'mappingLocations' feature. " + ex);
}
//为指定字段值创建Ibatis映射解析器
return new SqlMapParser(state);
}
}
}

SqlMapClientFactoryBean实现了Spring的FactoryBean接口，是Spring中管理Ibatis的IoC容器，在IoC容器初始化过程中主要完成定位Ibatis配置文件和Ibatis映射文件等工作。同时SqlMapClientFactoryBean实现了InitializingBean接口，实现了afterPropertiesSet方法，该方法是在IoC容器初始化完成之后由IoC容器进行回调的，在该方法中主要是根据定义的Ibatis配置和映射文件创建Ibatis的SqlMapClient对象的过程。

2.SqlMapClientTemplate：

Spring通过SqlMapClientTemplate对Ibatis一些通用操作做统一的封装处理，同时也对Ibatis的API做了一些封装，方便开发者使用，下面我们继续分析SqlMapClientTemplate对Ibatis封装的实现。

(1).execute方法的实现：

同JdbcTemplate和HibernateTemplate一样，Spring在SqlMapClientTemplate中也是通过execute方法封装Ibatis增删改查前的通用操作，同时在execute方法中调用相应的回调对象的回调方法来真正完成Ibatis的处理操作，execute方法源码如下：

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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");
//通过SqlMapClient对象打开一个Ibatis SqlMapSession
SqlMapSession session = this.sqlMapClient.openSession();
if (logger.isDebugEnabled()) {
logger.debug("Opened SqlMapSession [" + session + "] for iBATIS operation");
}
Connection ibatisCon = null;
try {
Connection springCon = null;
//获取数据源
DataSource dataSource = getDataSource();
//根据数据源是否是事务包装数据源代理类型，判断数据源是否需要事务包装
boolean transactionAware = (dataSource instanceof TransactionAwareDataSourceProxy);
try {
//获取连接
ibatisCon = session.getCurrentConnection();
//如果当前Ibatis SqlMapSession还没有创建过连接
if (ibatisCon == null) {
//如果Ibatis数据源已经在Spring事务管理之下，则直接使用数据源//创建连接，否则，使用DataSourceUtils创建连接，并且创建的连//接置于Spring事务管理之中
springCon = (transactionAware ?
dataSource.getConnection() : DataSourceUtils.doGetConnection(dataSource));
session.setUserConnection(springCon);
if (logger.isDebugEnabled()) {
logger.debug("Obtained JDBC Connection [" + springCon + "] for iBATIS operation");
}
}
//如果当前Ibatis SqlMapSession已经创建过连接，则直接使用
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);
}
//调用具体增删改查操作回调对象的方法
try {
return action.doInSqlMapClient(session);
}
catch (SQLException ex) {
throw getExceptionTranslator().translate("SqlMapClient operation", null, ex);
}
finally {
try {
//释放连接
if (springCon != null) {
if (transactionAware) {
springCon.close();
}
else {
DataSourceUtils.doReleaseConnection(springCon, dataSource);
}
}
}
catch (Throwable ex) {
logger.debug("Could not close JDBC Connection", ex);
}
}
}
//关闭Ibatis的SqlMapSession
finally {
if (ibatisCon == null) {
session.close();
}
}
}

(2).Spring封装Ibatis API的方法：

我们以Spring的queryForObject方法为例，分析Spring封装Ibatis API的实现，源码如下：

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//查询对象
public Object queryForObject(final String statementName, final Object parameterObject)
throws DataAccessException {
//调用execute方法，参数是实现了SqlMapClientCallback接口的匿名内部类，
//execute方法中回调该对象的doInSqlMapClient方法
return execute(new SqlMapClientCallback<Object>() {
//真正调用Ibatis API做具体操作处理的方法
public Object doInSqlMapClient(SqlMapExecutor executor) throws SQLException {
//调用Ibatis SqlMapSession对象的queryForObejct方法
return executor.queryForObject(statementName, parameterObject);
}
});
}

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