1. 在创建好sqlSessionFactory之后，接着就要配置sqlSession的创建。
<bean id="simpleTempalte" class="org.mybatis.spring.SqlSessionTemplate">
<constructor-arg index="0" ref="sqlSessionFactory" />
<constructor-arg index="1" value="SIMPLE" />
</bean>
- 构造参数，包括sqlSessionFactory对象，以及ExecutorType（simple）
2. sqlSession接口
- 我们的应用程序，是直接注入sqlSessionTemplate ，操作数据库
simpleTempalte.delete(Statement.getStatement(CxCaseMapper.class, "deleteById"), id);
- 实现类sqlSessionTemplate
public class SqlSessionTemplate implements SqlSession {
//session 工场的引用
private final SqlSessionFactory sqlSessionFactory;
// 对于数据库的操作类型
private final ExecutorType executorType;
//sqlSession代理
private final SqlSession sqlSessionProxy;
private final PersistenceExceptionTranslator exceptionTranslator;
}- sqlSession对每一个数据库的操作，实际上是引用代理对象sqlSessionProxy 对于目标方法的执行。
@Override
public int delete(String statement) {
return this.sqlSessionProxy.delete(statement);
}
- 在构造方法中，给代理对象已经其他属性赋予的默认值
public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType,
PersistenceExceptionTranslator exceptionTranslator) {
this.sqlSessionFactory = sqlSessionFactory;
this.executorType = executorType;
this.exceptionTranslator = exceptionTranslator;
//构造代理对象
this.sqlSessionProxy = (SqlSession) newProxyInstance(
SqlSessionFactory.class.getClassLoader(),
new Class[] { SqlSession.class },
new SqlSessionInterceptor());
} private class SqlSessionInterceptor implements InvocationHandler {
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
//这里获取的sqlSession 其实是DefaultSqlSession
SqlSession sqlSession = getSqlSession(
SqlSessionTemplate.this.sqlSessionFactory,
SqlSessionTemplate.this.executorType,
SqlSessionTemplate.this.exceptionTranslator);
try {
// 代理对象对于目标对象的调用，其实是defaultSqlSession 对于目标方法的调用
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) {
//调用目标方法后，关闭Session。 后续会重点讲解
closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
}
}
}
}
- defaultSqlSession 对于目标方法的执行
public class DefaultSqlSession implements SqlSession {
private Configuration configuration;
private Executor executor;
private boolean autoCommit;
private boolean dirty;
@Override
public void select(String statement, Object parameter, RowBounds rowBounds, ResultHandler handler) {
try {
MappedStatement ms = configuration.getMappedStatement(statement);
executor.query(ms, wrapCollection(parameter), rowBounds, handler);
} catch (Exception e) {
throw ExceptionFactory.wrapException("Error querying database. Cause: " + e, e);
} finally {
ErrorContext.instance().reset();
}
}
}3. 代理的优点
无论是多个dao使用一个SqlSessionTemplate，还是一个dao使用一个SqlSessionTemplate，SqlSessionTemplate都是对应一个sqlSession，当多个web线程调用同一个dao时，它们使用的是同一个SqlSessionTemplate，也就是同一个SqlSession，保证线程安全，
4 .总结