<settings>
    <!-- 打印查询语句 -->
    <setting name="logImpl" value="STDOUT_LOGGING" />
  </settings>

/**
 * 测试spring里的mybatis为啥用不上缓存
 *
 * @author 何锦彬 2017.02.15
 */
@Component
public class TestDao {
  private Logger logger = Logger.getLogger(TestDao.class.getName());
  @Autowired
  private SqlSessionTemplate sqlSessionTemplate;
  @Autowired
  private SqlSessionFactory sqlSessionFactory;
  /**
   * 两次SQL
   *
   * @param id
   * @return
   */
  public TestDto selectBySpring(String id) {
    TestDto testDto = (TestDto) sqlSessionTemplate.selectOne("com.hejb.TestDto.selectByPrimaryKey", id);
    testDto = (TestDto) sqlSessionTemplate.selectOne("com.hejb.TestDto.selectByPrimaryKey", id);
    return testDto;
  }
  /**
   * 一次SQL
   *
   * @param id
   * @return
   */
  public TestDto selectByMybatis(String id) {
    SqlSession session = sqlSessionFactory.openSession();
    TestDto testDto = session.selectOne("com.hejb.TestDto.selectByPrimaryKey", id);
    testDto = session.selectOne("com.hejb.TestDto.selectByPrimaryKey", id);
    return testDto;
  }
}

@Component
public class TestService {
  @Autowired
  private TestDao testDao;
  /**
   * 未开启事务的spring Mybatis查询
   */
  public void testSpringCashe() {
    //查询了两次SQL
    testDao.selectBySpring("1");
  }
  /**
   * 开启事务的spring Mybatis查询
   */
  @Transactional
  public void testSpringCasheWithTran() {
    //spring开启事务后，查询1次SQL
    testDao.selectBySpring("1");
  }
  /**
   * mybatis查询
   */
  public void testCash4Mybatise() {
    //原生态mybatis，查询了1次SQL
    testDao.selectByMybatis("1");
  }
}

try {
   queryStack++;
   list = resultHandler == null ? (List<E>) localCache.getObject(key) : null; //先从缓存中取
   if (list != null) {
    handleLocallyCachedOutputParameters(ms, key, parameter, boundSql); //注意里面的key是CacheKey
   } else {
    list = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);
   }

private void handleLocallyCachedOutputParameters(MappedStatement ms, CacheKey key, Object parameter, BoundSql boundSql) {
  if (ms.getStatementType() == StatementType.CALLABLE) {
   final Object cachedParameter = localOutputParameterCache.getObject(key);//从localOutputParameterCache取出缓存对象
   if (cachedParameter != null && parameter != null) {
    final MetaObject metaCachedParameter = configuration.newMetaObject(cachedParameter);
    final MetaObject metaParameter = configuration.newMetaObject(parameter);
    for (ParameterMapping parameterMapping : boundSql.getParameterMappings()) {
     if (parameterMapping.getMode() != ParameterMode.IN) {
      final String parameterName = parameterMapping.getProperty();
      final Object cachedValue = metaCachedParameter.getValue(parameterName);
      metaParameter.setValue(parameterName, cachedValue);
     }
    }
   }
  }
 }

<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
    <property name="dataSource" ref="dataSource" />
    <property name="configLocation" value="classpath:configuration.xml" />
    <property name="mapperLocations">
      <list>
        <value>classpath*:com/hejb/sqlmap/*.xml</value>
      </list>
    </property>
  </bean>
  <bean id="sqlSessionTemplate" class="org.mybatis.spring.SqlSessionTemplate">
    <constructor-arg ref="sqlSessionFactory" />
  </bean>

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 {
   // 每次执行前都创建一个新的sqlSession
   SqlSession sqlSession = getSqlSession(
     SqlSessionTemplate.this.sqlSessionFactory,
     SqlSessionTemplate.this.executorType,
     SqlSessionTemplate.this.exceptionTranslator);
   try {
   // 执行方法
    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) {
     closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
    }
   }
  }
 }

public static SqlSession getSqlSession(SqlSessionFactory sessionFactory, ExecutorType executorType, PersistenceExceptionTranslator exceptionTranslator) {
  notNull(sessionFactory, NO_SQL_SESSION_FACTORY_SPECIFIED);
  notNull(executorType, NO_EXECUTOR_TYPE_SPECIFIED);
  SqlSessionHolder holder = (SqlSessionHolder) TransactionSynchronizationManager.getResource(sessionFactory);
  // 首先从SqlSessionHolder里取出session
  SqlSession session = sessionHolder(executorType, holder);
  if (session != null) {
   return session;
  }
  if (LOGGER.isDebugEnabled()) {
   LOGGER.debug("Creating a new SqlSession");
  }
  session = sessionFactory.openSession(executorType);
  registerSessionHolder(sessionFactory, executorType, exceptionTranslator, session);
  return session;
 }