之前了解到mybatis的一级缓存是默认开启的,作用域是sqlSession,是基 HashMap的本地缓存。不同的SqlSession之间的缓存数据区域互不影响。
当进行select、update、delete操作后并且commit事物到数据库之后,sqlSession中的Cache自动被清空
<setting name="localCacheScope" value="SESSION"/>
结论
spring结合mybatis后,一级缓存作用:
在未开启事物的情况之下,每次查询,spring都会关闭旧的sqlSession而创建新的sqlSession,因此此时的一级缓存是没有启作用的
在开启事物的情况之下,spring使用threadLocal获取当前资源绑定同一个sqlSession,因此此时一级缓存是有效的
案例
情景一:未开启事物
@Service("countryService") public class CountryService { @Autowired private CountryDao countryDao; // @Transactional 未开启事物 public void noTranSactionMethod() throws JsonProcessingException { CountryDo countryDo = countryDao.getById(1L); CountryDo countryDo1 = countryDao.getById(1L); ObjectMapper objectMapper = new ObjectMapper(); String json = objectMapper.writeValueAsString(countryDo); String json1 = objectMapper.writeValueAsString(countryDo1); System.out.println(json); System.out.println(json1); } }
测试案例:
@Test public void transactionTest() throws JsonProcessingException { countryService.noTranSactionMethod(); }
结果:
[DEBUG] SqlSessionUtils Creating a new SqlSession [DEBUG] SpringManagedTransaction JDBC Connection [com.mysql.jdbc.JDBC4Connection@14a54ef6] will not be managed by Spring [DEBUG] getById ==> Preparing: SELECT * FROM country WHERE country_id = ? [DEBUG] getById ==> Parameters: 1(Long) [DEBUG] getById <== Total: 1 [DEBUG] SqlSessionUtils Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@3359c978] [DEBUG] SqlSessionUtils Creating a new SqlSession [DEBUG] SqlSessionUtils SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@2aa27288] was not registered for synchronization because synchronization is not active [DEBUG] SpringManagedTransaction JDBC Connection [com.mysql.jdbc.JDBC4Connection@14a54ef6] will not be managed by Spring [DEBUG] getById ==> Preparing: SELECT * FROM country WHERE country_id = ? [DEBUG] getById ==> Parameters: 1(Long) [DEBUG] getById <== Total: 1 [DEBUG] SqlSessionUtils Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@2aa27288] {"countryId":1,"country":"Afghanistan","lastUpdate":"2006-02-15 04:44:00.0"} {"countryId":1,"country":"Afghanistan","lastUpdate":"2006-02-15 04:44:00.0"}
可以看到,两次查询,都创建了新的sqlSession,并向数据库查询,此时缓存并没有起效果
情景二: 开启事物
打开@Transactional注解:
@Service("countryService") public class CountryService { @Autowired private CountryDao countryDao; @Transactional public void noTranSactionMethod() throws JsonProcessingException { CountryDo countryDo = countryDao.getById(1L); CountryDo countryDo1 = countryDao.getById(1L); ObjectMapper objectMapper = new ObjectMapper(); String json = objectMapper.writeValueAsString(countryDo); String json1 = objectMapper.writeValueAsString(countryDo1); System.out.println(json); System.out.println(json1); } }
使用原来的测试案例,输出结果:
[DEBUG] SqlSessionUtils Creating a new SqlSession [DEBUG] SqlSessionUtils Registering transaction synchronization for SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@109f5dd8] [DEBUG] SpringManagedTransaction JDBC Connection [com.mysql.jdbc.JDBC4Connection@55caeb35] will be managed by Spring [DEBUG] getById ==> Preparing: SELECT * FROM country WHERE country_id = ? [DEBUG] getById ==> Parameters: 1(Long) [DEBUG] getById <== Total: 1 [DEBUG] SqlSessionUtils Releasing transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@109f5dd8] // 从当前事物中获取sqlSession [DEBUG] SqlSessionUtils Fetched SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@109f5dd8] from current transaction [DEBUG] SqlSessionUtils Releasing transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@109f5dd8] {"countryId":1,"country":"Afghanistan","lastUpdate":"2006-02-15 04:44:00.0"} {"countryId":1,"country":"Afghanistan","lastUpdate":"2006-02-15 04:44:00.0"}
可以看到,两次查询,只创建了一次sqlSession,说明一级缓存起作用了
跟踪源码
从SqlSessionDaoSupport作为路口,这个类在mybatis-spring包下,sping为sqlSession做了代理
public abstract class SqlSessionDaoSupport extends DaoSupport { private SqlSession sqlSession; private boolean externalSqlSession; public void setSqlSessionFactory(SqlSessionFactory sqlSessionFactory) { if (!this.externalSqlSession) { this.sqlSession = new SqlSessionTemplate(sqlSessionFactory); } } //....omit }
创建了SqlSessionTemplate后,在SqlSessionTemplate中:
public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType, PersistenceExceptionTranslator exceptionTranslator) { notNull(sqlSessionFactory, "Property 'sqlSessionFactory' is required"); notNull(executorType, "Property 'executorType' is required"); this.sqlSessionFactory = sqlSessionFactory; this.executorType = executorType; this.exceptionTranslator = exceptionTranslator; //代理了SqlSession this.sqlSessionProxy = (SqlSession) newProxyInstance( SqlSessionFactory.class.getClassLoader(), new Class[] { SqlSession.class }, new SqlSessionInterceptor()); }
再看SqlSessionInterceptor,SqlSessionInterceptor是SqlSessionTemplate的内部类:
public class SqlSessionTemplate implements SqlSession, DisposableBean { // ...omit.. private class SqlSessionInterceptor implements InvocationHandler { @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { SqlSession sqlSession = getSqlSession( SqlSessionTemplate.this.sqlSessionFactory, SqlSessionTemplate.this.executorType, SqlSessionTemplate.this.exceptionTranslator); try { Object result = method.invoke(sqlSession, args); //如果尚未开启事物(事物不是由spring来管理),则sqlSession直接提交 if (!isSqlSessionTransactional(sqlSession, SqlSessionTemplate.this.sqlSessionFactory)) { // force commit even on non-dirty sessions because some databases require // a commit/rollback before calling close() // 手动commit 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 { //一般情况下,默认都是关闭sqlSession if (sqlSession != null) { closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory); } } } } }
再看getSqlSession方法,这个方法是在SqlSessionUtils.java中的:
public static SqlSession getSqlSession(SqlSessionFactory sessionFactory, ExecutorType executorType, PersistenceExceptionTranslator exceptionTranslator) { notNull(sessionFactory, NO_SQL_SESSION_FACTORY_SPECIFIED); notNull(executorType, NO_EXECUTOR_TYPE_SPECIFIED); //获取holder SqlSessionHolder holder = (SqlSessionHolder) TransactionSynchronizationManager.getResource(sessionFactory); //从sessionHolder中获取SqlSession SqlSession session = sessionHolder(executorType, holder); if (session != null) { return session; } if (LOGGER.isDebugEnabled()) { LOGGER.debug("Creating a new SqlSession"); } //如果sqlSession不存在,则创建一个新的 session = sessionFactory.openSession(executorType); //将sqlSession注册在sessionHolder中 registerSessionHolder(sessionFactory, executorType, exceptionTranslator, session); return session; } private static void registerSessionHolder(SqlSessionFactory sessionFactory, ExecutorType executorType, PersistenceExceptionTranslator exceptionTranslator, SqlSession session) { SqlSessionHolder holder; //在开启事物的情况下 if (TransactionSynchronizationManager.isSynchronizationActive()) { Environment environment = sessionFactory.getConfiguration().getEnvironment(); //由spring来管理事物的情况下 if (environment.getTransactionFactory() instanceof SpringManagedTransactionFactory) { if (LOGGER.isDebugEnabled()) { LOGGER.debug("Registering transaction synchronization for SqlSession [" + session + "]"); } holder = new SqlSessionHolder(session, executorType, exceptionTranslator); //将sessionFactory绑定在sessionHolde相互绑定 TransactionSynchronizationManager.bindResource(sessionFactory, holder); TransactionSynchronizationManager.registerSynchronization(new SqlSessionSynchronization(holder, sessionFactory)); holder.setSynchronizedWithTransaction(true); holder.requested(); } else { if (TransactionSynchronizationManager.getResource(environment.getDataSource()) == null) { if (LOGGER.isDebugEnabled()) { LOGGER.debug("SqlSession [" + session + "] was not registered for synchronization because DataSource is not transactional"); } } else { throw new TransientDataAccessResourceException( "SqlSessionFactory must be using a SpringManagedTransactionFactory in order to use Spring transaction synchronization"); } } } else { if (LOGGER.isDebugEnabled()) { LOGGER.debug("SqlSession [" + session + "] was not registered for synchronization because synchronization is not active"); } }
再看TransactionSynchronizationManager.bindResource的方法:
public abstract class TransactionSynchronizationManager { //omit... private static final ThreadLocal<Map<Object, Object>> resources = new NamedThreadLocal<Map<Object, Object>>("Transactional resources"); // key:sessionFactory, value:SqlSessionHolder(Connection) public static void bindResource(Object key, Object value) throws IllegalStateException { Object actualKey = TransactionSynchronizationUtils.unwrapResourceIfNecessary(key); Assert.notNull(value, "Value must not be null"); //从threadLocal类型的resources中获取与当前线程绑定的资源,如sessionFactory,Connection等等 Map<Object, Object> map = resources.get(); // set ThreadLocal Map if none found if (map == null) { map = new HashMap<Object, Object>(); resources.set(map); } Object oldValue = map.put(actualKey, value); // Transparently suppress a ResourceHolder that was marked as void... if (oldValue instanceof ResourceHolder && ((ResourceHolder) oldValue).isVoid()) { oldValue = null; } if (oldValue != null) { throw new IllegalStateException("Already value [" + oldValue + "] for key [" + actualKey + "] bound to thread [" + Thread.currentThread().getName() + "]"); } if (logger.isTraceEnabled()) { logger.trace("Bound value [" + value + "] for key [" + actualKey + "] to thread [" + Thread.currentThread().getName() + "]"); } } }
这里可以看到,spring是如何做到获取到的是同一个SqlSession,前面的长篇大论,就是为使用ThreadLocal将当前线程绑定创建SqlSession相关的资源,从而获取同一个sqlSession
以上这篇解决spring结合mybatis时一级缓存失效的问题就是小编分享给大家的全部内容了,希望能给大家一个参考,也希望大家多多支持易盾网络。