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关于mybatis里面的Executor--转载
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原文地址：http://blog.csdn.net/w_intercool/article/details/7893344
使用mybatis查尋數(shù)據(jù)，跟蹤其執(zhí)行流程
最開始執(zhí)行的語句
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this.getSqlSession().selectList("QUERY-QUESTION",?data,?rowBounds);?? 這里需要找到sqlsession是從哪里來的
getSqlSession是SqlSessionDaoSupport類里面的方法，該類通過spring的自動注入可以把sqlSessionTemplate注入進來，當然這里的sqlSessionTemplate是需要spring配置的
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@Autowired(required?=?false)??public?final?void?setSqlSessionTemplate(SqlSessionTemplate?sqlSessionTemplate)?{????this.sqlSession?=?sqlSessionTemplate;????this.externalSqlSession?=?true;??}?? ?
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<bean?id="sqlSession"?class="org.mybatis.spring.SqlSessionTemplate">??????????<constructor-arg?index="0"?ref="sqlSessionFactory"/>??????????<constructor-arg?index="1"?value="BATCH"/>??????</bean>?? @Autowired(required = false)是通過類型匹配來注入的，如果沒有找到相應對，就不用注入
所以selectList方法為SqlSessionTemlate里面的，再看SqlSessionTemplage，里面的都是通過sqlSessionProxy來執(zhí)行selectList方法的，也就是通過代理方式來的
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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;????this.sqlSessionProxy?=?(SqlSession)?newProxyInstance(????????SqlSessionFactory.class.getClassLoader(),????????new?Class[]?{?SqlSession.class?},????????new?SqlSessionInterceptor());??}??
這里用到了java的動態(tài)代理，詳細可以見java api，有詳細的說明
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SqlSessionInterceptor實現(xiàn)了InvocationHandler，在invoke方法里面的開始有這樣代碼，那里是真正的sqlsession
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final?SqlSession?sqlSession?=?getSqlSession(???????????SqlSessionTemplate.this.sqlSessionFactory,???????????SqlSessionTemplate.this.executorType,???????????SqlSessionTemplate.this.exceptionTranslator);?? 跟蹤geteSqlSession可以找到他的創(chuàng)建來源，見
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SqlSession?session?=?sessionFactory.openSession(executorType);??
繼續(xù)跟蹤可以找到DefaultSqlSessionFactory里面的該方法
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private?SqlSession?openSessionFromDataSource(ExecutorType?execType,?TransactionIsolationLevel?level,?boolean?autoCommit)?{????Transaction?tx?=?null;????try?{??????final?Environment?environment?=?configuration.getEnvironment();??????final?TransactionFactory?transactionFactory?=?getTransactionFactoryFromEnvironment(environment);??????tx?=?transactionFactory.newTransaction(environment.getDataSource(),?level,?autoCommit);??????final?Executor?executor?=?configuration.newExecutor(tx,?execType,?autoCommit);??????return?new?DefaultSqlSession(configuration,?executor);????}?catch?(Exception?e)?{??????closeTransaction(tx);?????throw?ExceptionFactory.wrapException("Error?opening?session.??Cause:?"?+?e,?e);????}?finally?{??????ErrorContext.instance().reset();????}??}??
通過
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final?Executor?executor?=?configuration.newExecutor(tx,?execType,?autoCommit);?? ?
你就知道executor是怎么回來的了
mybatis默認使用了cache，在創(chuàng)建exector時，外面就包了一層CacheExecutor，詳細見
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public?Executor?newExecutor(Transaction?transaction,?ExecutorType?executorType,?boolean?autoCommit)?{????executorType?=?executorType?==?null???defaultExecutorType?:?executorType;????executorType?=?executorType?==?null???ExecutorType.SIMPLE?:?executorType;????Executor?executor;????if?(ExecutorType.BATCH?==?executorType)?{??????executor?=?new?BatchExecutor(this,?transaction);????}?else?if?(ExecutorType.REUSE?==?executorType)?{??????executor?=?new?ReuseExecutor(this,?transaction);????}?else?{??????executor?=?new?SimpleExecutor(this,?transaction);????}????if?(cacheEnabled)?{??????executor?=?new?CachingExecutor(executor,?autoCommit);????}????executor?=?(Executor)?interceptorChain.pluginAll(executor);????return?executor;??}??
CachingExecutor可以使mybatis先從緩存中提取數(shù)據(jù)，數(shù)據(jù)緩存中沒有數(shù)據(jù)時才從數(shù)據(jù)庫里面提取數(shù)據(jù)。
轉(zhuǎn)載于:https://www.cnblogs.com/davidwang456/p/4693090.html
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