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获取SqlSession对象的实现分析与源码解读

一、获取SqlSession对象

SqlSession对象是数据库操作的核心单元，获取过程涉及多个关键步骤。以下是具体实现方法：

1.openSession()

通过调用sqlSessionFactory.openSession()方法获取SqlSession实例：

SqlSession session = sqlSessionFactory.openSession();

2.openSessionFromDataSource()

根据全局配置获取默认的Executor类型，创建事务上下文：

public SqlSession openSession() {    return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false);}

3.创建事务管理器

获取环境信息，创建事务工厂并初始化默认事务：

private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {    Transaction tx = null;    try {        // 获取环境信息        final Environment environment = configuration.getEnvironment();        // 创建事务        tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);        // 创建执行器        final Executor executor = configuration.newExecutor(tx, execType);        // 创建SqlSession        return new DefaultSqlSession(configuration, executor, autoCommit);    } catch (Exception e) {        closeTransaction(tx);        throw ExceptionFactory.wrapException("Error opening session. Cause: " + e, e);    } finally {        ErrorContext.instance().reset();    }}

4.newExecutor()

根据ExecutorType创建相应的执行器实例：

public Executor newExecutor(Transaction transaction, ExecutorType executorType) {    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);    }    // 二级缓存配置    if (cacheEnabled) {        executor = new CachingExecutor(executor);    }    // 拦截器链    executor = (Executor) interceptorChain.pluginAll(executor);    return executor;}

5.二级缓存配置

CachingExecutor类的构造方法：

public CachingExecutor(Executor delegate) {    this.delegate = delegate;    delegate.setExecutorWrapper(this);}

6.拦截器链处理

pluginAll方法实现：

public Object pluginAll(Object target) {    for (Interceptor interceptor : interceptors) {        target = interceptor.plugin(target);    }    return target;}

7.创建SqlSession实例

DefaultSqlSession类的构造：

public DefaultSqlSession(Configuration configuration, Executor executor, boolean autoCommit) {    this.configuration = configuration;    this.executor = executor;    this.autoCommit = autoCommit;}

二、源码分析

1.openSession()

SqlSession session = sqlSessionFactory.openSession();

2.openSessionFromDataSource()

根据默认ExecutorType创建事务上下文：

@Overridepublic SqlSession openSession() {    return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false);}

3.事务管理器创建

获取环境信息，创建事务工厂并初始化默认事务：

final Environment environment = configuration.getEnvironment();final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);

4.执行器创建

根据ExecutorType创建相应的执行器实例：

final Executor executor = configuration.newExecutor(tx, execType);

5.二级缓存配置

对二级缓存的具体操作：

public CachingExecutor(Executor delegate) {    this.delegate = delegate;    delegate.setExecutorWrapper(this);}

6.拦截器链处理

pluginAll方法实现：

public Object pluginAll(Object target) {    for (Interceptor interceptor : interceptors) {        target = interceptor.plugin(target);    }    return target;}

7.创建SqlSession实例

DefaultSqlSession类的构造：

public DefaultSqlSession(Configuration configuration, Executor executor, boolean autoCommit) {    this.configuration = configuration;    this.executor = executor;    this.autoCommit = autoCommit;}

通过以上步骤，可以清晰地了解SqlSession对象的获取与创建过程，包括事务管理、执行器创建以及二级缓存配置等关键环节。

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