Spring事务的实现源码分析，以及事务不起作用原因分析

protected final class TransactionInfo {
   // 事务管理器
    @Nullable
    private final PlatformTransactionManager transactionManager;
    // 事务注解的属性配置
    @Nullable
    private final TransactionAttribute transactionAttribute;
    // 切入点标志
    private final String joinpointIdentification;
    // 事务状态
    @Nullable
    private TransactionStatus transactionStatus;
    // 前一个事务的事务信息
    @Nullable
    private TransactionInfo oldTransactionInfo;
}

public interface TransactionStatus extends SavepointManager {
  // 是否是新创建的事务
  boolean isNewTransaction();
  // 是否存在保存点
  boolean hasSavepoint();
  void setRollbackOnly();
  // 是否只回滚
  boolean isRollbackOnly();
  // 事务是否为已完成，即已提交或已回滚。
  boolean isCompleted();
}

public abstract class JdbcTransactionObjectSupport 
        implements SavepointManager, SmartTransactionObject {
   // 持有数据库连接
  @Nullable
  private ConnectionHolder connectionHolder;
  // 之前的事务隔离级别，用于当事务退出时，还原Connection的事务隔离级别
  @Nullable
  private Integer previousIsolationLevel;
  // 是否允许使用保存点
  private boolean savepointAllowed = false;
 }

 private static class DataSourceTransactionObject 
                  extends JdbcTransactionObjectSupport {
        // 持有的ConnectionHolder是否是新创建的
        private boolean newConnectionHolder;
        // 事务结束时是否需要重置连接为自动提交
        private boolean mustRestoreAutoCommit;
 }

public class ConnectionHolder extends ResourceHolderSupport {
  @Nullable
  private ConnectionHandle connectionHandle;
  // 当前数据库连接
  @Nullable
  private Connection currentConnection;
  // 当前事务状态
  private boolean transactionActive = false;
  // 是否支持保存点
  @Nullable
  private Boolean savepointsSupported;
  // 当前连接的事务的保存点总数
  private int savepointCounter = 0;
  }

// 判断当前是否已经存在事务，其实是判断DataSourceTransactionObject
// 是否已经从TransactionSynchronizationManager
// 拿到了一个ConnectionHolder，且ConnectionHolder的transactionActive状态是否为true
@Override
  protected boolean isExistingTransaction(Object transaction) {
    DataSourceTransactionObject txObject = (DataSourceTransactionObject) transaction;
    return (txObject.hasConnectionHolder() && txObject.getConnectionHolder().isTransactionActive());
  }

retVal = invocation.proceedWithInvocation();

否则如果方法执行正常，则执行提交逻辑。

public class SqlSessionTemplate implements SqlSession,    
                                DisposableBean {


  private final SqlSessionFactory sqlSessionFactory;
  // 执行器类型，通过解析Mapper标签的<insert>、<update>、<delete>、<select>标签获得
  private final ExecutorType executorType;
  // SqlSession代理类，jdk动态代理创建
  private final SqlSession sqlSessionProxy;
  private final PersistenceExceptionTranslator exceptionTranslator;


  public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType) {
    this(sqlSessionFactory, executorType,
        new MyBatisExceptionTranslator(
            sqlSessionFactory.getConfiguration().getEnvironment().getDataSource(), true));
  }
  
  public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType,
      PersistenceExceptionTranslator exceptionTranslator) {


    this.sqlSessionFactory = sqlSessionFactory;
    this.executorType = executorType;
    this.exceptionTranslator = exceptionTranslator;
     // 创建代理类
    this.sqlSessionProxy = (SqlSession) newProxyInstance(
        SqlSessionFactory.class.getClassLoader(),
        new Class[] { SqlSession.class },
        new SqlSessionInterceptor());
  }


}

public MapperProxy(
            // SqlSessionTemplate
             SqlSession sqlSession, 
             // Mapper接口
             Class<T> mapperInterface, 
             // 反射获取的Method与MapperMethod映射
             Map<Method, MapperMethod> methodCache){
}

public Object invoke(Object proxy, Method method, Object[] args){
}

【org.apache.ibatis.binding.MapperMethod#execute】
public Object execute(SqlSession sqlSession, Object[] args){


}

// 三者的关系
DefaultSqlSession-> 调用Executor执行方法 -> 调用SpringManagedTransaction获取连接

示例一：

   @Bean(name = DsConstant.DEFAULT_MYSQL_DB_01)
    public DataSource mysqlDatabase01() {
        DruidDataSource druidDataSource = new DruidDataSource();
        ......
        return druidDataSource;
    }
    
    @Bean(name = DsConstant.DEFAULT_MYSQL_DB_02)
    public DataSource mysqlDatabase02() {
        DruidDataSource druidDataSource = new DruidDataSource();
        ......
        return druidDataSource;
    }
    
   /**
     * 动态数据源
     * 
     * @return
     */
    @Bean(name = DsConstant.DS)
    public DynamicDataSource dynamicDataSource(
                @Qualifier(DsConstant.DEFAULT_MYSQL_DB_01) DataSource db1,
                 @Qualifier(DsConstant.DEFAULT_MYSQL_DB_02) DataSource db2) {
        DynamicDataSource ds = new DynamicDataSource();
        ......
        return ds;
    }
    
    /**
     *  SqlSessionFactory配置
     */
    @Bean
    public SqlSessionFactoryBean platformSqlSessionFactory(@Qualifier(DsConstant.DS) DataSource dynamicDataSource,
                                                           @Autowired MybatisProperties mybatisProperties) {
        SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
        // 配置数据源
        sqlSessionFactoryBean.setDataSource(dataSource);
        PathMatchingResourcePatternResolver resourcePatternResolver = new PathMatchingResourcePatternResolver();
        // mapper文件位置
        sqlSessionFactoryBean.setMapperLocations(mybatisProperties.resolveMapperLocations());
        sqlSessionFactoryBean.setConfigLocation(resourcePatternResolver.getResource(mybatisProperties.getConfigLocation()));
        // 使用mybatis-spring提供的事务工厂
        TransactionFactory transactionFactory = new SpringManagedTransactionFactory();
        sqlSessionFactoryBean.setTransactionFactory(transactionFactory);
        return sqlSessionFactoryBean;
    }
    
    /**
     * 事务管理者
     *
     * @param platformDataSource
     * @return
     */
    @Bean
    public PlatformTransactionManager mysqlPlatformTransactionManager(@Qualifier(DsConstant.DS) DynamicDataSource dynamicDataSource) {
        return new DataSourceTransactionManager(dynamicDataSource);
    }

   @Bean(name = DsConstant.DEFAULT_MYSQL_DB_01)
    public DataSource mysqlDatabase01() {
        DruidDataSource druidDataSource = new DruidDataSource();
        ......
        return druidDataSource;
    }
    
    @Bean(name = DsConstant.DEFAULT_MYSQL_DB_02)
    public DataSource mysqlDatabase02() {
        DruidDataSource druidDataSource = new DruidDataSource();
        ......
        return druidDataSource;
    }
    
   /**
     * 动态数据源
     *  
     *  @Primary注解：声明这个bean为同类型bean的高优先级bean，
     *   当自动注入不指定bean的name时，且存在多个同类型的bean时，
     *   自动注入会优先使用这个bean
     */
    @Primary
    @Bean(name = DsConstant.DS)
    public DynamicDataSource dynamicDataSource(
                @Qualifier(DsConstant.DEFAULT_MYSQL_DB_01) DataSource db1,
                 @Qualifier(DsConstant.DEFAULT_MYSQL_DB_02) DataSource db2) {
        DynamicDataSource ds = new DynamicDataSource();
        ......
        return ds;
    }
    
    /**
     * 事务管理者
     *
     * @param platformDataSource
     * @return
     */
    @Bean
    public PlatformTransactionManager mysqlPlatformTransactionManager(@Qualifier(DsConstant.DS) DynamicDataSource dynamicDataSource) {
        return new DataSourceTransactionManager(dynamicDataSource);
    }

@org.springframework.context.annotation.Configuration
// 条件注入：存在指定的类型才注入这个配置类
@ConditionalOnClass({ SqlSessionFactory.class, SqlSessionFactoryBean.class })
// 条件注入：容器中存在数据源才注入这个配置类
@ConditionalOnBean(DataSource.class)
@EnableConfigurationProperties(MybatisProperties.class)
// 自动配置在DataSourceAutoConfiguration完成之后
// 如果项目中自己实现配置，则需要导出DataSourceAutoConfiguration这个自动配置
@AutoConfigureAfter(DataSourceAutoConfiguration.class)
public class MybatisAutoConfiguration {
.....
 // 当前未注册SqlSessionFactory，则自动创建SqlSessionFactory
 @Bean
 @ConditionalOnMissingBean
  public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception {
  }
  
  // SqlSessionTemplate也是由此自动创建的
  @Bean
  @ConditionalOnMissingBean
  public SqlSessionTemplate sqlSessionTemplate(SqlSessionFactory sqlSessionFactory) {
  }
....
}