Spring是如何保证同一事务获取同一个Connection的？使用Spring的事务同步机制解决：数据库刚插入的记录却查询不到的问题【享学Spring】(上)

java.sql.SQLException: Connection has already been closed

public abstract class DataSourceUtils {
  ...
  public static Connection getConnection(DataSource dataSource) throws CannotGetJdbcConnectionException { ... }
  ...
  // 把definition和connection进行一些准备工作~
  public static Integer prepareConnectionForTransaction(Connection con, @Nullable TransactionDefinition definition) throws SQLException { ...}
  // Reset the given Connection after a transaction,
  // con.setTransactionIsolation(previousIsolationLevel);和con.setReadOnly(false);等等
  public static void resetConnectionAfterTransaction(Connection con, @Nullable Integer previousIsolationLevel) { ... }
  // 该JDBC Connection 是否是当前事务内的链接~
  public static boolean isConnectionTransactional(Connection con, @Nullable DataSource dataSource) { ... }
  // Statement 给他设置超时时间  不传timeout表示不超时
  public static void applyTransactionTimeout(Statement stmt, @Nullable DataSource dataSource) throws SQLException { ... }
  public static void applyTimeout(Statement stmt, @Nullable DataSource dataSource, int timeout) throws SQLException { ... }
  // 此处可能是归还给连接池，也有可能是close~（和连接池参数有关）
  public static void releaseConnection(@Nullable Connection con, @Nullable DataSource dataSource) { ... }
  public static void doReleaseConnection(@Nullable Connection con, @Nullable DataSource dataSource) throws SQLException { ... }
  // 这个是真close
  public static void doCloseConnection(Connection con, @Nullable DataSource dataSource) throws SQLException { ... }
  // 如果链接是代理，会拿到最底层的connection
  public static Connection getTargetConnection(Connection con) { ... }
}

// 此处生路而关于DataSource、PlatformTransactionManager事务管理器等的配置
@Slf4j
@Service
public class HelloServiceImpl implements HelloService {
    @Autowired
    private JdbcTemplate jdbcTemplate;
    @Transactional
    @Override
    public Object hello(Integer id) {
        // 向数据库插入一条记录
        String sql = "insert into user (id,name,age) values (" + id + ",'fsx',21)";
        jdbcTemplate.update(sql);
        // 做其余的事情  可能抛出异常
        System.out.println(1 / 0);
        return "service hello";
    }
}

    @Transactional
    @Override
    public Object hello(Integer id) {
        // 向数据库插入一条记录
        String sql = "insert into user (id,name,age) values (" + id + ",'fsx',21)";
        jdbcTemplate.update(sql);
        // 根据id去查询获取 总数（若查询到了肯定是count=1）
        String query = "select count(1) from user where id = " + id;
        Integer count = jdbcTemplate.queryForObject(query, Integer.class);
        log.info(count.toString());
        return "service hello";
    }

    @Transactional
    @Override
    public Object hello(Integer id) {
        // 向数据库插入一条记录
        String sql = "insert into user (id,name,age) values (" + id + ",'fsx',21)";
        jdbcTemplate.update(sql);
        // 生产环境一般会把些操作交给线程池，此处我只是模拟一下效果而已~
        new Thread(() -> {
            String query = "select count(1) from user where id = " + id;
            Integer count = jdbcTemplate.queryForObject(query, Integer.class);
            log.info(count.toString());
        }).start();
        // 把问题放大
        try {
            TimeUnit.SECONDS.sleep(2);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return "service hello";
    }

@Slf4j
@Service
public class HelloServiceImpl implements HelloService {
    @Autowired
    private JdbcTemplate jdbcTemplate;
    @Transactional
    @Override
    public Object hello(Integer id) {
        // 向数据库插入一条记录
        String sql = "insert into user (id,name,age) values (" + id + ",'fsx',21)";
        jdbcTemplate.update(sql);
        TransactionSynchronizationManager.registerSynchronization(new TransactionSynchronizationAdapter() {
            // 在事务提交之后执行的代码块（方法）  此处使用TransactionSynchronizationAdapter，其实在Spring5后直接使用接口也很方便了~
            @Override
            public void afterCommit() {
                new Thread(() -> {
                    String query = "select count(1) from user where id = " + id;
                    Integer count = jdbcTemplate.queryForObject(query, Integer.class);
                    log.info(count.toString());
                }).start();
            }
        });
        // 把问题放大
        try {
            TimeUnit.SECONDS.sleep(2);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return "service hello";
    }
}