Spring JDBC Oracle Session 改线程下

Posted 2023-03-27

【中文标题】Spring JDBC Oracle Session 改线程下

【英文标题】：Spring JDBC Oracle Session changed under the thread

【发布时间】：2020-12-23 09:32:17

【问题描述】：

我想在 Spring 中使用 ORACLE DBMS_ALERT 包来接收来自数据库的信号。

在 pl/sql 中，如果在 10 秒内可用，以下代码会收到一条消息：

DECLARE 
  name VARCHAR2(4000 CHAR);
  message VARCHAR2(1800 CHAR);
  status NUMBER;
BEGIN

    DBMS_ALERT.REGISTER('mytopic');
  
    DBMS_ALERT.WAITANY(name, message, status, 10);
   
    DBMS_OUTPUT.put_line('name: '||name);
    DBMS_OUTPUT.put_line('status: '||status);
    DBMS_OUTPUT.put_line('message: "'||message||'"');

END;

在我的 Java 代码中，我尝试使用以下代码接收消息：

private static final String TOPIC = "NAME";
    private static final String MESSAGE = "MESSAGE";
    private static final String STATUS = "STATUS";
    private static final String TIMEOUT = "TIMEOUT";

    public static final String CALL_DBMS_ALERT_REGISTER = " CALL DBMS_ALERT.REGISTER(?) ";
    public static final String CALL_DBMS_ALERT_WAITANY = " CALL DBMS_ALERT.WAITANY(?, ?, ?, ?) ";

    private final JdbcTemplate jdbcTemplate;


    public DbmsAlertRepository(final JdbcTemplate jdbcTemplate) 
        this.jdbcTemplate = jdbcTemplate;
    

    public void dbmsAlertRegister(final String topic) 
        final List<SqlParameter> parameters = new ArrayList();
        parameters.add(new SqlParameter(TOPIC, Types.VARCHAR));

        final Map<String, Object> resultData = jdbcTemplate.call(connection -> 
            final CallableStatement callableStatement = connection.prepareCall(CALL_DBMS_ALERT_REGISTER);
            callableStatement.setString(1, topic);
            return callableStatement;
        , parameters);
        logger.trace("DBMS_ALERT.REGISTER output: ", resultData);
    

    public Optional<DbmsAlertMessage> dbmsAlertWaitAny(final int timeout) 
        final List<SqlParameter> parameters = new ArrayList();
        final Optional<DbmsAlertMessage> result;
        parameters.add(new SqlOutParameter(TOPIC, Types.VARCHAR));
        parameters.add(new SqlOutParameter(MESSAGE, Types.VARCHAR));
        parameters.add(new SqlOutParameter(STATUS, Types.NUMERIC));
        parameters.add(new SqlParameter(TIMEOUT, Types.NUMERIC));

        final Map<String, Object> resultData = jdbcTemplate.call(connection -> 
            final CallableStatement callableStatement = connection.prepareCall(CALL_DBMS_ALERT_WAITANY);
            callableStatement.registerOutParameter(1, Types.VARCHAR);
            callableStatement.registerOutParameter(2, Types.VARCHAR);
            callableStatement.registerOutParameter(3, Types.NUMERIC);
            callableStatement.setInt(4, timeout);
            return callableStatement;
        , parameters);

        logger.trace("DBMS_ALERT.WAITANY output: ", resultData);

        final int status = BigDecimal.class.cast(resultData.get(STATUS)).intValue();
        if (status == 1) 
            result = Optional.empty();
         else 
            result = Optional.of(
                    new DbmsAlertMessage(
                            String.class.cast(resultData.get(TOPIC)),
                            String.class.cast(resultData.get(MESSAGE))
                    )
            );
        
        return result;
    

我在后台线程中通过无限循环调用上面的代码：

public void run() 
    dbmsAlertRepository.dbmsAlertRegister("mytopic");

    while (!Thread.currentThread().isInterrupted()) 
        final Try<Optional<DbmsAlertMessage>> message = Try.of(() -> dbmsAlertRepository.dbmsAlertWaitAny(DBMS_ALERT_TIMEOUT));
        message.onSuccess(msg -> 
            msg.ifPresent(alertMessage -> 
                final DbmsAlertMessageProcessTask task = new DbmsAlertMessageProcessTask(alertMessage);
                threadPoolTaskExecutor.execute(task);
            );
        );
        message.onFailure(e -> 
           logger.error(e.getMessage(), e);
        );
    

它可以工作，但有时我会收到以下错误：

2020-12-23 09:52:57.199 DEBUG 20206 --- [s-alert-watch-1] o.s.jdbc.core.JdbcTemplate               : Calling stored procedure
2020-12-23 09:52:57.294  INFO 20206 --- [s-alert-watch-1] h.e.common.service.DbmsAlertService      : Message arrived: Failure(org.springframework.jdbc.UncategorizedSQLException: CallableStatementCallback; uncategorized SQLException; SQL state [72000]; error code [20000]; ORA-20000: ORU-10024: there are no alerts registered.
ORA-06512: a(z) "SYS.DBMS_ALERT", helyen a(z) 295. sornál
ORA-06512: a(z) helyen a(z) 1. sornál
; nested exception is java.sql.SQLException: ORA-20000: ORU-10024: there are no alerts registered.
ORA-06512: a(z) "SYS.DBMS_ALERT", helyen a(z) 295. sornál
ORA-06512: a(z) helyen a(z) 1. sornál

在我看来，Oracle 会话已更改。如何避免？

【参考方案1】：

会话将不可避免地由于某种原因而结束。例如，如果 RDBMS 崩溃/重新启动，则您的会话无效。虽然您无法确保不会发生会话过期，但您可以确保您的代码能够恢复。正如我们所看到的，这段代码有自己的线程。因此，运行线程的代码的另一部分可以同步，并且每当该线程加入父线程时，您都将重新启动它。

这意味着您用作该线程的父线程的线程肯定不是主线程，因此，您可能需要稍微更改线程策略。

【讨论】：

我使用一个ThreadPoolTask​​Executor来执行每个线程，我认为不可能在threadpoolexecutor中创建一个自己的主线程