4

我有一个线程尝试使用 JDBCTemplate 连接到数据库，如下所示：

JDBCTemplate jdbcTemplate =  new JdbcTemplate(dataSource); 

try{
    jdbcTemplate.execute(new CallableStatementCreator() {
        @Override
        public CallableStatement createCallableStatement(Connection con)
        throws SQLException {
            return con.prepareCall(query);
        }
    }, new CallableStatementCallback() {
        @Override
        public Object doInCallableStatement(CallableStatement cs)
        throws SQLException {
            cs.setString(1, subscriberID);
            cs.execute();
            return null;
        }
    });
 } catch (DataAccessException dae) {
     throw new CougarFrameworkException(
             "Problem removing subscriber from events queue: "
             + subscriberID, dae);
 }

我想确保如果上面的代码抛出 DataAccessException 或 SQLException，线程会等待几秒钟并尝试重新连接，比如再连接 5 次然后放弃。我怎样才能做到这一点？此外，如果在执行期间数据库出现故障并再次出现，我如何确保我的程序从中恢复并继续运行而不是抛出异常并退出？

提前致谢。

4

4 回答 4

2

试试这个。我的考虑是：运行一个循环，直到语句成功执行。如果有失败，容忍失败5次，每次等待2秒等待下一次执行。

JDBCTemplate jdbcTemplate =  new JdbcTemplate(dataSource); 
boolean successfullyExecuted = false;
int failCount = 0;
while (!successfullyExecuted){
 try{
    jdbcTemplate.execute(new CallableStatementCreator() {
        @Override
        public CallableStatement createCallableStatement(Connection con)
        throws SQLException {
            return con.prepareCall(query);
        }
    }, new CallableStatementCallback() {
        @Override
        public Object doInCallableStatement(CallableStatement cs)
        throws SQLException {
            cs.setString(1, subscriberID);
            cs.execute();
            return null;
        }
    });
    successfullyExecuted = true;
 } catch (DataAccessException dae) {
     if (failedCount < 5){
        failedCount ++;
        try{java.lang.Thread.sleep(2 * 1000L); // Wait for 2 seconds
        }catch(java.lang.Exception e){}
     }else{
     throw new CougarFrameworkException(
             "Problem removing subscriber from events queue: "
             + subscriberID, dae);
     }
 } catch (java.sql.SQLException sqle){
     if (failedCount < 5){
        failedCount ++;
     }else{
     try{java.lang.Thread.sleep(2 * 1000L); // Wait for 2 seconds
     }catch(java.lang.Exception e){}
     throw new CougarFrameworkException(
             "Problem removing subscriber from events queue: "
             + subscriberID, dae);
     }
 }
}
于 2010-05-19T15:30:45.243 回答
1

您可能值得研究一下 Spring 的 Aspect 支持。您所描述的是使用（恒定）退避重试，并且您可能最终会在其他地方需要它，无论是与 Web 服务、电子邮件服务器还是任何其他容易受到瞬时故障影响的复杂系统。

例如，只要抛出异常，这个简单的方法就会调用底层方法最多 maxAttempts 次，除非它是 noRetryFor 中列出的 Throwable 的子类。

private Object doRetryWithExponentialBackoff(ProceedingJoinPoint pjp, int maxAttempts,
        Class<? extends Throwable>[] noRetryFor) throws Throwable {
    Throwable lastThrowable = null;

    for (int attempts = 0; attempts < maxAttempts; attempts++) {
        try {
            pauseExponentially(attempts, lastThrowable);
            return pjp.proceed();
        } catch (Throwable t) {
            lastThrowable = t;

            for (Class<? extends Throwable> noRetryThrowable : noRetryFor) {
                if (noRetryThrowable.isAssignableFrom(t.getClass())) {
                    throw t;
                }
            }
        }
    }

    throw lastThrowable;
}


private void pauseExponentially(int attempts, Throwable lastThrowable) {
    if (attempts == 0)
        return;

    long delay = (long) (Math.random() * (Math.pow(4, attempts) * 100L));
    log.warn("Retriable error detected, will retry in " + delay + "ms, attempts thus far: "
            + attempts, lastThrowable);

    try {
        Thread.sleep(delay);
    } catch (InterruptedException e) {
        // Nothing we need to do here
    }
}

这个建议可以应用到你希望使用 Spring 的 Aspect 支持的任何 bean。有关详细信息，请参阅http://static.springsource.org/spring/docs/2.5.x/reference/aop.html 。

于 2010-05-19T22:16:26.433 回答
0

像这样的东西：

private int retries;

/**
 * Make this configurable.
 */
public void setRetries(final int retries) {
    Assert.isTrue(retries > 0);
    this.retries = retries;

}

public Object yourMethod() {

    final int tries = 0;
    Exception lastException = null;
    for (int i = 0; i < this.retries; i++) {
        try {

            return jdbcTemplate.execute ... (your code here);

        } catch (final SQLException e) {
            lastException = e;
        } catch (final DataAccessException e) {
            lastException = e;
        }
    }
    throw lastException;

}
于 2010-05-19T15:30:40.737 回答
0

在上面写一个方面（DBRetryAspect）怎么样；它会更透明。

于 2011-01-03T06:14:38.573 回答