ScheduledExecutorFactoryBean忽略异常继续执行

男娘i 2024-04-17 23:45 66阅读 0赞

# ScheduledExecutorFactoryBean忽略异常继续执行 #

程序中有一个定时任务，每10分钟把满足条件的任务从一个表迁移到另一张表，程序启动的时候数据库异常了一段时间，之后数据库恢复了。但是通过观察，发现此定时任务挂掉了，再也没有重启起来。

解决此问题的办法是要在任务线程的run方法中中捕获runtime异常，如果使用ScheduledExecutorFactoryBean，只要配置continueScheduledExecutionAfterException属性为true即可。Spring文档描述的很清楚：

setsup a JDK 1.5 `ScheduledExecutorService` (bydefault: `ScheduledThreadPoolExecutor` asimplementation) and exposes it for bean references.

Allowsfor registration of `ScheduledExecutorTasks`,automatically starting the `ScheduledExecutorService` oninitialization and cancelling it on destruction of the context. Inscenarios that just require static registration of tasks at startup,there is no need to access the `ScheduledExecutorService` instanceitself in application code.

Notethat `ScheduledExecutorService` usesa `Runnable` instancethat is shared between repeated executions, in contrast to Quartzwhich instantiates a new Job for each execution.

**WARNING:**`Runnables`submittedvia a native `ScheduledExecutorService` areremoved from the execution schedule once they throw an exception. Ifyou would prefer to continue execution after such an exception,switch thisFactoryBean's`"continueScheduledExecutionAfterException"` propertyto "true

对于定时任务，java原生支持有Timer,和ScheduledExecutor,前文中已经有介绍，参见：

[http://blog.csdn.net/xiaojianpitt/article/details/7659422][http_blog.csdn.net_xiaojianpitt_article_details_7659422]

如果使用spring的话，可以使用org.springframework.scheduling.concurrent.ScheduledExecutorFactoryBean，完全超越ScheduledExecutor。

ScheduledExecutorFactoryBean使用`ScheduledThreadPoolExecutor``作为内部实现，定时调用使用``ScheduledThreadPoolExecutor``的方法``.`

但是continueScheduledExecutionAfterException如何让异常任务继续运行的呢？代码是最好的说明：我们可以跟踪其源代码来找出：

protected Runnable getRunnableToSchedule(ScheduledExecutorTasktask) \{

return this.continueScheduledExecutionAfterException

? new DelegatingErrorHandlingRunnable(task.getRunnable(),TaskUtils.LOG\_AND\_SUPPRESS\_ERROR\_HANDLER)

: newDelegatingErrorHandlingRunnable(task.getRunnable(),TaskUtils.LOG\_AND\_PROPAGATE\_ERROR\_HANDLER);

我们可以看到，如果我们设置了在异常之后继续执行任务，那么在实现中对Runnable进行了封装，封装类为DelegatingErrorHandlingRunnable，我们继续追踪其源代码：

publicclass DelegatingErrorHandlingRunnable implements Runnable\{

…

public void run()\{

try\{

this.delegate.run();

\}catch(Throwable ex)\{

this.errorHandler.handleError(ex):

…

注意这个DelegatingErrorHandlingRunnable实现了Runnable接口，作为原始任务的代理，需要注意的是run里面的trycatch 对异常的处理，在这里catch了Throwable异常（具体可见java异常结构），这java异常的基类，包括Error和RuntimeException所有的java异常都被捕获，之后交给了errorHandler处理，ErrorHandler可以继续抛出异常或者不抛出，其中TaskUtils.LOG\_AND\_SUPPRESS\_ERROR\_HANDLER只是log打印异常，TaskUtils.LOG\_AND\_PROPAGATE\_ERROR\_HANDLER要继续抛出runtimeException。

`TiskUtils``代码如下：`

`public``static``final``ErrorHandlerLOG_AND_SUPPRESS_ERROR_HANDLER =``new``LoggingErrorHandler();`

`…``.`

static class LoggingErrorHandler implements ErrorHandler \{

private final Log logger =LogFactory.getLog(LoggingErrorHandler.class);

public void handleError(Throwable t) \{

if (logger.isErrorEnabled()) \{

logger.error("Unexpected error occurred in scheduledtask.", t);

….

static class PropagatingErrorHandler extends LoggingErrorHandler \{

public void handleError(Throwable t) \{

super.handleError(t);