详解如何配置Spring Batch批处理失败重试机制
作者:陆理手记
1. 引言
默认情况下,Spring批处理作业在执行过程中出现任何错误都会失败。然而有些时候,为了提高应用程序的弹性,我们就需要处理这类间歇性的故障。 在这篇短文中,我们就来一起探讨 如何在Spring批处理框架中配置重试逻辑。
2. 简单举例
假设有一个批处理作业,它读取一个CSV文件作为输入:
username, userid, transaction_date, transaction_amount
sammy, 1234, 31/10/2015, 10000
john, 9999, 3/12/2015, 12321
然后,它通过访问REST端点来处理每条记录,获取用户的 age 和 postCode 属性:
public class RetryItemProcessor implements ItemProcessor<Transaction, Transaction> { @Override public Transaction process(Transaction transaction) throws IOException { log.info("RetryItemProcessor, attempting to process: {}", transaction); HttpResponse response = fetchMoreUserDetails(transaction.getUserId()); //parse user's age and postCode from response and update transaction ... return transaction; } ... }
最后,它生成并输出一个合并的XML:
<transactionRecord> <transactionRecord> <amount>10000.0</amount> <transactionDate>2015-10-31 00:00:00</transactionDate> <userId>1234</userId> <username>sammy</username> <age>10</age> <postCode>430222</postCode> </transactionRecord> ... </transactionRecord>
3. ItemProcessor 中添加重试
现在假设,如果到REST端点的连接由于某些网络速度慢而超时,该怎么办?如果发生这种情况,则我们的批处理工作将失败。
在这种情况下,我们希望失败的 item 处理重试几次。因此,接下来我将批处理作业配置为:在出现故障时执行最多三次重试:
@Bean public Step retryStep( ItemProcessor<Transaction, Transaction> processor, ItemWriter<Transaction> writer) throws ParseException { return stepBuilderFactory .get("retryStep") .<Transaction, Transaction>chunk(10) .reader(itemReader(inputCsv)) .processor(processor) .writer(writer) .faultTolerant() .retryLimit(3) .retry(ConnectTimeoutException.class) .retry(DeadlockLoserDataAccessException.class) .build(); }
这里调用了 faultTolerant() 来启用重试功能。另外,我们使用 retry 和 retryLimit 分别定义符合重试条件的异常和 item 的最大重试次数。
4. 测试重试次数
假设我们有一个测试场景,其中返回 age 和 postCode 的REST端点关闭了一段时间。在这个测试场景中,我们只对前两个 API 调用获取一个 ConnectTimeoutException ,而第三个调用将成功:
@Test public void whenEndpointFailsTwicePasses3rdTime_thenSuccess() throws Exception { FileSystemResource expectedResult = new FileSystemResource(EXPECTED_OUTPUT); FileSystemResource actualResult = new FileSystemResource(TEST_OUTPUT); when(httpResponse.getEntity()) .thenReturn(new StringEntity("{ \"age\":10, \"postCode\":\"430222\" }")); //fails for first two calls and passes third time onwards when(httpClient.execute(any())) .thenThrow(new ConnectTimeoutException("Timeout count 1")) .thenThrow(new ConnectTimeoutException("Timeout count 2")) .thenReturn(httpResponse); JobExecution jobExecution = jobLauncherTestUtils .launchJob(defaultJobParameters()); JobInstance actualJobInstance = jobExecution.getJobInstance(); ExitStatus actualJobExitStatus = jobExecution.getExitStatus(); assertThat(actualJobInstance.getJobName(), is("retryBatchJob")); assertThat(actualJobExitStatus.getExitCode(), is("COMPLETED")); AssertFile.assertFileEquals(expectedResult, actualResult); }
在这里,我们的工作成功地完成了。另外,从日志中可以明显看出 第一条记录 id=1234 失败了两次,最后在第三次重试时成功了:
19:06:57.742 [main] INFO o.s.batch.core.job.SimpleStepHandler - Executing step: [retryStep]
19:06:57.758 [main] INFO o.b.batch.service.RetryItemProcessor - Attempting to process user with id=1234
19:06:57.758 [main] INFO o.b.batch.service.RetryItemProcessor - Attempting to process user with id=1234
19:06:57.758 [main] INFO o.b.batch.service.RetryItemProcessor - Attempting to process user with id=1234
19:06:57.758 [main] INFO o.b.batch.service.RetryItemProcessor - Attempting to process user with id=9999
19:06:57.773 [main] INFO o.s.batch.core.step.AbstractStep - Step: [retryStep] executed in 31ms
同样,看下另一个测试用例,当所有重试次数都用完时会发生什么:
@Test public void whenEndpointAlwaysFail_thenJobFails() throws Exception { when(httpClient.execute(any())) .thenThrow(new ConnectTimeoutException("Endpoint is down")); JobExecution jobExecution = jobLauncherTestUtils .launchJob(defaultJobParameters()); JobInstance actualJobInstance = jobExecution.getJobInstance(); ExitStatus actualJobExitStatus = jobExecution.getExitStatus(); assertThat(actualJobInstance.getJobName(), is("retryBatchJob")); assertThat(actualJobExitStatus.getExitCode(), is("FAILED")); assertThat(actualJobExitStatus.getExitDescription(), containsString("org.apache.http.conn.ConnectTimeoutException")); }
在这个测试用例中,在作业因 ConnectTimeoutException
而失败之前,会尝试对第一条记录重试三次。
5. 使用XML配置重试
最后,让我们看一下与上述配置等价的XML:
<batch:job id="retryBatchJob"> <batch:step id="retryStep"> <batch:tasklet> <batch:chunk reader="itemReader" writer="itemWriter" processor="retryItemProcessor" commit-interval="10" retry-limit="3"> <batch:retryable-exception-classes> <batch:include class="org.apache.http.conn.ConnectTimeoutException"/> <batch:include class="org.springframework.dao.DeadlockLoserDataAccessException"/> </batch:retryable-exception-classes> </batch:chunk> </batch:tasklet> </batch:step> </batch:job>
6. 简单总结
在本文中,我们学习了如何在Spring批处理中配置重试逻辑,其中包括使用Java和XML配置。以及使用单元测试来观察重试在实践中是如何工作的。
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