1. Introduction

By default, Spring batch jobs will fail with any errors during execution. However, sometimes, in order to improve the flexibility of applications, we need to deal with such intermittent faults.
In this short article, we will discuss how to configure retry logic in Spring batch processing framework.

2. Simple examples

Suppose there is a batch job that reads a CSV file as input:

username, userid, transaction_date, transaction_amount
sammy, 1234, 31/10/2015, 10000
john, 9999, 3/12/2015, 12321

Then, it processes each record by accessing the REST endpoint and obtains the user's age and postCode attributes:

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;
    }
    ...
}

Finally, it generates and outputs a merged 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. Add retry in itemprocessor

Now suppose that what if the connection to the REST endpoint times out due to some slow network speed? If this happens, our batch work will fail.

In this case, we want to retry the failed item processing several times. So next, I configure the batch job to perform up to three retries in the event of a failure:

@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();
}

Faulttolerance () is called here to enable the retry function. In addition, we use retry and retryLimit to define the maximum number of retries of exceptions and item s that meet the retry conditions respectively.

4. Test retry times

Suppose we have a test scenario in which the REST endpoint that returns age and postCode is closed for a period of time. In this test scenario, we only get a ConnectTimeoutException for the first two API calls, and the third call will succeed:

@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);
}

Here, our work has been successfully completed. In addition, it is obvious from the log that the first record id=1234 failed twice, and finally succeeded in the third retry:

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

Similarly, look at another test case. What happens when all retries are exhausted:

@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"));
}

In this test case, before the job fails due to ConnectTimeoutException, it will try to retry the first record three times.

5. Use XML configuration to retry

Finally, let's take a look at XML equivalent to the above configuration:

<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. Brief summary

In this article, we learned how to configure retry logic in Spring batch processing, including using Java and XML configuration. And using unit tests to see how retrying works in practice.
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