Configuring a Step for Restart

In the “Configuring and Running a Job” section , restarting a Job was discussed. Restart has numerous impacts on steps, and, consequently, may require some specific configuration.spring-doc.cn

Setting a Start Limit

There are many scenarios where you may want to control the number of times a Step can be started. For example, you might need to configure a particular Step so that it runs only once because it invalidates some resource that must be fixed manually before it can be run again. This is configurable on the step level, since different steps may have different requirements. A Step that can be executed only once can exist as part of the same Job as a Step that can be run infinitely.spring-doc.cn

The following code fragment shows an example of a start limit configuration in Java:spring-doc.cn

Java Configuration
@Bean
public Step step1(JobRepository jobRepository, PlatformTransactionManager transactionManager) {
	return new StepBuilder("step1", jobRepository)
				.<String, String>chunk(10, transactionManager)
				.reader(itemReader())
				.writer(itemWriter())
				.startLimit(1)
				.build();
}

The following code fragment shows an example of a start limit configuration in XML:spring-doc.cn

XML Configuration
<step id="step1">
    <tasklet start-limit="1">
        <chunk reader="itemReader" writer="itemWriter" commit-interval="10"/>
    </tasklet>
</step>

The step shown in the preceding example can be run only once. Attempting to run it again causes a StartLimitExceededException to be thrown. Note that the default value for the start-limit is Integer.MAX_VALUE.spring-doc.cn

Restarting a Completed Step

In the case of a restartable job, there may be one or more steps that should always be run, regardless of whether or not they were successful the first time. An example might be a validation step or a Step that cleans up resources before processing. During normal processing of a restarted job, any step with a status of COMPLETED (meaning it has already been completed successfully), is skipped. Setting allow-start-if-complete to true overrides this so that the step always runs.spring-doc.cn

The following code fragment shows how to define a restartable job in Java:spring-doc.cn

Java Configuration
@Bean
public Step step1(JobRepository jobRepository, PlatformTransactionManager transactionManager) {
	return new StepBuilder("step1", jobRepository)
				.<String, String>chunk(10, transactionManager)
				.reader(itemReader())
				.writer(itemWriter())
				.allowStartIfComplete(true)
				.build();
}

The following code fragment shows how to define a restartable job in XML:spring-doc.cn

XML Configuration
<step id="step1">
    <tasklet allow-start-if-complete="true">
        <chunk reader="itemReader" writer="itemWriter" commit-interval="10"/>
    </tasklet>
</step>

Step Restart Configuration Example

The following Java example shows how to configure a job to have steps that can be restarted:spring-doc.cn

Java Configuration
@Bean
public Job footballJob(JobRepository jobRepository, Step playerLoad, Step gameLoad, Step playerSummarization) {
	return new JobBuilder("footballJob", jobRepository)
				.start(playerLoad)
				.next(gameLoad)
				.next(playerSummarization)
				.build();
}

@Bean
public Step playerLoad(JobRepository jobRepository, PlatformTransactionManager transactionManager) {
	return new StepBuilder("playerLoad", jobRepository)
			.<String, String>chunk(10, transactionManager)
			.reader(playerFileItemReader())
			.writer(playerWriter())
			.build();
}

@Bean
public Step gameLoad(JobRepository jobRepository, PlatformTransactionManager transactionManager) {
	return new StepBuilder("gameLoad", jobRepository)
			.allowStartIfComplete(true)
			.<String, String>chunk(10, transactionManager)
			.reader(gameFileItemReader())
			.writer(gameWriter())
			.build();
}

@Bean
public Step playerSummarization(JobRepository jobRepository, PlatformTransactionManager transactionManager) {
	return new StepBuilder("playerSummarization", jobRepository)
			.startLimit(2)
			.<String, String>chunk(10, transactionManager)
			.reader(playerSummarizationSource())
			.writer(summaryWriter())
			.build();
}

The following XML example shows how to configure a job to have steps that can be restarted:spring-doc.cn

XML Configuration
<job id="footballJob" restartable="true">
    <step id="playerload" next="gameLoad">
        <tasklet>
            <chunk reader="playerFileItemReader" writer="playerWriter"
                   commit-interval="10" />
        </tasklet>
    </step>
    <step id="gameLoad" next="playerSummarization">
        <tasklet allow-start-if-complete="true">
            <chunk reader="gameFileItemReader" writer="gameWriter"
                   commit-interval="10"/>
        </tasklet>
    </step>
    <step id="playerSummarization">
        <tasklet start-limit="2">
            <chunk reader="playerSummarizationSource" writer="summaryWriter"
                   commit-interval="10"/>
        </tasklet>
    </step>
</job>

The preceding example configuration is for a job that loads in information about football games and summarizes them. It contains three steps: playerLoad, gameLoad, and playerSummarization. The playerLoad step loads player information from a flat file, while the gameLoad step does the same for games. The final step, playerSummarization, then summarizes the statistics for each player, based upon the provided games. It is assumed that the file loaded by playerLoad must be loaded only once but that gameLoad can load any games found within a particular directory, deleting them after they have been successfully loaded into the database. As a result, the playerLoad step contains no additional configuration. It can be started any number of times is skipped if complete. The gameLoad step, however, needs to be run every time in case extra files have been added since it last ran. It has allow-start-if-complete set to true to always be started. (It is assumed that the database table that games are loaded into has a process indicator on it, to ensure new games can be properly found by the summarization step). The summarization step, which is the most important in the job, is configured to have a start limit of 2. This is useful because, if the step continually fails, a new exit code is returned to the operators that control job execution, and it can not start again until manual intervention has taken place.spring-doc.cn

This job provides an example for this document and is not the same as the footballJob found in the samples project.

The remainder of this section describes what happens for each of the three runs of the footballJob example.spring-doc.cn

Run 1:spring-doc.cn

  1. playerLoad runs and completes successfully, adding 400 players to the PLAYERS table.spring-doc.cn

  2. gameLoad runs and processes 11 files worth of game data, loading their contents into the GAMES table.spring-doc.cn

  3. playerSummarization begins processing and fails after 5 minutes.spring-doc.cn

Run 2:spring-doc.cn

  1. playerLoad does not run, since it has already completed successfully, and allow-start-if-complete is false (the default).spring-doc.cn

  2. gameLoad runs again and processes another 2 files, loading their contents into the GAMES table as well (with a process indicator indicating they have yet to be processed).spring-doc.cn

  3. playerSummarization begins processing of all remaining game data (filtering using the process indicator) and fails again after 30 minutes.spring-doc.cn

Run 3:spring-doc.cn

  1. playerLoad does not run, since it has already completed successfully, and allow-start-if-complete is false (the default).spring-doc.cn

  2. gameLoad runs again and processes another 2 files, loading their contents into the GAMES table as well (with a process indicator indicating they have yet to be processed).spring-doc.cn

  3. playerSummarization is not started and the job is immediately killed, since this is the third execution of playerSummarization, and its limit is only 2. Either the limit must be raised or the Job must be executed as a new JobInstance.spring-doc.cn