## Configuring and Running a Job

XML Java Both

In the domain section , the overall architecture design was discussed, using the following diagram as a guide:

Figure 1. Batch Stereotypes

While the `Job` object may seem like a simple container for steps, you must be aware of many configuration options. Furthermore, you must consider many options about how a `Job` can be run and how its meta-data can be stored during that run. This chapter explains the various configuration options and runtime concerns of a `Job`.

### Configuring a Job

There are multiple implementations of the `Job` interface. However, builders abstract away the difference in configuration. The following example creates a `footballJob`:

    @Bean
    public Job footballJob() {
        return this.jobBuilderFactory.get("footballJob")
                         .start(playerLoad())
                         .next(gameLoad())
                         .next(playerSummarization())
                         .build();
    }

A `Job` (and, typically, any `Step` within it) requires a `JobRepository`. The configuration of the `JobRepository` is handled through the `BatchConfigurer`.

The preceding example illustrates a `Job` that consists of three `Step` instances. The job related builders can also contain other elements that help with parallelisation (`Split`), declarative flow control (`Decision`), and externalization of flow definitions (`Flow`).

Whether you use Java or XML, there are multiple implementations of the `Job` interface. However, the namespace abstracts away the differences in configuration. It has only three required dependencies: a name, `JobRepository` , and a list of `Step` instances.

    <job id="footballJob">
        <step id="playerload"          parent="s1" next="gameLoad"/>
        <step id="gameLoad"            parent="s2" next="playerSummarization"/>
        <step id="playerSummarization" parent="s3"/>
    </job>

The examples here use a parent bean definition to create the steps. See the section on step configuration for more options when declaring specific step details inline. The XML namespace defaults to referencing a repository with an ID of `jobRepository`, which is a sensible default. However, you can explicitly override it:

    <job id="footballJob" job-repository="specialRepository">
        <step id="playerload"          parent="s1" next="gameLoad"/>
        <step id="gameLoad"            parent="s3" next="playerSummarization"/>
        <step id="playerSummarization" parent="s3"/>
    </job>

In addition to steps, a job configuration can contain other elements that help with parallelization (`<split>`), declarative flow control (`<decision>`) and externalization of flow definitions (`<flow/>`).

#### Restartability

One key issue when executing a batch job concerns the behavior of a `Job` when it is restarted. The launching of a `Job` is considered to be a “restart” if a `JobExecution` already exists for the particular `JobInstance`. Ideally, all jobs should be able to start up where they left off, but there are scenarios where this is not possible. In this scenario, it is entirely up to the developer to ensure that a new `JobInstance` is created. However, Spring Batch does provide some help. If a `Job` should never be restarted but should always be run as part of a new `JobInstance`, you can set the restartable property to `false`.

The following example shows how to set the `restartable` field to `false` in XML:

Example 1. XML Configuration

    <job id="footballJob" restartable="false">
        ...
    </job>

The following example shows how to set the `restartable` field to `false` in Java:

Example 2. Java Configuration

    @Bean
    public Job footballJob() {
        return this.jobBuilderFactory.get("footballJob")
                         .preventRestart()
                         ...
                         .build();
    }

To phrase it another way, setting `restartable` to `false` means “this `Job` does not support being started again”. Restarting a `Job` that is not restartable causes a `JobRestartException` to be thrown. The following Junit code causes the exception to be thrown:

    Job job = new SimpleJob();
    job.setRestartable(false);

    JobParameters jobParameters = new JobParameters();

    JobExecution firstExecution = jobRepository.createJobExecution(job, jobParameters);
    jobRepository.saveOrUpdate(firstExecution);

    try {
        jobRepository.createJobExecution(job, jobParameters);
        fail();
    }
    catch (JobRestartException e) {
        // expected
    }

The first attempt to create a `JobExecution` for a non-restartable job causes no issues. However, the second attempt throws a `JobRestartException`.

#### Intercepting Job Execution

During the course of the execution of a `Job`, it may be useful to be notified of various events in its lifecycle so that custom code can be run. `SimpleJob` allows for this by calling a `JobListener` at the appropriate time:

    public interface JobExecutionListener {

        void beforeJob(JobExecution jobExecution);

        void afterJob(JobExecution jobExecution);
    }

You can add `JobListeners` to a `SimpleJob` by setting listeners on the job.

The following example shows how to add a listener element to an XML job definition:

Example 3. XML Configuration

    <job id="footballJob">
        <step id="playerload"          parent="s1" next="gameLoad"/>
        <step id="gameLoad"            parent="s2" next="playerSummarization"/>
        <step id="playerSummarization" parent="s3"/>
        <listeners>
            <listener ref="sampleListener"/>
        </listeners>
    </job>

The following example shows how to add a listener method to a Java job definition:

Example 4. Java Configuration

    @Bean
    public Job footballJob() {
        return this.jobBuilderFactory.get("footballJob")
                         .listener(sampleListener())
                         ...
                         .build();
    }

Noted that the `afterJob` method is called regardless of the success or failure of the `Job`. If you need to determine success or failure, you can get that information from the `JobExecution`:

    public void afterJob(JobExecution jobExecution){
        if (jobExecution.getStatus() == BatchStatus.COMPLETED ) {
            //job success
        }
        else if (jobExecution.getStatus() == BatchStatus.FAILED) {
            //job failure
        }
    }

The annotations corresponding to this interface are:

- `@BeforeJob`

- `@AfterJob`

#### Inheriting from a Parent Job

If a group of Jobs share similar but not identical configurations, it may help to define a “parent” `Job` from which the concrete `Job` instances may inherit properties. Similar to class inheritance in Java, a “child” `Job` combines its elements and attributes with the parent’s.

In the following example, `baseJob` is an abstract `Job` definition that defines only a list of listeners. The `Job` (`job1`) is a concrete definition that inherits the list of listeners from `baseJob` and merges it with its own list of listeners to produce a `Job` with two listeners and one `Step`, `step1`.

    <job id="baseJob" abstract="true">
        <listeners>
            <listener ref="listenerOne"/>
        <listeners>
    </job>

    <job id="job1" parent="baseJob">
        <step id="step1" parent="standaloneStep"/>

        <listeners merge="true">
            <listener ref="listenerTwo"/>
        <listeners>
    </job>

See the section on Inheriting from a Parent Step for more detailed information.

#### JobParametersValidator

A job declared in the XML namespace or using any subclass of `AbstractJob` can optionally declare a validator for the job parameters at runtime. This is useful when, for instance, you need to assert that a job is started with all its mandatory parameters. There is a `DefaultJobParametersValidator` that you can use to constrain combinations of simple mandatory and optional parameters. For more complex constraints, you can implement the interface yourself.

The configuration of a validator is supported through the XML namespace through a child element of the job, as shown in the following example:

    <job id="job1" parent="baseJob3">
        <step id="step1" parent="standaloneStep"/>
        <validator ref="parametersValidator"/>
    </job>

You can specify the validator as a reference (as shown earlier) or as a nested bean definition in the `beans` namespace.

The configuration of a validator is supported through the Java builders:

    @Bean
    public Job job1() {
        return this.jobBuilderFactory.get("job1")
                         .validator(parametersValidator())
                         ...
                         .build();
    }

### Java Configuration

Spring 3 brought the ability to configure applications with java instead of XML. As of Spring Batch 2.2.0, you can configure batch jobs by using the same Java configuration. There are three components for the Java-based configuration: the `@EnableBatchProcessing` annotation and two builders.

The `@EnableBatchProcessing` annotation works similarly to the other `@Enable*` annotations in the Spring family. In this case, `@EnableBatchProcessing` provides a base configuration for building batch jobs. Within this base configuration, an instance of `StepScope` is created in addition to a number of beans being made available to be autowired:

- `JobRepository`: a bean named `jobRepository`

- `JobLauncher`: a bean named `jobLauncher`

- `JobRegistry`: a bean named `jobRegistry`

- `PlatformTransactionManager`: a bean named `transactionManager`

- `JobBuilderFactory`: a bean named `jobBuilders`

- `StepBuilderFactory`: a bean named `stepBuilders`

The core interface for this configuration is the `BatchConfigurer`. The default implementation provides the beans mentioned in the preceding list and requires a `DataSource` to be provided as a bean within the context. This data source is used by the `JobRepository` instance. You can customize any of these beans by creating a custom implementation of the `BatchConfigurer` interface. Typically, extending the `DefaultBatchConfigurer` (which is provided if a `BatchConfigurer` is not found) and overriding the required getter is sufficient. However, you may need to implement your own from scratch. The following example shows how to provide a custom transaction manager:

    @Bean
    public BatchConfigurer batchConfigurer(DataSource dataSource) {
    	return new DefaultBatchConfigurer(dataSource) {
    		@Override
    		public PlatformTransactionManager getTransactionManager() {
    			return new MyTransactionManager();
    		}
    	};
    }

| Only one configuration class needs to have the `@EnableBatchProcessing` annotation. Once you have a class annotated with it, you have all of the configuration described earlier.

With the base configuration in place, you can use the provided builder factories to configure a job. The following example shows a two-step job configured with the `JobBuilderFactory` and the `StepBuilderFactory`:

    @Configuration
    @EnableBatchProcessing
    @Import(DataSourceConfiguration.class)
    public class AppConfig {

        @Autowired
        private JobBuilderFactory jobs;

        @Autowired
        private StepBuilderFactory steps;

        @Bean
        public Job job(@Qualifier("step1") Step step1, @Qualifier("step2") Step step2) {
            return jobs.get("myJob").start(step1).next(step2).build();
        }

        @Bean
        protected Step step1(ItemReader<Person> reader,
                             ItemProcessor<Person, Person> processor,
                             ItemWriter<Person> writer) {
            return steps.get("step1")
                .<Person, Person> chunk(10)
                .reader(reader)
                .processor(processor)
                .writer(writer)
                .build();
        }

        @Bean
        protected Step step2(Tasklet tasklet) {
            return steps.get("step2")
                .tasklet(tasklet)
                .build();
        }
    }

### Configuring a JobRepository

When using `@EnableBatchProcessing`, a `JobRepository` is provided for you. This section describes how to configure your own.

As described earlier, the `JobRepository` is used for basic CRUD operations of the various persisted domain objects within Spring Batch, such as `JobExecution` and `StepExecution`. It is required by many of the major framework features, such as the `JobLauncher`, `Job`, and `Step`.

The batch namespace abstracts away many of the implementation details of the `JobRepository` implementations and their collaborators. However, there are still a few configuration options available, as shown in the following example:

Example 5. XML Configuration

    <job-repository id="jobRepository"
        data-source="dataSource"
        transaction-manager="transactionManager"
        isolation-level-for-create="SERIALIZABLE"
        table-prefix="BATCH_"
    	max-varchar-length="1000"/>

Other than the `id`, none of the configuration options listed earlier are required. If they are not set, the defaults shown earlier are used. The `max-varchar-length` defaults to `2500`, which is the length of the long `VARCHAR` columns in the sample schema scripts.

When you use Java configuration, a `JobRepository` is provided for you. A JDBC-based one is provided if a `DataSource` is provided, and the `Map`-based one is provided if no `DataSource` is provided. However, you can customize the configuration of the `JobRepository` through an implementation of the `BatchConfigurer` interface, as the following example shows:

Example 6. Java Configuration

    ...
    // This would reside in your BatchConfigurer implementation
    @Override
    protected JobRepository createJobRepository() throws Exception {
        JobRepositoryFactoryBean factory = new JobRepositoryFactoryBean();
        factory.setDataSource(dataSource);
        factory.setTransactionManager(transactionManager);
        factory.setIsolationLevelForCreate("ISOLATION_SERIALIZABLE");
        factory.setTablePrefix("BATCH_");
        factory.setMaxVarCharLength(1000);
        return factory.getObject();
    }
    ...

Other than the `dataSource` and the `transactionManager`, none of the configuration options listed earlier are required. If they are not set, the defaults shown earlier are used. The max `varchar` length defaults to `2500`, which is the length of the long `VARCHAR` columns in the sample schema scripts

#### Transaction Configuration for the JobRepository

If the namespace or the provided `FactoryBean` is used, transactional advice is automatically created around the repository. This is to ensure that the batch metadata, including state that is necessary for restarts after a failure, is persisted correctly. The behavior of the framework is not well defined if the repository methods are not transactional. The isolation level in the `create*` method attributes is specified separately to ensure that, when jobs are launched, if two processes try to launch the same job at the same time, only one succeeds. The default isolation level for that method is `SERIALIZABLE`, which is quite aggressive. `READ_COMMITTED` usually works just as well. `READ_UNCOMMITTED` is fine if two processes are not likely to collide in this way. However, since a call to the `create*` method is quite short, it is unlikely that `SERIALIZED` causes problems, as long as the database platform supports it. However, you can override this setting.

The following example shows how to override the isolation level in XML:

Example 7. XML Configuration

    <job-repository id="jobRepository"
                    isolation-level-for-create="REPEATABLE_READ" />

The following example shows how to override the isolation level in Java:

Example 8. Java Configuration

    // This would reside in your BatchConfigurer implementation
    @Override
    protected JobRepository createJobRepository() throws Exception {
        JobRepositoryFactoryBean factory = new JobRepositoryFactoryBean();
        factory.setDataSource(dataSource);
        factory.setTransactionManager(transactionManager);
        factory.setIsolationLevelForCreate("ISOLATION_REPEATABLE_READ");
        return factory.getObject();
    }

If the namespace or factory beans are not used, you must also configure the transactional behavior of the repository using AOP.

The following example shows how to configure the transactional behavior of the repository in XML:

Example 9. XML Configuration

    <aop:config>
        <aop:advisor
               pointcut="execution(* org.springframework.batch.core..*Repository+.*(..))"/>
        <advice-ref="txAdvice" />
    </aop:config>

    <tx:advice id="txAdvice" transaction-manager="transactionManager">
        <tx:attributes>
            <tx:method name="*" />
        </tx:attributes>
    </tx:advice>

You can use the preceding fragment nearly as is, with almost no changes. Remember also to include the appropriate namespace declarations and to make sure `spring-tx` and `spring-aop` (or the whole of Spring) are on the classpath.

The following example shows how to configure the transactional behavior of the repository in Java:

Example 10. Java Configuration

    @Bean
    public TransactionProxyFactoryBean baseProxy() {
    	TransactionProxyFactoryBean transactionProxyFactoryBean = new TransactionProxyFactoryBean();
    	Properties transactionAttributes = new Properties();
    	transactionAttributes.setProperty("*", "PROPAGATION_REQUIRED");
    	transactionProxyFactoryBean.setTransactionAttributes(transactionAttributes);
    	transactionProxyFactoryBean.setTarget(jobRepository());
    	transactionProxyFactoryBean.setTransactionManager(transactionManager());
    	return transactionProxyFactoryBean;
    }

#### Changing the Table Prefix

Another modifiable property of the `JobRepository` is the table prefix of the meta-data tables. By default, they are all prefaced with `BATCH_`. `BATCH_JOB_EXECUTION` and `BATCH_STEP_EXECUTION` are two examples. However, there are potential reasons to modify this prefix. If the schema names need to be prepended to the table names or if more than one set of metadata tables is needed within the same schema, the table prefix needs to be changed.

The following example shows how to change the table prefix in XML:

Example 11. XML Configuration

    <job-repository id="jobRepository"
                    table-prefix="SYSTEM.TEST_" />

The following example shows how to change the table prefix in Java:

Example 12. Java Configuration

    // This would reside in your BatchConfigurer implementation
    @Override
    protected JobRepository createJobRepository() throws Exception {
        JobRepositoryFactoryBean factory = new JobRepositoryFactoryBean();
        factory.setDataSource(dataSource);
        factory.setTransactionManager(transactionManager);
        factory.setTablePrefix("SYSTEM.TEST_");
        return factory.getObject();
    }

Given the preceding changes, every query to the metadata tables is prefixed with `SYSTEM.TEST_`. `BATCH_JOB_EXECUTION` is referred to as `SYSTEM.TEST_JOB_EXECUTION`.

| Only the table prefix is configurable. The table and column names are not.

#### Non-standard Database Types in a Repository

If you are using a database platform that is not in the list of supported platforms, you may be able to use one of the supported types, if the SQL variant is close enough. To do this, you can use the raw `JobRepositoryFactoryBean` instead of the namespace shortcut and use it to set the database type to the closest match.

The following example shows how to use `JobRepositoryFactoryBean` to set the database type to the closest match in XML:

Example 13. XML Configuration

    <bean id="jobRepository" class="org...JobRepositoryFactoryBean">
        <property name="databaseType" value="db2"/>
        <property name="dataSource" ref="dataSource"/>
    </bean>

The following example shows how to use `JobRepositoryFactoryBean` to set the database type to the closest match in Java:

Example 14. Java Configuration

    // This would reside in your BatchConfigurer implementation
    @Override
    protected JobRepository createJobRepository() throws Exception {
        JobRepositoryFactoryBean factory = new JobRepositoryFactoryBean();
        factory.setDataSource(dataSource);
        factory.setDatabaseType("db2");
        factory.setTransactionManager(transactionManager);
        return factory.getObject();
    }

If the database type is not specified, the `JobRepositoryFactoryBean` tries to auto-detect the database type from the `DataSource`. The major differences between platforms are mainly accounted for by the strategy for incrementing primary keys, so it is often be necessary to override the `incrementerFactory` as well (by using one of the standard implementations from the Spring Framework).

If even that does not work or if you are not using an RDBMS, the only option may be to implement the various `Dao` interfaces that the `SimpleJobRepository` depends on and wire one up manually in the normal Spring way.

### Configuring a JobLauncher

When you use `@EnableBatchProcessing`, a `JobRegistry` is provided for you. This section describes how to configure your own.

The most basic implementation of the `JobLauncher` interface is the `SimpleJobLauncher`. Its only required dependency is a `JobRepository` (needed to obtain an execution).

The following example shows a `SimpleJobLauncher` in XML:

Example 15. XML Configuration

    <bean id="jobLauncher"
          class="org.springframework.batch.core.launch.support.SimpleJobLauncher">
        <property name="jobRepository" ref="jobRepository" />
    </bean>

The following example shows a `SimpleJobLauncher` in Java:

Example 16. Java Configuration

    ...
    // This would reside in your BatchConfigurer implementation
    @Override
    protected JobLauncher createJobLauncher() throws Exception {
    	SimpleJobLauncher jobLauncher = new SimpleJobLauncher();
    	jobLauncher.setJobRepository(jobRepository);
    	jobLauncher.afterPropertiesSet();
    	return jobLauncher;
    }
    ...

Once a JobExecution is obtained, it is passed to the execute method of `Job`, ultimately returning the `JobExecution` to the caller, as shown in the following image:

Figure 2. Job Launcher Sequence

The sequence is straightforward and works well when launched from a scheduler. However, issues arise when trying to launch from an HTTP request. In this scenario, the launching needs to be done asynchronously so that the `SimpleJobLauncher` returns immediately to its caller. This is because it is not good practice to keep an HTTP request open for the amount of time needed by long running processes (such as batch jobs). The following image shows an example sequence:

Figure 3. Asynchronous Job Launcher Sequence

You can configure the `SimpleJobLauncher` to allow for this scenario by configuring a `TaskExecutor`.

The following XML example shows a `SimpleJobLauncher` configured to return immediately:

Example 17. XML Configuration

    <bean id="jobLauncher"
          class="org.springframework.batch.core.launch.support.SimpleJobLauncher">
        <property name="jobRepository" ref="jobRepository" />
        <property name="taskExecutor">
            <bean class="org.springframework.core.task.SimpleAsyncTaskExecutor" />
        </property>
    </bean>

The following Java example shows a `SimpleJobLauncher` configured to return immediately:

Example 18. Java Configuration

    @Bean
    public JobLauncher jobLauncher() {
    	SimpleJobLauncher jobLauncher = new SimpleJobLauncher();
    	jobLauncher.setJobRepository(jobRepository());
    	jobLauncher.setTaskExecutor(new SimpleAsyncTaskExecutor());
    	jobLauncher.afterPropertiesSet();
    	return jobLauncher;
    }

Any implementation of the spring `TaskExecutor` interface can be used to control how jobs are asynchronously executed.

### Running a Job

At a minimum, launching a batch job requires two things: the `Job` to be launched and a `JobLauncher`. Both can be contained within the same context or different contexts. For example, if you launch jobs from the command line, a new JVM is instantiated for each `Job`. Thus, every job has its own `JobLauncher`. However, if you run from within a web container within the scope of an `HttpRequest`, there is usually one `JobLauncher` (configured for asynchronous job launching) that multiple requests invoke to launch their jobs.

#### Running Jobs from the Command Line

For users that want to run their jobs from an enterprise scheduler, the command line is the primary interface. This is because most schedulers (with the exception of Quartz, unless using `NativeJob`) work directly with operating system processes, primarily kicked off with shell scripts. There are many ways to launch a Java process besides a shell script, such as Perl, Ruby, or even build tools, such as ant or maven. However, because most people are familiar with shell scripts, this example focuses on them.

##### The CommandLineJobRunner

Because the script launching the job must kick off a Java Virtual Machine, there needs to be a class with a `main` method to act as the primary entry point. Spring Batch provides an implementation that serves this purpose: `CommandLineJobRunner`. Note that this is just one way to bootstrap your application. There are many ways to launch a Java process, and this class should in no way be viewed as definitive. The `CommandLineJobRunner` performs four tasks:

- Load the appropriate `ApplicationContext`

- Parse command line arguments into `JobParameters`

- Locate the appropriate job based on arguments

- Use the `JobLauncher` provided in the application context to launch the job.

All of these tasks are accomplished using only the arguments passed in. The following table describes the required arguments:

Table 1. CommandLineJobRunner arguments
`jobPath` | The location of the XML file that is used to create an `ApplicationContext`. This file should contain everything needed to run the complete `Job`.
`jobName` | The name of the job to be run.

These arguments must be passed in with the path first and the name second. All arguments after these are considered to be job parameters, are turned into a `JobParameters` object, and must be in the format of `name=value`.

The following example shows a date passed as a job parameter to a job defined in XML:

    <bash$ java CommandLineJobRunner endOfDayJob.xml endOfDay schedule.date(date)=2007/05/05

The following example shows a date passed as a job parameter to a job defined in Java:

    <bash$ java CommandLineJobRunner io.spring.EndOfDayJobConfiguration endOfDay schedule.date(date)=2007/05/05

| By default, the `CommandLineJobRunner` uses a `DefaultJobParametersConverter` that implicitly converts key/value pairs to identifying job parameters. However, you can explicitly specify which job parameters are identifying and which are not by prefixing them with `+` or `-`, respectively. In the following example, `schedule.date` is an identifying job parameter, while `vendor.id` is not:

    <bash$ java CommandLineJobRunner endOfDayJob.xml endOfDay \
                                     +schedule.date(date)=2007/05/05 -vendor.id=123

    <bash$ java CommandLineJobRunner io.spring.EndOfDayJobConfiguration endOfDay \
                                     +schedule.date(date)=2007/05/05 -vendor.id=123

You can override this behavior by using a custom `JobParametersConverter`.

In most cases, you would want to use a manifest to declare your `main` class in a jar. However, for simplicity, the class was used directly. This example uses the same `EndOfDay` example from the The Domain Language of Batch. The first argument is `endOfDayJob.xml`, which is the Spring ApplicationContext that contains the `Job`. The second argument, `endOfDay,` represents the job name. The final argument, `schedule.date(date)=2007/05/05`, is converted into a `JobParameters` object.

The following example shows a sample configuration for `endOfDay` in XML:

    <job id="endOfDay">
        <step id="step1" parent="simpleStep" />
    </job>

    <!-- Launcher details removed for clarity -->
    <beans:bean id="jobLauncher"
             class="org.springframework.batch.core.launch.support.SimpleJobLauncher" />

In most cases, you would want to use a manifest to declare your `main` class in a jar. However, for simplicity, the class was used directly. This example uses the same `EndOfDay` example from the The Domain Language of Batch. The first argument is `io.spring.EndOfDayJobConfiguration`, which is the fully qualified class name to the configuration class that contains the Job. The second argument, `endOfDay`, represents the job name. The final argument, `schedule.date(date)=2007/05/05`, is converted into a `JobParameters` object.

The following example shows a sample configuration for `endOfDay` in Java:

    @Configuration
    @EnableBatchProcessing
    public class EndOfDayJobConfiguration {

        @Autowired
        private JobBuilderFactory jobBuilderFactory;

        @Autowired
        private StepBuilderFactory stepBuilderFactory;

        @Bean
        public Job endOfDay() {
            return this.jobBuilderFactory.get("endOfDay")
        				.start(step1())
        				.build();
        }

        @Bean
        public Step step1() {
            return this.stepBuilderFactory.get("step1")
        				.tasklet((contribution, chunkContext) -> null)
        				.build();
        }
    }

The preceding example is overly simplistic, since there are many more requirements to a run a batch job in Spring Batch in general, but it serves to show the two main requirements of the `CommandLineJobRunner`: `Job` and `JobLauncher`.

##### Exit Codes

When launching a batch job from the command-line, an enterprise scheduler is often used. Most schedulers are fairly dumb and work only at the process level. This means that they only know about some operating system process (such as a shell script that they invoke). In this scenario, the only way to communicate back to the scheduler about the success or failure of a job is through return codes. A return code is a number that is returned to a scheduler by the process to indicate the result of the run. In the simplest case, 0 is success and 1 is failure. However, there may be more complex scenarios, such as “If job A returns 4, kick off job B, and, if it returns 5, kick off job C.” This type of behavior is configured at the scheduler level, but it is important that a processing framework such as Spring Batch provide a way to return a numeric representation of the exit code for a particular batch job. In Spring Batch, this is encapsulated within an `ExitStatus`, which is covered in more detail in Chapter 5. For the purposes of discussing exit codes, the only important thing to know is that an `ExitStatus` has an exit code property that is set by the framework (or the developer) and is returned as part of the `JobExecution` returned from the `JobLauncher`. The `CommandLineJobRunner` converts this string value to a number by using the `ExitCodeMapper` interface:

    public interface ExitCodeMapper {

        public int intValue(String exitCode);

    }

The essential contract of an `ExitCodeMapper` is that, given a string exit code, a number representation will be returned. The default implementation used by the job runner is the `SimpleJvmExitCodeMapper` that returns 0 for completion, 1 for generic errors, and 2 for any job runner errors such as not being able to find a `Job` in the provided context. If anything more complex than the 3 values above is needed, then a custom implementation of the `ExitCodeMapper` interface must be supplied. Because the `CommandLineJobRunner` is the class that creates an `ApplicationContext`, and thus cannot be 'wired together', any values that need to be overwritten must be autowired. This means that if an implementation of `ExitCodeMapper` is found within the `BeanFactory`, it will be injected into the runner after the context is created. All that needs to be done to provide your own `ExitCodeMapper` is to declare the implementation as a root level bean and ensure that it is part of the `ApplicationContext` that is loaded by the runner.

#### Running Jobs from within a Web Container

Historically, offline processing (such as batch jobs) has been launched from the command-line, as described earlier. However, there are many cases where launching from an `HttpRequest` is a better option. Many such use cases include reporting, ad-hoc job running, and web application support. Because a batch job (by definition) is long running, the most important concern is ensuring to launch the job asynchronously:

Figure 4. Asynchronous Job Launcher Sequence From Web Container

The controller in this case is a Spring MVC controller. See the Spring Framework Reference Guide for more about Spring MVC. The controller launches a `Job` by using a `JobLauncher` that has been configured to launch asynchronously, which immediately returns a `JobExecution`. The `Job` is likely still running. However, this nonblocking behavior lets the controller return immediately, which is required when handling an `HttpRequest`. The following listing shows an example:

    @Controller
    public class JobLauncherController {

        @Autowired
        JobLauncher jobLauncher;

        @Autowired
        Job job;

        @RequestMapping("/jobLauncher.html")
        public void handle() throws Exception{
            jobLauncher.run(job, new JobParameters());
        }
    }

### Advanced Metadata Usage

So far, both the `JobLauncher` and `JobRepository` interfaces have been discussed. Together, they represent the simple launching of a job and basic CRUD operations of batch domain objects:

Figure 5. Job Repository

A `JobLauncher` uses the `JobRepository` to create new `JobExecution` objects and run them. `Job` and `Step` implementations later use the same `JobRepository` for basic updates of the same executions during the running of a `Job`. The basic operations suffice for simple scenarios. However, in a large batch environment with hundreds of batch jobs and complex scheduling requirements, more advanced access to the metadata is required:

Figure 6. Advanced Job Repository Access

The `JobExplorer` and `JobOperator` interfaces, which are discussed in the coming sections, add additional functionality for querying and controlling the metadata.

#### Querying the Repository

The most basic need before any advanced features is the ability to query the repository for existing executions. This functionality is provided by the `JobExplorer` interface:

    public interface JobExplorer {

        List<JobInstance> getJobInstances(String jobName, int start, int count);

        JobExecution getJobExecution(Long executionId);

        StepExecution getStepExecution(Long jobExecutionId, Long stepExecutionId);

        JobInstance getJobInstance(Long instanceId);

        List<JobExecution> getJobExecutions(JobInstance jobInstance);

        Set<JobExecution> findRunningJobExecutions(String jobName);
    }

As is evident from its method signatures, `JobExplorer` is a read-only version of the `JobRepository`, and, like the `JobRepository`, it can be easily configured by using a factory bean.

The following example shows how to configure a `JobExplorer` in XML:

Example 19. XML Configuration

    <bean id="jobExplorer" class="org.spr...JobExplorerFactoryBean"
          p:dataSource-ref="dataSource" />

The following example shows how to configure a `JobExplorer` in Java:

Example 20. Java Configuration

    ...
    // This would reside in your BatchConfigurer implementation
    @Override
    public JobExplorer getJobExplorer() throws Exception {
    	JobExplorerFactoryBean factoryBean = new JobExplorerFactoryBean();
    	factoryBean.setDataSource(this.dataSource);
    	return factoryBean.getObject();
    }
    ...

Earlier in this chapter, we noted that you can modify the table prefix of the `JobRepository` to allow for different versions or schemas. Because the `JobExplorer` works with the same tables, it also needs the ability to set a prefix.

The following example shows how to set the table prefix for a `JobExplorer` in XML:

Example 21. XML Configuration

    <bean id="jobExplorer" class="org.spr...JobExplorerFactoryBean"
    		p:tablePrefix="SYSTEM."/>

The following example shows how to set the table prefix for a `JobExplorer` in Java:

Example 22. Java Configuration

    ...
    // This would reside in your BatchConfigurer implementation
    @Override
    public JobExplorer getJobExplorer() throws Exception {
    	JobExplorerFactoryBean factoryBean = new JobExplorerFactoryBean();
    	factoryBean.setDataSource(this.dataSource);
    	factoryBean.setTablePrefix("SYSTEM.");
    	return factoryBean.getObject();
    }
    ...

#### JobRegistry

A `JobRegistry` (and its parent interface, `JobLocator`) is not mandatory, but it can be useful if you want to keep track of which jobs are available in the context. It is also useful for collecting jobs centrally in an application context when they have been created elsewhere (for example, in child contexts). You can also use custom `JobRegistry` implementations to manipulate the names and other properties of the jobs that are registered. There is only one implementation provided by the framework and this is based on a simple map from job name to job instance.

The following example shows how to include a `JobRegistry` for a job defined in XML:

    <bean id="jobRegistry" class="org.springframework.batch.core.configuration.support.MapJobRegistry" />

When using `@EnableBatchProcessing`, a `JobRegistry` is provided for you. The following example shows how to configure your own `JobRegistry`:

    ...
    // This is already provided via the @EnableBatchProcessing but can be customized via
    // overriding the getter in the SimpleBatchConfiguration
    @Override
    @Bean
    public JobRegistry jobRegistry() throws Exception {
    	return new MapJobRegistry();
    }
    ...

You can populate a `JobRegistry` in either of two ways: by using a bean post processor or by using a registrar lifecycle component. The coming sections describe these two mechanisms.

##### JobRegistryBeanPostProcessor

This is a bean post-processor that can register all jobs as they are created.

The following example shows how to include the `JobRegistryBeanPostProcessor` for a job defined in XML:

Example 23. XML Configuration

    <bean id="jobRegistryBeanPostProcessor" class="org.spr...JobRegistryBeanPostProcessor">
        <property name="jobRegistry" ref="jobRegistry"/>
    </bean>

The following example shows how to include the `JobRegistryBeanPostProcessor` for a job defined in Java:

Example 24. Java Configuration

    @Bean
    public JobRegistryBeanPostProcessor jobRegistryBeanPostProcessor() {
        JobRegistryBeanPostProcessor postProcessor = new JobRegistryBeanPostProcessor();
        postProcessor.setJobRegistry(jobRegistry());
        return postProcessor;
    }

Although it is not strictly necessary, the post-processor in the example has been given an `id` so that it can be included in child contexts (for example, as a parent bean definition) and cause all jobs created there to also be registered automatically.

##### `AutomaticJobRegistrar`

This is a lifecycle component that creates child contexts and registers jobs from those contexts as they are created. One advantage of doing this is that, while the job names in the child contexts still have to be globally unique in the registry, their dependencies can have “natural” names. So, for example, you can create a set of XML configuration files that each have only one Job but that all have different definitions of an `ItemReader` with the same bean name, such as `reader`. If all those files were imported into the same context, the reader definitions would clash and override one another, but, with the automatic registrar, this is avoided. This makes it easier to integrate jobs that have been contributed from separate modules of an application.

The following example shows how to include the `AutomaticJobRegistrar` for a job defined in XML:

Example 25. XML Configuration

    <bean class="org.spr...AutomaticJobRegistrar">
       <property name="applicationContextFactories">
          <bean class="org.spr...ClasspathXmlApplicationContextsFactoryBean">
             <property name="resources" value="classpath*:/config/job*.xml" />
          </bean>
       </property>
       <property name="jobLoader">
          <bean class="org.spr...DefaultJobLoader">
             <property name="jobRegistry" ref="jobRegistry" />
          </bean>
       </property>
    </bean>

The following example shows how to include the `AutomaticJobRegistrar` for a job defined in Java:

Example 26. Java Configuration

    @Bean
    public AutomaticJobRegistrar registrar() {

        AutomaticJobRegistrar registrar = new AutomaticJobRegistrar();
        registrar.setJobLoader(jobLoader());
        registrar.setApplicationContextFactories(applicationContextFactories());
        registrar.afterPropertiesSet();
        return registrar;

    }

The registrar has two mandatory properties: an array of `ApplicationContextFactory` (created from a convenient factory bean in the preceding example) and a `JobLoader`. The `JobLoader` is responsible for managing the lifecycle of the child contexts and registering jobs in the `JobRegistry`.

The `ApplicationContextFactory` is responsible for creating the child context. The most common usage is (as in the preceding example) to use a `ClassPathXmlApplicationContextFactory`. One of the features of this factory is that, by default, it copies some of the configuration down from the parent context to the child. So, for instance, you need not redefine the `PropertyPlaceholderConfigurer` or AOP configuration in the child, provided it should be the same as the parent.

You can use `AutomaticJobRegistrar` in conjunction with a `JobRegistryBeanPostProcessor` (as long as you also use `DefaultJobLoader`). For instance, this might be desirable if there are jobs defined in the main parent context as well as in the child locations.

#### JobOperator

As previously discussed, the `JobRepository` provides CRUD operations on the meta-data, and the `JobExplorer` provides read-only operations on the meta-data. However, those operations are most useful when used together to perform common monitoring tasks such as stopping, restarting, or summarizing a Job, as is commonly done by batch operators. Spring Batch provides these types of operations via the `JobOperator` interface:

    public interface JobOperator {

        List<Long> getExecutions(long instanceId) throws NoSuchJobInstanceException;

        List<Long> getJobInstances(String jobName, int start, int count)
              throws NoSuchJobException;

        Set<Long> getRunningExecutions(String jobName) throws NoSuchJobException;

        String getParameters(long executionId) throws NoSuchJobExecutionException;

        Long start(String jobName, String parameters)
              throws NoSuchJobException, JobInstanceAlreadyExistsException;

        Long restart(long executionId)
              throws JobInstanceAlreadyCompleteException, NoSuchJobExecutionException,
                      NoSuchJobException, JobRestartException;

        Long startNextInstance(String jobName)
              throws NoSuchJobException, JobParametersNotFoundException, JobRestartException,
                     JobExecutionAlreadyRunningException, JobInstanceAlreadyCompleteException;

        boolean stop(long executionId)
              throws NoSuchJobExecutionException, JobExecutionNotRunningException;

        String getSummary(long executionId) throws NoSuchJobExecutionException;

        Map<Long, String> getStepExecutionSummaries(long executionId)
              throws NoSuchJobExecutionException;

        Set<String> getJobNames();

    }

The above operations represent methods from many different interfaces, such as `JobLauncher`, `JobRepository`, `JobExplorer`, and `JobRegistry`. For this reason, the provided implementation of `JobOperator` (`SimpleJobOperator`) has many dependencies.

The following example shows a typical bean definition for `SimpleJobOperator` in XML:

    <bean id="jobOperator" class="org.spr...SimpleJobOperator">
        <property name="jobExplorer">
            <bean class="org.spr...JobExplorerFactoryBean">
                <property name="dataSource" ref="dataSource" />
            </bean>
        </property>
        <property name="jobRepository" ref="jobRepository" />
        <property name="jobRegistry" ref="jobRegistry" />
        <property name="jobLauncher" ref="jobLauncher" />
    </bean>

The following example shows a typical bean definition for `SimpleJobOperator` in Java:

     /**
      * All injected dependencies for this bean are provided by the @EnableBatchProcessing
      * infrastructure out of the box.
      */
     @Bean
     public SimpleJobOperator jobOperator(JobExplorer jobExplorer,
                                    JobRepository jobRepository,
                                    JobRegistry jobRegistry) {

    	SimpleJobOperator jobOperator = new SimpleJobOperator();

    	jobOperator.setJobExplorer(jobExplorer);
    	jobOperator.setJobRepository(jobRepository);
    	jobOperator.setJobRegistry(jobRegistry);
    	jobOperator.setJobLauncher(jobLauncher);

    	return jobOperator;
     }

| If you set the table prefix on the job repository, don’t forget to set it on the job explorer as well.

#### JobParametersIncrementer

Most of the methods on `JobOperator` are self-explanatory, and you can find more detailed explanations in the javadoc of the interface. However, the `startNextInstance` method is worth noting. This method always starts a new instance of a `Job`. This can be extremely useful if there are serious issues in a `JobExecution` and the `Job` needs to be started over again from the beginning. Unlike `JobLauncher` (which requires a new `JobParameters` object that triggers a new `JobInstance`), if the parameters are different from any previous set of parameters, the `startNextInstance` method uses the `JobParametersIncrementer` tied to the `Job` to force the `Job` to a new instance:

    public interface JobParametersIncrementer {

        JobParameters getNext(JobParameters parameters);

    }

The contract of `JobParametersIncrementer` is that, given a JobParameters object, it returns the 'next' JobParameters object by incrementing any necessary values it may contain. This strategy is useful because the framework has no way of knowing what changes to the `JobParameters` make it the “next” instance. For example, if the only value in `JobParameters` is a date and the next instance should be created, should that value be incremented by one day? Or one week (if the job is weekly, for instance)? The same can be said for any numerical values that help to identify the Job, as the following example shows:

    public class SampleIncrementer implements JobParametersIncrementer {

        public JobParameters getNext(JobParameters parameters) {
            if (parameters==null || parameters.isEmpty()) {
                return new JobParametersBuilder().addLong("run.id", 1L).toJobParameters();
            }
            long id = parameters.getLong("run.id",1L) + 1;
            return new JobParametersBuilder().addLong("run.id", id).toJobParameters();
        }
    }

In this example, the value with a key of 'run.id' is used to discriminate between `JobInstances`. If the `JobParameters` passed in is null, it can be assumed that the `Job` has never been run before and thus its initial state can be returned. However, if not, the old value is obtained, incremented by one, and returned.

For jobs defined in XML, you can associate an incrementer with a `Job` through the `incrementer` attribute in the namespace, as follows:

    <job id="footballJob" incrementer="sampleIncrementer">
        ...
    </job>

For jobs defined in Java, you can associate an incrementer with a `Job` through the `incrementer` method provided in the builders, as follows:

    @Bean
    public Job footballJob() {
        return this.jobBuilderFactory.get("footballJob")
        				 .incrementer(sampleIncrementer())
        				 ...
                         .build();
    }

#### Stopping a Job

One of the most common use cases of `JobOperator` is gracefully stopping a Job:

    Set<Long> executions = jobOperator.getRunningExecutions("sampleJob");
    jobOperator.stop(executions.iterator().next());

The shutdown is not immediate, since there is no way to force immediate shutdown, especially if the execution is currently in developer code that the framework has no control over, such as a business service. However, as soon as control is returned back to the framework, it sets the status of the current `StepExecution` to `BatchStatus.STOPPED`, saves it, and then does the same for the `JobExecution` before finishing.

#### Aborting a Job

A job execution that is `FAILED` can be restarted (if the `Job` is restartable). A job execution whose status is `ABANDONED` cannot be restarted by the framework. The `ABANDONED` status is also used in step executions to mark them as skippable in a restarted job execution. If a job is running and encounters a step that has been marked `ABANDONED` in the previous failed job execution, it moves on to the next step (as determined by the job flow definition and the step execution exit status).

If the process died (`"kill -9"` or server failure) the job is, of course, not running, but the `JobRepository` has no way of knowing because no one told it before the process died. You have to tell it manually that you know that the execution either failed or should be considered aborted (change its status to `FAILED` or `ABANDONED`). This is a business decision, and there is no way to automate it. Change the status to `FAILED` only if it is not restartable or if you know the restart data is valid.