Configuring and Running a Job
In the domain section , the overall architecture design was discussed, using the following diagram as a guide:
![Figure 2.1: Batch Stereotypes](./images/spring-batch-reference-model.png)
While the Job
object may seem like a simple
container for steps, there are many configuration options of which a
developer must be aware. Furthermore, there are many considerations for
how a Job
will be run and how its meta-data will be
stored during that run. This chapter will explain 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.
@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 via the BatchConfigurer
.
The above 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
).
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, a 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 declaring specific step details inline. The XML namespace defaults to referencing a repository with an id of 'jobRepository', which is a sensible default. However, this can be overridden explicitly:
<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 parallelisation (<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. It is entirely up to the developer to ensure that a new JobInstance
is created in this scenario. 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
, then the
restartable property may be set to 'false':
<job id="footballJob" restartable="false">
...
</job>
@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 will cause a JobRestartException
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
}
This snippet of JUnit code shows how attempting to create a
JobExecution
the first time for a non restartable
job will cause no issues. However, the second
attempt will throw 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 may be executed. The
SimpleJob
allows for this by calling a
JobListener
at the appropriate time:
public interface JobExecutionListener {
void beforeJob(JobExecution jobExecution);
void afterJob(JobExecution jobExecution);
}
JobListeners
can be added to a
SimpleJob
via the listeners element on the
job:
<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>
@Bean
public Job footballJob() {
return this.jobBuilderFactory.get("footballJob")
.listener(sampleListener())
...
.build();
}
It should be noted that afterJob
will be
called regardless of the success or failure of the
Job. If success or failure needs to be determined
it can be obtained 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, then it may be helpful to define a "parent"
Job
from which the concrete
Jobs may inherit properties. Similar to class
inheritance in Java, the "child" Job
will combine
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>
Please 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 can be used to constrain combinations
of simple mandatory and optional parameters, and 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, e.g:
<job id="job1" parent="baseJob3">
<step id="step1" parent="standaloneStep"/>
<validator ref="parametersValidator"/>
</job>
The validator can be specified as a reference (as above) or as a nested bean definition in the beans namespace.
The configuration of a validator is supported through the java builders, e.g:
@Bean
public Job job1() {
return this.jobBuilderFactory.get("job1")
.validator(parametersValidator())
...
.build();
}
Java Config
Spring 3 brought the ability to configure applications via java in addition to XML.
As of Spring Batch 2.2.0, batch jobs can be configured using the same
java config. There are two components for the java based configuration:
the @EnableBatchProcessing
annotation and two builders.
The @EnableBatchProcessing
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 made
available to be autowired:
-
JobRepository
- bean name "jobRepository" -
JobLauncher
- bean name "jobLauncher" -
JobRegistry
- bean name "jobRegistry" -
PlatformTransactionManager
- bean name "transactionManager" -
JobBuilderFactory
- bean name "jobBuilders" -
StepBuilderFactory
- bean name "stepBuilders"
The core interface for this configuration is the BatchConfigurer
.
The default implementation provides the beans mentioned above and requires a
DataSource
as a bean within the context to be provided. This data
source will be used by the JobRepository. 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, implementing your own from scratch may be required. 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
|
With the base configuration in place, a user can use the provided builder factories
to configure a job. Below is an example of a two step job configured via 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 out of the box for you.
This section addresses configuring your own.
As described in 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:
<job-repository id="jobRepository"
data-source="dataSource"
transaction-manager="transactionManager"
isolation-level-for-create="SERIALIZABLE"
table-prefix="BATCH_"
max-varchar-length="1000"/>
None of the configuration options listed above are required except
the id. If they are not set, the defaults shown above will be used. They
are shown above for awareness purposes. The
max-varchar-length
defaults to 2500, which is the
length of the long VARCHAR
columns in the sample schema scripts
When using java configuration, a JobRepository
is provided for you. A JDBC based one is
provided out of the box if a DataSource
is provided, the Map
based one if not. However
you can customize the configuration of the JobRepository
via an implementation of the
BatchConfigurer
interface.
...
// 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();
}
...
None of the configuration options listed above are required except
the dataSource and transactionManager. If they are not set, the defaults shown above
will be used. They are shown above for awareness purposes. 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 will be
automatically created around the repository. This is to ensure that the
batch meta data, 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 are trying to launch the same job at the same time, only one
will succeed. The default isolation level for that method is
SERIALIZABLE, which is quite aggressive: READ_COMMITTED would work just
as well; READ_UNCOMMITTED would be 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 the SERIALIZED will cause problems, as long as the database
platform supports it. However, this can be overridden:
<job-repository id="jobRepository"
isolation-level-for-create="REPEATABLE_READ" />
// 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 aren’t used then it is also essential to configure the transactional behavior of the repository using AOP:
<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>
This fragment can be used 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.
@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
needs to be prepended to the table names, or if more than one set of
meta data tables is needed within the same schema, then the table prefix
will need to be changed:
<job-repository id="jobRepository"
table-prefix="SYSTEM.TEST_" />
// 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 above changes, every query to the meta data tables will be prefixed with "SYSTEM.TEST_". BATCH_JOB_EXECUTION will be referred to as SYSTEM.TEST_JOB_EXECUTION.
Only the table prefix is configurable. The table and column names are not. |
In-Memory Repository
There are scenarios in which you may not want to persist your domain objects to the database. One reason may be speed; storing domain objects at each commit point takes extra time. Another reason may be that you just don’t need to persist status for a particular job. For this reason, Spring batch provides an in-memory Map version of the job repository:
<bean id="jobRepository"
class="org.springframework.batch.core.repository.support.MapJobRepositoryFactoryBean">
<property name="transactionManager" ref="transactionManager"/>
</bean>
// This would reside in your BatchConfigurer implementation
@Override
protected JobRepository createJobRepository() throws Exception {
MapJobRepositoryFactoryBean factory = new MapJobRepositoryFactoryBean();
factory.setTransactionManager(transactionManager);
return factory.getObject();
}
Note that the in-memory repository is volatile and so does not
allow restart between JVM instances. It also cannot guarantee that two
job instances with the same parameters are launched simultaneously, and
is not suitable for use in a multi-threaded Job, or a locally
partitioned Step
. So use the database version of the repository wherever
you need those features.
However it does require a transaction manager to be defined
because there are rollback semantics within the repository, and because
the business logic might still be transactional (e.g. RDBMS access). For
testing purposes many people find the
ResourcelessTransactionManager
useful.
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:
<bean id="jobRepository" class="org...JobRepositoryFactoryBean">
<property name="databaseType" value="db2"/>
<property name="dataSource" ref="dataSource"/>
</bean>
// 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();
}
(The JobRepositoryFactoryBean
tries to
auto-detect the database type from the DataSource
if it is not specified.) The major differences between platforms are
mainly accounted for by the strategy for incrementing primary keys, so
often it might be necessary to override the
incrementerFactory
as well (using one of the standard
implementations from the Spring Framework).
If even that doesn’t work, or you are not using an RDBMS, then 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 using @EnableBatchProcessing
, a JobRegistry
is provided out of the box for you.
This section addresses configuring your own.
The most basic implementation of the
JobLauncher
interface is the
SimpleJobLauncher
. Its only required dependency is
a JobRepository
, in order to obtain an
execution:
<bean id="jobLauncher"
class="org.springframework.batch.core.launch.support.SimpleJobLauncher">
<property name="jobRepository" ref="jobRepository" />
</bean>
...
// 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:
![Job Launcher Sequence](./images/job-launcher-sequence-sync.png)
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. An example sequence is below:
![Async Job Launcher Sequence](./images/job-launcher-sequence-async.png)
The SimpleJobLauncher
can easily be
configured to allow for this scenario by configuring a
TaskExecutor
:
<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>
@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 launching a job from the
command line, a new JVM will be instantiated for each Job, and thus every
job will have its own JobLauncher
. However, if
running from within a web container within the scope of an
HttpRequest
, there will usually be one
JobLauncher
, configured for asynchronous job
launching, that multiple requests will 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 the 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 will focus 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 just this purpose:
CommandLineJobRunner
. It’s important to note
that this is just one way to bootstrap your application, but 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 are required arguments:
jobPath |
The location of the XML file that will be used to
create an |
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
JobParameters
and must be in the format of 'name=value':
<bash$ java CommandLineJobRunner endOfDayJob.xml endOfDay schedule.date(date)=2007/05/05
<bash$ java CommandLineJobRunner io.spring.EndOfDayJobConfiguration endOfDay schedule.date(date)=2007/05/05
In most cases you would want to use a manifest to declare your
main class in a jar, but for simplicity, the class was used directly.
This example is using the same 'EndOfDay' example from the domainLanguageOfBatch. The first argument is
'endOfDayJob.xml', which is the Spring
ApplicationContext
containing the
Job. The second argument, 'endOfDay' represents
the job name. The final argument, 'schedule.date(date)=2007/05/05'
will be converted into JobParameters
. An
example of the XML configuration is below:
<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, but for simplicity, the class was used directly. This example is using the same 'EndOfDay' example from the domainLanguageOfBatch. The first argument is 'io.spring.EndOfDayJobConfiguration', which is the fully qualified class name to the configuration class containing the Job. The second argument, 'endOfDay' represents the job name. The final argument, 'schedule.date(date)=2007/05/05' will be converted into JobParameters. An example of the java configuration is below:
@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();
}
}
This 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
ExitCodes
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’re invoking.
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
that indicates the result of the run. In the simplest case: 0 is
success and 1 is failure. However, there may be more complex
scenarios: 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 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 have been
launched from the command-line, as described above. 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:
![Async Job Launcher Sequence from web container](./images/launch-from-request.png)
The controller in this case is a Spring MVC controller. More
information on Spring MVC can be found here: https://docs.spring.io/spring/docs/current/spring-framework-reference/web.html#mvc.
The controller launches a Job
using a
JobLauncher
that has been configured to launch
asynchronously, which
immediately returns a JobExecution
. The
Job
will likely still be running, however, this
nonblocking behaviour allows the controller to return immediately, which
is required when handling an HttpRequest
. An
example is below:
@Controller
public class JobLauncherController {
@Autowired
JobLauncher jobLauncher;
@Autowired
Job job;
@RequestMapping("/jobLauncher.html")
public void handle() throws Exception{
jobLauncher.run(job, new JobParameters());
}
}
Advanced Meta-Data Usage
So far, both the JobLauncher
and JobRepository
interfaces have been
discussed. Together, they represent simple launching of a job, and basic
CRUD operations of batch domain objects:
![Job Repository](./images/job-repository.png)
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, but in a large batch
environment with hundreds of batch jobs and complex scheduling
requirements, more advanced access of the meta data is required:
![Job Repository Advanced](./images/job-repository-advanced.png)
The JobExplorer
and
JobOperator
interfaces, which will be discussed
below, add additional functionality for querying and controlling the meta
data.
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 the method signatures above,
JobExplorer
is a read-only version of the
JobRepository
, and like the
JobRepository
, it can be easily configured via a
factory bean:
<bean id="jobExplorer" class="org.spr...JobExplorerFactoryBean"
p:dataSource-ref="dataSource" />
...
// 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, it was mentioned that the table prefix of the
JobRepository
can be modified to allow for
different versions or schemas. Because the
JobExplorer
is working with the same tables, it
too needs the ability to set a prefix:
<bean id="jobExplorer" class="org.spr...JobExplorerFactoryBean"
p:tablePrefix="SYSTEM."/>
...
// 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 (e.g. in child contexts). Custom JobRegistry
implementations
can also be used 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.
<bean id="jobRegistry" class="org.springframework.batch.core.configuration.support.MapJobRegistry" />
When using @EnableBatchProcessing
, a JobRegistry
is provided out of the box for you.
If you want to configure your own:
...
// 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();
}
...
There are two ways to populate a JobRegistry
automatically: using
a bean post processor and using a registrar lifecycle component. These
two mechanisms are described in the following sections.
JobRegistryBeanPostProcessor
This is a bean post-processor that can register all jobs as they are created:
<bean id="jobRegistryBeanPostProcessor" class="org.spr...JobRegistryBeanPostProcessor">
<property name="jobRegistry" ref="jobRegistry"/>
</bean>
@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 (e.g. 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 each having only one Job,
but all having different definitions of an
ItemReader
with the same bean name, e.g.
"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 contributed from separate modules of an
application.
<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>
@Bean
public AutomaticJobRegistrar registrar() {
AutomaticJobRegistrar registrar = new AutomaticJobRegistrar();
registrar.setJobLoader(jobLoader());
registrar.setApplicationContextFactories(applicationContextFactories());
registrar.afterPropertiesSet();
return registrar;
}
The registrar has two mandatory properties, one is an array of
ApplicationContextFactory
(here created from a
convenient factory bean), and the other is 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 and the most common usage
would be as above using 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 don’t have to re-define the
PropertyPlaceholderConfigurer
or AOP
configuration in the child, if it should be the same as the
parent.
The AutomaticJobRegistrar
can be used in
conjunction with a JobRegistryBeanPostProcessor
if desired (as long as the DefaultJobLoader
is
used as well). 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:
<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>
/**
* 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 more detailed explanations can be found on the
javadoc of the interface. However, the
startNextInstance
method is worth noting. This
method will always start 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
though, which requires a new
JobParameters
object that will trigger a new
JobInstance
if the parameters are different from
any previous set of parameters, the
startNextInstance
method will use 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 will return 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 shown below:
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.
An incrementer can
be associated with Job
via the 'incrementer'
attribute in the namespace:
<job id="footballJob" incrementer="sampleIncrementer">
...
</job>
An incrementer can be associated with a 'Job' via the incrementer
method provided in the
builders:
@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 will set the status of the current
StepExecution
to
BatchStatus.STOPPED
, save it, then do the same
for the JobExecution
before finishing.
Aborting a Job
A job execution which is FAILED
can be
restarted (if the Job
is restartable). A job execution whose status is
ABANDONED
will not 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 executing and encounters a step that has been marked
ABANDONED
in the previous failed job execution, it
will move 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
) - it’s
a business decision and there is no way to automate it. Only change the
status to FAILED
if it is not restartable, or if
you know the restart data is valid. There is a utility in Spring Batch
Admin JobService
to abort a job execution.