Update README with instructions to generate docs

Update Spring dependencies to latest snapshots

Upgrade gradle version to 6.9
Resolves #3917

Exclude spring-batch-docs from being published to Artifactory
Resolves #3922

Update README with instructions to generate docs

Exclude spring-batch-docs from being published to Artifactory
Resolves #3922

Upgrade gradle version to 6.9

Update Spring dependencies to latest snapshots

Exclude spring-batch-docs from being published to Artifactory
Resolves #3922

Update Spring dependencies to latest snapshots

Upgrade gradle version to 6.9

Update README with instructions to generate docs

Update contributor guide by replacing master with main
Issue #3879

Add instructions to build the project with Docker

Add instructions to build the project with Docker

Update contributor guide by replacing master with main
Issue #3879

Update dependencies

Update maven version to 3.8.1 in maven wrapper

Update maven version to 3.8.1 in maven wrapper

Update dependencies

Add timeout when flushing items to Kafka in KafkaItemWriter
Issue #3773

Refine contribution #3827
* Update year in licence headers
* Update Javadoc
* Add `this` keyword where appropriate

Polish contribution 58b2a7a2
* Update year in license headers
* Refactor test

Fix typo in CONTRIBUTING.md

Polish contribution 58b2a7a2
* Update year in license headers
* Refactor test

Fix regression in docs
Master/Slave terms were replaced
with Manager/Worker in 85b3e9002
but this seems to be lost when
merging efdce562b0e71695221f6.

Fix regression in docs
Master/Slave terms were replaced
with Manager/Worker in 85b3e9002
but this seems to be lost when
merging efdce562b0e71695221f6.

Update Spring projects dependencies to latest SNAPSHOT

Temporarily ignore intermittently failing tests
This commit temporarily ignores tests that are failing
intermittently on Windows. A link to the corresponding
issue has been added to each test.

FTR, I tried to ignore those tests only on Windows by
using `Assume.assumeFalse(SystemUtils.IS_OS_WINDOWS);`
where `SystemUtils` is from `org.apache.commons.lang3`
but this assumption does not seem to work as expected.

Update dependencies

Disable SSL usage in MySQL test container
By default, testcontainers does not use SSL. This commit
disable SSL usage in the datasource configuration to
prevent `SSLHandshakeException`s.

Upgrade XStream dependency to version 1.4.16
Resolves #3877

Fix documentation of chunk-oriented processing
Resolves #1629 #1179 #1069 #3833

(cherry picked from commit 3fbfbb95033c228a02d03c90d2bf0fe566b4e5f5)

Add java.sql.Timestamp to trusted classes in Jackson serializer
Resolves #3855

Add java.sql.Timestamp to trusted classes in Jackson serializer
Resolves #3855

Temporarily ignore intermittently failing tests
This commit temporarily ignores tests that are failing
intermittently on Windows. A link to the corresponding
issue has been added to each test.

FTR, I tried to ignore those tests only on Windows by
using `Assume.assumeFalse(SystemUtils.IS_OS_WINDOWS);`
where `SystemUtils` is from `org.apache.commons.lang3`
but this assumption does not seem to work as expected.

Fix PartitionParserTests
Some tests in PartitionParserTests were
failing intermittently due to the usage
of non-synchronized shared state between
concurrent threads.

This commit updates the test code to use
`AtomicInteger` instead of `int` for the
state shared between concurrent threads.

(cherry picked from commit 98fba4a03bb13ef407a52c4fd01b9566eaf61085)

Remove unused code in DecisionStepTests
(cherry picked from commit 287eace69fd03fc24d101f03bcbc9944b4cb717f)

Fix OptimisticLockingFailureTests#testAsyncStopOfStartingJob
This test was failing intermittently due to an incorrect
way of waiting for a job execution to finish, which is:

```
while(jobExecution.isRunning()) {
   // wait for async launched job to complete execution
}
```

`JobExecution#isRunning()` is based on the status
of the job execution in memory which might not be
persisted yet. Here is an excerpt from the Javadoc:

```
Test if this JobExecution indicates that it is
running. It should be noted that this does not
necessarily mean that it has been persisted as
such yet.
```

That's why in the case where `isRunning` returns
false and the JobExecution is not persisted yet
(which is still in a running status in db),
the second attempt of re-running the job fails
with a `JobExecutionAlreadyRunningException`.

This commit fixes the loop by continuously
checking the status of the Job execution
in the job repository until it reaches one
of the end statuses.

Issue #1121

(cherry picked from commit cf2642223d6736514d8d9c6574e72d486ee590b5)

Fix KafkaItemReaderTests
Tests in this class fail intermittently because
they send messages to Kafka in an asynchronous
way and assert on the results immediately without
waiting for the send operation to complete.

This commit updates the tests to wait for
send results before asserting on them
(similar to a140a9f5).

(cherry picked from commit 5826111b853d2ae4a2e6f061ae1a079ad524da89)

Fix flaky tests
JsrSplitParsingTests#test and DecisionStepTests#testDecisionAfterSplit
were failing intermittently with:

```
org.springframework.batch.core.JobExecutionException: Flow execution ended unexpectedly
    at org.springframework.batch.core.jsr.job.flow.JsrFlowJob.doExecute(JsrFlowJob.java:88) ~[main/:?]
    at org.springframework.batch.core.job.AbstractJob.execute(AbstractJob.java:320) [main/:?]
    at org.springframework.batch.core.jsr.launch.JsrJobOperator$2.run(JsrJobOperator.java:674) [main/:?]
    at java.lang.Thread.run(Thread.java:748) [?:1.8.0_232]
Caused by: org.springframework.batch.core.job.flow.FlowExecutionException: Ended flow=flow1.step1 at state=flow1.step1.flow1.step1 with exception
    at org.springframework.batch.core.job.flow.support.SimpleFlow.resume(SimpleFlow.java:178) ~[main/:?]
    at org.springframework.batch.core.job.flow.support.SimpleFlow.start(SimpleFlow.java:144) ~[main/:?]
    at org.springframework.batch.core.job.flow.support.state.SplitState$1.call(SplitState.java:94) ~[main/:?]
    at org.springframework.batch.core.job.flow.support.state.SplitState$1.call(SplitState.java:91) ~[main/:?]
    at java.util.concurrent.FutureTask.run(FutureTask.java:266) ~[?:1.8.0_232]
    ... 1 more
Caused by: org.springframework.dao.ConcurrencyFailureException: PreparedStatementCallback; SQL [INSERT INTO BATCH_STEP_EXECUTION_CONTEXT (SHORT_CONTEXT, SERIALIZED_CONTEXT, STEP_EXECUTION_ID) VALUES(?, ?, ?)]; transaction rollback: serialization failure; nested exception is java.sql.SQLTransactionRollbackException: transaction rollback: serialization failure
    at org.springframework.jdbc.support.SQLExceptionSubclassTranslator.doTranslate(SQLExceptionSubclassTranslator.java:73) ~[spring-jdbc-5.3.0.jar:5.3.0]
    at org.springframework.jdbc.support.AbstractFallbackSQLExceptionTranslator.translate(AbstractFallbackSQLExceptionTranslator.java:70) ~[spring-jdbc-5.3.0.jar:5.3.0]
    at org.springframework.jdbc.support.AbstractFallbackSQLExceptionTranslator.translate(AbstractFallbackSQLExceptionTranslator.java:79) ~[spring-jdbc-5.3.0.jar:5.3.0]
    at org.springframework.jdbc.core.JdbcTemplate.translateException(JdbcTemplate.java:1541) ~[spring-jdbc-5.3.0.jar:5.3.0]
    at org.springframework.jdbc.core.JdbcTemplate.execute(JdbcTemplate.java:667) ~[spring-jdbc-5.3.0.jar:5.3.0]
    at org.springframework.jdbc.core.JdbcTemplate.update(JdbcTemplate.java:960) ~[spring-jdbc-5.3.0.jar:5.3.0]
    at org.springframework.jdbc.core.JdbcTemplate.update(JdbcTemplate.java:1015) ~[spring-jdbc-5.3.0.jar:5.3.0]
    at org.springframework.batch.core.repository.dao.JdbcExecutionContextDao.persistSerializedContext(JdbcExecutionContextDao.java:236) ~[main/:?]
    at org.springframework.batch.core.repository.dao.JdbcExecutionContextDao.saveExecutionContext(JdbcExecutionContextDao.java:189) ~[main/:?]
    at org.springframework.batch.core.repository.support.SimpleJobRepository.add(SimpleJobRepository.java:177) ~[main/:?]
    at sun.reflect.GeneratedMethodAccessor101.invoke(Unknown Source) ~[?:?]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_232]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_232]
    at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:344) ~[spring-aop-5.3.0.jar:5.3.0]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:198) ~[spring-aop-5.3.0.jar:5.3.0]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163) ~[spring-aop-5.3.0.jar:5.3.0]
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:371) ~[spring-tx-5.3.0.jar:5.3.0]
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:134) ~[spring-tx-5.3.0.jar:5.3.0]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.0.jar:5.3.0]
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:215) ~[spring-aop-5.3.0.jar:5.3.0]
    at com.sun.proxy.$Proxy41.add(Unknown Source) ~[?:?]
    at org.springframework.batch.core.job.SimpleStepHandler.handleStep(SimpleStepHandler.java:144) ~[main/:?]
    at org.springframework.batch.core.job.flow.JobFlowExecutor.executeStep(JobFlowExecutor.java:68) ~[main/:?]
    at org.springframework.batch.core.job.flow.support.state.StepState.handle(StepState.java:68) ~[main/:?]
    at org.springframework.batch.core.jsr.job.flow.support.state.JsrStepState.handle(JsrStepState.java:53) ~[main/:?]
    at org.springframework.batch.core.job.flow.support.SimpleFlow.resume(SimpleFlow.java:169) ~[main/:?]
    at org.springframework.batch.core.job.flow.support.SimpleFlow.start(SimpleFlow.java:144) ~[main/:?]
    at org.springframework.batch.core.job.flow.support.state.SplitState$1.call(SplitState.java:94) ~[main/:?]
    at org.springframework.batch.core.job.flow.support.state.SplitState$1.call(SplitState.java:91) ~[main/:?]
    at java.util.concurrent.FutureTask.run(FutureTask.java:266) ~[?:1.8.0_232]
    ... 1 more
Caused by: java.sql.SQLTransactionRollbackException: transaction rollback: serialization failure
    at org.hsqldb.jdbc.JDBCUtil.sqlException(Unknown Source) ~[hsqldb-2.5.1.jar:2.5.1]
    at org.hsqldb.jdbc.JDBCUtil.sqlException(Unknown Source) ~[hsqldb-2.5.1.jar:2.5.1]
    at org.hsqldb.jdbc.JDBCPreparedStatement.fetchResult(Unknown Source) ~[hsqldb-2.5.1.jar:2.5.1]
    at org.hsqldb.jdbc.JDBCPreparedStatement.executeUpdate(Unknown Source) ~[hsqldb-2.5.1.jar:2.5.1]
    at org.apache.commons.dbcp2.DelegatingPreparedStatement.executeUpdate(DelegatingPreparedStatement.java:136) ~[commons-dbcp2-2.8.0.jar:2.8.0]
    at org.apache.commons.dbcp2.DelegatingPreparedStatement.executeUpdate(DelegatingPreparedStatement.java:136) ~[commons-dbcp2-2.8.0.jar:2.8.0]
    at org.springframework.jdbc.core.JdbcTemplate.lambda$update$2(JdbcTemplate.java:965) ~[spring-jdbc-5.3.0.jar:5.3.0]
    at org.springframework.jdbc.core.JdbcTemplate.execute(JdbcTemplate.java:651) ~[spring-jdbc-5.3.0.jar:5.3.0]
    at org.springframework.jdbc.core.JdbcTemplate.update(JdbcTemplate.java:960) ~[spring-jdbc-5.3.0.jar:5.3.0]
    at org.springframework.jdbc.core.JdbcTemplate.update(JdbcTemplate.java:1015) ~[spring-jdbc-5.3.0.jar:5.3.0]
    at org.springframework.batch.core.repository.dao.JdbcExecutionContextDao.persistSerializedContext(JdbcExecutionContextDao.java:236) ~[main/:?]
    at org.springframework.batch.core.repository.dao.JdbcExecutionContextDao.saveExecutionContext(JdbcExecutionContextDao.java:189) ~[main/:?]
    at org.springframework.batch.core.repository.support.SimpleJobRepository.add(SimpleJobRepository.java:177) ~[main/:?]
    at sun.reflect.GeneratedMethodAccessor101.invoke(Unknown Source) ~[?:?]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_232]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_232]
    at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:344) ~[spring-aop-5.3.0.jar:5.3.0]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:198) ~[spring-aop-5.3.0.jar:5.3.0]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163) ~[spring-aop-5.3.0.jar:5.3.0]
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:371) ~[spring-tx-5.3.0.jar:5.3.0]
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:134) ~[spring-tx-5.3.0.jar:5.3.0]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.0.jar:5.3.0]
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:215) ~[spring-aop-5.3.0.jar:5.3.0]
    at com.sun.proxy.$Proxy41.add(Unknown Source) ~[?:?]
    at org.springframework.batch.core.job.SimpleStepHandler.handleStep(SimpleStepHandler.java:144) ~[main/:?]
    at org.springframework.batch.core.job.flow.JobFlowExecutor.executeStep(JobFlowExecutor.java:68) ~[main/:?]
    at org.springframework.batch.core.job.flow.support.state.StepState.handle(StepState.java:68) ~[main/:?]
    at org.springframework.batch.core.jsr.job.flow.support.state.JsrStepState.handle(JsrStepState.java:53) ~[main/:?]
    at org.springframework.batch.core.job.flow.support.SimpleFlow.resume(SimpleFlow.java:169) ~[main/:?]
    at org.springframework.batch.core.job.flow.support.SimpleFlow.start(SimpleFlow.java:144) ~[main/:?]
    at org.springframework.batch.core.job.flow.support.state.SplitState$1.call(SplitState.java:94) ~[main/:?]
    at org.springframework.batch.core.job.flow.support.state.SplitState$1.call(SplitState.java:91) ~[main/:?]
    at java.util.concurrent.FutureTask.run(FutureTask.java:266) ~[?:1.8.0_232]
    ... 1 more
Caused by: org.hsqldb.HsqlException: transaction rollback: serialization failure
    at org.hsqldb.error.Error.error(Unknown Source) ~[hsqldb-2.5.1.jar:2.5.1]
    at org.hsqldb.error.Error.error(Unknown Source) ~[hsqldb-2.5.1.jar:2.5.1]
    at org.hsqldb.Session.handleAbortTransaction(Unknown Source) ~[hsqldb-2.5.1.jar:2.5.1]
    at org.hsqldb.Session.executeCompiledStatement(Unknown Source) ~[hsqldb-2.5.1.jar:2.5.1]
    at org.hsqldb.Session.execute(Unknown Source) ~[hsqldb-2.5.1.jar:2.5.1]
    at org.hsqldb.jdbc.JDBCPreparedStatement.fetchResult(Unknown Source) ~[hsqldb-2.5.1.jar:2.5.1]
    at org.hsqldb.jdbc.JDBCPreparedStatement.executeUpdate(Unknown Source) ~[hsqldb-2.5.1.jar:2.5.1]
    at org.apache.commons.dbcp2.DelegatingPreparedStatement.executeUpdate(DelegatingPreparedStatement.java:136) ~[commons-dbcp2-2.8.0.jar:2.8.0]
    at org.apache.commons.dbcp2.DelegatingPreparedStatement.executeUpdate(DelegatingPreparedStatement.java:136) ~[commons-dbcp2-2.8.0.jar:2.8.0]
    at org.springframework.jdbc.core.JdbcTemplate.lambda$update$2(JdbcTemplate.java:965) ~[spring-jdbc-5.3.0.jar:5.3.0]
    at org.springframework.jdbc.core.JdbcTemplate.execute(JdbcTemplate.java:651) ~[spring-jdbc-5.3.0.jar:5.3.0]
    at org.springframework.jdbc.core.JdbcTemplate.update(JdbcTemplate.java:960) ~[spring-jdbc-5.3.0.jar:5.3.0]
    at org.springframework.jdbc.core.JdbcTemplate.update(JdbcTemplate.java:1015) ~[spring-jdbc-5.3.0.jar:5.3.0]
    at org.springframework.batch.core.repository.dao.JdbcExecutionContextDao.persistSerializedContext(JdbcExecutionContextDao.java:236) ~[main/:?]
    at org.springframework.batch.core.repository.dao.JdbcExecutionContextDao.saveExecutionContext(JdbcExecutionContextDao.java:189) ~[main/:?]
    at org.springframework.batch.core.repository.support.SimpleJobRepository.add(SimpleJobRepository.java:177) ~[main/:?]
    at sun.reflect.GeneratedMethodAccessor101.invoke(Unknown Source) ~[?:?]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_232]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_232]
    at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:344) ~[spring-aop-5.3.0.jar:5.3.0]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:198) ~[spring-aop-5.3.0.jar:5.3.0]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163) ~[spring-aop-5.3.0.jar:5.3.0]
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:371) ~[spring-tx-5.3.0.jar:5.3.0]
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:134) ~[spring-tx-5.3.0.jar:5.3.0]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.0.jar:5.3.0]
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:215) ~[spring-aop-5.3.0.jar:5.3.0]
    at com.sun.proxy.$Proxy41.add(Unknown Source) ~[?:?]
    at org.springframework.batch.core.job.SimpleStepHandler.handleStep(SimpleStepHandler.java:144) ~[main/:?]
    at org.springframework.batch.core.job.flow.JobFlowExecutor.executeStep(JobFlowExecutor.java:68) ~[main/:?]
    at org.springframework.batch.core.job.flow.support.state.StepState.handle(StepState.java:68) ~[main/:?]
    at org.springframework.batch.core.jsr.job.flow.support.state.JsrStepState.handle(JsrStepState.java:53) ~[main/:?]
    at org.springframework.batch.core.job.flow.support.SimpleFlow.resume(SimpleFlow.java:169) ~[main/:?]
    at org.springframework.batch.core.job.flow.support.SimpleFlow.start(SimpleFlow.java:144) ~[main/:?]
    at org.springframework.batch.core.job.flow.support.state.SplitState$1.call(SplitState.java:94) ~[main/:?]
    at org.springframework.batch.core.job.flow.support.state.SplitState$1.call(SplitState.java:91) ~[main/:?]
    at java.util.concurrent.FutureTask.run(FutureTask.java:266) ~[?:1.8.0_232]
    ... 1 more
```

This failure is due to a concurrency issue when executing
the split flow with the default SimpleAsyncTaskExecutor.

Several attempts have been made to fix this issue with no success:

* use `@DirtiesContext` annotation
* use a separate db for each test
* use `READ_COMMITTED` isolation level in the job repository
* downgrade hsqldb from v2.5.1 to v2.4.1 (since v2.5.1 has
introduced several changes in the MVCC mode)

The issue seems to be related to how the in-memory database
is shared between tests *and* how the test context is cached
(ie the combination of both).

This commit moves these tests to a separate test class which
seem to fix the issue.

(cherry picked from commit 109073130216b950f3b1201ec6d4764a799d071c)

Update testcontainers version to 1.15.1

Fix Javadoc errors

Fix assumption in ScriptItemProcessorTests.testItemBinding
This test fails on Java 15 because the Javascript engine
has been removed in Java 15 (JEP 372).

This commit updates the test to assume that the JavaScript
engine is provided to the JVM through a factory (similar
to other tests).

Fix build on Java 11+

Fix plugin repositories order in build script
Issue #3823

(cherry picked from commit 1e433dca8583f5b11748d52ee8cad75cca771ede)