Spring batch use JpaPagingItemReader JpaItemWriter no transaction is in progress - jpa

Question

My project uses java config, the DataSource entityManagerFactory PlatformTransactionManager created by other java config file.
When ItemReader read data, ItemProcessor data transformed ItemWriter has some error
How can I solve this problem?
Error message
2015-01-17 16:26:30.390 ERROR AbstractStep:225 - Encountered an error executing step testStep in job validJob
javax.persistence.TransactionRequiredException: no transaction is in progress
at org.hibernate.jpa.spi.AbstractEntityManagerImpl.checkTransactionNeeded(AbstractEntityManagerImpl.java:1171)
at org.hibernate.jpa.spi.AbstractEntityManagerImpl.flush(AbstractEntityManagerImpl.java:1332)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
How can I enable transactions on the following Code:
#Configuration
#EnableBatchProcessing
public class JobConfiguration {
#Inject
private PlatformTransactionManager transactionManager;
#Inject
private EntityManagerFactory emf;
#Bean
public Job validJob(JobBuilderFactory jobBuilderFactory,Step step) {
return jobBuilderFactory.get("validJob").flow(step).end().build();
}
#Bean
public Step testStep(StepBuilderFactory stepBuilderFactory, ItemReader<PurchaseOrder> reader,
ItemWriter<PurchaseOrder> writer, ItemProcessor<PurchaseOrder, PurchaseOrder> processor) {
return stepBuilderFactory.get("testStep")//
.transactionManager(transactionManager)//
.<PurchaseOrder, PurchaseOrder>chunk(100)//
.reader(reader)//
.processor(processor)//
.writer(writer)//
.build();
}
#Bean
public ItemReader<PurchaseOrder> reader() {
JpaPagingItemReader<PurchaseOrder> reader = new JpaPagingItemReader<PurchaseOrder>();
reader.setEntityManagerFactory(emf);
reader.setQueryString(" select p from PurchaseOrder p ");
reader.setTransacted(false);
return reader;
}
#Bean
public ItemProcessor<PurchaseOrder, PurchaseOrder> processor() {
return new PurchaseOrderItemProcessor();
}
#Bean
public ItemWriter<PurchaseOrder> writer() {
JpaItemWriter<PurchaseOrder> writer = new JpaItemWriter<PurchaseOrder>();
writer.setEntityManagerFactory(emf);
return writer;
}