org.springframework.batch.item.database

Class JpaPagingItemReader<T>

java.lang.Object

org.springframework.batch.item.ItemStreamSupport

org.springframework.batch.item.support.AbstractItemStreamItemReader<T>

org.springframework.batch.item.support.AbstractItemCountingItemStreamItemReader<T>

org.springframework.batch.item.database.AbstractPagingItemReader<T>

org.springframework.batch.item.database.JpaPagingItemReader<T>

All Implemented Interfaces:

ItemReader<T>, ItemStream, ItemStreamReader<T>, org.springframework.beans.factory.InitializingBean

public class JpaPagingItemReader<T>
extends AbstractPagingItemReader<T>

ItemReader for reading database records built on top of JPA.

It executes the JPQL setQueryString(String) to retrieve requested data. The query is executed using paged requests of a size specified in AbstractPagingItemReader.setPageSize(int). Additional pages are requested when needed as AbstractItemCountingItemStreamItemReader.read() method is called, returning an object corresponding to current position.

The performance of the paging depends on the JPA implementation and its use of database specific features to limit the number of returned rows.

Setting a fairly large page size and using a commit interval that matches the page size should provide better performance.

In order to reduce the memory usage for large results the persistence context is flushed and cleared after each page is read. This causes any entities read to be detached. If you make changes to the entities and want the changes persisted then you must explicitly merge the entities.

The reader must be configured with an EntityManagerFactory. All entity access is performed within a new transaction, independent of any existing Spring managed transactions.

The implementation is thread-safe in between calls to AbstractItemCountingItemStreamItemReader.open(ExecutionContext), but remember to use saveState=false if used in a multi-threaded client (no restart available).

Since:

2.0

Author:

Thomas Risberg, Dave Syer, Will Schipp

Field Summary

Fields inherited from class org.springframework.batch.item.database.AbstractPagingItemReader

logger, results

Constructor Summary

Constructors

Constructor and Description
JpaPagingItemReader()

Method Summary

Modifier and Type	Method and Description
void	afterPropertiesSet() Check mandatory properties.
protected void	doClose() Close the resources opened in AbstractItemCountingItemStreamItemReader.doOpen().
protected void	doJumpToPage(int itemIndex)
protected void	doOpen() Open resources necessary to start reading input.
protected void	doReadPage()
void	setEntityManagerFactory(javax.persistence.EntityManagerFactory entityManagerFactory)
void	setParameterValues(java.util.Map<java.lang.String,java.lang.Object> parameterValues) The parameter values to be used for the query execution.
void	setQueryProvider(JpaQueryProvider queryProvider)
void	setQueryString(java.lang.String queryString)
void	setTransacted(boolean transacted) By default (true) the EntityTransaction will be started and committed around the read.

Methods inherited from class org.springframework.batch.item.database.AbstractPagingItemReader

doRead, getPage, getPageSize, jumpToItem, setPageSize

Methods inherited from class org.springframework.batch.item.support.AbstractItemCountingItemStreamItemReader

close, getCurrentItemCount, isSaveState, open, read, setCurrentItemCount, setMaxItemCount, setSaveState, update

Methods inherited from class org.springframework.batch.item.ItemStreamSupport

getExecutionContextKey, setExecutionContextName, setName

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

JpaPagingItemReader

public JpaPagingItemReader()

Method Detail

setEntityManagerFactory

public void setEntityManagerFactory(javax.persistence.EntityManagerFactory entityManagerFactory)

setParameterValues

public void setParameterValues(java.util.Map<java.lang.String,java.lang.Object> parameterValues)

The parameter values to be used for the query execution.

Parameters:

parameterValues - the values keyed by the parameter named used in the query string.

setTransacted

public void setTransacted(boolean transacted)

By default (true) the EntityTransaction will be started and committed around the read. Can be overridden (false) in cases where the JPA implementation doesn't support a particular transaction. (e.g. Hibernate with a JTA transaction). NOTE: may cause problems in guaranteeing the object consistency in the EntityManagerFactory.

Parameters:

transacted - indicator

afterPropertiesSet

public void afterPropertiesSet()
                        throws java.lang.Exception

Description copied from class: AbstractPagingItemReader

Check mandatory properties.

Specified by:

afterPropertiesSet in interface org.springframework.beans.factory.InitializingBean

Overrides:

afterPropertiesSet in class AbstractPagingItemReader<T>

Throws:

java.lang.Exception

See Also:

InitializingBean.afterPropertiesSet()

setQueryString

public void setQueryString(java.lang.String queryString)

Parameters:

queryString - JPQL query string

setQueryProvider

public void setQueryProvider(JpaQueryProvider queryProvider)

Parameters:

queryProvider - JPA query provider

doOpen

protected void doOpen()
               throws java.lang.Exception

Description copied from class: AbstractItemCountingItemStreamItemReader

Open resources necessary to start reading input.

Overrides:

doOpen in class AbstractPagingItemReader<T>

Throws:

java.lang.Exception - Allows subclasses to throw checked exceptions for interpretation by the framework

doReadPage

protected void doReadPage()

Specified by:

doReadPage in class AbstractPagingItemReader<T>

doJumpToPage

protected void doJumpToPage(int itemIndex)

Specified by:

doJumpToPage in class AbstractPagingItemReader<T>

doClose

protected void doClose()
                throws java.lang.Exception

Description copied from class: AbstractItemCountingItemStreamItemReader

Close the resources opened in AbstractItemCountingItemStreamItemReader.doOpen().

Overrides:

doClose in class AbstractPagingItemReader<T>

Throws:

java.lang.Exception - Allows subclasses to throw checked exceptions for interpretation by the framework