org.springframework.batch.item.database

Class JdbcPagingItemReader<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.JdbcPagingItemReader<T>

All Implemented Interfaces:

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

public class JdbcPagingItemReader<T>
extends AbstractPagingItemReader<T>
implements org.springframework.beans.factory.InitializingBean

ItemReader for reading database records using JDBC in a paging fashion.

It executes the SQL built by the PagingQueryProvider 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. On restart it uses the last sort key value to locate the first page to read (so it doesn't matter if the successfully processed items have been removed or modified). It is important to have a unique key constraint on the sort key to guarantee that no data is lost between executions.

The performance of the paging depends on the database specific features available 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.

The implementation is thread-safe in between calls to 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, Michael Minella, Mahmoud Ben Hassine

Field Summary

Fields

Modifier and Type	Field and Description
static int	VALUE_NOT_SET

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

logger, results

Constructor Summary

Constructors

Constructor and Description
JdbcPagingItemReader()

Method Summary

Modifier and Type	Method and Description
void	afterPropertiesSet() Check mandatory properties.
protected void	doJumpToPage(int itemIndex)
protected void	doReadPage()
void	open(ExecutionContext executionContext) No-op.
void	setDataSource(javax.sql.DataSource dataSource)
void	setFetchSize(int fetchSize) Gives the JDBC driver a hint as to the number of rows that should be fetched from the database when more rows are needed for this ResultSet object.
void	setParameterValues(java.util.Map<java.lang.String,java.lang.Object> parameterValues) The parameter values to be used for the query execution.
void	setQueryProvider(PagingQueryProvider queryProvider) A PagingQueryProvider.
void	setRowMapper(org.springframework.jdbc.core.RowMapper<T> rowMapper) The row mapper implementation to be used by this reader.
void	update(ExecutionContext executionContext) Return empty ExecutionContext.

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

doClose, doOpen, doRead, getPage, getPageSize, jumpToItem, setPageSize

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

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

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

Field Detail

VALUE_NOT_SET

public static final int VALUE_NOT_SET

See Also:

Constant Field Values

Constructor Detail

JdbcPagingItemReader

public JdbcPagingItemReader()

Method Detail

setDataSource

public void setDataSource(javax.sql.DataSource dataSource)

setFetchSize

public void setFetchSize(int fetchSize)

Gives the JDBC driver a hint as to the number of rows that should be fetched from the database when more rows are needed for this ResultSet object. If the fetch size specified is zero, the JDBC driver ignores the value.

Parameters:

fetchSize - the number of rows to fetch

See Also:

ResultSet.setFetchSize(int)

setQueryProvider

public void setQueryProvider(PagingQueryProvider queryProvider)

A PagingQueryProvider. Supplies all the platform dependent query generation capabilities needed by the reader.

Parameters:

queryProvider - the PagingQueryProvider to use

setRowMapper

public void setRowMapper(org.springframework.jdbc.core.RowMapper<T> rowMapper)

The row mapper implementation to be used by this reader. The row mapper is used to convert result set rows into objects, which are then returned by the reader.

Parameters:

rowMapper - a RowMapper implementation

setParameterValues

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

The parameter values to be used for the query execution. If you use named parameters then the key should be the name used in the query clause. If you use "?" placeholders then the key should be the relative index that the parameter appears in the query string built using the select, from and where clauses specified.

Parameters:

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

afterPropertiesSet

public void afterPropertiesSet()
                        throws java.lang.Exception

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()

doReadPage

protected void doReadPage()

Specified by:

doReadPage in class AbstractPagingItemReader<T>

update

public void update(ExecutionContext executionContext)
            throws ItemStreamException

Description copied from class: ItemStreamSupport

Return empty ExecutionContext.

Specified by:

update in interface ItemStream

Overrides:

update in class AbstractItemCountingItemStreamItemReader<T>

Parameters:

executionContext - to be updated

Throws:

ItemStreamException

See Also:

ItemStream.update(ExecutionContext)

open

public void open(ExecutionContext executionContext)

Description copied from class: ItemStreamSupport

No-op.

Specified by:

open in interface ItemStream

Overrides:

open in class AbstractItemCountingItemStreamItemReader<T>

Parameters:

executionContext - current step's ExecutionContext. Will be the executionContext from the last run of the step on a restart.

See Also:

ItemStream.open(ExecutionContext)

doJumpToPage

protected void doJumpToPage(int itemIndex)

Specified by:

doJumpToPage in class AbstractPagingItemReader<T>